1. Unit 5: Genetics, evolution & biodiversity
5H.1 & 5B.4 Genetics & evolution; sources of new inherited variation
By Mr. Wilson

2. Origins of variation During meiosis of gametogenesis:
Independent assortment of chromosomes (sometimes called random assortment or random segregation).
Crossing over
Mutation
Sexual reproduction:
Fusing of random gametes in populations.
Fusing of 1 of 2 gametes at each fertilisation (4 possible outcomes).

3. Independent assortment of chromosomes in meiosis
Meiosis I – In metapahase homologous pairs of chromosomes line up on the equator randomly as bivalents.
It is chance which of each pair ends up on the right or left side of the row (mother derived or father derived).
The pairs are separated and one from each side goes into each daughter cell.
There are thousands of possible combinations in the daughter cells.

4. Independent assortment of chromosomes in meiosis
In metaphase of meiosis II there is also random assortment of chromatids.
In all there are over 8 million possible chromosome combinations for each gamete. (8,324,608).
This produces massive variation in offspring but there are yet more origins of variation……..

5. Independent assortment of chromosomes in meiosis

6. Independent assortment of chromosomes in meiosis

7. Crossing over
Occurs in the prophase of meiosis I when chromosomes are at synapsis.
Non-sister chromatids may overlap (at chiasmata) and gene combinations can be swapped creating RECOMBINANT chromosomes.
Alleles that are normally ‘linked’ may no longer be inherited together. This unlinking is more likely for genes that are far part on the same chromosome.

8. Crossing over

9. Sexual reproduction
After all of the variant generating processes in meiosis there is yet more variation via sexual reproduction & the random fusing of gametes in a population.
There are also four possible outcomes/combinations at each fertilisation as gametes are HAPLOID (containing 1 allele for a characteristic).

10. Mutations
Point and chromosome mutations are also sources of new inherited variation.
Task – prepare a fact-sheet on point (gene) mutations using the textbook page 371 or the internet/revision guide.
Homework – complete the task sheet boxes with the best description. Use 3 or more sources for info then put it into your own words. Due next week.