Going Beyond Mendel
True and False Questions
A sperm cell carries two alleles for each gene.
Suppose two pea plants heterozygous for pea shape are crossed; the chance that a pollen grain and an ovule will both carry recessive alleles and form a homozygous recessive zygote is 1/2.
The cross Rr x rr should give 1/2 dominant phenotype and 1/2 recessive phenotype progeny.
Assume each of a married couple is heterozygous for Tay-Sachs disease, a lethal recessive disorder. If they have four children, we know that only one will develop the disease.
Boys get their Y chromosomes only from their fathers, and girls get their X chromosomes only from their mother.
If two genes assort independently at meiosis, then they must be on separate chromosomes.
Multiple Choice Questions - Choose the best available answer.
Individuals heterozygous for a hair color gene (Yy) are crossed with one another. What is the probability that any one sperm or egg carried the recessive (y) allele?
Some guinea pigs can have black fur (BB or Bb), while others have recessive brown fur (bb). Which cross would be best to determine whether a particular black-furred animal is homozygous or heterozygous?
a) Cross it with another black-furred animal
b) Cross it with one of its siblings
c) Cross it with a true-breeding black-furred animal
d) Cross it with a true-breeding brown-furred animal
Suppose guinea pigs can also have curly hair (CC or Cc) or straight hair (cc). Which of the following crosses would be likely to produce the most progeny with black curly hair?
a) BBCC x bbcc
b) BbCc x BbCc
c) BbCc x bbcc
d) BBc x BBCc
When a pea plant heterozygous for pea shape and pea color (RrYy) produces pollen,
a) 1/2 the pollen is Rr and 1/2 is Yy
b) 1/2 the pollen is RY and 1/2 is ry
c) 1/4 the pollen is Ry, 1/4 is rY, 1/4 is RY, and 1/4 is ry
A recessive mutant such as a genetically albino flower might lack colored pigment because
a) the plant did not grow in the sun.
b) the plant was deficient is some essential nutrient that it needed.
c) the plant lacked an enzyme necessary to produce pigment.
d) the temperature level was incorrect for the production of pigment.
Two white sheep are mated, and of several lambs produced, one is black. What can you conclude?
a) White fleece is recessive to black, and the lamb is heterozygous.
b) White fleece is recessive to black, and the parents are homozygous.
c) Black fleece is recessive to white, and the black lamb is heterozgous.
d) Black fleece is recessive to white, and the parents are heterozygous.
Which of the following crosses will produce a 3:1 phenotopic ratio
a) WW x ww
b) Ww x ww
c) Ww x Ww
d) ww x ww
e) none of the above
An individual with genotype IAIB produces both A and B antigens. This is an example of
a) partial dominance
c) recessive lethals
d) dominant lethals
Armadillos give birth to four genetically identical babies, derived from a single egg. Suppose we weigh four newborn siblings and find their weights to be nearly identical, but when captured and weighed one year later they differ substantially. What is this variation due to?
a) A large number of multiple alleles at a single locus influences weight.
b) Differing alleles at a number of gene loci affect the final weight.
c) Environmental effects have introduced nongenetic variation during growth.
d) We are seeing the effects of epistatis and pleiotropy.
A general statement about linked genes would be
a) they do not conform to Mendels law of dominance.
b) they do not conform to Mendels law of segregation.
c) they do not conform to Mendels law of independent assortment.
d) they do not conform to Mendels laws at all.
You have: answers correct out of a possible eighteen.
The question numbers that were not correct are:
Instructor: Professor Clyde Herreid, firstname.lastname@example.org