Asexual Cell ReproductionAsexual Cell Reproduction

Asexual Cell Reproduction Asexual Cell Reproduction – Called asexual because no combination of Called asexual because no combination of

cellular material occurs – all new cells cellular material occurs – all new cells produced contain the same genetic material produced contain the same genetic material as the original cell.as the original cell.

Why do cells reproduce?Why do cells reproduce?– GrowthGrowth– RepairRepair– DifferentiationDifferentiation

Genetic MaterialGenetic Material– The genetic material in a cell is DNA The genetic material in a cell is DNA

(deoxyribonucleic acid)(deoxyribonucleic acid)– It is found in a different form depending on the It is found in a different form depending on the

stage of the cell cyclestage of the cell cycle

Chromatin – long, thin threadlike material - Chromatin – long, thin threadlike material - present in this state during interphasepresent in this state during interphase

Chromosomes – small, sausage-like, may Chromosomes – small, sausage-like, may be found as a individual chromatids (late be found as a individual chromatids (late stages of cell division) or as paired stages of cell division) or as paired chromatids (sisters) connected at the chromatids (sisters) connected at the centromere.centromere.

All somatic cells contain homologous pairs All somatic cells contain homologous pairs of chromosomes - one from the mother’s of chromosomes - one from the mother’s egg (maternal chromosome) and one from egg (maternal chromosome) and one from the father’s sperm (paternal chromosome) the father’s sperm (paternal chromosome) – in the human, 23 sets (46 chromosomes – in the human, 23 sets (46 chromosomes total)total)

Each homologous pair is similar in shape Each homologous pair is similar in shape and length and is responsible for the same and length and is responsible for the same types of characteristicstypes of characteristics

Sister chromatids are IDENTICAL to each Sister chromatids are IDENTICAL to each other (exact copies)other (exact copies)

The levels of organization of genetic material in a eukaryotic cell.

MitosisMitosis: : – Process by which cells divide Process by which cells divide – Occurs in all somatic (non-sex cells) in the Occurs in all somatic (non-sex cells) in the

bodybody– All of the cells produced by mitosis are All of the cells produced by mitosis are

IDENTICAL in genetic makeup to the original IDENTICAL in genetic makeup to the original cells (particularly important is that the cells (particularly important is that the chromosome # doesn’t change)chromosome # doesn’t change)

– The unique appearance and functionality The unique appearance and functionality found in different cells of the body (excepting found in different cells of the body (excepting the sex cells) is NOT due to difference in the sex cells) is NOT due to difference in cellular content, but a difference in the way cellular content, but a difference in the way that content is expressed (differentiation)that content is expressed (differentiation)

Cell CycleCell Cycle – The cell cycle does not start and stop, but The cell cycle does not start and stop, but

continues – different cells may go through the continues – different cells may go through the cycle at a different pace.cycle at a different pace.

Overall CycleOverall Cycle– consists of Interphase (time for growth, consists of Interphase (time for growth,

synthesis of DNA and organelles) & cell synthesis of DNA and organelles) & cell division (mitosis & cytokinesis)division (mitosis & cytokinesis)

InterphaseInterphase– (up to 90% of the cell cycle) – divided into (up to 90% of the cell cycle) – divided into

three separate phases three separate phases G1 phase – (growth 1) – general growth & G1 phase – (growth 1) – general growth & organelle replication, DNA consists of a single organelle replication, DNA consists of a single (unreplicated) chromatin molecule (46 strands)(unreplicated) chromatin molecule (46 strands)

S phase – (synthesis) – replication of S phase – (synthesis) – replication of chromosomal material (DNA) chromosomal material (DNA) 2 copies of each 2 copies of each chromosome (23 chromosome (23 pairspairs in humans), can be in humans), can be identified by the uptake of a radioactive baseidentified by the uptake of a radioactive base

G2 phase (growth 2) – structures associated with G2 phase (growth 2) – structures associated with mitosis & cytokinesis are replicated (cell mitosis & cytokinesis are replicated (cell membrane proteins, centrioles) membrane proteins, centrioles)

Mitosis Mitosis (cell division) – divided into four (cell division) – divided into four separate phasesseparate phases

