Questions & Answers
Question
AnswersFunction of meiosis I is to separate
(a)Homologous chromosome
(b)Sister chromatid
(c)Cross over
(d)Parental chromosome
Answer
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Hint: These sets of chromosomes are two pieces of DNA within a diploid organism. They carry the same genes that are one from each parental source.
Complete answer:
Chromosomes in a diploid cell re-segregate during meiosis I, producing four haploid daughter cells. It is one of the most important steps in meiosis that generates genetic diversity.
The phases of meiosis I
-Prophase I: During this phase, homologous chromosomes pair up and form synapses, a step unique to meiosis. The paired chromosomes are termed as bivalents, and the formation of chiasmata caused by genetic recombination becomes apparent.
-Prometaphase I: The nuclear membrane starts disappearing. One kinetochore forms on each chromosome rather and the chromosomes attach themselves to spindle fibers and begin to move.
-Metaphase I: Bivalents or two chromosomes (four chromatids) align at the metaphase plate in the centre of the cell. The orientation is random, with either of the parental homologs on aside. Therefore, there is a 50-50 chance for the daughter cells to get either the mother’s or father’s homolog for each chromosome.
-Anaphase I: During this phase, chromosomes, each with two chromatids, move to separate poles. Each of the daughter cells is now haploid (23 chromosomes), but now each chromosome has two chromatids.
-Telophase I: Nuclear envelopes may appear, or the cell may quickly start meiosis II.
-Cytokinesis
Additional information:
Comparison between Meiosis and Mitosis on the basis of:
-Chromosome behaviour
In mitosis homologous chromosomes are independent
In meiosis homologous chromosomes pair to form bivalents until anaphase I
-Chromosome number- reduction in meiosis
Mitosis produces identical daughter cells
Meiosis produces daughter cells that are haploid
-Genetic identity of progeny:
Mitosis produces identical daughter cells
Meiosis produces daughter cells have a new assortment of parental chromosomes
So, the correct answer is option (A) ‘homologous chromosome’.
Note: Non-dis-junction is a disorder, in which chromatids do not separate and one of the resulting gametes receives an extra copy of the same chromosome. Down syndrome is a genetic defect and the most common example of this mistake in meiosis in which a person receives an extra copy of chromosome 21 from one of the parents. Another common example of this nondisjunction occurs when the sex chromosomes (XX, XY) do not divide properly, resulting in individuals with Klinefelter syndrome or Turner syndrome.
Complete answer:
Chromosomes in a diploid cell re-segregate during meiosis I, producing four haploid daughter cells. It is one of the most important steps in meiosis that generates genetic diversity.
The phases of meiosis I
-Prophase I: During this phase, homologous chromosomes pair up and form synapses, a step unique to meiosis. The paired chromosomes are termed as bivalents, and the formation of chiasmata caused by genetic recombination becomes apparent.
-Prometaphase I: The nuclear membrane starts disappearing. One kinetochore forms on each chromosome rather and the chromosomes attach themselves to spindle fibers and begin to move.
-Metaphase I: Bivalents or two chromosomes (four chromatids) align at the metaphase plate in the centre of the cell. The orientation is random, with either of the parental homologs on aside. Therefore, there is a 50-50 chance for the daughter cells to get either the mother’s or father’s homolog for each chromosome.
-Anaphase I: During this phase, chromosomes, each with two chromatids, move to separate poles. Each of the daughter cells is now haploid (23 chromosomes), but now each chromosome has two chromatids.
-Telophase I: Nuclear envelopes may appear, or the cell may quickly start meiosis II.
-Cytokinesis
Additional information:
Comparison between Meiosis and Mitosis on the basis of:
-Chromosome behaviour
In mitosis homologous chromosomes are independent
In meiosis homologous chromosomes pair to form bivalents until anaphase I
-Chromosome number- reduction in meiosis
Mitosis produces identical daughter cells
Meiosis produces daughter cells that are haploid
-Genetic identity of progeny:
Mitosis produces identical daughter cells
Meiosis produces daughter cells have a new assortment of parental chromosomes
So, the correct answer is option (A) ‘homologous chromosome’.
Note: Non-dis-junction is a disorder, in which chromatids do not separate and one of the resulting gametes receives an extra copy of the same chromosome. Down syndrome is a genetic defect and the most common example of this mistake in meiosis in which a person receives an extra copy of chromosome 21 from one of the parents. Another common example of this nondisjunction occurs when the sex chromosomes (XX, XY) do not divide properly, resulting in individuals with Klinefelter syndrome or Turner syndrome.