Chapters: 12-15

Cell Division and Genetics

Why do we need cell division?

2 REASONS:1.Growth and maintenance

2.Reproduction

http://gaskinsanatomy.wikispaces.com/file/view/CellCycle_L.jpg/252096666/CellCycle_L.jpg

Cell Cycle Overview

The Cell Cycle Control System

A cyclically operating set of molecules in the cell that both triggers and coordinates key events in the cell cycle

• regulated at certain checkpoints by both internal and external signals

The Checkpoints

A control point where stop and go-ahead signals can regulate the cycle

•animal cells have built-in stop signals that halt the cell cycle at checkpoints until overridden by go ahead signalso signals come from cellular surveillance mechanisms

inside the cello determine if the major processes of the cell cycle have

been completed

•Three major check points: G1, G2, M

G1 Checkpoint

“Restriction Point"

• if a cell receives the go ahead at G1 checkpoint, then the cell will continue with the cell cycle.

• If the cell DOES NOT get the go ahead it will enter G0o the nondividing state of a cell o most cells in body are in G0 (nerves and muscle cells)o liver cells can be taken out of G0 phase if necessary

(growth factors released during injury)

The Cell Cycle Clock

The cell cycle is controlled by fluctuations of cycle control molecules that occur in intervals

• these rhythmic abundances pace the events of the cell cycle

Regulatory molecules are two proteins

•cyclins

•protein kinaseo enzymes that will activate or inactivate other proteins

by phosphorylating them give the go ahead signal at the G1 and G2 checkpoints

Cell Division in Prokaryotes

Called Binary Fission

• means "division in half" (asexual reproduction)

a. starts at the origin of replication where the circular DNA begins replicating

b. once the DNA is fully replicated, the cell begins to stretch toward the poles of the cell

c. the membrane begins pinching off in the middle

d. you now have two new daughter cells

Interphase

• the longest phase of the cell cycleo accounts for 90% of the cell's lifeo the cell is producing proteins and cytoplasmic organelles

• The chromatin is not condensed during interphase because it is needed for protein synthesis

• Divided into 3 subphases:o G1 Phase => first gapo S Phase => synthesis (chromosome duplication)o G2 Phase => second gap

Mitosis

The part of the cell cycle where the cell is actually undergoing cell division

• Consists of 5 stageso prophaseo metaphaseo anaphaseo telophase

• Timing and rate of cell division are crucial to normal growth, development and maitenanceo varies with type of cell

Cytokinesis is part of the Mitotic (M) phase, but not apart of mitosis itself.Different in plants and animals

Prophase

1st stage of mitosis

• the chromatin condenses into two identical chromosomes and the nuclear envelope begins to disappear

http://www.google.com/search?client=safari&rls=en&q=prophase%20in%20animal%20cells&oe=UTF-8&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&ei=7712UeO9FcL1iwLLp4HwCA&biw=1189&bih=636&sei=9L12UaiuN9HZigKfp4DYBQ#imgrc=85fmDMAZOzjvuM%3A%3BgeNrf4q9_1ueeM%3Bhttp%253A%252F%252Fstudent.ccbcmd.edu%252F~gkaiser%252Fbiotutorials%252Fdna%252Fmitosis%252Fimages%252Fearly_late_prophase1_pc.jpg%3Bhttp%253A%252F%252Fstudent.ccbcmd.edu%252F~gkaiser%252Fbiotutorials%252Fdna%252Fmitosis%252FpcprophaseB.html%3B360%3B270

Metaphase

2nd stage of mitosis

• the chromosomes line up on the equatorial plate

• spindle fibers are attached to the kinetochore of each chromosome pair

• "tug of war"

http://www.google.com/search?client=safari&rls=en&q=metaphase&oe=UTF-8&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&ei=S752UbHeBcn9iwKZ5IGIBA&biw=1189&bih=636&sei=yr52UfnNN4qyiQLnjIDADQ#imgrc=BPdNkm2cwZ3kZM%3A%3Bzg5i6Qihw8xmiM%3Bhttp%253A%252F%252Fstudent.ccbcmd.edu%252F~gkaiser%252Fbiotutorials%252Fdna%252Fmitosis%252Fimages%252Fmetaphase1_pc.jpg%3Bhttp%253A%252F%252Fstudent.ccbcmd.edu%252F~gkaiser%252Fbiotutorials%252Fdna%252Fmitosis%252Fpcmetaphase.html%3B360%3B270

