Meiosis

Question 1

What is meiosis?

Answer 1

• The division of a diploid cell to four haploid daughter cells
• Occurs in gonads (testes and ovaries)
• the daughter cells are not genetically identical

Question 2

What happens in the 2 division in meiosis?

Answer 2

Meiosis 1: the homologous chromosomes are separated. Crossing over and independent segregation of homologous chromosomes occurs here
Meiosis 2: the sister chromatids are separated

Question 3

How does meiosis ensure that chromosome numbers are kept constant from one generation to the next?

Answer 3

When two haploid gametes fuse the diploid chromosome number is restored. This ensures that in sexual reproduction fusion of haploid gametes restore the original chromosome and that chromosome numbers are kept constant from one generation to the next.

Question 4

Describe the process of crossing over

Answer 4

• homologous chromosomes pair and come together to form a bivalent
• non-sister chromatids wrap around each other and attach at points called chiasmata
• the chromosomes break and rejoin swapping sections of non-sister chromatids.
• this leads to new combinations of alleles in the gametes, increasing genetic diversity

Question 5

What is independent segregation?

Answer 5

• in the 1st meiotic division on homologous pairs of chromosomes randomly align at equator of the cell and then the pair separates to opposite poles of the cell.
• the paternal and maternal chromosomes of one pair segregate independently of the other pairs
• the number of different combinations of maternal and paternal chromosomes in the gametes is 2^n where n is the number of pairs of chromosomes
•in a species with only two pairs of chromosomes there are 2^2 = 4 possible combinations of paternal and maternal chromosomes in the gametes

Question 6

Are any two gametes more likely to fuse than others

Answer 6

No any two gametes are equally likely to fuse regardless of the combinations of alleles they carry. Genetic diversity within a species is further increased by the random fertilisation of haploid gametes

Question 7

State 4 differences between mitosis and meiosis

Answer 7

Mitosis
1) daughter cells are genetically identical to parent cells
2) one cell divides to give two daughter cells
3) the cell only divides once
4) Haploid cells divide to give haploid daughter cells. Diploid cells divide to give diploid daughter cells

Meiosis
1) daughter cells are not genetically identical
2) one cell divides to give 4 daughter cells
3) cell divides twice
4) diploid cells divide to give haploid daughter cells

Question 8

How to interpret life cycle diagrams:

Answer 8

Haploid/Gametes = (n)
Diploid/Zygotes = (2n)