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Cytological bases Cytological bases of heredityof heredity
College of Medical College of Medical technologytechnology
CytogeneticsCytogenetics
C.A.IgnacioC.A.Ignacio
Mendel’s analysis- by representing Mendel’s analysis- by representing abstract, hypothetical factors of abstract, hypothetical factors of inheritance by symbols to predict out inheritance by symbols to predict out comes of future crosses.comes of future crosses.
Chromosome theory of inheritanceChromosome theory of inheritance Genetics + cytology = means of Genetics + cytology = means of
correlating the results of breeding correlating the results of breeding experiments with the behaviour of experiments with the behaviour of structures that can actually be seen in structures that can actually be seen in the microscopes.the microscopes.
How chromosome number is How chromosome number is maintained?maintained?
All living things are made up of a living All living things are made up of a living material, the PROTOPLASM.material, the PROTOPLASM.
The protoplasm and the boundary are The protoplasm and the boundary are organized to form a unit – CELL.organized to form a unit – CELL.
2 distinct areas :2 distinct areas : Cytoplasm – major portion of the Cytoplasm – major portion of the
protoplasmic substance contained in a cell protoplasmic substance contained in a cell membranemembrane
Nucleus – dark staining body in the Nucleus – dark staining body in the cytoplasm.cytoplasm.
There are 2 kinds of organism:There are 2 kinds of organism:
Within the cytoplasm is a number of Within the cytoplasm is a number of organelles with active cell function. organelles with active cell function.
The most important chemical The most important chemical constituent of the living organism constituent of the living organism are Proteins.are Proteins.
How did the chromosome theory How did the chromosome theory take shape?take shape? One of the first lines of evidence came One of the first lines of evidence came
from observations of how chromosomes from observations of how chromosomes behave during the division of the cell’s behave during the division of the cell’s nucleus.nucleus.
Nature of chromosomes:Nature of chromosomes: Chromosomes vary in size, shape and number Chromosomes vary in size, shape and number
among species. It may be as short as ¼ among species. It may be as short as ¼ micron or as long as 3.5 microns.micron or as long as 3.5 microns.
Under the light microscope, staining by Under the light microscope, staining by various chemical dyes, the nucleus consist of various chemical dyes, the nucleus consist of a dark network called CHROMATIN.a dark network called CHROMATIN.
In which during the process of cell division In which during the process of cell division becomes organized as distinct bodies called becomes organized as distinct bodies called CHROMOSOMESCHROMOSOMES
Chromosomes undergoing mitosis are usually Chromosomes undergoing mitosis are usually rod like bodies each with a constriction at the rod like bodies each with a constriction at the centromerecentromere
Chromosomes – a linear end to end Chromosomes – a linear end to end arrangement of arrangement of genesgenes and DNA and DNA ( some proteins and RNA)( some proteins and RNA)
Chromosomes may be Chromosomes may be classified on the basis of their classified on the basis of their
centromerecentromere
MetacentricMetacentric submetacentric submetacentric acrocentricacrocentric telocentrictelocentric
karyotypingkaryotyping The characterization of the chromosomal The characterization of the chromosomal
complement of an individual or a species, complement of an individual or a species, including number, form, and size of the including number, form, and size of the chromosomes. chromosomes.
A photomicrograph of chromosomes A photomicrograph of chromosomes arranged according to a standard arranged according to a standard classification.classification.
To classify and array (the chromosome To classify and array (the chromosome complement of an organism or a species) complement of an organism or a species) according to the arrangement, number, size, according to the arrangement, number, size, shape, or other characteristics of the shape, or other characteristics of the chromosomes.chromosomes.
G-banded metaphase karyotype of a human male cell. Every chromosome pair can be identified by its banding pattern.
Chromosome 1 is about 12 μm long.
Asexual reproductionAsexual reproduction Occurs when a single individual Occurs when a single individual
produces a new individuals identical to produces a new individuals identical to itself.itself.
Simple animalsSimple animals Parthenogenetic – female organism can Parthenogenetic – female organism can
also produce offspring without also produce offspring without fertilizationfertilization
Sexual reproductionSexual reproduction When individual produce male and When individual produce male and
female gametes or sex cells.female gametes or sex cells.
Some organism and their Some organism and their diploid chromosome diploid chromosome
numbernumberorganismorganism Chromosome Chromosome numbernumber
CatCat 3838
chickenchicken 7878
gorillagorilla 4848
horsehorse 6464
kangarookangaroo 1212
antant 22
There are two kinds of There are two kinds of cells:cells:
Somatic – found in skin, muscles, bones, Somatic – found in skin, muscles, bones, lungs, heart and other internal organ. lungs, heart and other internal organ. Diploid (2N) complete set of chromosomes Diploid (2N) complete set of chromosomes
Somatic chromosomes of diploid organism Somatic chromosomes of diploid organism are found in pairs, the members of each pair are found in pairs, the members of each pair being alike is size, position of spindle being alike is size, position of spindle attachment and in bearing genes related to attachment and in bearing genes related to some hereditary characters.some hereditary characters.
