Bell Work

• 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).

Biology – Lecture 51

Double Punnett Squares Genotype

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.

TODAY

• 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.

Additional Info on Step 2

• Since each Parent produces 4 different combinations of alleles in the gametes, draw a 4 square by 4 square punnett square.

Additional Info on Step 3

• After setting up the punnett square and placing the correct 4 letters in each box, arrange the letters so that they are in a similar order as the original gene combination.

Example 1

• Mr. and Mrs. Mouse both had one copy of each allele for teeth (one normal copy, one vampire fangs copy). In that sense, they were hybrids for the vampire allele. Well, they are also hydrids for the fur allele – one copy of the fluffy fur allele, and one copy of the wiry fur allele. (Let's assume that fluffy fur is a recessive trait, like vampire fangs).

Example 2

• In summer squash, white fruit color (W) is dominant over yellow fruit color (w) and disk-shaped fruit (D) is dominant over sphere-shaped fruit (d). If a squash plant is homogeneous for white fruit color that is disk-shaped is crossed with a yellow, sphere-shaped fruit plant, what are the possible outcomes of the offspring?

Practice 1

• Carrion beetles lay their eggs in dead animals and then bury them in the ground until they hatch. Assume that the preference for fresh meat (F) is dominant to the preference for rotted meat and that the tendency to bury the meat shallow (S) is dominant to the tendency to bury the meat deep. Suppose a female carrion beetle homozygous dominant for both traits mates with a male homozygous recessive for both traits.

Practice 2

• Suppose in a strain of soybeans, high oil (H) content in the seeds is dominant to low oil content and four seeds (E) in a pod is dominant to two seeds in a pod. A farmer crosses two soybean plants, one that is heterozygous for both high oil and four seeds, and one that is homozygous for both high oil and 2 seeds in a pod. What is the result of their offspring?

Practice 3

• Suppose that black hair (B) is co-dominant with blonde hair (b) and brown eyes (E) are dominant over blue eyes (e).

• The father has black hair (heterozygous) and brown eyes (heterozygous) and the mother has blonde hair and blue eyes.

• What are the possible genotypes of their children?

Practice 4

• Yellow fruit and dwarf vines are recessive traits in tomatoes. Red fruit and tall vines are dominant. Cross a completely dominant red and tall plant crossed with a heterozygous red and dwarf plant.