Anaphase

4th stage of mitosis

• shortest

• cohesion proteins are cut and the sister chromatids are now separated

• the cell beings elongating

http://www.google.com/search?client=safari&rls=en&q=anaphase&biw=1189&bih=636&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&ei=z8B2UaamLoOKjALb5oHwDw#imgrc=rB3kR2CfgC2p6M%3A%3BKIBxp-ZsomYcLM%3Bhttp%253A%252F%252Fbotit.botany.wisc.edu%252FResources%252FBotany%252FMitosis%252FAllium%252FAnaphase.jpg%3Bhttp%253A%252F%252Fbotit.botany.wisc.edu%252FResources%252FBotany%252FMitosis%252FAllium%252FAnaphase.jpg.html%3B780%3B600

Telophase

Final stage of mitosis

•daughter cells begin to form

•nuclear envelope is visible again

•nucleoli reappear

• spindle fibers disappear

http://www.google.com/imgres?imgurl=http://student.ccbcmd.edu/~gkaiser/biotutorials/dna/mitosis/images/telophase_ac.jpg&imgrefurl=http://student.ccbcmd.edu/~gkaiser/biotutorials/dna/mitosis/actelophase.html&h=270&w=360&sz=40&tbnid=ojFA9wFcm3h54M:&tbnh=107&tbnw=142&prev=/search%3Fq%3Dtelophase%2Bof%2Banimal%2Bcell%26tbm%3Disch%26tbo%3Du&zoom=1&q=telophase+of+animal+cell&usg=__k6YCcShPZlGr1PoUmvpC3MzJlY4=&docid=VHiqpekBdaBjfM&sa=X&ei=AsN2UcSAL8KUiQKC-YHgAw&ved=0CDMQ9QEwAA&dur=352

Comparing Cytokinesis

http://www.google.com/search?client=safari&rls=en&q=cytokinesis%20of%20animal%20cells&oe=UTF-8&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&ei=18R2Ubz9Beb6igL3_oHIBQ&biw=1189&bih=636&sei=2cR2UazNEoW4iwLrkIGYCw#imgrc=PlZTpAvHJ3NARM%3A%3BwQIPcLTXtlrN_M%3Bhttp%253A%252F%252Fcourse1.winona.edu%252Fsberg%252FIMAGES%252Fcleavagefurrow1.jpg%3Bhttp%253A%252F%252Fcourse1.winona.edu%252Fsberg%252F241f05%252FLec-note%252FMitosis.htm%3B600%3B482

http://www.google.com/search?q=cytokinesis+of+plant+cells+image&client=safari&rls=en&tbm=isch&tbo=u&source=univ&sa=X&ei=JsV2Ub_CIcOFiAL4zIDQCw&ved=0CDEQsAQ&biw=1189&bih=636#imgrc=DijPBLdx6RGeTM%3A%3Bc1gTydf0GcSvoM%3Bhttp%253A%252F%252Fiknow.net%252Fimages%252Fscreen_cellplate_512.jpg%3Bhttp%253A%252F%252Fiknow.net%252FCDROMs%252Fcell_cdrom%252Fcell_dvd.html%3B512%3B384

Animals: Plants:In animals: •occurs by cleavage•a cleavage furrow will form in what was the middle of the parent cell

o the furrow is a contractile ring of actin filaments that contract

o eventually splits the cell into two daughter cells

• There is NO cleavage furrow

• because plant cells have cell walls in addition to cell membranes, they need to build a new cell wall

