20.3 & 4 Dihybrid Inheritance & Phenotypic Ratios

Question 1

Dihybrid inheritance

Answer 1

Shows the inheritance of two genes

Question 2

Why is expected ratio of phenotypes different to actual phenotypes?

Answer 2

Fertilisation of gametes is a random process - chance events can cause a change
Genes being studied are on the same chromosome - linked genes. If there is no crossing over, two characteristics will always be inherited together

Question 3

Autosomal linkage

Answer 3

Genes that are linked are found on one of the other pairs of chromosomes

Question 4

Linked genes

Answer 4

Inherited as one unit - no independent assortment during meiosis unless alleles are separated by chiasmata

Question 5

Recombinant offspring

Answer 5

They have different allele combinations to both parents

Question 6

Recombination frequency formula

Answer 6

Number of recombinant offspring/total number of offspring

Question 7

Recombination frequency result meaning

Answer 7

50% - no linkage
Less than 50% - gene linkage, random assortment is hindered

Question 8

Chi squared test

Answer 8

Statistical test that measures the size of difference between observed values and expected values - can see whether the differences are significant or not

Question 9

Chi squared formula

Answer 9

Sum of (observed - expected) ^2/expected

Question 10

How to use chi squared values

Answer 10

If chi squared value is larger than p, reject null hypothesis, there is a significant difference

Question 11

Recessive epistasis

Answer 11

If the presence of two recessive alleles at a gene locus causes a lack of an enzyme

Question 12

Dominant epistasis

Answer 12

If a dominant allele results in a gene having an effect on another gene