1. 1. ProphaseProphase– – contents of the nucleus become visible (DNA contents of the nucleus become visible (DNA

strands shorten & thicken; chromatin strands shorten & thicken; chromatin chromosomes) (supercoiling)chromosomes) (supercoiling)

– centrioles separate & move to opposite poles centrioles separate & move to opposite poles of the cell, spindle fibres start to appear of the cell, spindle fibres start to appear (fibres that don’t extend as far as the (fibres that don’t extend as far as the chromosomes called asters)chromosomes called asters)

– nuclear envelope disappearsnuclear envelope disappears– nucleolus becomes invisiblenucleolus becomes invisible

2. 2. MetaphaseMetaphase – – chromosomes move to the center of the cell,chromosomes move to the center of the cell,

centromeres on the equatorcentromeres on the equator– Spindle fibres attach to the centromeres Spindle fibres attach to the centromeres

3. 3. AnaphaseAnaphase – chromatids separate at the centromereschromatids separate at the centromeres– Chromatids move to opposite poles of the cellChromatids move to opposite poles of the cell– The same number of single-copy The same number of single-copy

chromosomes should be at each polechromosomes should be at each pole

4. 4. TelophaseTelophase – chromosomes at opposite ends of the cellchromosomes at opposite ends of the cell– Uncondense to form chromatinUncondense to form chromatin– Nuclear envelope reappearsNuclear envelope reappears

CytokinesisCytokinesis – (cytoplasm division) – cell membrane pinches (cytoplasm division) – cell membrane pinches

in to form two distinct cellsin to form two distinct cells– in plant cells, a cell-plate forms first, separating in plant cells, a cell-plate forms first, separating

the two cells by the forming cell wallthe two cells by the forming cell wall– in animal cells, the cell membrane pinches in in animal cells, the cell membrane pinches in

at the cleavage furrowat the cleavage furrow

FYIFYI

Some very specialized cells – mature muscle, Some very specialized cells – mature muscle, red blood cells, nerve cells no longer divide and red blood cells, nerve cells no longer divide and remain in G1remain in G1

DNA exists as chromatin during growth – DNA exists as chromatin during growth – uncoiled DNA is easier to interpret to synthesize uncoiled DNA is easier to interpret to synthesize proteinsproteins

DNA exists as chromosomes during mitosis – DNA exists as chromosomes during mitosis – coiled & condensed, chromosomes are more coiled & condensed, chromosomes are more easily moved around and separated equallyeasily moved around and separated equally

Overall result – more cells, smaller SA:VOLOverall result – more cells, smaller SA:VOL

Sexual Cell Reproduction Sexual Cell Reproduction – Chapter 16.3– Chapter 16.3

Called sexual because a combination of cellular Called sexual because a combination of cellular material occurs –new cells produced contain material occurs –new cells produced contain genetic material from two combining cells.genetic material from two combining cells.

Takes place in both plants and animal cells (in Takes place in both plants and animal cells (in animals – ova and sperm, in plants, pollen)animals – ova and sperm, in plants, pollen)

Why sexual reproduction?Why sexual reproduction?– Genetic variation!!!!!Genetic variation!!!!!

Asexual reproduction is faster and more Asexual reproduction is faster and more foolproof but does not provide genetic variation. foolproof but does not provide genetic variation. Dogs, although they reproduce sexually Dogs, although they reproduce sexually introduce some of the problems of asexual introduce some of the problems of asexual reproduction when they are bred to pure lines – reproduction when they are bred to pure lines – some breeds of dogs have inbred weaknesses some breeds of dogs have inbred weaknesses due to a lack of genetic variationdue to a lack of genetic variation

For cells to join to form new cells with the correct For cells to join to form new cells with the correct # of chromosomes, the chromosome # must first # of chromosomes, the chromosome # must first be decreased by ½ to maintain the correct # of be decreased by ½ to maintain the correct # of chromosomes in the adultchromosomes in the adult

Meiosis: process by which gametes (sex cells) Meiosis: process by which gametes (sex cells) are produced which are combined during sexual are produced which are combined during sexual reproductionreproduction – Every human cell (except the sex cells) have Every human cell (except the sex cells) have