• vesicles will form in the middle of the original parent cell from the golgi apparatus (starts during telophase)o merge and

become the cell plate

o enlarges until the membranes fuse

Cyclins and Protein Kinases

Timing of the cell cycle is initiated by growth factors and controlled by two kinds of molecules: cyclins and protein kinases

•protein kinases (cell signal transduction) catalyze the phosphorylation of target proteins that regulate the cell cycleo Cyclin-dependent kinases (CDKs)

Cyclin-dependent Kinase

• Activated by binding to the protein cyclino exposes the active site to the

CDK and activates the molecule allosteric regulation

• Several CDKs regulate the cell cycle at specific stages called cell cycle checkpointso each cyclin is manufactured at

a precise time during the cell cycle and therefore each CDK is activated at a precise time

• The activity of CDKs rises and falls with changes in the concentration of its cyclin partner MPF

The Chain Reaction that Controls the Cell Cycle

growth factor

cyclin synthesis

CDK activation

Cell Cycle events

Meiosis

**this video made us laugh, if you get the gist of it, move on**

http://www.youtube.com/watch?v=iCL6d0OwKt8

Meiosis: Different than Mitosis

Meiosis generates the genetic diversity taht is the raw material for natural selection and evolution

•produces gametes (egg and sperm) or sex cellso that are haploid the chromosome number (n) of the

parent cell the chromosome number will return to diploid (2n)

during sexual fusion

•NOT MITOSIS TWICE

Meiosis I: The Source of Genetic Variation

Known as reduction division

•Meiosis I is characterized by:o homologous chromosomes pairing upo crossing over genetic information

the nonsister chromatids exchange genetic information results in recombination of genetic material CROSSING OVER ENSURES GREATER VARIATION AMONG

GAMETES

Meiosis: Prophase I

• Synapsis: the pairing of homologous chromosomes occur

• crossing over occurs

• Chiasmata: the point where the crossing over occurs

Prophase vs. Prophase I

chiasmataProphase: Mitosis•the chromosomes condense and sister chromatids meet at the kinetochore Prophase I: Meiosis

•homologous chromosomes pair up•non-sister chromatids exchange genetic information (crossing over) at the chiasmata

http://www.google.com/search?client=safari&rls=en&q=chromosome%20kinetochore&biw=1024&bih=670&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&ei=fat-UcGhD6WIiALh6ID4DQ#imgrc=7f1nBsoCqPPpCM%3A%3BHxZOfUbhmRiPkM%3Bhttp%253A%252F%252Fiws.collin.edu%252Fbiopage%252Ffaculty%252Fmcculloch%252F1406%252Foutlines%252Fchapter%25252011%252FMa4-12.JPG%3Bhttp%253A%252F%252Fiws.collin.edu%252Fbiopage%252Ffaculty%252Fmcculloch%252F1406%252Foutlines%252Fchapter%25252011%252Fchap11.htm%3B648%3B486

http://www.google.com/search?client=safari&rls=en&q=crossing%20over&oe=UTF-8&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&ei=oat-Uc3IDoSbiAL6joHIDA&biw=1024&bih=670&sei=o6t-UdWkEOWsiQKQhoCACQ#imgrc=GqFKVxw1ZWYopM%3A%3BrFAfPa6SaJh0ZM%3Bhttp%253A%252F%252Fwww.phschool.com%252Fscience%252Fbiology_place%252Flabbench%252Flab3%252Fimages%252Fcrossovr.gif%3Bhttp%253A%252F%252Fwww.phschool.com%252Fscience%252Fbiology_place%252Flabbench%252Flab3%252Fcrossovr.html%3B240%3B320

Meiosis I: Overview

http://www.google.com/imgres?imgurl=http://legacy.owensboro.kctcs.edu/gcaplan/anat2/notes/meiosis1.gif&imgrefurl=http://legacy.owensboro.kctcs.edu/gcaplan/anat2/notes/APIINotes2%2520meiosis.htm&h=390&w=648&sz=62&tbnid=e3OITVb0QiXm7M:&tbnh=82&tbnw=137&prev=/search%3Fq%3Dmeiosis%2BI%26tbm%3Disch%26tbo%3Du&zoom=1&q=meiosis+I&usg=__Gqg8bkHhISddeNTTwKvPdQzlSMY=&docid=IJ3RFKtSBKpfcM&sa=X&ei=5q5-UcKEBeOZiQLi84HYDg&ved=0CDYQ9QEwAQ&dur=254

