Mitosis

Question 1

What is a gene?

Answer 1

a functional unit of hereditary, a section of DNA

Question 2

What are the 3 stages of interphase and what happens at each?

Answer 2

G1 - the cell increases its supply of proteins, increases the number of organelles, and grows in size
S - DNA is synthesised
G2 - cell grows

Question 3

Describe the steps of mitosis

Answer 3

Prophase - chromosomes condense and the spindle forms. Centrosomes are pushed by microtubules

Prometaphase - nuclear envelope fragments. Microtubules stick to chromosomes and push each other away

Metaphase - chromosomes line up down the midline of the cell (the metaphase plate) and the spindle forms

Anaphase - chromatids separate as single contracts and migrate to the poles of the cell

Telophase - chromosomes begin to uncoil and the nuclear envelope reforms. Cytokinesis begins (like a drawstring bag separating the cell into 2 cells.

Question 4

In terms of haploid and diploid what is the amount of DNA in meiosis 1 and 2?

Answer 4

Meiosis 1 - diploid (2n)

Meiosis 2 - haploid (n)

Question 5

How much DNA is there in the cell just before meiosis 1?

Answer 5

4n - 2xs diploid

Question 6

Describe the stages of meiosis 1

Answer 6

Prophase 1 - synapsis occurs (homologous chromosomes pair) and crossing over occurs between chiasmata

Metaphase 1 - chromosomes line up along the metaphase plate (midline of the cell) in their pairs. Spindle/kinetochore microtubes attach to each chromosome

Anaphase 1 - homologous pairs separate (independent segregation is here as maternal or paternal chromosomes can split to each pole randomly)

Telophase 1 - cytokinesis

Question 7

What are the 3 ways in which genetic variation comes about?

Answer 7

Crossing over - allows maternal and paternal chromosomes to exchange genes producing recombinant chromosomes

Independent variation - orientation of homologous pairs during meiosis 1 along the metaphase plate is random

Random fertilisation - 1/8000000 is the chances for the egg + sperm combination