Gene interactions

Question 1

dihybrid crosses reveal law of independent assortment

Answer 1

9:3:3:1 ratio observed
- at fertilisation these combine randomly to produce 16 possible genotypes

Question 2

dyhbrid cross reveal law of independent assortment…

Answer 2

9:3:3:1 phenotypic ratio
- in a cross between 2 individuals with the same phenotype a ratio adds up to 16 will tell you:
- 2 genes
- dihybrid cross
- independent assortment 4 gametes produced in equal proportions

Question 3

in most cases a trait is controlled by 2 or more genes

Answer 3

• when 2 or more genes influence the same phenotypic trait

Question 4

modifiers

Answer 4

changes the phenotype we are able to observe
- dense/dilute controls the distribution of coloured pigment granules called a modifier gene
- makes the 9:3:3:1 ratio

Question 5

epistasis

Answer 5

phenotype produced by a mutant allele of one gene (epistatic allele) masks or blocks the phenotype produced by alleles of another gene locus
- generally occurs because the genes act in the same pathway
- no new phenotypes are produced (fewer than 4)

Question 6

recessive epistasis

Answer 6

ratio: 9:3:4
- recessive genotype at one locus masks phenotypic effects of either alleles of the other gene
(need to have both genes in the same pathway)

Question 7

dominant epistasis

Answer 7

12:3:1 ratio
- no new phenotype is produced
- dominant genotype at one locus masks phenotypic effects of the other gene

Question 8

complementary gene action

Answer 8

9:7 ratio
- no new phenotypes are produced there are fewer than 4
- need a functional allele for each gene to produce the trait

Question 9

duplicate gene

Answer 9

15:1 dihybrid ratio
- no new phenotypes are produced there are fewer than 4
usually occurs beacause genes are functional redundant
- need a functional allele for eith gene to produce the trait
- sometimes both genes may be able to make the same gene