18.2 Variation in phenotype

Question 1

What is the primary source of genetic variation
And describe it

Answer 1

Mutation
Sudden changes to the base sequence of DNA, so changes genes and chromosomes that may be passed down to next generation.

Question 2

How does meiosis cause variation

Answer 2

This form of nuclear division produces new combinations of alleles before they are passed into the gametes.

Through crossing over where parental alleles are swapped, and through independent segregation of homologous chromosomes where they randomly line up along the equator

Question 3

How does random fertilisation of gametes cause variation

Answer 3

In sexual reproduction, it produces new combinations of alleles, so the offspring are different from their parents

Which gamete fuses with which at fertilisation is a random process, further adding to the variety of offspring two parents can produce

Question 4

How does the environment influence organisms phenotype

Answer 4

The environment exerts an influence on all organisms, as it affects the way all organisms genes are expressed

The genes set limits, but the environment determines where within those limits the organism lies

Eg in flowers, one seed may have the genes to grow taller than all the others, however due to the seed germinating without enough sunlight and nitrate ions in the soil, it may not grow properly and will be short

Question 5

Name some possible environmental conditions that affect growth of plants

Answer 5

Temperature, rainfall, sunlight, soil conditions, PH and food availability

Question 6

Some characteristics aren’t controlled by a single gene, but by many genes (polygenes)
Eg height and mass

What shaped graph would we get for this

Answer 6

A normal distribution curve is bell shaped