Lecture 11

Question 1

Distinguish between homologous chromosomes and sister chromatids

Answer 1

homologous chromosomes are not identical and do not originate from the same organism
Sister chromatids result after DNA replication has occurred, and thus are identical, side-by-side duplicates of each other.

Question 2

First meiotic division

Answer 2

Prophase
Crossing over or recombination of non-sister chromatids.
Sister chromatids are held together by proteins = cohenins
Metaphase
Homologous pairs of chromosomes line up in metaphase, held together by chiasma formed
Anaphase
Two pairs of homologous chromosomes are separated
At the end of meiosis the two cells are haploid.

Question 3

Second meiostic division

Answer 3

No DNA replication between the two divisions
Anaphase II
sister chromatids are separated from each other
Haploid nuclei

Question 4

Compare and contrast the processes and outcomes of mitosis and meiosis

Answer 4

Mitosis consists of one stage
Mitosis produces diploid cells (46 chromosomes)
Mitosis produces two identical daughter cells
Meiosis consists of two stages.
Meiosis produces haploid cells (23 chromosomes).
Meiosis produces four genetically different daughter cells.

Question 5

Explain how meiosis and sexual reproduction contribute to genetic variation

Answer 5

During prophase of meiosis I, the double-chromatid homologous pairs of chromosomes cross over with each other and often exchange chromosome segments. This recombination creates genetic diversity by allowing genes from each parent to intermix, resulting in chromosomes with a different genetic complement.

Question 6

Describe the role of sex chromosomes in human sex determination and their behaviour in meiosis

Answer 6

Chromosomal sex is determined at the time of fertilisation; a chromosome from the sperm cell, either X or Y, fuses with the X chromosome in the egg cell. Gonadal sex refers to the gonads, that is the testis or ovaries, depending on which genes are expressed.