Chapter 5.5 The Dihybrid Cross ✓

Question 1

Define dihybrid cross

Answer 1

A cross between two organisms that are heterozygous at two gene locus

Question 2

What can be analysed with a dihybrid cross?

Answer 2

Inheritance for two unlinked autosomal genes

Question 3

Define independent assortment

Answer 3

Random orientation of maternal and paternal homologous chromosomes at the equator during metaphase 1

Question 4

State the expected phenotypic ratio for a dihybrid cross for an organism heterozygous for both genes

Answer 4

9:3:3:1

Question 5

Define the difference between homologous chromosomes and non-homologous chromosomes.

Answer 5

Homologous chromosomes contain alleles of the same gene type in the same loci, whereas non-homologous chromosomes contain alleles of different gene types.

Question 6

Relate the term ‘non-homologous chromosomes’ to the 9:3:3:1 phenotypic ratio seen in the F2 generation of a dihybrid cross.

Answer 6

Non-homologous chromosomes refer to chromosomes that carry different genes, and they are inherited independently during meiosis.
In a dihybrid cross, two traits are being studied, each controlled by genes on non-homologous chromosomes.
The 9:3:3:1 phenotypic ratio in the F2 generation results from the independent assortment of these non-homologous chromosomes. This means that the alleles for each gene segregate independently, leading to four possible combinations, producing 9:3:3:1 ratio.