Meiosis II

Meiosis II is exactly like mitosis in the sense that the sister chromatids are separating and forming two new cells

• remember that after Meiosis I, there are two haploid cells (half of the number of chromosomes) that are genetically differento meiosis II continues as cell division, separating the

sister chromatidso In the end, each gamete should have half the

chromosomes of the parent cell and no sister chromatids

Egg sex cells vs. Sperm cells

Male sex cells (sperm)

•undergo meiosis where each sperm is equalo like you think a normal cell would undergo meiosiso quantity over quality

Female sex cells (eggs)

• specialized meiosis

•an egg will undergo meiosis to "get rid of" half of genetic material, but will keep the rest of the cells resourceso leftover cells are called polar bodieso quality over quantity

Egg cells vs sperm cells

http://veterinary-online.blogspot.com/2012/12/development-of-animals-formation-of.html#.UX86879qpNY

Ch. 14 Ch. 14 Mendel and the Gene Mendel and the Gene IdeaIdea

Law of DominanceLaw of Dominance

Mendel’s first law is the Mendel’s first law is the law of dominancelaw of dominance

Law of dominanceLaw of dominance: states that when two organisms, each : states that when two organisms, each homozygoushomozygous (pure) for two opposing traits are crossed, the (pure) for two opposing traits are crossed, the offspring will be offspring will be hybridhybrid (carry two different alleles) but will (carry two different alleles) but will exhibit only the exhibit only the dominant traitdominant trait

The trait that remains hidden is known as the The trait that remains hidden is known as the recessive traitrecessive trait

Parent (P): TT X tt (pure tall) (pure dwarf)

Offspring (F1): Tt All hybrid

T T

t

t

Law of dominance

All offspring are tall

Law of SegregationLaw of Segregation

The The law of segregation law of segregation states that during the states that during the formation of gametes, the two traits carried by each formation of gametes, the two traits carried by each parent separateparent separate

GametesGametes

The cross that best exemplifies this law the The cross that best exemplifies this law the monohybrid crossmonohybrid cross, Tt X Tt. In the monohybrid , Tt X Tt. In the monohybrid cross, a trait that was not evident in either parent cross, a trait that was not evident in either parent appears in the F1 generationappears in the F1 generation

Tt

T t

Law of Independent Law of Independent AssortmentAssortment

The only factor that determines how these The only factor that determines how these alleles alleles segregatesegregate or assort is how the or assort is how the homologous pairs line up in metaphase of homologous pairs line up in metaphase of meiosis I, which is random.meiosis I, which is random.

http://2.bp.blogspot.com/-J9gE_FJmHIc/TZZc9lsPQhI/AAAAAAAAACE/KuMgphh-1jU/s1600/science+10.png

Law of Independent Law of Independent AssortmentAssortment

The The law of independent assortment law of independent assortment applies applies when a cross is carried out between two when a cross is carried out between two individuals hybrids for two or more traits that individuals hybrids for two or more traits that are are notnot on the same chromosomeon the same chromosome. . This cross is called the This cross is called the dihybrid crossdihybrid cross. . This law states that during gamete formation, the This law states that during gamete formation, the

alleles of a gene for one trait segregate alleles of a gene for one trait segregate independently from the allele of a gene for independently from the allele of a gene for another trait.another trait.