46 chromosomes (23 homologous pairs) 46 chromosomes (23 homologous pairs) diploid number (2n)diploid number (2n)

– Each pair of chromosomes 1-22 contain Each pair of chromosomes 1-22 contain genes for the same type of characteristics and genes for the same type of characteristics and are similar in size and shape are similar in size and shape homologous homologous chromosomes (the autosomes)chromosomes (the autosomes)

Which of your parents’ traits you show Which of your parents’ traits you show depends on the interaction between the depends on the interaction between the genes on the homologous pairgenes on the homologous pair

– The last “pair” of chromosomes #23, The last “pair” of chromosomes #23, determines gender (sex chromosomes)determines gender (sex chromosomes)

if it is a homologous pair if it is a homologous pair 2X 2X chromosomes, femalechromosomes, female

if the pair is made of one rod shaped and if the pair is made of one rod shaped and one hook shaped, maleone hook shaped, male

– Gametes (sex cells) have 23 single Gametes (sex cells) have 23 single chromosomes chromosomes haploid number (n) haploid number (n)

When the ova is fertilized by the sperm, When the ova is fertilized by the sperm, the original number of chromosomes (46 = the original number of chromosomes (46 = 2n) is restored 2n) is restored zygote zygote

The life cycle of all sexually reproducing The life cycle of all sexually reproducing organisms alternates between haploid and organisms alternates between haploid and diploid cellsdiploid cells

MeiosisMeiosis (see diagrams : Stages of Meiosis, (see diagrams : Stages of Meiosis, Meiosis stages: Nelson pp.450-451)Meiosis stages: Nelson pp.450-451)

Meiosis – special form of cell division occurring Meiosis – special form of cell division occurring only in the reproductive tissue of sexually only in the reproductive tissue of sexually reproducing organisms where n (haploid) reproducing organisms where n (haploid) gametes are formed, having half the DNA gametes are formed, having half the DNA content of the original sex-forming cell.content of the original sex-forming cell.

Occurs only in the sex cells!Occurs only in the sex cells!

Involves two cell divisions (instead of the one in Involves two cell divisions (instead of the one in mitosis) leading to four haploid cells formed mitosis) leading to four haploid cells formed (instead of two diploid in mitosis)(instead of two diploid in mitosis)

Stages of MeiosisStages of Meiosis

Meiosis I (Reduction Division) - during this Meiosis I (Reduction Division) - during this division, the chromosome # is reduced from division, the chromosome # is reduced from 2n 2n n n1. Prophase I1. Prophase I

contents of the nucleus become visible contents of the nucleus become visible (DNA strands shorten & thicken; chromatin (DNA strands shorten & thicken; chromatin chromosomes) chromosomes)centrioles separate & move to opposite centrioles separate & move to opposite poles of the cell, spindle fibres start to poles of the cell, spindle fibres start to appear (fibres that don’t extend as far as appear (fibres that don’t extend as far as the chromosomes called asters)the chromosomes called asters)

* all of the information in italics is identical for meiosis and * all of the information in italics is identical for meiosis and mitosismitosis

homologous chromosomes pair up side by homologous chromosomes pair up side by side (synapsis) so that corresponding side (synapsis) so that corresponding genes are lined up side by side forming a genes are lined up side by side forming a tetrad (4 chromatids)tetrad (4 chromatids)

the homologous chromosomes will cris-the homologous chromosomes will cris-cross over each other, and occasionally cross over each other, and occasionally break and exchange segments break and exchange segments crossing crossing over (provides even more genetic variation) over (provides even more genetic variation) – identical segment sizes are exchanged– identical segment sizes are exchanged

nuclear envelope disappearsnuclear envelope disappears

nucleolus becomes invisiblenucleolus becomes invisible

2. Metaphase I 2. Metaphase I

chromosomes move to the center of the cell, chromosomes move to the center of the cell, centromeres on the equator centromeres on the equator

Spindle fibres attach to the centromeresSpindle fibres attach to the centromeres

Random Orientation of ChromosomesRandom Orientation of Chromosomes

3. Anaphase I 3. Anaphase I

homologous pairshomologous pairs separate (not sister chromatids separate (not sister chromatids separating at the centromere)separating at the centromere)