Reproductive – sperm/egg. Haploid (N) Reproductive – sperm/egg. Haploid (N)
Cell division:Cell division:
Important activity of all kinds of cells.Important activity of all kinds of cells. Two different types of nuclear division: Two different types of nuclear division:
mitosis and meoisismitosis and meoisis In unicellular organism in order to In unicellular organism in order to
reproduce.reproduce. In multicellular organism, cell division In multicellular organism, cell division
results to growth and development.results to growth and development. Two integrated activities – Two integrated activities –
Karyokinesis and Cytokinesis.Karyokinesis and Cytokinesis.
Somatic cells and reproductive cells
divide by mitosis but only reproductive cells
undergo meiosis
mitosismitosis
Nuclear division associated with the Nuclear division associated with the division of somatic cells- cells of division of somatic cells- cells of eukaryotic body that are destined eukaryotic body that are destined not to become sex cells.not to become sex cells. Produces two genetically identical Produces two genetically identical
daughter cellsdaughter cells
MitosisMitosis
Four stages:Four stages: PProphaserophase MMetaphaseetaphase AAnaphase naphase TTelophaseelophase
The sequence of The sequence of events transpiring events transpiring from the close of from the close of one nuclear one nuclear division to the division to the beginning of the beginning of the next one is the next one is the interphase stage.interphase stage.
Interphase:Interphase: G1 – stage in which G1 – stage in which
nucleus and cytoplasm are nucleus and cytoplasm are enlarging toward mature enlarging toward mature size. Active synthesis of size. Active synthesis of RNA and Proteins takes RNA and Proteins takes place during this stage.place during this stage.
S – stage whereby S – stage whereby replication of DNA and replication of DNA and synthesis of histones synthesis of histones (simple protein containing (simple protein containing mainly basic amino acids mainly basic amino acids occurs)occurs)
G2- new DNA is rapidly G2- new DNA is rapidly complexed with complexed with chromosomal proteins; chromosomal proteins; RNA and Protein synthesis RNA and Protein synthesis continuescontinuesG1 and G2- gap between M and S
G1, S and G2 – interphase between mitosis
Prophase- onset of mitosis-Contraction into --a series of spiralschromatids
Metaphase-Nuclear spindle becomes prominent--chromosome to equatorial plane
Anaphase-Sister chromatids separate, one pair moving to each pole-Set of V-structure
Telophase-chromosomes uncoil- Resultant nuclei
MeiosisMeiosis
Nuclear divisions of the special cells that are Nuclear divisions of the special cells that are destined to produce gametes (meiocyte).destined to produce gametes (meiocyte).
oogenesis/ spermatogenesis (products of oogenesis/ spermatogenesis (products of meiosis)meiosis)
Reduction of chromosomes to the haploid Reduction of chromosomes to the haploid numbernumber
2 cell divisions2 cell divisions Occur during production of gametesOccur during production of gametes During 1During 1stst meotic division – DNA has already meotic division – DNA has already
formed 2 twin strands at this point crossing formed 2 twin strands at this point crossing over explains why you have the mothers eyes over explains why you have the mothers eyes and fathers hair.and fathers hair.
While some parts of this cell division While some parts of this cell division process are similar to the asexual cell process are similar to the asexual cell division process of mitosis, there are several division process of mitosis, there are several key differences. key differences.
Meiosis produces gametes, while mitosis Meiosis produces gametes, while mitosis produces other cell types. produces other cell types.
The process of meiosis halves the The process of meiosis halves the chromosome number from the original chromosome number from the original parent cell in the four cells it forms. It does parent cell in the four cells it forms. It does this by having two cell divisions forming this by having two cell divisions forming four cells, where mitosis has only one cell four cells, where mitosis has only one cell division forming two cells. division forming two cells.
Both processes start out with one doubling Both processes start out with one doubling or replication of the chromosome material. or replication of the chromosome material.
Another important way that meiosis differs from Another important way that meiosis differs from mitosis is the exchange of chromosome pieces mitosis is the exchange of chromosome pieces which occurs in the first division of this process. which occurs in the first division of this process.
This exchange of chromosome pieces is called This exchange of chromosome pieces is called crossing over. Crossing over assures that the crossing over. Crossing over assures that the cells produced as a result of meiosis will be cells produced as a result of meiosis will be different from and exhibit variations from the different from and exhibit variations from the parent cell that produced them.parent cell that produced them.
This process is chiefly responsible for the This process is chiefly responsible for the variations seen in members of the same species variations seen in members of the same species of sexually reproducing organisms. The process of sexually reproducing organisms. The process of meiosis is a two step process. of meiosis is a two step process.
