Exam 2: Single-Gene Inheritance

The wild-type flower color of a particular species of plant is blue.The diagram below shows a simplified version of the biochemical pathways responsible for the synthesis of the blue pigment.Suppose that gene "A" codes for Enzyme A and gene "B" for Enzyme B. A friend provides you with a pure-breeding plant that makes colorless (white)flowers.What genetic experiment(s)could you perform to determine whether your plant lacks Enzyme A or Enzyme B? (Suppose that you have access to any pure-breeding lines that you need.)

Mendel studied the inheritance of phenotypic characters determined by alleles of seven different genes.It is an interesting coincidence that the pea plant has seven pairs of chromosomes (n = 7).What is the probability that,by chance,Mendel's seven genes would each be located on a different chromosome? You may assume that the pea's chromosomes are all the same size.

In Labrador retrievers,black color coat (B/-)is dominant to brown color coat (b/b).A breeder crosses two black individuals who have previously produced some brown puppies.If the cross produces six puppies: a)what is the probability that the first born will be brown? b)what is the probability that four of them will be brown and two will be black? c)what is the probability that at least one of them will be brown?

A recessive X-linked gene mutation is known to generate premature baldness in males but is without effect in women.If a heterozygous female marries an affected male,what proportion of all their children is expected to be prematurely bald?

A couple is both heterozygous for the autosomal recessive disease cystic fibrosis (CF).What is the probability that their first child will either be a boy or have CF?

The following pedigree shows the inheritance of attached earlobes (black symbols)and unattached earlobes (white symbol).Both alternative phenotypes are quite common in human populations. If the phenotypes are determined by alleles of one gene,then attached earlobes are inherited as:

A laboratory mouse homozygous for an RFLP marker is mated to a wild mouse that is heterozygous for that marker.One of the heterozygous individuals resulting from this cross is mated back to the wild parent.What proportion of the offspring will have the same RFLP pattern as the original laboratory mouse?

If a plant of genotype A/a is selfed,and numerous offspring are scored,what proportion of the progeny is expected to have homozygous genotypes?

Wild-type Drosophila melanogaster have a brown/grey body color.Mutants exist that have a yellow body color.Several crosses were performed between phenotypically wild type and yellow individuals,and the results of each cross are reported in the table below. Deduce the mode of inheritance of the yellow body phenotype and genotypes of the parents and offspring in the following crosses.

A wild-type strain of haploid yeast is crossed to a mutant strain with phenotype d.What phenotypic ratios will be observed in the progeny?

Cystic fibrosis is an autosomal recessive condition.If the parents of a boy with cystic fibrosis have two more children,what is the probability that both of these children will be unaffected?

The diagram below shows a part of the biochemical pathway responsible for fruit color in peppers (Caspicum annuum).Enzyme 1 is responsible for catalyzing the reaction that turns the colorless precursor into yellow pigment,whereas Enzyme 2 catalyzes the step that turns the yellow pigment into red pigment.A breeder crosses a pure-breeding plant that makes yellow peppers to a pure-breeding plant that makes red peppers.What proportion of the offspring will make red peppers?

A female Drosophila with the mutant phenotype a is crossed to a male who has the mutant phenotype b.In the resulting F₁ generation all females are wild-type and all males have the a mutant phenotype.Based on these results,we can conclude that the mode of inheritance of the phenotypes of interest is:

A mutation occurs in a germ cell of a pure-breeding,wild-type male mouse prior to DNA replication.The mutation is not corrected,and the cell undergoes DNA replication and a normal meiosis producing four gametes.How many of these gametes will carry the mutation?

In mountain rabbits,the EL-1 gene is located on chromosome 3.Four alleles of this gene have been identified in the population.With respect to EL-1,what is the maximum number of genotypes in the progeny of a $\underline{\text{ single cross }}$ between two mountain rabbits?

In the human pedigree shown below,black symbols indicate individuals suffering from a rare genetic disease,whereas white symbols represent people who do not have the disease. Based on the pedigree,what is the most likely mode of inheritance of this rare genetic disease?

A rare,curly winged mutant of Drosophila was found in nature.A mating of this fly with a true-breeding,normal laboratory stock produced progeny in the ratio 1 curly winged to 1 normal (both sexes had the same ratio).All curly winged progeny of this cross,mated with normal progeny of the same cross,again yielded 1 curly winged to 1 normal fly.When mated with one another,the curly winged progeny of the first cross yielded a progeny of 623 curly : 323 normal.This ratio strongly suggests which of the following?

A plant with small red flowers is crossed to a plant with large white flowers.The resulting F₁ is comprised of 75 plants with small red flowers and 72 plants with small white flowers. If flower color and flower size are controlled by a single gene each,what can be concluded from these results?

Suppose that the length of a duck's tail is determined by a single autosomal gene with two alleles: L (long tail)and l (short tail).When a female duck with a long tail was backcrossed to her father,she produced three ducklings with a long tail and three with a short tail. a)What are the possible genotypes of the female duck and of her father? b)What is the most likely genotype of the female duck's father? (Justify your answer using probabilities).