Multiplication RuleMultiplication Rule

Multiply the chance of one happening by the Multiply the chance of one happening by the chance that the other will happenchance that the other will happen

For exampleFor example:: The chance of a couple having two boys The chance of a couple having two boys

depends on two independent events. The depends on two independent events. The chance of the first child being a boy is ½ ; and chance of the first child being a boy is ½ ; and the chance of the next child being a boy is ½the chance of the next child being a boy is ½

Therefore, the chance that the couple will have Therefore, the chance that the couple will have two boy is ½ x ½ = ¼ two boy is ½ x ½ = ¼

The chance of having three boys is ½ x ½ x ½ The chance of having three boys is ½ x ½ x ½ = 1/8= 1/8

Addition RuleAddition Rule

When more than one arrangement of events When more than one arrangement of events producing the specified outcome is possible, producing the specified outcome is possible, the probabilities for each outcome are added the probabilities for each outcome are added together.together.

For example: For example: if a couple is planning on having if a couple is planning on having two children, what is the chance that they will two children, what is the chance that they will have one boy and one girlhave one boy and one girl

The probability of having a girl and then a boy The probability of having a girl and then a boy is ½ x ½ = ½is ½ x ½ = ½

The probability of having one boy and one girl The probability of having one boy and one girl is ¼ + ¼ = ½ is ¼ + ¼ = ½

Monohybrid crossMonohybrid cross

The monohybrid cross (Tt XTt) is a cross between two The monohybrid cross (Tt XTt) is a cross between two organisms that are each hybrid for one trait. organisms that are each hybrid for one trait.

The phenotype (appearance) ration from this cross is The phenotype (appearance) ration from this cross is 3 tall to 1 dwarf plant.3 tall to 1 dwarf plant.

The genotype (type of genes) ratio, 1 to 2 to 1, given The genotype (type of genes) ratio, 1 to 2 to 1, given as percentages: 25% homozygous dominant, 50% as percentages: 25% homozygous dominant, 50% heterozygous, and 25% homozygous recessive. These heterozygous, and 25% homozygous recessive. These results are always the same for any monohybrid cross.results are always the same for any monohybrid cross.

F1: Tt X Tt

F2: TT, Tt, or tt

T t

T

t

Monohybrid cross

TestcrossTestcross

The testcross is way to determine the genotype of an The testcross is way to determine the genotype of an individual plant or animal showing only the dominant trait. individual plant or animal showing only the dominant trait.

If the parent of unknown genotype is BB, there can be no white offspringIf the parent of unknown genotype is BB, there can be no white offspring

B= blackB= black

b= whiteb= white

If the parent of the unknown genotype is hybrid, there is a 50% chance that any If the parent of the unknown genotype is hybrid, there is a 50% chance that any offspring will be white.offspring will be white.

B B

B b

b

b

b

b

The Dihybrid CrossThe Dihybrid Cross

A dihybrid cross is a cross between two F1 plants A dihybrid cross is a cross between two F1 plants because it is a cross between individual that are because it is a cross between individual that are hybrid fro two different traitshybrid fro two different traits

This cross can produce 4 different types of gametes, This cross can produce 4 different types of gametes, such as: TY, Ty, tY, and ty.such as: TY, Ty, tY, and ty.

TY

TY

Ty

Ty

tY

ty

tY ty

Phenotype ratio:9:3:3:1

Incomplete dominanceIncomplete dominance

Incomplete dominance is characterized by blending.Incomplete dominance is characterized by blending.

For example: A red flower (For example: A red flower (RRRR) crossed with a white ) crossed with a white flower (flower (WWWW) produces all pink offspring () produces all pink offspring (RWRW))

• If 2 pink flowers are crossed, there is a 25% If 2 pink flowers are crossed, there is a 25% chance that the offspring will be red, a 25% chance that the offspring will be red, a 25% chance the offspring will be white, and a 50% chance the offspring will be white, and a 50% chance the offspring will be pinkchance the offspring will be pink

R R

W

W

R

R

W

W

CodominanceCodominance

In codominance, both traits show.In codominance, both traits show.