Chromosomes move to opposite poles of the cell Chromosomes move to opposite poles of the cell segregationsegregation

There should be 23 doubled chromosomes at each There should be 23 doubled chromosomes at each pole (each chromosome remains double stranded)pole (each chromosome remains double stranded)

4. Telophase I4. Telophase I

chromosomes at opposite ends of the cellchromosomes at opposite ends of the cell

Chromosomes don’t uncondense to form Chromosomes don’t uncondense to form chromatinchromatin

Nuclear envelope occasionally reappears Nuclear envelope occasionally reappears (in some cells)(in some cells)

Cytokinesis occursCytokinesis occurs

5. Prophase II5. Prophase II

6. Metaphase II 6. Metaphase II

the cell moves directly to metaphase since the cell moves directly to metaphase since there is no DNA replication and there is no there is no DNA replication and there is no formal organization of the nucleus formal organization of the nucleus

chromosomes move to the center of the chromosomes move to the center of the cell, centromeres on the equatorcell, centromeres on the equator

Spindle fibres attach to the centromeresSpindle fibres attach to the centromeres

7. Anaphase II 7. Anaphase II

chromatids separate at the centromereschromatids separate at the centromeres

Chromatids move to opposite poles of the Chromatids move to opposite poles of the cellcell

There should be 23 single stranded There should be 23 single stranded chromosomes at each polechromosomes at each pole

8. Telophase II 8. Telophase II

chromosomes at opposite ends of the cellchromosomes at opposite ends of the cell

Uncondense to form chromatinUncondense to form chromatin

Nuclear envelope reappearsNuclear envelope reappears

8. Telophase II 8. Telophase II

chromosomes at opposite ends of the cellchromosomes at opposite ends of the cell

Uncondense to form chromatinUncondense to form chromatin

Nuclear envelope reappearsNuclear envelope reappears

9. Cytokinesis9. Cytokinesis

the separation of cytoplasm and organellesthe separation of cytoplasm and organelles

Comparison of Mitosis and MeiosisComparison of Mitosis and Meiosis

Unique Features of MeiosisUnique Features of Meiosis

FYIFYI– in oocytes, meiosis I is put on hold at the end in oocytes, meiosis I is put on hold at the end

of prophase I until the girl reaches puberty, of prophase I until the girl reaches puberty, when meiosis I will completewhen meiosis I will complete

– once meiosis is complete, the gametes once meiosis is complete, the gametes produced cannot undergo any further division, produced cannot undergo any further division, only specializationonly specialization

– for organisms with just 3 chromosomes for organisms with just 3 chromosomes (2n=6) (omitting the increased variation (2n=6) (omitting the increased variation because of crossing-over), there are 8 because of crossing-over), there are 8 possible assortments of chromosomes (23), in possible assortments of chromosomes (23), in humans, with 23 pairs of chromosomes, humans, with 23 pairs of chromosomes, 8 388 608 different gametes could be formed 8 388 608 different gametes could be formed due to the random assortment of genes due to the random assortment of genes during meiosisduring meiosis

GametogenesisGametogenesis

The formation of ova and sperm follow the The formation of ova and sperm follow the process of meiosis, specializations process of meiosis, specializations dependent on their functiondependent on their function– Sperm are designed for movement (little Sperm are designed for movement (little

cytoplasm), lots of cell division, 4 small sperm cytoplasm), lots of cell division, 4 small sperm producedproduced

– Eggs are designed to nourish the zygote – Eggs are designed to nourish the zygote – only one ovum is produced per oocyte only one ovum is produced per oocyte the the other 3 polar bodies sacrifice their cytoplasm other 3 polar bodies sacrifice their cytoplasm to produce one large eggto produce one large egg

Since males contain the chromosome that Since males contain the chromosome that determines gender, their sperm determine the determines gender, their sperm determine the gender of the childgender of the child

