Cell Cycle
Definition
An orderly sequence of events in which one cell divides and forms daughter cells and the daughter cell again divides is called cell cycle.
OR
Round of cell growth and cell division is known as cell cycles.
Phases of Cell Cycle
Cell cycles consist of two phases
1. Inter Phase Or Resting stage or (non-division)
2. Division Phase
1. Inter Phase
The period of the cell cycle between two consecutive divisions is called Interphase.
OR
The phase of cell cycle in which the cell cannot be divided but perform its metabolic function for the preparation of its division are called Interphase.
Sub – Stages of Interphase
Inter phase divide into three sub-stages.
i. G1 – Stage
ii. S – Stage
iii. G2 – Stage
i. G1 – Stage
This phase involves actual cell division and consists of two stages.
Karyotinesis
Cytokinesis
Karyokinesis
Division of nucleus is called as karyokinesis.
Cytokinesis
Division of cytoplasm is called as cytokinesis.
Types of Cell Division
There are three types of cell division.
1. Mitosis
2. Meiosis
3. Amitosis
1. Mitosis (Somatic Or Vegetative Division)
The type of cell divides in which a parent cell divides into two daughter cell and each daughter cell gets same number of chromosomes from parent cell is called mitosis.
Phases of Mitosis
It can be divides into two phases.
1. Karyokinesis
2. Cytokinesis
1. Karyokinesis
Karyokinesis is the division of nucleus and occurs in four different phases.
(Pro=before, phase=appearance)
Phrophase is the main phase of nuclear division it is the longest stage the following main change occur in nucleus and cytoplasm.
Changes in Nucleus
These fibers continuously running from one pole to other pole.
Half Or Discontinuous Spindle Fibers
These fibers running one pole to the broader region of cell.
Astral Fibers
These fibers arise from to Centriole and give the position to Centriole in the cytoplasm.
In Plant Cell
In higher plant and insects the Centriole is absent and spindle fibres are formed without it. In them the spindle appears with its fibers converging to piole regions comparable to the area occupied by Centriole in the animal cells.
2. Meta Phase
(Meta = after)
(Ana = upper)
(Telo = end)
The division of cytoplasm is called cytokinesis. There are two types of cytokinesis.
Cell – Plate Formation
In plant cell the division of cytoplasm begin with the formation of a structure called cell – plate at the equator. It grows outward dividing the mother cell into two daughter cells.
Cleavage
In animal cell construction or depression arise in the cell membrane from outer side to the inner side due to which cell divides into two daughter cell is known as cell-cleavage.
Important of Mitosis
i. No Change in Hereditary Materials
As there is no crossing over during this cell division, the genetic information remains unchanged generation after generation.
ii. Asexual Reproduction
All plants and some animals show asexual reproduction with the help of mitosis such as regeneration in starfish.
iii. Development
New organs are formed with the help of controlled and planned mitosis.
iv. Growth
Young individuals grow with the help of mitosis.
v. Healing of Wounds
Formation of lost organ (regeneration), healing of wounds and replacement of older cells takes place due to mitosis.
vi. Tissue Culture and Cloning
Tissue culture in plant and cloning in animal is carried out through mitosis.
2. Meiosis (Reduction Division)
(Meiosis => meioum => to reduce)
The type of cell division in which one cell divide into four daughter cells and each daughter cell gets half number of chromosome from parent cell called meiosis.
OR
Cell division in which one diploid cell divide into four haploid cells called meiosis.
Phases of Meiosis
Meiosis consists of two phases.
1. Karyokinesis
2. Cytokinesis
1. Karyokinesis
Karyokinesis is the divisions of nucleus. Karyokinesis in meiosis consist of two divisions.
i. First Meiotic Division
ii. Second Meiotic Division OR Mitotic Division
i. First Meiotic Division
In first meiotic division, one nucleus divides into two nuclei and number of chromosome reduce to half. It is consist of following stages.
a. Prophase I
b. Metaphase I
c. Anaphase I
d. Telophase I
a. Prophase I
Prophase I is the longest phase of meiosis consisting of a complicated chain of events. It further divide into following sub stages.
