Key Principles

Question 1

What are somatic cells?

Answer 1

All cells in the body adapt from germ (sperm&egg) cells. Are diploid so contain 46 chromosomes (2n)

Question 2

How are chromosomes counted in mitosis?

Answer 2

Based on the number of centromeres - not chromatids. (This is the central point of the chromosome where the chromatids connect.)

Question 3

How long is spent in each phase of mitosis cell cycle roughly?

Answer 3

Mitosis - 1 hour
G1- 10 hours
S - 9 hours
G2 - 10 hours

Question 4

When and why are there checkpoints in mitosis?

Answer 4

• 1 - in G1 - ensures cell has grown and has proteins for synthesis.
• 2 - end of G2 - ensure dna has replicated and cell has grown.
• 3 - in metaphase - check chromosomes are on the equator and that spindle fibres have the same tension.

Question 5

Mitosis stages

Answer 5

G1 - cell growth
S - DNA synthesis
G2 - cell growth & preperation for mitosis.
Cell division - mitosis
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis

Question 6

What is Mendels law of segregation

Answer 6

Each allele of each trait will independently separate into gametes. Alleles pass to gametes with equal frequency.

Question 7

What is Mendels law of independent assortment?

Answer 7

Each chromosome will behave indecently of the other. You will have 4 cells at the end that are all different.

Question 8

What is linkage?

Answer 8

When 2 genes are close together on the same chromosome so won’t experience crossing over. Eg. Hair and eye colour.

Question 9

Recombination.

Answer 9

The process where DNA strands are broken and repaired, producing new combinations of alleles. The probability of recombination between 2 loci is directly proportional to the distance between them.

Question 10

How to calculate the distance between the loci?

Answer 10

By looking at the number of recombinants as recombination between 2 loci is directly proportional to the distance between them. The distance is measured in centimorgans.

Question 11

Meisosis

Answer 11

Cell division of germ cells. A single cell divides twice to produce 4 daughter cells that contain half the amount of the genetic material. Produced a haploid number of chromosomes (n=23)

Question 12

Meisosis I

Answer 12

Separates homologous chromosomes
- interphase - chromosomes duplicate.
- prophase 1 - homologous chromosomes pair and exchange segments. Chromosome condense & crossing over occurs.
- metaphase 1 - tetrads line up.
- anaphase 1 - pairs of homologous chromosomes split up.
- telophase 1& cytokinesis - 2 haploid cells form, chromosomes are still double.

Question 13

Meisosis II

Answer 13

Separates sister chromatids
- prophase II - new spindle forms around chromosomes.
- metaphase II - chromosomes line up at the equator.
- anaphase II - centromeres divide. Chromatids move to opposite poles.
- telophase II & cytokineses- nuclear envelope forms around each set of chromosomes, cytoplasm divides.
Results in 4 haploid daughter cells containing single chromosomes.