Dihybrid inheritance

Question 1

What is Dihybrid Inheritance

Answer 1

A Dihybrid cross or Dihybrid Punnett square follows the inheritance of alleles for two genes.

The genes may be carried on the same chromosome (= linked genes or linkage), or they may be on different chromosomes (= not linked or no linkage).

Genes carried on different chromosomes can independently assort so all the possible combinations of alleles between the two genes can be produced in gametes, whereas linked genes cannot assort independently during meiosis, which limits the allele combinations that can be produced in gametes

Question 2

How do you write Dihybrid genotypes and phenotypes

Answer 2

to write the dihybrid genotype for two genes you just write the genotypes for the two genes next to each other
And the phenotype for a dihybrid genotype is just the phenotype for each gene written next to each other

Question 3

How to complete a Dihybrid punnet square

Answer 3

To complete a Dihybrid Inheritance Punnett Square you have to be able to use the dihybrid genotype of a parent to identify all of the possible allele combinations that could occur between the two genes through meiosis and therefore the different types of gametes that the parent could produce:

Use the “foil method” 🡪

combine the first allele of the first gene with each allele of the second gene. then combine the second allele of the first gene with each allele of the second gene

Remember: each gamete gets a single copy/allele of each gene, so we only look at combinations of an allele from one gene with an allele from the other gene, so AB in a gamete is showing an “A” allele from one gene and a “B” allele from the other gene.

Question 4

Dihybrid inheritance (no linkage)
F1 and F2 offspring explain

Answer 4

offspring produced from the cross of the first two parents are called the F1 generation (= the first filial generation)

If a cross is then done using F1 offspring as the parents, then the offspring produced are called the F2 generation

E.g. In a cross between a parent homozygous dominant for both genes and a parent homozygous recessive for both genes, the only possible genotype in the F1 offspring is heterozygous for both genes e.g. RrYy

Then a cross using the heterozygous F1 offspring as the parents, e.g. a RrYy x RrYy cross, would produce F2 offspring with all the possible genotypes and phenotypes.