In second meiotic division, one nucleus further divide into two nuclei and number of chromosomes remain same. It consists of following stage.
a. Prophase II
b. Metaphase II
c. Anaphase II
d. Telophase II
a. Prophase II
i. Crossing Over
Crossing over during meiosis brings about re-shuffling of genes. As a result new combination of character in the off spring occurs.
ii. Gamet Formation
Meiosis is responsible for the formation of haploid gametes and spores. Thus after fertilization, the constant diploid number of chromosomes is restored.
iii. Random Assortment
Separation of homologous chromosomes and their random distribution to different daughter cells, also bring about genetic variations, which are raw material for evolution.
Amitosis
Definition
A cell division without spindle formation is called Amitosis.
Mechanism of Amitosis
Amitosis is also called the direct cell divisions. In this cell division first the nucleus of the cell become dumbbell shaped and finally it splits into two nuclei. In this way karyokinesis is completed.
Then an invagination appears in the centre of the cell which becomes deep and at the end it divides the parent cell completely into the two daughter cells.
Nuclear Budding
When nuclear portion unequally divide is called nuclear budding.
Nuclear Fragmentation
When nuclear portion divides more than two in number is called nuclear fragmentation.
Example
This type of cell division usually occurs in bacteria, protozoa, abnormal and diseased tissues such as cancer and tumor.
Cancer
Definition
A process of uncontrolled cell division, cells divide rapidly and abnormally and caused cancer.
Types of Cancer
There are two types of cancer.
1. Malignant
2. Benign
1. Malignant
A tumor can invade adjacent tissues and destroy them. Such tumors are called malignant.
2. Benign
A tumor is said to be benign if it does not attack the other tissues.
Causes of Cancer
The main causes of cancer are
1. Mutation
2. Hereditary
3. Virus
1. Mutation
The cancer is caused by mutation of cellular gene that control cell growth and cell division.
The mutation in cellular gene may be due to the X-rays, Gamma Rays and radiation from radioactive substance.
2. Hereditary
There may be a hereditary tendency for cancer.
3. Virus
In animals so many viruses can cause some kinds of caealike leukamia. In this case DNA of virus is inserted directly in chromosome and caused gene mutation.
Cancer Cell kills Other Cells
Cancer cells multiply their number day by day and required all essential nutrients available in the body due to which normal tissues suffer regularly and after some time they become dead.
Cell Death
Cell death in multicellular organisms is controlled by two ways.
1. Autophagy
2. Necrosis
1. Autophagy
Auto => itself, Phagy => eat
The cell commits suicide carries self destruction in the absence of survival signals is called autophagy.
2. Necrosis
The cell dies due to injury of tissues is called necrosis.
During this, cell swells and bursts while releasing toxic substance which can damage neighbouring cells and cause inflammation.
Apoptosis
Definition
Apoptosis means dropping off or falling off.
OR
The naturally cell death programme is called apoptosis.
Mechanism of Apoptosis
Definition
The abnormalities in the process of meiosis are termed as meiotic error.
Non-Disjunction
The failure in the separation of the homologous chromosome due to meiotic error is known as non-disjunction.
Heteroploidy
A change in the normal chromosome number is called heteroploidy.
There are two types of Heteroploidy
1. Aneuploidy
2. Polyploidy
1. Aneuploidy
Definition
The kind of heteroploidy in which an individual has one chromosome more or less than the normal number is called as aneuploidy.
OR
There will be change in number of one homologous pair is called Aneuploidy.
Aneuploidy is of following types
i. Monosomy
ii. Trisomy
i. Monosomy
When there is loss of one chromosome in a cell is called as monosomy. It’s denoted by (2n-1) = 1
Example
Human having monosomic condition possess 45 chromosomes instead of normal 46.
ii. Trisomy
When there is addition of one chromosome in the cell is called as trisomy.
Example
Human having trisomic condition posses 47 chromosome instead of normal 46.
2. Polyploidy
Definition
When sometimes two set or more sets of chromosome are present in a body the organism is called polyploid and the phenomenon is known as polyploid.
According to the number of chromosome sets the organism may be of different types. These are as follows
i. Triploid
ii. Tetraploid
i. Triploid
The organism contain 3 sets of chromosome is called triploid.
It is denoted by 3n.
ii. Tetraploid
The organism contain 4 sets of chromosome is called tetraploid.
Non disjunction of homologous chromosome causes several abnormalities in the off spring which are all follows
Definition
A group of signs or symptoms occurring together which characterize a disease or abnormality.