Mules are sterile because they cannot form Mules are sterile because they cannot form gametes- there are no homologus pairs to gametes- there are no homologus pairs to synapse during prophase I (horse 2n=64, synapse during prophase I (horse 2n=64, donkey 2n=62, mule 2n=63)donkey 2n=62, mule 2n=63)

Problems During Cell Division (Meiosis or Mitosis)Problems During Cell Division (Meiosis or Mitosis)

Nondisjunction – when chromosomes don’t separate Nondisjunction – when chromosomes don’t separate during anaphase – one of the daughter cells produced during anaphase – one of the daughter cells produced during that separation will be lacking information, one will during that separation will be lacking information, one will have too muchhave too much– the daughter cell will either have one too many the daughter cell will either have one too many

chromosomes chromosomes 24 or one too few 24 or one too few 22 22– when the ovum or sperm fuse with the abnormal when the ovum or sperm fuse with the abnormal

gamete, the zygote will have either 47 or 45 gamete, the zygote will have either 47 or 45 chromosomes instead of 46chromosomes instead of 46

if there is one too many chromosomes, one pair if there is one too many chromosomes, one pair will be a triplet will be a triplet trisomy trisomy

if there is one too few chromosomes, one pair will if there is one too few chromosomes, one pair will be a singlet be a singlet monosomy monosomy

– although nondisjunction may occur in any although nondisjunction may occur in any cells of the body, it is much more devastating cells of the body, it is much more devastating in a gamete (all cells in the body of the fetus in a gamete (all cells in the body of the fetus will be short/extra chromosomes)will be short/extra chromosomes)

– nondisjunction is actually a desired nondisjunction is actually a desired characteristic in the development of large characteristic in the development of large luscious fruit – big strawberries might be 4n or luscious fruit – big strawberries might be 4n or even 6n (polyploidy)even 6n (polyploidy)

Karyotyping Karyotyping (see diagram p.455, Nelson Biology)(see diagram p.455, Nelson Biology)

To evaluate the chormosomal composition To evaluate the chormosomal composition of cells in an embryo, fetus or full-grown of cells in an embryo, fetus or full-grown organism, a karyotype is made – rapidly organism, a karyotype is made – rapidly dividing cells are isolated and stained, dividing cells are isolated and stained, then the chromosomes from cells in then the chromosomes from cells in metaphase are analyzed metaphase are analyzed – Chromosomes are cut out and matched Chromosomes are cut out and matched

according to the banding patterns (grey bands according to the banding patterns (grey bands with Giemsa dye, or coloured chromosomes with Giemsa dye, or coloured chromosomes with spectral analysis)with spectral analysis)

– The new spectral analysis shows more than The new spectral analysis shows more than just gross chromosomal abnormalitiesjust gross chromosomal abnormalities

Abnormal karyotyping will show the result of Abnormal karyotyping will show the result of non-disjunction during meiosis or mitosis non-disjunction during meiosis or mitosis (important in cancer research and diagnosis)(important in cancer research and diagnosis)

Karyotyping will also determine gender – 23 Karyotyping will also determine gender – 23 pairs, one pair (#23, the sex chromosomes – if pairs, one pair (#23, the sex chromosomes – if XY male, if XX female)XY male, if XX female)

Nondisjunction Disorders (Meiosis)Nondisjunction Disorders (Meiosis)

Most nondisjunctions during Most nondisjunctions during gametogenesis will produce sperm/ova gametogenesis will produce sperm/ova resulting in a nonviable fetus that will resulting in a nonviable fetus that will spontaneously abort during early spontaneously abort during early developmentdevelopment– If the nondisjunction still allows the fetus to If the nondisjunction still allows the fetus to

develop to term, a number of specific develop to term, a number of specific syndromes (groups of disorders) may result:syndromes (groups of disorders) may result:

– Down syndrome (trisomy 21) – mental Down syndrome (trisomy 21) – mental retardation, webbed fingers & toes, slanted retardation, webbed fingers & toes, slanted eyes, short statureeyes, short stature

– Turner syndrome (XO, monosomy), the Turner syndrome (XO, monosomy), the fertilized egg is missing the X chromosome, fertilized egg is missing the X chromosome, short statured, wide neck, many are short statured, wide neck, many are miscarried before birthmiscarried before birth

