Honors Biology
Extra Genetics Practice KEY
1. Below are the different types of inheritance patterns you learned about. For each describe what characteristics you would use to uniquely identify each.
· Simple Mendelian- only two traits, one must be dominant to the other
· Sex Linked- traits affect one gender, usually the males, more than the other
· Incomplete dominance- you see three phenotypes, one of which is a blend of the other two
· Co-dominance- you see three phenotypes, one of which is the simultaneous expression of the other two
· Polygenic- there is a broad distribution of phenotypes, which cannot be sorted into distinct groups
· Linked genes- two traits are often inherited together because they are on the same chromosome
· Multiple alleles- hard to identify; a single gene has more than two alleles (describes human blood types)
2. A scientist is studying a species of moth that eats bamboo. Some moths in this population have the ability to digest levulose, a rare sugar. Others do not. When a moth with the ability to digest levulose is mated with a moth that cannot, all of the offspring inherit the ability to digest levulose. When you mate siblings from this F1 cross, 276 of the offspring of the F2 have the ability to digest levulose and 93 do not.
Describe the inheritance. Simple Mendelian, with levulose digestion dominant.
Give the genotypes of the following: Parents: ______LL_____ x _____ll______
digest levulose cannot digest levulose
F1: ______Ll______
3. In a species of small fish, blue scales (B) is dominant to white scales (b) and forked tails (F) are dominant to straight tails (f). What are the phenotypes and probabilities of possible offspring from a mating between a Bbff and BbFf fish.
BF / Bf / bF / bfBf / BBFf / BBff / BbFf / Bbff
bf / BbFf / Bbff / bbFf / bbff
Bbff x BbFf
Possible gametes: Bf BF
bf Bf
bF
bf
Offspring: Blue, forked 3/8 or 38%; blue, straight 3/8 or 38%; white, forked 1/8 or 13%; white, straight 1/8 or 13%
4. In sheep, curved horns (C) are dominant to straight horns (c), and black wool (W) is dominant to white wool (w). After two dihybrids mate, what percentage of the offspring would you expect to have curved horns and white wool?
A dihybrid is heterozygous for both genes studied: CcWw. Since this is a mating of two dihybrids you can use the short-cut ratio of 9:3:3:1, so 3/16 or 18.75% would be C-ww.
5. You are studying the inheritance of flower color in a Death Valley cactus. They range in color from white to dark red, along with every possible hue in between. This inheritance pattern is most likely what?
A continuous range of phenotypes with no distinct groups is polygenic inheritance.
6. A colorblind man marries a non-colorblind woman. They have two colorblind sons, two normal daughters, and a colorblind daughter. What are the genotypes of the parents, sons, normal daughters, and colorblind daughter? What was the chance of the colorblind daughter?
Xc / XXc / XcXc / XcX
Y / XcY / XY
You should know colorblindness is sex-linked. If you did not, you should have figured it out because we discuss inheritance in males and females separately. Father must be XcY. Sons must be XcY. Mom must be XcX. Colorblind daughters are XcXc. The normal daughters must be XcX, or carriers. There is a 25% chance of having a colorblind daughter.
R / R’R / RR
red / RR’
pink
R’ / RR’
pink / R’R’
white
7. You cross a true-breeding red Japanese 5 o’clock flower with a true-breeding white Japanese 5 o’clock flower. All of the offspring are pink. If you mate two pink flowers together, what is the probability of producing a white flower?
This is incomplete dominance. If red is encoded by R and white is encoded by R’, then the pink flowers are RR’. There is a 25% chance of producing a white flower.
8. When doing a survey of an isolated bog, you come across a population of dragonflies. You notice that the dragonflies with blue bodies often have crosshatched wings, and those with brown bodies often have solid wings. You very rarely see dragonflies with blue bodies and solid wings, and vice versa. What does this mean?
This must be a case of linked genes. Since there are often inherited together, they must be on the same chromosome.
CGreen / CGoldCGreen / CGreenCGreen / CGreenCGold
CGold / CGreen CGold / CGold CGold
9. You are studying a species of beetle that has gold splashes of color on its carapace (shell). Other beetles have green splashes on their carapace. When crossed, the offspring have both gold and green spots on their shells. When you mate these beetles together, what offspring would you expect, and what percentage of each?
This is codominance. Both traits are expressed simultaneously in the heterozygotes. If CGreenCGreen beetles are green, CGoldCGold are gold, then CGreenCGold have both colors. You would get 25% green, 50% green and gold, and 25% gold beetles from a mating.