Co-Dominance

Question 1

Define co dominance.

Answer 1

Where 2 dominant alleles are expressed as the phenotype.

Question 2

What does ‘multiple alleles’ mean?
How does this affect chromosomes?

Answer 2

There are more than 2 alleles.
Only 2 may be present at the loci of an individuals homologous chromosomes.

Question 3

In cows, for example, there are 2 dominant alleles for either white or red hair.
What happens when these cows are homozygous?
What happens when they are heterozygous? Why?

Answer 3

Homozygous cows will either have white hair or red hair. This is because both homozygous traits are dominant.
Heterozygous cows are roan, a mix of red and white. This is because the 2 dominant traits mix.

Question 4

If 2 heterozygous roan cows bred, state the percentage chance of each hair colour being produced in offspring.
Draw a punnet square and us CW and CR to help.

Answer 4

50% roan
25% red
25% white

Question 5

When a homozygous dominant individual is crossed with a homozygous recessive individual, what percentage of the next generation of offspring will be heterozygous?
What is this generation called?

Answer 5

100% heterozygous.
This is called the F1 generation

Question 5

How do we write a genotype for co-dominance?

Answer 5

The gene is symbolised as a capital letter and the alleles of the gene are represented by different small subscripts.

Question 6

If 2 individuals from the F1 generation are crossed, what will the next generation of offspring be called?

Answer 6

F2