BICD 100 Lecture Notes - Reciprocal Cross, Aneuploidy, Genetic Testing
4 Jun 2018
School
Department
Course
Professor
1) (6 point question)
Background info: About 30% of the Irish population has red hair and an inability to tan
(MC1R). This is due to an unusual variant of the pigment molecule melanin, called red
melanin. Another fairly common inherited condition is restless legs syndrome (RLS). It is
characterized by an irresistible urge to move ones legs and can interfere with sleep,
leading to chronic sleep deprivation. Both red melanin and restless leg syndrome are
recessive, and their genes are on different chromosomes.
Molly and Sean met in San Francisco
and were drawn to each other because
of their striking red hair and very pale
skin (both had parents who emigrated
from Ireland). Neither has a family
history of restless leg syndrome. A few
years later they married and had
identical twins, Jerry and Garcia, both
are red heads and their legs are fine.
Danny and Betty lived in San Francisco
too. They both had brown hair, and
Danny suffers from restless leg
syndrome. Their daughter, Cali, has dark brown hair and her legs are fine.
Jerry and Cali have a son, Henry. He has red hair, does not tan and has restless leg syndrome.
Complete the family tree by assigning the genotypes based on the phenotypes described above
(Hint: obviously you can get some information from the phenotype of the individual. Further
clues can be obtained from the phenotypes of the progeny). Use R or r for restless leg syndrome
alleles or an underscore if the allele could be either R or r. For example, R_ would represent
either Rr or RR. Use M or m for the red melanin alleles, M_ would represent MM or Mm.
A) (1.5 point) Which individuals must be heterozygous for restless leg syndrome?
G, C and J
B) (1.5 point) Which individuals might be heterozygous for restless leg syndrome?
M, S and B
C) (1 point) Which individuals must be heterozygous for the red melanin gene?
C
find more resources at oneclass.com
find more resources at oneclass.com
D) (2 point) Garcia marries a woman who has restless leg syndrome and red hair, what is
the probability that a child of theirs will inherit both traits? Show your logic using probability, or
draw a Punnett square to show the potential genotypes of their progeny.
Childs genotype would be rr mm.
Garcia genotype Rr, mm: 50% chance of gamete being r m genotype (other would
be R m genotype).
Wife genotype rr, mm: 100% chance of gamete being r m genotype.
Therefore: 50% chance of child having rr mm genotype.
Punnett square would look as follows:
gametes
from mother
rm
from
father
R m
Rr, mm
r m
rr, mm
2) (10 point question) Cats have an X-linked orange gene (O and o alleles) that is important for
the coloration of fur pigment. A pair of recessive alleles will give black fur.
A) (2 points) Using your knowledge of genetic nomenclature what would be the
genotype of a male black cat? Explain your reasoning.
Dominant alleles are usually written in the form of a capital. The small o allele would
represent the recessive allele. For an X-linked allele the male cat would be hemizygous for
the X chromosome and have one Y chromosome too.
A male black cat, therefore, would have a genotype of o/Y.
Since it is sex linked a better nomenclature would be Xo/Y
B) (2 points) Using your knowledge of genetics what would be the most likely genotype
of an orange female cat? Explain your reasoning.
Due to X-inactivation a heterozygous female would be a tortoiseshell or calico cat.
Consequently, a solid black or orange coat color indicates the cat is homozygous at the
orange gene locus. In this case, two dominant alleles lead to the orange color. i.e. XOXO
C) (3 points) Describe both the phenotype and genotype of the different progeny classes
you would expect to see from a cross between a black male cat with an orange female cat
(based on the genotypes you describe above).
find more resources at oneclass.com
find more resources at oneclass.com
Black male Orange female
Parents Xo/Y X XO/ XO
Possible progeny Xo/ XO (Tortoiseshell female)
Y/ XO (Orange male)
Genotype Phenotype
D) (3 points) Describe both the phenotype and genotype of the different progeny classes
you would expect to see from the reciprocal cross of the one performed in part c of this
question?
Orange male Black female
Parents XO /Y X Xo / Xo
Possible progeny XO / Xo (Tortoiseshell female)
Y/ Xo (Black male)
Genotype Phenotype
3) ( 9 point question) This question
continues our cat theme for this
homework.
a) (2 points) In the photo to the right
are two different tortoise shell cats.
What is the reason for the coat pattern
differing between the two cats?
Cat on left is more speckled
indicating smaller patches of ginger hair.
Cat on the right has two large patches.
This is an indication of when the X-activation started in these two cats. It was an early event
for the cat on the right but a late event for the cat on the left.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Background info: about 30% of the irish population has red hair and an inability to tan (mc1r). This is due to an unusual variant of the pigment molecule melanin, called red melanin. Another fairly common inherited condition is restless legs syndrome (rls). It is characterized by an irresistible urge to move ones legs and can interfere with sleep, leading to chronic sleep deprivation. Both red melanin and restless leg syndrome are recessive, and their genes are on different chromosomes. Molly and sean met in san francisco and were drawn to each other because of their striking red hair and very pale skin (both had parents who emigrated from ireland). Neither has a family history of restless leg syndrome. A few years later they married and had identical twins, jerry and garcia, both are red heads and their legs are fine. Danny and betty lived in san francisco too. Their daughter, cali, has dark brown hair and her legs are fine.