Down’s Syndrome
The disease is also called Mongolism because the affected persons show strong facial resemblance to Mongolian race.
Causes
It is an autosomal non-disjuction in man in which 21st chromosome fails to segregate, resulting in gametes with 24 chromosomes. This gamete fertilizes with normal gamete so the new individual will have 47 chromosomes (2n+1).
Symptoms
17 years and only 8% can survive up to 40 or more.
1. Kline Filter’s Syndrome
It is a male sexual abnormality.
Causes
These individuals have additional sex chromosomes e.g. 47 chromosomes (44 autosomes + XXY). They are phenotypically male. It occurs due to trisomic condition which take place due to chromosomal disjunction in sex-chromosome.
Symptoms
Turner’s syndrome is the female sexual abnormality.
Causes
These individuals have one missing X-chromosome with only 45 chromosomes (44 autosomes + X chromosome). These individual have female appearance. It occurs due to monosomic condition.
Symptoms
Due to NOn-disjunction on sex chromosomes of men and women causes defects in their young one.
Non-disjunction in men produces sperm without sex-chromosomes or with XY. Chromosomes instead of X or Y.
In female eggs contain no sex-chromosomes or contain XX chromosome instead of X, when normal and abnormal gametes fuse together to form these type of zygote XXY, XXX, XO, YO. (Zygote cannot be dev x chromosomes).
Definition
An orderly sequence of events in which one cell divides and forms daughter cells and the daughter cell again divides is called cell cycle.
OR
Round of cell growth and cell division is known as cell cycles.
Phases of Cell Cycle
Cell cycles consist of two phases
1. Inter Phase Or Resting stage or (non-division)
2. Division Phase
1. Inter Phase
The period of the cell cycle between two consecutive divisions is called Interphase.
OR
The phase of cell cycle in which the cell cannot be divided but perform its metabolic function for the preparation of its division are called Interphase.
Sub – Stages of Interphase
Inter phase divide into three sub-stages.
i. G1 – Stage
ii. S – Stage
iii. G2 – Stage
i. G1 – Stage
- The inter phase begins with this phase.
- Enzyme for the formation of DNA is produced.
- During this stage cell grows rapidly by synthesis of protein and cytoplasmic organelles.
- Duration of G1 is about 25-50% of Interphase.
- In this stage synthesis of DNA occurs and numbers of chromosomes become double.
- Duration of s-phase is 35-40% of Interphase.
- It is the end stage of Interphase.
- In this period, production of protein and microtubules occur that are required for cell division.
- Numbers of mitochondria also increase for energy production.
- The size of cell becomes doubled and cell starts division.
- Human Cell (animal cell)
- 18-24 hours for cell cycle
- Mitosis 30 minutes
- G1 phase 9 hours
- S phase 10 hours
- G2 phase 4.5 hours
- 10-30 hours for cell cycle
This phase involves actual cell division and consists of two stages.
Karyotinesis
Cytokinesis
Karyokinesis
Division of nucleus is called as karyokinesis.
Cytokinesis
Division of cytoplasm is called as cytokinesis.
Types of Cell Division
There are three types of cell division.
1. Mitosis
2. Meiosis
3. Amitosis
1. Mitosis (Somatic Or Vegetative Division)
The type of cell divides in which a parent cell divides into two daughter cell and each daughter cell gets same number of chromosomes from parent cell is called mitosis.
Phases of Mitosis
It can be divides into two phases.
1. Karyokinesis
2. Cytokinesis
1. Karyokinesis
Karyokinesis is the division of nucleus and occurs in four different phases.
- Prophase
- Meta phase
- Ana phase
- Telophase
(Pro=before, phase=appearance)
Phrophase is the main phase of nuclear division it is the longest stage the following main change occur in nucleus and cytoplasm.
Changes in Nucleus
- The chromatin material in nucleus break into thread like structure called chromosome.
- As the prophase further proceeds Chromosomes become thick and short.
- Each chromosomes consist of two thread known as chromatids. These chromatids are attached together by a spherical body is known as Centromere or kinetochore.
- In the nucleus chromosome move to its peripheral, part and central part of nucleus remain empty.
- Nucleoli disappear.
- Nuclear membrane disappears and nuclear material is released in the cytoplasm.
- The most important change which take place in cytoplasm is formation of mitotic apparatus.
- The formation of mitotic apparatus varies in plant cells and in animal cells.