For example: Different blood groups: M, N, and For example: Different blood groups: M, N, and MNMN

MM NN MN

Multiple allelesMultiple alleles

Occurs when there are are more than two allelic Occurs when there are are more than two allelic forms of a geneforms of a gene

For exampleFor example: Human blood types- A, B, AB and O: Human blood types- A, B, AB and OThe 3 alleles= A, B, and O The 3 alleles= A, B, and O

determine 4 different blood typesdetermine 4 different blood types

Gene Interactions:Gene Interactions:PleiotropyPleiotropy

Pleiotropy is the ability of one single Pleiotropy is the ability of one single gene to affect an organism in several or gene to affect an organism in several or many ways.many ways.

For exampleFor example: autosomal recessive disease : autosomal recessive disease cystic fibrosiscystic fibrosis abnormal thickening to abnormal thickening to mucus that coats certain cellsmucus that coats certain cells

thick mucus builds up in the pancreas, thick mucus builds up in the pancreas, lungs, digestive tract and other organslungs, digestive tract and other organs

leads to multiple leads to multiple pleiotropic pleiotropic effects effects including poor absorption of nutrients in the including poor absorption of nutrients in the intestine and chronic bronchitisintestine and chronic bronchitis

Gene Interactions: Gene Interactions: EpistasisEpistasis

Where two separate genes control one trait, but Where two separate genes control one trait, but one gene masks the expression of the other geneone gene masks the expression of the other gene

The gene that masks the expression of the other gene is The gene that masks the expression of the other gene is epistatic to the gene it masksepistatic to the gene it masks

For exampleFor example: agouti coat color in mice: agouti coat color in mice2 genes control different enzymes in 2 different 2 genes control different enzymes in 2 different pathways that both contribute to coat colorpathways that both contribute to coat color

Both genes A and B must be present in order to produce Both genes A and B must be present in order to produce that agouti colorthat agouti color

AaBb X AaBb

In the absence of B, even if A is present, the coat is colorless (albino)Therefore gene B is epistasis to gene A

Polygenic InheritancePolygenic Inheritance Polygenic traitsPolygenic traits: many characteristics such as skin : many characteristics such as skin

color, hair color, and height result from blending of color, hair color, and height result from blending of several separate genes that vary along a continuumseveral separate genes that vary along a continuum

The wide variation in genotypes always results in a The wide variation in genotypes always results in a bell-shaped curve in an entire population bell-shaped curve in an entire population

http://photos1.blogger.com/blogger/4252/2243/400/Skin_Pigmentation.jpg

The PedigreeThe Pedigree

A A pedigreepedigree is a family tree that indicates the phenotype of one is a family tree that indicates the phenotype of one trait being studied for every member of a familytrait being studied for every member of a family

It can determine how a particular trait is inheritedIt can determine how a particular trait is inherited

Females are represented by a and males by a Females are represented by a and males by a

A shape is completely shaded in if a person exhibits A shape is completely shaded in if a person exhibits the traitthe trait

http://www.oculist.net/downaton502/prof/ebook/duanes/graphics/figures/v9/0510/007f.gif

Ch. 15The Chromosomal Basis of Inheritance

The Chromosomal Basis of Inheritance

Chromosome theory of inheritance:

•Genes have specific loci along chromosomes

•Chromosomes undergo segregation and independent assortment

Thomas Hunt Morgan's Experiment:

•Fruit fly (drosophila melanogaster)

•Bred flies for 2 years with no conclusion

•Finally, 1 male had white eyes instead of the usual red (red is the wild type-- characteristic most commonly observed)

o White eyes were a mutant phenotype

•Continued mating females with white-eyed maleo Discovered the gene for eye color is gender

related and on the X chromosomeo Supported chromosome theory of

inheritance that a specific gene is on a specific chromosome

http://en.wikipedia.org/wiki/File:Sexlinked_inheritance_white.jpg

Sex-linked genes

• X and Y chromosomeso XX-- female; XY-- male (sex determination is 50-50

chance)

• Sex-linked gene- gene located on either X chromosomeo Very few Y-linked genes, passed from father to sono About 1,100 X-linked genes

