Cell Replication & Division 2.2

Question 1

Gametes are ____

Body cells are ____

Answer 1

1. Haploid (n)

2. Diploid (2n)

Question 2

What are homologous chromosomes?

Answer 2

A pair of chromosomes containing a paternal and maternal chromosome joined by a centromere with the same genes (but possibly different alleles, loci (position) and size)

Question 3

What are identical and non-identical sister chromatids?

Answer 3

Identical sister chromatids are single chromosome copies with the same genes and alleles
(Two identical sister chromatids/one pair make up 1 REPLICATED chromosome)

Question 4

What is a chromatid?

Answer 4

A chromatid is one copy of a chromosome after DNA replication which is still joined to the template chromosome by a centromere (created ONLY during replication)

Question 5

Why are chromosomes not identical?

Answer 5

Chromosomes are not exact copies of each other. The 23 maternal and paternal chromosomes are homologous so have different alleles for the same gene.

Question 6

Where does variation occur in Meiosis?

Answer 6

1. Independent segregation (metaphase 1&2, homologous pairs of chromosomes line up randomly at equator - the first division can lead to either the maternal or paternal C of pair ending up in either daughter cell)
2. Crossing-over (swapping of chromatid strands to form a chiasmata leading to new chromatids with different selections of alleles)
3. Random Fertilisation (the specific sperm that fertilises the specific egg cell is completely random - Any sperm can fertilise any egg)

Question 7

Mitosis is important in the life of an organism. Give two reasons why.

Answer 7

1. Growth and reproduction;

2. Repairs and replaces dead/old/damaged cells (identical somatic cells)

Question 8

Mitotic Index = (MS)

Answer 8

Number of cells undergoing mitosis
______________________________
Total number of cells