– Klinefelter syndrome (XXY, trisomy) – the Klinefelter syndrome (XXY, trisomy) – the presence of a Y indicates a male, but at presence of a Y indicates a male, but at puberty, the XX leads to a lot of female puberty, the XX leads to a lot of female hormones produced resulting in a sterile malehormones produced resulting in a sterile male

– ““Supermale” (XYY, trisomy) – tendency to be Supermale” (XYY, trisomy) – tendency to be taller, but many “characteristics” associated taller, but many “characteristics” associated with increased aggression, etc. have not been with increased aggression, etc. have not been provenproven

FYIFYI– Down syndrome is much more common in Down syndrome is much more common in

babies born to mothers over age 35 (see babies born to mothers over age 35 (see p.456) – hypothesized that may be due to p.456) – hypothesized that may be due to older ova that have been present since the older ova that have been present since the woman’s birth in combination with increased woman’s birth in combination with increased exposure to radiationexposure to radiation

Mitosis as a method of cell reproduction (Cloning)Mitosis as a method of cell reproduction (Cloning)

Cloning – process in which identical Cloning – process in which identical offspring are formed from a single cell or offspring are formed from a single cell or tissue (clone = cutting)tissue (clone = cutting)

all cells formed in this manner are identical all cells formed in this manner are identical (or almost – some small variations due to (or almost – some small variations due to mutation are expected)mutation are expected)

used in some plants and animals for used in some plants and animals for reproductionreproduction

Asexual Reproductive StrategiesAsexual Reproductive Strategiesbinary fission: equal division of the cytoplasm binary fission: equal division of the cytoplasm and nucleus of an organism resulting in two new and nucleus of an organism resulting in two new organisms exs. ameba, paramecium, euglena organisms exs. ameba, paramecium, euglena

budding: nucleus of an organism's cell divides budding: nucleus of an organism's cell divides equally but the cytoplasm divides unequally -- equally but the cytoplasm divides unequally -- the new cells formed may live as individuals or the new cells formed may live as individuals or as colonies exs. yeast, hydra as colonies exs. yeast, hydra

sporulation: the production of spores ex. molds sporulation: the production of spores ex. molds spores: single, specialized cells which are spores: single, specialized cells which are released from the parent -- they are enclosed in released from the parent -- they are enclosed in a protective case and develop when a protective case and develop when environmental conditions are favorable environmental conditions are favorable

regeneration: the development of an entire regeneration: the development of an entire new organism from part of an original new organism from part of an original organism ex. starfish -- one ray and part of organism ex. starfish -- one ray and part of central body can develop into an entire central body can develop into an entire new organismnew organism– may also involve the restoration of lost body may also involve the restoration of lost body

parts parts – invertebrates have greater powers of invertebrates have greater powers of

regeneration than do vertebrates regeneration than do vertebrates

vegetative propagation: regeneration in plants vegetative propagation: regeneration in plants – Complete new plants develop from part of the original Complete new plants develop from part of the original

plant. plant.

bulbs: enlarged underground stems surrounded by bulbs: enlarged underground stems surrounded by leaves and containing stored food exs. onions, leaves and containing stored food exs. onions, tulips tulips

tubers: enlarged underground stem with buds or tubers: enlarged underground stem with buds or "eyes" that contain stored food -- new plants "eyes" that contain stored food -- new plants develop from the bud ex. potato develop from the bud ex. potato

runners: stems that grow along the ground -- at runners: stems that grow along the ground -- at intervals roots form and penetrate the soil and new intervals roots form and penetrate the soil and new plants develop at these points (ex. strawberries) plants develop at these points (ex. strawberries)

rhizomes: underground stems from which new rhizomes: underground stems from which new plants develop at intervals ex. quackgrassplants develop at intervals ex. quackgrass

natural

layering: occurs when part of an old plant is bent layering: occurs when part of an old plant is bent and covered with soil -- a new plant develops from and covered with soil -- a new plant develops from the covered plant ex. blackberry the covered plant ex. blackberry

cuttings (slips): a piece of a plant is placed in moist cuttings (slips): a piece of a plant is placed in moist soil or water and a complete plant develops from it soil or water and a complete plant develops from it

grafting: the stem of one plant to be propagated is grafting: the stem of one plant to be propagated is attached to the cut end of another growing plant attached to the cut end of another growing plant

embryo splittingembryo splitting

FYIFYI– cloning may be used on plants that normally cloning may be used on plants that normally

reproduce sexually to produce genetically reproduce sexually to produce genetically “superior” plants “superior” plants

