Summary: Genetics

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• Final Exam

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• Short hair (H) in rabbits is dominant to long hair (h). A pure-breeding short haired rabbit is crossed to a long haired rabbit. The F1 offspring are mated to produce an F2 generation. Draw a Punnett square to show the gametes produced by the F1 offspring and the expected F2 offspring. What percentage of the F2 offspring are expected to have long hair?  a 0%  b 25%  c 75%  d 100%

  b 25%

• In the Labrador retriever, black and brown coat colors are alternate traits of a single gene. Black (B) is dominant. Brown (b) is recessive. A black dog is crossed to a brown dog. In the litter of 10 puppies, all are black. What is the genotype of the black parent? a BB  b Bb  c bb  d Need more information

   a BB 

• Sofia and Ben are both heterozygous for two traits that assort independently: (1) having a Widow’s Peak (W), and (2) having a Dimple (D). What are the genotypes of gametes (eggs and sperm) made by Sofia and Ben? a WD and wd  b WW and dd  c WD, wd, Wd, and wD  d WD  e WwDd

  c WD, wd, Wd, and wD

• Having a dimple (gene D) and having a widow's peak (gene W) are determined by dominant alleles of two independently assorting genes. Sofia and Ben are heterozygous at genes D and W. If they have two children together, what is the probability that both children have a widow’s peak and will not have a dimple? a 3/4  b 3/16  c 9/256  d 3/8

  c 9/256

• In humans, having a dimple is due to a dominant allele of gene D, detached earlobes are determined by a dominant allele of gene A, and a Hitchhiker’s thumb is controlled by a recessive allele of gene H. The genotypes of two people are Dd aa Hh and Dd AA Hh. What is the chance their first child has no dimple, detached earlobes, and no Hitchhiker’s thumb? a 1/16  b 3/32  c 3/16  d 3/8

  c 3/16

• What is the probability that person VI-3 is a carrier of the cystic fibrosis allele? a 0  b 1/4  c 1/2  d 2/3  e 1

  d 2/3

• Imagine that you are a genetic counselor, and a couple planning to start a family comes to you for information. Charles was married once before, and he and his first wife had a child with cystic fibrosis. The brother of his current wife, Elaine, died of cystic fibrosis. What is the probability that Charles and Elaine’s first child will have cystic fibrosis? (Neither Charles, Elaine, nor their parents have cystic fibrosis.) a 0  b 1/6  c 1/4  d 1/3  e 1/2

  b 1/6

• One type of dwarfism in humans is caused by a single dominant allele of a single gene; the condition is called Achondroplastic Dwarfism. Dwarf individuals are heterozygous (Dd), while persons who are homozygous dd are of normal stature. Homozygous DD individuals all die before birth. If two achondroplastic dwarfs have children together, what fraction of their living offspring will also be dwarfs? a 1/4  b 1/2  c 2/3  d 3/4

  c 2/3

• A true-breeding plant that produces grey lentils is crossed with a true-breeding plant that produces tan lentils. All of the F1 offspring are brown. What ratio of F2 offspring is expected if lentil color were controlled by a single gene with two incompletely dominant alleles? a 9 brown: 3 tan: 3 grey: 1 green  b 1 tan: 2 brown: 1 grey  c All brown  d 3 tan: 1 grey

  b 1 tan: 2 brown: 1 grey

• In the Primula plant, the pigment malvidin creates blue-colored flowers. Synthesis of malvidin is controlled by gene K, yet production of this pigment can be suppressed by gene D. In this case, the D allele is dominant to the K allele, so plants with the genotype KkDd will not produce malvidin (and will be white) because of the presence of the D allele. So, in this cross KkDd x KkDd, what type of gene interaction determines flower color? a complementary gene action  b recessive epistasis  c dominant epistasis  d redundancy  e independent pathways

  c dominant epistasis