Dihybrid Inheritance 20.3

Question 1

What are dihybrid crosses used for?

Answer 1

Used to show the inheritance of two different characteristics, caused by 2 genes which may be located on different pairs of homologous chromosomes

Question 2

How are dihybrid crosses different to monohybrid crosses?

Answer 2

4 alleles are shown instead of 2

Question 3

When 2 homozygous parents are crossed what is the expected ration (dihybrid)

Answer 3

9:3:3:1

Question 4

Why can the phenotypes of offspring be different than expected?

Answer 4

> fertilisation of gametes is a random process
genes being studied are both on the same chromosome. If no crossing over occurs the alleles for the 2 characteristics will always be inherited together

Question 5

State the difference between monogenic inheritance and dihybrid inheritance

Answer 5

Monogenic = The study of inheritance of one gene
Dihybrid = The study of inheritance of two genes

Question 6

State and explain 2 reasons why the offspring produced from a particular genetic cross may differ from the expected ratio

Answer 6

Genes are linked and cannot be inherited independently

sample size is too small

Random nature of crossing over during prophase 1

Question 7

Work through a dihybrid cross between a pea plant which produces green wrinkled seeds and a heterozygous pea plant which produces yellow round seeds to determine the ratio of the F1 offspring

Answer 7

Genotype of round yellow seed: YyRr

Genotype of green wrinkled seed:
yyrr

Gametes from round yellow seed:
YR yR YR yr

Gametes from green wrinkled seed:
yr

Genotypes from Punnett Square:
YyRr Yyrr yyRr yyrr

ratio: 1:1:1:1

Question 8

Define Dihybrid inheritance

Answer 8

Where two phenotypic characteristics are determined by two different genes present on two different chromosomes at the same time