Genetic diversity can arise as a result of mutation or during meiosis

What does meiosis produce?

4 genetically different haploid cells

What is the parent cell in meiosis?

A diploid cell

What are 3 ways that meiosis introduces variation?

• Independent segregation of homologous chromosome

• Crossing over between homologous chromosomes

• Random fertilisation

Describe the process of independent segregation (3 stages)

1. In meiosis I, homologous pairs of chromosomes line up opposite to each other at the equator of the cell

2. Paternal and maternal chromosomes from each homologous pair lie randomly on either side of the equator

3. Pairs are separated, so one chromosome of each homologous pair ends up in the daughter cell

What is the formula to calculate the number of possible daughter cell combinations from independent segregation?

• 2ⁿ

• n=the number of homologous pairs you have (23 in human)

Describe the process of crossing over (4 stages)

1. When homologous pairs line up opposite each other at the equator in meiosis, parts of the chromatids become twisted around each other

2. This puts tension on the chromatids, causing parts of the chromatids to break

3. The broken parts of the chromatid recombine with other chromatid in the homologous pair

4. This results in a new combination of alleles

What section of the chromosome does crossing over occur?

Chiasmata

What are 4 differences between meiosis and mitosis?

• 2 divisions/ 4 divisions

• 4 daughter cells/ 2 daughter cells

• Haploid daughter cells/ Diploid daughter cells

• Introduces genetic variation/ Creates genetically identical cells

Diploid cell

• 2n

• 2 copies of each chromosome

Haploid cell

• n

• One copy of each chromosome

What happens in non-disjunction?

• Meiosis 1= Chromosomes do not split equally in anaphase

• Meiosis 2= Chromatids do not split equally during anaphase

What is a chromosome mutation and how do they occur?

• Spontaneous change in number of chromosomes

• Non-disjunction

What are the 2 types of non-disjunction?

• Polyploidy

• Aneuploidy

Describe polyploidy

Whole set of chromosomes are affected

Describe aneuploidy

Changes in number of individual chromosomes

What zygote cells does polyploidy result in?

• Tetraploid zygote

• Triploid zygote

What gametes does polyploidy result in?

2n diploid gamete

What gametes does aneuploidy result in?

Haploid gametes with an additional or missing chromosome (n+1 or n-1)