8b Dihybrid Crosses

Question 1

What is an unlinked dihybrid cross?

Answer 1

Definition: An unlinked dihybrid cross involves two traits controlled by genes located on different chromosomes, allowing independent assortment.
Example: Crossing pea plants for seed color (yellow, Y or green, y) and seed shape (round, R or wrinkled, r), where the genes for these traits are on different chromosomes.

Question 2

Can you complete a dihybrid Punnett square?

Answer 2

Definition: A dihybrid Punnett square examines the inheritance of two different traits, involving a 4x4 grid.
Example: Cross YyRr (yellow, round) x YyRr (yellow, round).
YR (Parent 1) Yr (Parent 1) yR (Parent 1) yr (Parent 1)
YR YYRR YYRr YyRR YyRr
Yr YYRr YYrr YyRr Yyrr
yR YyRR YyRr yyRR yyRr
yr YyRr Yyrr yyRr yyrr
Genotype Ratio: 9:3:3:1 (dominant for both traits: dominant for one trait and recessive for the other: recessive for one trait and dominant for the other: recessive for both traits)
Phenotype Ratio: 9 (yellow, round): 3 (yellow, wrinkled): 3 (green, round): 1 (green, wrinkled)

Question 3

Can you determine different gametes using the FOIL method?

Answer 3

FOIL Method: FOIL stands for First, Outer, Inner, Last. It’s used to determine the possible gametes produced by an individual with two heterozygous traits.
Example: For YyRr, the gametes are:
First: YR
Outer: Yr
Inner: yR
Last: yr
Thus, the gametes are YR, Yr, yR, and yr.

Question 4

What is a linked dihybrid cross?

Answer 4

Definition: A linked dihybrid cross involves two traits controlled by genes located on the same chromosome, which tend to be inherited together.
Linkage: These genes do not assort independently, and the typical 9:3:3:1 ratio is not observed.
Example: In Drosophila, genes for body color and wing size are linked.

Question 5

Would you recognize a linked or an unlinked cross from the resulting gamete ratios or percentage chance?

Answer 5

Unlinked Cross: Produces a 9:3:3:1 phenotypic ratio in the F2 generation if the traits are completely dominant.
Linked Cross: Deviates from the expected 9:3:3:1 ratio due to the genes being inherited together more frequently than would be expected from independent assortment. Recombinant phenotypes (new combinations of traits) are less frequent.
Recognition: By analyzing the offspring’s phenotypic ratios, you can identify if genes are linked or unlinked based on deviations from expected Mendelian ratios.