Meiosis I – reduction Meiosis I – reduction division division
Meiosis II – similar Meiosis II – similar to mitosis (involves to mitosis (involves 2 cell divisions) 2 cell divisions)
Steps of Meiosis Steps of Meiosis Interphase – Interphase –
replication of replication of chromosomes (when chromosomes (when the chromosome the chromosome first appears in first appears in Prophase II, they are Prophase II, they are double stranded) double stranded)
Prophase I – pairing Prophase I – pairing homologous homologous chromosomes into chromosomes into tetrads (four tetrads (four chromatids on each chromatids on each side) in a process side) in a process called synapsis – called synapsis – crossing over occurs crossing over occurs here (crossing genes here (crossing genes – brown hair, blue – brown hair, blue eyes) eyes)
Anaphase I – Anaphase I – disjunction of disjunction of chromosome (when chromosome (when the centromeres the centromeres divide and divide and chromosomes begin chromosomes begin to move to opposite to move to opposite poles) poles)
Results of Meiosis •A 2n primary sex cell will divide into four specialized “n” cells (for reproduction) •The distribution of homologous chromosomes between nuclei is random.
Interphase Prophase I Metaphase I Anaphase
Final result of meiosis – The process of crossing over and how it produces variation when these chromosomes
are recombined in the process of fertilization.
Genetic variability:Genetic variability: Random assortment of maternal and Random assortment of maternal and
paternal chromosomespaternal chromosomes Crossing overCrossing over
spermatogenesisspermatogenesis – occurs – occurs in the male gonad in the male gonad (testes). A type of meiotic (testes). A type of meiotic cell division in which four cell division in which four sperm cells are produced sperm cells are produced for each primary sex cell. for each primary sex cell. The primary sex cell is The primary sex cell is spermocyte. During the spermocyte. During the division, they lose division, they lose baggage and gain a tail baggage and gain a tail because they need to because they need to swim to the egg. swim to the egg.
Oogenesis Oogenesis – a type of – a type of meiotic division in which meiotic division in which one ovum and three polar one ovum and three polar bodies are produced from bodies are produced from each primary sex cell. each primary sex cell. Occurs in the female Occurs in the female gonad (ovary). The gonad (ovary). The primary sex cell is the primary sex cell is the oocyte. The result is one oocyte. The result is one viable egg cell and 3 non-viable egg cell and 3 non-functioning polar bodies. functioning polar bodies. There is an unequal cell There is an unequal cell division – ovum has a division – ovum has a large cytoplasm because large cytoplasm because it contains yolk it contains yolk (nutrients for embryo). (nutrients for embryo).
spermsperm eggegg
(N)(N) (N)(N)
Adult maleAdult male zygotezygote adult adult femalefemale
(2N)(2N) (2N)(2N)(2N)(2N)
How many human sperms will be How many human sperms will be formed from 40 primary formed from 40 primary spermatocytes?spermatocytes?
How many human eggs will be How many human eggs will be formed fromformed from 40 primary oocytes40 primary oocytes 40 secondary oocytes40 secondary oocytes 40 ootids40 ootids
MitosisMitosis MeiosisMeiosis
ConservativeConservative Generates enormous Generates enormous combinational combinational
variationvariation
1 CD = 2 daughter 1 CD = 2 daughter cellscells
2 CD= 4 daughter 2 CD= 4 daughter cellscells
Chromosome number Chromosome number maintainedmaintained
Chromosome number Chromosome number halved in the products halved in the products
of meiosisof meiosis
No cross overNo cross over At least one crossover At least one crossover per homologous pairper homologous pair
Centromeres divide at Centromeres divide at anaphaseanaphase
centromeres do not centromeres do not divide at anaphase I divide at anaphase I but at anaphase IIbut at anaphase II
Diploid/ haploidDiploid/ haploid diploiddiploid
The chromosome theory of The chromosome theory of heredityheredity
The parallel behavior of genes and The parallel behavior of genes and chromosomes led to the concept that genes chromosomes led to the concept that genes are located in chromosomesare located in chromosomes
Variation and heredityVariation and heredity Major clues – mitosis is a conservative Major clues – mitosis is a conservative
process that maintains the genetic status process that maintains the genetic status whereas Meiosis is a process that generates whereas Meiosis is a process that generates enormous combinatorial variationenormous combinatorial variation
Phenotype of an organism is determined by Phenotype of an organism is determined by gene action at cellular levelgene action at cellular level
Sally and Harry fall in love. They Sally and Harry fall in love. They introduce Sally's identical twin, Emily, introduce Sally's identical twin, Emily, to Harry's identical twin, Ken. Soon to Harry's identical twin, Ken. Soon there is a double wedding where Sally there is a double wedding where Sally marries Harry and Emily marries Ken. marries Harry and Emily marries Ken. Both Sally and Emily get pregnant. Both Sally and Emily get pregnant. They wonder "Will their babies look They wonder "Will their babies look exactly alike?" Answer their question, exactly alike?" Answer their question, and explain your reasoning. and explain your reasoning.