– even though all of the cells are identical to the even though all of the cells are identical to the parents’, they differentiate to perform parents’, they differentiate to perform separate dutiesseparate duties

– to make cloning work, scientists must delay to make cloning work, scientists must delay differentiationdifferentiation

– organisms (cells) that are able to produce an organisms (cells) that are able to produce an adult from one cell are called TOTIPOTENTadult from one cell are called TOTIPOTENT

– although until recently (p.438) cloning of although until recently (p.438) cloning of mammals was only achievable by taking a mammals was only achievable by taking a fertilized egg’s nucleus and placing it in fertilized egg’s nucleus and placing it in another egg cell, Dolly the sheep was cloned another egg cell, Dolly the sheep was cloned from an ADULT cell’s nucleusfrom an ADULT cell’s nucleus

– cloning may find a use in “transplants” – if the cloning may find a use in “transplants” – if the cells transplanted are regenerative, they will cells transplanted are regenerative, they will reproduce and grow into a working organ reproduce and grow into a working organ (liver)(liver)

– identical twins are nature’s clones – how identical twins are nature’s clones – how much of their lives is dictated by their genes?much of their lives is dictated by their genes?

Cell Death and the Aging ProcessCell Death and the Aging Process– Cells in the body divide at different rates, and Cells in the body divide at different rates, and

have different life spanshave different life spans– Only spermatocytes & cancerous cells appear Only spermatocytes & cancerous cells appear

to have no defined life span (although mature to have no defined life span (although mature sperm do not have an infinite life span)sperm do not have an infinite life span)

– All other cells appear to have a finite # of cell All other cells appear to have a finite # of cell divisions built in – maximum life span remains divisions built in – maximum life span remains at ~115 yrsat ~115 yrs

– Reproductive ability appears to Reproductive ability appears to as as specialization specialization

WHY? WHY? – maybe spontaneous mutations cause the maybe spontaneous mutations cause the

cells to be declared incompetent & shuts them cells to be declared incompetent & shuts them down (no)down (no)

– maybe aging genes shut the cells down (ex. maybe aging genes shut the cells down (ex. graying of hair – but at different ages)graying of hair – but at different ages)

– maybe cell lineages die maybe cell lineages die no longer able to no longer able to divide, so worn-out cells are not replaceddivide, so worn-out cells are not replaced

CancerCancer

Defined as the rapid, uncontrolled growth of cells Defined as the rapid, uncontrolled growth of cells too much life too much life

Tumors are believed to be monoclonal (the Tumors are believed to be monoclonal (the result of one transformed cell dividing rapidly)result of one transformed cell dividing rapidly)

Abnormal growth (unlike normal controlled Abnormal growth (unlike normal controlled growth replacing dying & dead cells), without the growth replacing dying & dead cells), without the signals of the body directing growth.signals of the body directing growth.

Outside of the human body, cancer cells show Outside of the human body, cancer cells show growth more rapid than fetal growth (10kg mass growth more rapid than fetal growth (10kg mass in 6 weeks)in 6 weeks)

Metastasis (the spreading of cancer cells Metastasis (the spreading of cancer cells through the body) caused by the fact that through the body) caused by the fact that cancerous cells have lost the attraction to each cancerous cells have lost the attraction to each other that other cells haveother that other cells haveCancer cells have lost the ability to differentiate Cancer cells have lost the ability to differentiate and carry out cell processesand carry out cell processesPrevention focuses on the elimination of Prevention focuses on the elimination of carcinogenic/teratogenic/mutagenic substances carcinogenic/teratogenic/mutagenic substances – diet, tobacco, sun– diet, tobacco, sunTreatments are focused on processes that affect Treatments are focused on processes that affect rapidly growing cells, stopping their mitosis, rapidly growing cells, stopping their mitosis, gene therapy that “turn on” the immune system gene therapy that “turn on” the immune system and removal of the cancerand removal of the cancerAll cancers are different and require different All cancers are different and require different treatmentstreatments

