Name ______Date ______

lAP Biology Genetics Problem Set

Simple Mendelian Genetics Problems

In peas, seeds may be round (R) or wrinkled (r).

  1. What proportion of the offspring in the following crosses would probably be wrinkled?
  • RR x rr
  • Rr x Rr
  • Rr x rr
  1. In mice, the ability to run normally is a dominant trait. Mice with this trait are called running mice (R). The recessive trait causes mice to run in circles only. Mice with this trait are called waltzing mice (r). Hair color is also inherited in mice. Black hair (B) is dominant over brown hair (b).
  • Cross a heterozygous running, heterozygous black mouse with a homozygous running, homozygous black mouse. List the parental genotypes and the possible offspring genotypes with percentages.
  1. Explain the difference between incomplete dominance and codominance.

Codominance

  1. In some chickens, the gene for feather color is controlled by codominance. The allele for black is B and the allele for white is W. The heterozygous phenotype is known as erminette. (Erminette fowls have mostly light-colored feathers with an occasional black one, giving a flecked appearance –both black and white are on the feathers.)
  2. What is the genotype for black chickens? ____
  3. What is the genotype for white chickens? ____
  4. What is the genotype for erminette chickens? ____
  1. If two erminette chickens were crossed, what is the probability that:
  2. They would have a black chick? ____%
  3. They would have a white chick? ____%
  1. In a maternity ward, four babies become accidentally mixed up. The ABO types of the four babies are known to be O, A, B, and AB. The ABO types of the four sets of parents are determined. Indicate which baby belongs to each set of parents: (a) AB × O, (b) A × O, (c) A × AB, (d) O × O.

Incomplete Dominance

  1. In humans straight hair (SS) and curly hair (CC) are traits, that result in hybrids who have wavy hair (SC). Cross a curly hair female with a wavy haired male. List the genotypes and phenotypes of the offspring.
  1. In snapdragons, flower color is controlled by incomplete dominance. The two alleles are red (R) and white (W). The heterozygous genotype is expressed as pink.
  2. What is the phenotype of a plant with the genotype RR? ______
  3. What is the phenotype of a plant with the genotype WW? ______
  4. What is the phenotype of a plant with the genotype RW? ______
  5. Cross a RW X WW and list the genotypes and phenotypes.

Sex Influenced

  1. Baldness in humans is a dominant, sex-influenced trait. This gene is on the autosomes, not the sex chromosomes. A man who is BB or Bb will be bald and will be normal only if he is bb. A woman will only be bald if she is BB and normal if she is Bb or bb (it’s almost like B is dominant in males and b is dominant in females). If two parents are heterozygous for baldness, what are the chances of their children being bald? Use a Punnett square to illustrate this. Note: because the sex of a person does make a difference in how the gene is expressed, you need to set this up as a dihybrid cross to account for the sex of the children (XX and XY).

Male BB & Bb = Baldbb = not baldFemale BB = bald Bb & bb = not

Sex-Linked

  1. The inheritance of color blindness in humans is due to a recessive gene located on the X chromosome (X linked).

X+(normal) or Xc(color blind)

  • If a color-blind boy is born to parents both of whom have normal vision, what are the genotypes of the three individuals? HINT: You are using X and Y chromosomes with superscripts on the X because sex of the individual makes a difference.

Multiple Alleles

  1. Another type of non-Mendelian trait is multiple alleles. Human hair color is controlled by one gene with four alleles (with some incomplete dominance):

HBr= brown HBd= blonde hR= red hbk= black

The possible genotypes and phenotypes:

  • HBdHBdor HBdhbk= blonde
  • HBdHBr= mousy brown
  • HBdhR= strawberry blonde
  • HBrHBror HBrhbk= brown
  • HBrhR= auburn hRhRor hRhbk= red hbkhbk= black
  • If someone with auburn hair has children with someone with red hair (but whose mother had black hair), what are the genotype and phenotype probabilities for their children?

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AP Genetics Problem Set