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Biology
Genetics #3: A Few Mendelian Exceptions
2.3.17
The following genetic scenarios can exhibit simple dominance, incomplete dominance,
codominance, lethal alleles, or multiple alleles. They may exhibit only one of these phenomena
or any combination of them (sometimes two or three at once!). Make sure that you answer all
parts of the question and show all work (e.g. punnett – I mean funnett squares). I hope you
enjoy solving these as much as I enjoyed writing them!
1. If green flowers are dominant to yellow flowers, which cross would result in 50% of the
offspring w/ green flowers and 50% w/ yellow flowers?
2. A woman w/ free earlobes (dominant) has a mother with attached earlobes. The women
has a child w/ a man who also has attached earlobes. What is the probability that they will
have a child w/ free earlobes?
3. A couple has six children: 3 w/ type A blood, 3 w/ type AB blood. What are the two most
probable combinations of parents (show genotype please) that could have produced such a
family?
4. The father has type A blood and the mother has type B blood. What is the probability that
they will have children w/ type A? Type B? Type O? Type AB? Hint: ?/16th
5. A species of rabbit is almost always black, yet occasionally a tan one is born. Black mating
w/ black always gives birth to black, and black mating w/ tan usually gives birth to tan.
Why? Hint: three punnett squares required, simple dominance.
6. A mouse breeder recently created a short tailed mutant. When crossed with a long tailed
mouse, 8 long tailed and 7 short tailed offspring were created. When 2 of these short tailed
mice were bred with each other, 8 short tailed and 4 long tailed offspring were created.
What type of inheritance is this and which phenotype is dominant?
7. You have a hitchhikers thumb (recessive). Your mom also has one, but dad has a straight
thumb. What is the probability that your little brother (who is due in 2 months) will have a
hitchhikers thumb as well? How about any other brothers or sisters in the future?
8. A woman with dimples, a widow's peak, and a rolled tongue (all dominant traits) had a
father with no dimples, no widow's peak, and who couldn't roll his tongue. She has a child
with a man who looks a lot like dad - no dimples, no widows peak, and he can't roll his
tongue either. What is the probability that their child will have the three recessive traits
that both her dad and mate have in common? Hint: don't waste your time doing a punnett
square w/ 64 boxes.
9. A husband and wife (both w/ wavy hair) have three children with wavy hair. The fourth
child arrives and has a full head of totally straight hair. He accuses her of infidelity
(cheating on him). Explain to him how this could still be his child. Show your proof with a
punnett square.
10. Horses can be cremello (cream colored), chestnut (brown), or palomino ( both cream and
brown colored hairs that appears golden w/ white tail and mane). Of these phenotypes,
only palominos don’t have offspring that are look like the parents when crossed with other
palominos. Here are the results of some crosses: cremello x palamino = ½ cremello and ½
palamino; chestnut x palamino = ½ chestnut and ½ palamino; cremello x chestnut = all
palamino. Explain what type of inheritance is working here and prove your hypothesis with
some punnett squares. (Hint: Two different hair color are showing up at once in palamino
horses.)