Alternation of Generation & Other Alternation of Generation & Other Reproductive StrategiesReproductive Strategies

When organisms may use both sexual and asexual When organisms may use both sexual and asexual reproductive strategies at different stages during their life reproductive strategies at different stages during their life cycle, it is called “alternation of generation”cycle, it is called “alternation of generation” (see diagram (see diagram life cycle of moss/fern)life cycle of moss/fern)– Best of both worlds – the plant (animal) may Best of both worlds – the plant (animal) may

reproduce rapidly using asexual techniques, but may reproduce rapidly using asexual techniques, but may benefit from the genetic variation provided by sexual benefit from the genetic variation provided by sexual reproductionreproduction

– Plants (animals) that use this strategy may exist Plants (animals) that use this strategy may exist primarily as diploid (higher plants & animals) or primarily as diploid (higher plants & animals) or haploid (primitive plants) – but unlike most animals, haploid (primitive plants) – but unlike most animals, both the haploid and diploid organisms are both the haploid and diploid organisms are multicellularmulticellular

– Spores (n) are the most common source of haploid Spores (n) are the most common source of haploid plants, are produced by the sporophyte generation plants, are produced by the sporophyte generation (2n) by meiosis(2n) by meiosis

– The spores produce multicellular plants (haploid) The spores produce multicellular plants (haploid) which divide mitotically and produce gametes which divide mitotically and produce gametes mitotically. These haploid plants are called the mitotically. These haploid plants are called the gametophyte generation.gametophyte generation.

– These gametes will fuse to form the diploid form of These gametes will fuse to form the diploid form of the plant, which is capable of producing the spores the plant, which is capable of producing the spores (called the sporophyte generation)(called the sporophyte generation)

– In the fern, the gametophyte generation (n) is the In the fern, the gametophyte generation (n) is the predominant form of the plantpredominant form of the plant

– In the moss, the sporophyte generation (2n) is the In the moss, the sporophyte generation (2n) is the predominant form of the plantpredominant form of the plant

sporophyte (2n)

meiosis

spores (n)

female

gametophyte (n)

mitosis

male & female

gametophytes (n)

sperm

(fertilization)

Life Cycle of the Moss

– In the pine, the sporophyte is the most In the pine, the sporophyte is the most common – in fact, the cone produced is also common – in fact, the cone produced is also diploid, undergoing meiosis after the cone is diploid, undergoing meiosis after the cone is formed – the gametes from male cones (the formed – the gametes from male cones (the spores or pollen) are carried by the wind to spores or pollen) are carried by the wind to the female cones – final differentiation and the female cones – final differentiation and fertilization occurs in the female cone, then fertilization occurs in the female cone, then forming a seed, transported by the windforming a seed, transported by the wind

Very few animals show alternation of Very few animals show alternation of generation – the water flea, displays a generation – the water flea, displays a form of thisform of this– In the spring, all diploid eggs hatch into In the spring, all diploid eggs hatch into

femalesfemales– These females lay diploid eggs and hatch These females lay diploid eggs and hatch

diploid females all summer (asexual diploid females all summer (asexual reproduction)reproduction)

– Cold temperatures stimulate females to lay Cold temperatures stimulate females to lay haploid eggs, which hatch into haploid males, haploid eggs, which hatch into haploid males, which mate with the females and to fertilize which mate with the females and to fertilize their haploid eggs (which survive until the next their haploid eggs (which survive until the next summer)summer)

The housefly (see Nelson p.449), although not The housefly (see Nelson p.449), although not alternation of generation, is capable of alternation of generation, is capable of reproducing asexuallyreproducing asexually

Some animals are hermaphroditic (have both Some animals are hermaphroditic (have both male and female sex organs) – they may self-male and female sex organs) – they may self-fertilize or cross-fertilize when other worms are fertilize or cross-fertilize when other worms are around. (ex. worms)around. (ex. worms)