Meiosis

Question 1

What is meiosis

Answer 1

A form of cell division which is required for sexual reproduction to produce 4 genetically varied and different haploid cells (gametes)

Question 2

What cell begins meiosis?

Answer 2

A diploid cell (has homologous chromosomes)

Question 3

What are homologous chromosomes?

Answer 3

A pair of chromosomes where one chromosome comes form the mother and the other from the father.
They have same genes but may be different alleles

Question 4

What must the homologous chromosomes do before meiosis?

Answer 4

Replication: so each homologous chromosome is now composed of 2 genetically identical sister chromatids held together at the centromere

Question 5

What do the homologous chromosomes do before meiosis 1?

Answer 5

Arrange themselves in the centre by homologous chromosome pair
And crossing over

Question 6

Crossing over

Answer 6

Once the homologous chromosomes have paired up, crossing over of alleles occur where they overlap (to form chiasmata) and the non sister chromatids swap alleles
To form homologous chromosomes which have a unique combination of alleles

Question 7

The product of crossing over

Answer 7

In each chromosomes, they now contain a unique combination of alleles
when the chromatids separate later on each daughter cell will be different and genetically varied
Because NONE of the chromatids are identical

Question 8

What happens if crossing over doesn’t occur?

Answer 8

Then when the chromatids divide (that are genetically identical) so as a result decreases genetic variation of daughter cells, as they don’t have a unique combination of alleles

Question 9

What happens during meiosis 1?

Answer 9

The homologous chromosomes are separated into 2 haploid daughter cells
This is varied by independent assortment

Question 10

Independent assortment

Answer 10

When the homologous chromosomes are separating in meiosis 1, it is a random chance of which homologous chromosome will end up in which cell (because they have same genes but each have different alleles) eg which one will maternal or paternal go to?
So 4 daughter cells all have unique combination of maternal and paternal chromosomes

Question 11

Meiosis 2

Answer 11

When the sister chromatids separate when the centromere divides

Question 12

What does meiosis 2 produce?

Answer 12

4 haploid daughter cells that are genetically different from each other

Question 13

How many possible combinations are there for maternal and paternal chromosomes in meiosis 1 (for what cell they are divided into)?

Answer 13

2^n
Where n is the number of homologous pairs eg 23 in a human

Question 14

End of meiosis

Answer 14

Each haploids cell dna decondenses as it doesn’t need to be replicated

Question 15

Sexual reproduction

Answer 15

The fusion of 2 gametes in fertilisation to produce a zygote.

Question 16

Fertilisation

Answer 16

Each gamete has haploid number of chromosomes dependent on the organism
2 gametes fuse in this process to produce zygote which is a diploid cell
Half chromosomes from mother and half from father

Question 17

Random fertilisation

Answer 17

Any sperm can fuse with any egg in a random process so there are different combinations of chromosomes from each parent to produce different zygote

Question 18

Causes for genetic variation?

Answer 18

Mutations
Random fertilisation
Independent assortment
Crossing over