Question

3. A diploid cell with eight chromosomes undergoes meiosis. (7 pt) a. How many chromosomes are there in each cell after meiosis I? How many daughter cells are made after meiosis I? Are the daughter cells diploid or haploid? (1.5 pt) How many chromosomes are there in each cell after meiosis ll? How many daughter cells are made after meiosis II? Are the daughter cells diploid or haploid? (1.5 pt) What two mechanisms allow genetic variation among the gametes produced by an individual? When do they take place or are observed: meiosis I or meiosis II? (2 pt) How many autosomes do human somatic cells have? How many sex chromosomes do human somatic cells have? (1 pt) How many autosomes do human gametes (eggs or sperm) have? How many sex chromosome do human gametes have? (1 pt)

Answer 1

a) Before meiosis, the DNA replicates so each chromosome has two chromatids attached to each other at the centromere, cells in meiosis are diploid, the diploid number of chromosomes =8 so the number of chromosomes in the cells in meiosis I is 8.

Two daughter cells are produced by meiosis I, the homologous chromosomes are separated during meiosis I, so the daughter cells produced via meiosis I are haploid.

b) haploid daughter cells produced by meiosis I undergo meiosis II, meiosis II is similar to mitosis, the sister chromatids of the chromosomes are separated and moves to daughter cells, so gametes are haploid.

Number of chromosomes in cells in meiosis II=8/2=4

daughter cells formed by meiosis II= 2

daughter cells are haploid.

c) mechanisms of genetic variation are crossing over between non-sister chromatids and independent assortment of chromosomes.

during prophase of meiosis I the homologous chromosomes pair up and exchange genetic material between non-sister chromatids, so allele combination in the sister chromatids changes.

during metaphase I the paired homologous chromosomes align at the metaphase plate, the chromosomes align at the metaphase plate such that any one of the homologous chromosomes can move to the daughter cell, both these processes occur in the meiosis I.

d) In humans there are 46 chromosomes 2 are sex chromosomes, in females, there are 2 X chromosomes and in males, there are one X and one Y chromosome, rest are autosomes, so 46-2=44,

Number of autosomes in the human cell = 44

number of sex chromosomes=2

c) gametes are haploid and has one sex chromosome.

haploid number of chromosomes =46/2=23

number of autosomes=23-1=22

number of sex chromosomes=1