Bell Work

• A tan cat mates with a black cat. Tan is co-dominant with black fur in cats. What is the genotype and phenotype of the offspring?

Biology – Lecture 50

Intro to Double Punnett Squares (Dihybrid crosses)

Making a Double Punnett Square

• Step 1: Decide which possible allele combinations can be passed from each parent to the offspring.

• Step 2: Take those 4 allele combinations and set them at the top (parent 1) and sides (parent 2) of the double punnett square.

• Step 3: Cross the allele combinations in the punnett square to get the possible genotypes of the children.

• Step 4: Determine the phenotype of each gene trait for the children.

Mendel’s Second Law

• In sexually reproducing organisms, genes generally assort independently of each other.

• This means that the alleles of different genes get shuffled between parents to form offspring with many different combinations.

TODAY

• Step 1: Decide which possible allele combinations can be passed from each parent to the offspring.

How to Determine Possible Allele Combinations

• Step 1: Give each allele from each gene combination the numbers 1 and 2.

• Step 2: Match #1 from the first gene with #1 from the second gene. This is your first allele combination.

• Step 3: Match #1 from the first gene with #2 from the second gene. This is your second allele combination.

• Step 4: Match #2 from the first gene with #1 from the second gene. This is your third allele combination.

• Step 5: Match #2 from the first gene with #2 from the second gene. This is your first allele combination.

Example 1

• What are the possible allele combinations from a parent that is SsYy?

Practice 1

• What are the possible allele combinations from a father who is AahH?

Practice 2

• What are the possible allele combinations from a mother who is KkZZ?

Applying Knowledge

• Use your knowledge of heterozygous, homozygous recessive, and homozygous dominant to determine the genotype of the parent and the 4 different allele combinations of the offspring.

Example 1

• What are the possible allele combinations that can be made from a mother who is homozygous short (tall is dominant) and has homozygous brown eyes (blue eyes is recessive)?

Practice 1

• A mother is heterozygous tall (tall is dominant), and has blue eyes (brown eyes are dominant). What are the possible alleles she can pass on to her children?

Practice 2

• Determine the allele combination that can come from a father who is heterozygous brown eyed and homozygous black haired (blonde is recessive).

Practice 3

• Determine the allele combination from a dog who is droopy eared (erect ears are dominant) and brown and white spotted (brown and white are co-dominant).

Practice 4

• Determine the allele combination from a mouse who is heterozygous for having whiskers (no whiskers is recessive) and grey (white and black are incompletely dominant).

Pop Quiz

Pop Quiz

• What are the 4 allele combinations that can come from the following genotype of a mother?

• BbTt