Males more likely to have disorders from X-linked gene (have disease if either recessive or dominant because only one X chromosome)

ex. color blindness, Duchenne muscular dystrophy, hemophilia

Sex-linked Genes• X inactivation in Females

o Most of one X chromosome becomes inactivated when embryo is developing If did not become

inactivated, chromosomes would make 2x the amount of proteins for X-linked genes as males

Inactive X condenses into compact object called a Barr Body

Selection for which X chromosome is inactivated occurs randomly

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Linked Genes

• Linked genes- genes located near each other on the same chromosome tend to be inherited together in a genetic cross

o Genetic recombination- the production of offspring with combinations of traits that differ from those found in either parent Parental type- the half of the offspring

that inherit a phenotype that matches either parent's phenotype

Recombinant types (recombinants)- offspring that have non parental phenotypes

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Gene Recombination and Linkage

• The physical basis of recombination between unlinked genes is the random orientation of homologous chromosomeso Happens in metaphase I of meiosiso Leads to independent assortment of the 2 unlinked geneso Crossing over- reciprocal exchange of genes between one

paternal and one maternal chromatid. accounts for the recombination of linked genes

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Gene Recombination and Linkage

Alterations of Chromosomes

• Large-scale chromosomal changes can affect an organism's phenotypeo physical/ chemical disturbances or error

during meiosis results in developmental disorders

• Nondisjunction- members of a pair of homologous chromosomes don't move apart properly during meiosis I or sister chromatids fail to separate during meiosis II

http://www.nature.com/scitable/content/32851/10.1038_nrm1526-f1_large_2.jpg

Nondisjunction

• Aneuploidy- a condition where a normal gamete unites with an abnormal one, resulting in a zygote with an irregular amount of chromosomeso Monosomic- missing a chromosome (2n-1)o Trisomic- chromosome tripled (2n+1)o If organism survives, has a set of traits that result from

abnormal amount or missing chromosome ex. Down Syndrome (trisomy)

• Nondisjunction can occur during mitosis as wello If happens during embryonic development, mitosis will

pass aneuploid condition to large number of cells

Nondisjunction

• Polyploidy-general term for chromosomal alteration where organism has two complete chromosome setso triploidy (3n); tetraploidy (4n)o More common in plantso Have less effect than aneuploids because is a full set of

chromosomes and one missing chromosome disrupts genetic balance more

Alterations in Chromosome Structure

• Error in meiosis or damaging agents can in 4 types of changes in chromosome structure:o Deletion- when a chromosome fragment is lost

Results in chromosome missing certain geneso Duplication- the "deleted" fragment becomes attached as

an extra segment to a sister chromatid o Inversion- chromosome fragment reattaches to the original

chromosome, but in the reverse orientationo Translocation- fragment joins a nonhomologous

chromosome

• Deletions and duplications are likely to occur during meiosis (in crossing over)

Alterations of Chromosome Structure

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Genomic Imprinting

• Genomic Imprinting- Idea that the expression of an allele in offspring depends on whether the allele is inherited from the mother or fathero Genes are autosomal (not sex-linked)

• Zygote only expresses one allele of an imprinted gene, from mother or father

• Occurs during gamete formation and results in the silencing of particular alleles

• Only affects a small fraction of gene in mammalian genomes, but are usually genes critical for development

Organelle genes

• Extranuclear/cytoplasmic genes

o Genes located outside the nucleus Can be in mitochondria, chloroplast

o Are not distributed to offspring like with nuclear chromosomes

• Extranuclear genes first noticed by Karl Correns (1909)o Noticed inheritance of yellow and white patches on the

leaves of a green planto Coloration only determined by the maternal planto Research showed that coloration patterns are due to

mutations in genes that control pigmentation

http://s3.amazonaws.com/picable/2009/07/23/1195661_Lovely-green-Plant_620.jpg

Sources

Goldberg, Deborah M.S. Barron's AP Biology. 3rd ed. New York: Baron's Educational Series, 2013. Print.

Reece, Jane B., and Neil A. Campbell. Campbell Biology. 9th ed. Boston: Benjamin Cummings / Pearson Education, 2011. Print.