KEY

Mendelian Hybrids Key

  1. Black fur (W) is dominant over white fur (w) in guinea pigs.
    1. Use a Punnett square to show cross of a homozygous black guinea pig with a homozygous recessive guinea pig.
    2. Indicate phenotype and genotype ratios of the offspring.
      Female gametes
    Male gametes w w
    W Ww Ww
    W Ww Ww
    Phenotype
    4 : 0
    black : white
    Genotype
    0 : 4 : 0
    WW : Ww : ww
  2.  
      Female gametes
    Male gametes B b
    B BB Bb
    b Bb bb
    The Punnett square at right shows the possible combinations of alleles for fur color in rabbits. Black fur, B, is dominant over white fur, b. Given the combinations shown, what are the genotypes and phenotypes of the parents?

    Phenotype = black

    Genotype = Bb


  3. In humans, brown eyes (B) are usually dominant over blue eyes (b). If a blue-eyed man marries a brown-eyed woman whose father was blue-eyed, what proportion of their children would you predict will have blue eyes?
    1. Woman's father = bb (blue eyes)
    2. Woman = Bb (brown eyes)
    3. Man = bb (blue eyes)
    4. 50% would have blue eyes.
  4. A fruit fly with a genotype MmOo is mated with an identical fly. Use a dihybrid cross to show the genotype possibilities of their offspring.
      Female gametes
    Male gametes MO Mo mO mo
    MO MMOO MMOo MmOO MmOo
    Mo MMOo MMoo MmOo Mmoo
    mO MmOO MmOo mmOO mmOo
    mo MmOo Mmoo mmOo mmoo
     
  5. In guinea pigs, black fur (B) is dominant over white (b), and rough coat (R) is dominant over smooth (r). If a fully heterozygous black rough guinea pig is mated to a black rough animal that is also fully heterozygous, what is the chance that they will produce a white, smooth-coated guinea pig? a 1 in 16 chance.
      Female gametes
    Male gametes BR Br bR br
    BR BBRR BBRr BbRR BbRr
    Br BBRr BBrr BbRr Bbrr
    bR BbRR BbRr bbRR bbRr
    br BbRr Bbrr bbRr bbrr
  6. Tall tomato plants are produced by the action of a dominant allele (T) and dwarf plants by its recessive allele (t). Hairy stems are produced by a dominant gene (H) and hairless stems by its recessive allele (h). A tall, hairy plant, hetrozygous in both traits is crossed with a dwarf hairless tomato plant. Determine the phenotypic ratio for the F1 generation. 4 tall hairy : 4 tall hairless: 4 short hairy: 4 short hairless
      Female gametes
    Male gametes th th th th
    TH TtHh same same same
    Th Tthh same same same
    tH ttHh same same same
    th tthh same same same
  7. Black (B) coat color in Cocker Spaniels is dominant, while red (b) coat color is recessive; solid (S) pattern is dominant, while spotted (s) pattern is recessive. A solid black male is mated to a solid red female and produces a litter of six pups: two solid black, two solid red, one black and white, and one red and white. Determine the genotypes of the parents.
    Animal Dad Mom Pup 1 and 2 Pup 3 and 4 Pup 5 Pup 6
    Color black red black red black & white red & white
    Pattern solid solid solid solid spotted spotted
    Possible genotypes BbSs, BBSS, BbSS, BBSs bbSs, bbSS BbSs, BBSS, BbSS, BBSs bbSs, bbSS Bbss, BBss bbss
  8. In tomatoes, red fruit (R) is dominant over yellow fruit (r) and tallness (T) is dominant over shortness (t). A plant that is RrTT is crossed with a plant that is rrTt. What are the chances of an offspring being heterozygous for both traits?     25%       1 in 4
      Female gametes
    Male gametes rT rt rT rt
    RT RrTT RrTt RrTT RrTt
    RT RrTT RrTt RrTT RrTt
    rT rrTT rrTt rrTT rrTt
    rT rrTT rrTt rrTT rrTt