- In animal cell two rod like structure found in cytoplasm cell as centrosome, each centrosome divides into two centriole.
- One centriole remain at its place while another one moves towards the opposite pole.
- Between the centriole thread like structure arise known as spindle fibre or nuclear spindle, which is of three types.
These fibers continuously running from one pole to other pole.
Half Or Discontinuous Spindle Fibers
These fibers running one pole to the broader region of cell.
Astral Fibers
These fibers arise from to Centriole and give the position to Centriole in the cytoplasm.
In Plant Cell
In higher plant and insects the Centriole is absent and spindle fibres are formed without it. In them the spindle appears with its fibers converging to piole regions comparable to the area occupied by Centriole in the animal cells.
2. Meta Phase
(Meta = after)
- At this stage centromere of chromosome attached with the equator of half or discontinuous fiber by kinetochore.
- All chromosomes arrange an alignment line and formed equatorial plane.
- Chromatids of chromosome attain their maximum thickness.
- The faces of chromatids are towards the opposite poles as they are ready for separation.
(Ana = upper)
- Anaphase begins when centromere divide, separate the sister chromatids from each other.
- Two set of chromatids migrates toward the opposite pole due to the contraction of discontinuous spindle fibers.
- At the end of the anaphase, the two groups of chromatids reach the opposite pole.
(Telo = end)
- When two sets of chromosome reach to opposite poles telophase begins.
- The daughter chromosomes become thin and long.
- The coil with each other forming network again.
- Spindle fibers start to disappear.
- Nuclear membranes reappear around each set of chromosome.
- Nucleolus reappears.
- Now at this time two daughter nuclei are formed in a cell.
- The process of karyokinesis completed.
The division of cytoplasm is called cytokinesis. There are two types of cytokinesis.
Cell – Plate Formation
In plant cell the division of cytoplasm begin with the formation of a structure called cell – plate at the equator. It grows outward dividing the mother cell into two daughter cells.
Cleavage
In animal cell construction or depression arise in the cell membrane from outer side to the inner side due to which cell divides into two daughter cell is known as cell-cleavage.
Important of Mitosis
i. No Change in Hereditary Materials
As there is no crossing over during this cell division, the genetic information remains unchanged generation after generation.
ii. Asexual Reproduction
All plants and some animals show asexual reproduction with the help of mitosis such as regeneration in starfish.
iii. Development
New organs are formed with the help of controlled and planned mitosis.
iv. Growth
Young individuals grow with the help of mitosis.
v. Healing of Wounds
Formation of lost organ (regeneration), healing of wounds and replacement of older cells takes place due to mitosis.
vi. Tissue Culture and Cloning
Tissue culture in plant and cloning in animal is carried out through mitosis.
2. Meiosis (Reduction Division)
(Meiosis => meioum => to reduce)
The type of cell division in which one cell divide into four daughter cells and each daughter cell gets half number of chromosome from parent cell called meiosis.
OR
Cell division in which one diploid cell divide into four haploid cells called meiosis.
Phases of Meiosis
Meiosis consists of two phases.
1. Karyokinesis
2. Cytokinesis
1. Karyokinesis
Karyokinesis is the divisions of nucleus. Karyokinesis in meiosis consist of two divisions.
i. First Meiotic Division
ii. Second Meiotic Division OR Mitotic Division
i. First Meiotic Division
In first meiotic division, one nucleus divides into two nuclei and number of chromosome reduce to half. It is consist of following stages.
a. Prophase I
b. Metaphase I
c. Anaphase I
d. Telophase I
a. Prophase I
Prophase I is the longest phase of meiosis consisting of a complicated chain of events. It further divide into following sub stages.
- Leptotene
- Zygotene
- Pachytene
- Diplotene
- Diakinesis
- This is the first stage of meiosis.
- In this stage, cell is larger in size and has large nucleus.
- The chromosome become more uncoiled and seems as thin, long thread like shape.
- Beaded appearance found on chromosome at irregular interval is known as chromosome.
- In this stage chromosome are shorter and thicker.
- The homologous chromosome come very close to each other and make their pair. This pairing of chromosome is called synapsis.
- The pair of homologous chromosome are called bivalents.
- After pairing chromosome become thick and short.
- Each chromosomes of a bivalent forms two sister chromatids. Thsi called duplication.
