Genetics: Punnett Squares Problem Set 1
The Trouble with Tribbles
If you have trouble with this, go to http://dnaftb.org/ and do the tutorials!
Tribbles are cute furry balls that squeak! They come in many colors and patterns!
P = plaid
p = plain
F= regular fur
f = extra furry
S = stripes
s = spots
Monohybrid Crosses-
A heterozygous Plaid male tribble fell in love with a homozygous plain female tribble.
Three months later they had a litter of 4 tribbles. What are their possible genotypes and
phenotypes?
Dihybrid CrossesA heterozygous Striped and regular fur male tribble mates with a heterozygous Striped and
regular fur female tribble. What are the genotypic and phenotypic ratios of their prospective
progeny?
Sex LinkagesThe ability to “jiggle,” a special genetically dominantly inherited tribble dance is linked on the X
chromosome. If an especially “jiggy” (Heterozygous) female tribble attracts the attention of a
non-so “jiggy” (recessive) male, what are the genotypic and phenotypic ratios of their potential
tribblettes? Is there a difference between males and females?
Co-Dominance and Incomplete Dominance:
A. If tribble hazel eyes are a result of incomplete dominance (Blending of two traits in the
heterozygous=a combination of having one brown eye allele and one green eye allele),
then what is the chance of a male hazel eyed tribble having a child with green eyes if he
mates with a female hazel eyed tribble? Having a child with hazel eyes?
B. Blood types are a result of multiple alleles or Co-Dominance (expression of both alleles
at once) in which more than one allele is dominant or recessive. A and B blood types
are dominant and O blood type is recessive. What are the genotypic and phenotypic
ratios of the progeny if a male tribble heterozygous for blood type A mates with a female
tribble heterozygous for blood type B? (See- http://en.wikipedia.org/wiki/Blood_type)
C. Rh factor stands for Rhesus monkey factor. Possessing the Rh factor is dominant
(positive or corresponding letter code); non-possession is recessive (negative or
corresponding letter code). What would the above cross look like if the male was positive
for the Rh factor (RzRz) and the female was negative (RoRo) for the Rh factor? (See- for
what Rz and Ro mean http://en.wikipedia.org/wiki/Rh_blood_group_system) Is there a
chance for “hemolytic” blood disease of the newborn or a chance of erythroblastosis
fetalis (or rhesus disease)?
D. Go to: http://www.ncbi.nlm.nih.gov/books/NBK2268/ Explain what the Bombay phenotype is
and its significance. Challenge: How could H antigen be used as evidence in a crime scence?
Challenge- Multiple Traits:
If a male plaid (Pp), spotted, extra furry tribble that can jiggle (Jj) marries a female plain, striped
(Ss), regular fur (Ff) that can jiggle (Jj), what is the chance they will have a male offspring that is
plain, spotted, extra furry and can jiggle? Female offspring with same traits?