- Now at this time, bivalent has four complete homologous chromatids called tetrad.
- The force of repulsion arise between the homologous chromosomes of bivalent and they start to separate from each other.
- But they remain attached at one or more point. Their point of contact are called chiasmata.
- By chiasmata process of crossing over occurs (crossing is a process by which transfered of genetic material occurs between non-sister chromatics of tetrad).
- The separation processes of bivalent continue by a process called terminazation.
- In this process the chiasmala move from Centromere towards the end of the bivalent.
- The discontinuous spindle fibers are attached to the Centromere of homologous chromosomes.
- All chromosomes arranged an alignment line and formed equatorial plane.
- In this stage each chromosome of bivalent move toward the opposite pole due to contraction of half spindle fibers.
- At the end of this phase the chromosome are separated into haploid sets, on set being present at each pole.
- Nuclear membrane reorganized around each set at two poles.
- Nucleoli reappear thus two nuclei each with haploid number of chromosome are formed.
In second meiotic division, one nucleus further divide into two nuclei and number of chromosomes remain same. It consists of following stage.
a. Prophase II
b. Metaphase II
c. Anaphase II
d. Telophase II
a. Prophase II
- Nucleolus and nuclear membrane disappear.
- Centrioles duplicate and move towards the opposite pole.
- Spindle fibres are formed.
- The discontinues spindle fibres get attached to centromere.
- Chromosomes are arranged at the equatorial plane.
- The centromere divides and chromatide are separated from each other.
- Chromatids move to opposite poles on spindle fibre.
- Each chromatid is now called monad.
i. Crossing Over
Crossing over during meiosis brings about re-shuffling of genes. As a result new combination of character in the off spring occurs.
ii. Gamet Formation
Meiosis is responsible for the formation of haploid gametes and spores. Thus after fertilization, the constant diploid number of chromosomes is restored.
iii. Random Assortment
Separation of homologous chromosomes and their random distribution to different daughter cells, also bring about genetic variations, which are raw material for evolution.
Amitosis
Definition
A cell division without spindle formation is called Amitosis.
Mechanism of Amitosis
Amitosis is also called the direct cell divisions. In this cell division first the nucleus of the cell become dumbbell shaped and finally it splits into two nuclei. In this way karyokinesis is completed.
Then an invagination appears in the centre of the cell which becomes deep and at the end it divides the parent cell completely into the two daughter cells.
Nuclear Budding
When nuclear portion unequally divide is called nuclear budding.
Nuclear Fragmentation
When nuclear portion divides more than two in number is called nuclear fragmentation.
Example
This type of cell division usually occurs in bacteria, protozoa, abnormal and diseased tissues such as cancer and tumor.
Cancer
Definition
A process of uncontrolled cell division, cells divide rapidly and abnormally and caused cancer.
Types of Cancer
There are two types of cancer.
1. Malignant
2. Benign
1. Malignant
A tumor can invade adjacent tissues and destroy them. Such tumors are called malignant.
2. Benign
A tumor is said to be benign if it does not attack the other tissues.
Causes of Cancer
The main causes of cancer are
1. Mutation
2. Hereditary
3. Virus
1. Mutation
The cancer is caused by mutation of cellular gene that control cell growth and cell division.
The mutation in cellular gene may be due to the X-rays, Gamma Rays and radiation from radioactive substance.
2. Hereditary
There may be a hereditary tendency for cancer.
3. Virus
In animals so many viruses can cause some kinds of caealike leukamia. In this case DNA of virus is inserted directly in chromosome and caused gene mutation.
Cancer Cell kills Other Cells
Cancer cells multiply their number day by day and required all essential nutrients available in the body due to which normal tissues suffer regularly and after some time they become dead.
Cell Death
Cell death in multicellular organisms is controlled by two ways.
1. Autophagy
2. Necrosis
1. Autophagy
Auto => itself, Phagy => eat
The cell commits suicide carries self destruction in the absence of survival signals is called autophagy.
2. Necrosis
The cell dies due to injury of tissues is called necrosis.
During this, cell swells and bursts while releasing toxic substance which can damage neighbouring cells and cause inflammation.
Apoptosis
Definition
Apoptosis means dropping off or falling off.
OR
The naturally cell death programme is called apoptosis.
Mechanism of Apoptosis
- Apoptosis is thought to require the activation of a specific set of genes.
- Death by apoptosis is characterized by over all compaction of the cell and its nucleus by the orderly dissection of the chromatin by special DNA splitting endonuclease and the rapid engulfment of the dying cells by phagocytes.
- Apoptosis appears to be mediated primarily by the release of ca++ and the activation of certain protein kinesos.
- Apoptosis is common during the embryonic development the growth of the cells between finger that are no longer needed undergoes apoptosis.
- It also occurs in adult tissues where it destroys the cells that have potential to develop the malignant tumor.
Definition
The abnormalities in the process of meiosis are termed as meiotic error.
Non-Disjunction
The failure in the separation of the homologous chromosome due to meiotic error is known as non-disjunction.
Heteroploidy
A change in the normal chromosome number is called heteroploidy.
There are two types of Heteroploidy
1. Aneuploidy
2. Polyploidy
1. Aneuploidy
Definition
The kind of heteroploidy in which an individual has one chromosome more or less than the normal number is called as aneuploidy.
OR
There will be change in number of one homologous pair is called Aneuploidy.
Aneuploidy is of following types
i. Monosomy
ii. Trisomy
i. Monosomy
When there is loss of one chromosome in a cell is called as monosomy. It’s denoted by (2n-1) = 1
Example
Human having monosomic condition possess 45 chromosomes instead of normal 46.
ii. Trisomy
When there is addition of one chromosome in the cell is called as trisomy.
Example
Human having trisomic condition posses 47 chromosome instead of normal 46.
2. Polyploidy
Definition
When sometimes two set or more sets of chromosome are present in a body the organism is called polyploid and the phenomenon is known as polyploid.
According to the number of chromosome sets the organism may be of different types. These are as follows
i. Triploid
ii. Tetraploid
i. Triploid
The organism contain 3 sets of chromosome is called triploid.
It is denoted by 3n.
ii. Tetraploid
The organism contain 4 sets of chromosome is called tetraploid.
- It is denoted by 4n.
- Polyploidy is not found in animals, but its the characteristic of plants.
Non disjunction of homologous chromosome causes several abnormalities in the off spring which are all follows
- Down’s syndrome (mongolism)
- Kinefelter’s syndrome (homosexual)
- Tuner’s syndrome (Xo)
Definition
A group of signs or symptoms occurring together which characterize a disease or abnormality.
Down’s Syndrome
The disease is also called Mongolism because the affected persons show strong facial resemblance to Mongolian race.
Causes
It is an autosomal non-disjuction in man in which 21st chromosome fails to segregate, resulting in gametes with 24 chromosomes. This gamete fertilizes with normal gamete so the new individual will have 47 chromosomes (2n+1).
Symptoms
- In this disease the children are mentally retarded or their mental level I.Q is very low between 20 to 50.
- They have broad and flat face.
- They are short sized.
- They have folds of skin on their eyes.
- Their hands are short and long tongue.
- The female affected by Down’s syndrome may be fertile.
17 years and only 8% can survive up to 40 or more.
1. Kline Filter’s Syndrome
It is a male sexual abnormality.
Causes
These individuals have additional sex chromosomes e.g. 47 chromosomes (44 autosomes + XXY). They are phenotypically male. It occurs due to trisomic condition which take place due to chromosomal disjunction in sex-chromosome.
Symptoms
- In adult age the affected person contain mixed characters of both male and female. They have breast but with short testes, which don’t produce sperms.
- Such persons are sterile i.e. can not take part in reproduction.
Turner’s syndrome is the female sexual abnormality.
Causes
These individuals have one missing X-chromosome with only 45 chromosomes (44 autosomes + X chromosome). These individual have female appearance. It occurs due to monosomic condition.
Symptoms
- Such persons are sexually retarded.
- They have short size.
- They have skin folding on neck and shoulders.
- They have swollen hands.
- They may be colour blind.
- They are mentally normal with weak brain.
Due to NOn-disjunction on sex chromosomes of men and women causes defects in their young one.
Non-disjunction in men produces sperm without sex-chromosomes or with XY. Chromosomes instead of X or Y.
In female eggs contain no sex-chromosomes or contain XX chromosome instead of X, when normal and abnormal gametes fuse together to form these type of zygote XXY, XXX, XO, YO. (Zygote cannot be dev x chromosomes).
No comments:
Post a Comment