Mendelian Genetics

Mendelian Genetics Review Questions

Question 1 Homologous chromosomes move toward opposite poles of a dividing cell during a. mitosis b. meiosis I c. meiosis II d. fertilization

Answer 1 Homologous chromosomes move toward opposite poles of a dividing cell during b. meiosis I

Question 2 Meiosis II is similar to mitosis in that • Sister chromatids separate during anaphase. • DNA replicates before the division • The daughter cells are diploid • Homologous chromosomes synapse

Answer 2 Meiosis II is similar to mitosis in that • Sister chromatids separate during anaphase. • DNA replicates before the division • The daughter cells are diploid • Homologous chromosomes synapse

Question 3 Monohybrid cross • Variant for a character • Genetic makeup of an individual • An alternative version of a gene • A cross between individuals heterozygous for a single character

Answer 3 Monohybrid cross • Variant for a character • Genetic makeup of an individual • An alternative version of a gene • A cross between individuals heterozygous for a single character

Question 4 Allele • Alternative version of a gene • Has no effect on phenotype in a heterozygote • An organism's appearance • Genetic makeup of an individual

Answer 4 Allele • Alternative version of a gene • Has no effect on phenotype in a heterozygote • An organism's appearance • Genetic makeup of an individual

Question 5 A man with type A blood marries a woman with type B blood. Their child has type O blood. What are the genotypes of these individuals? What other genotypes, and in what frequencies, would you expect in offspring from this marriage?

Answer 5 Man IAi, Woman IBi, child ii Other genotypes for children are ¼ IAIB, ¼ IAi, ¼, IBi

Question 6 In tigers, a recessive allele causes an absence of fur pigmentation (white tiger) and a cross-eyed condition. If 2 phenotypically normal tigers that are heterozygous at this locus are mated, what % of their offspring will be cross-eyed? What % of cross-eyed tigers will be white?

Answer 6 25% will be cross-eyed; all of the cross-eyed offspring will also be white.

Question 7 A man with hemophilia (recessive, sex-linked) has a daughter of normal phenotype. She marries a man who is normal for the trait. What is the probability that a daughter of this mating will be a hemophiliac? That a son will be a hemophiliac? If the couple has four sons, what is the probability that all 4 will be born with hemophilia?

Answer 7 0;½; 1/16

Question 8 Red-green color blindness is caused by a sex-linked recessive allele. A color-blind man marries a woman with normal vision whose father was color-blind. What is the probability that they will have a color-blind daughter? What is the probability that their 1st son will be color-blind? (Note the different wording of the 2 questions)

Answer 8 ¼ for each daughter (½ chance that a child will be female x ½ chance of a homozygous recessive genotype); ½ for 1st son.

Question 9 A wild-type fruit fly (heterozygous for gray body color & normal wings) is mated with a black fly with vestigial wings. The offspring have the following phenotypic distribution: wild type, 778; black-vestigial, 758; black normal, 158; gray-vestigial, 162. What is the recombination frequency between these genes for body color & wing size?

Answer 9 17%

Question 10 What pattern of inheritance would lead a geneticist to suspect that an inherited disorder of cell metabolism is due to a defective mitochondrial gene?

Answer 10 The disorder would always be inherited from the mother.

Question 11 Pseudohypertrophic muscular dystrophy is an inherited disorder that causes gradual deterioration of the muscles. It is seen almost exclusively in boys born to apparently normal parents & usually results in death in the early teens. Is this disorder caused by a dominant or a recessive allele? Is its inheritance sex-linked or autosomal? Why?

Answer 11 Recessive, if it were dominant it would affect at least 1 parent of a child with the disorder. The disorder’s inheritance is sex-linked because it is seen only in boys. For a girl to have the disorder, she would have to inherit recessive alleles form both parents. This would be very rare, since males with the recessive allele on their X chromosome die in their early teens.

Question 12 How many chromatids are in a duplicated chromosome?

Answer 12 • 2

Question 13 A chicken has 78 chromosomes in its somatic cells. How many chromosomes did the chicken inherit from each parent? How many chromosomes are in each of the chicken’s gametes? How many chromosomes will be in each somatic cell of the chicken’s offspring?

Answer 13 • 39; 39; 78

Question 14 What phase are most of your body cells in?

Answer 14 • Non-dividing state called G₀.

Question 15 Each sperm of a pea plant contains 7 chromosomes. What are the haploid & diploid numbers for peas?

Answer 15 • Haploid = (n) 7 • Diploid = (2n) 14

Question 16 What is the original source of all the different alleles of a gene?

Answer 16 • Mutations in a gene lead to the different version (alleles) of that gene.

Question 17 A pea plant heterozygous for inflated pods (Ii) is crossed with a plant homozygous for constricted pods (ii). Draw a Punnett square for this cross. Assume pollen come from the ii plant.

Answer 17 i i I Ii Ii Genotype 2:2 Phenotype 2:2 i ii ii

Question 18 An organism with the genotype BbDD is mated to one with the genotype BBDd. Assuming independent assortment of these 2 genes, write the genotypes of all possible offspring from this cross & use the rules of probability to calculate the chance of each genotype occurring.

Answer 18 • ¼ BBDD, ¼ BbDD, ¼ BBDd, ¼ BbDd

Question 19 Incomplete dominance & epistasis are both terms that define genetic relationships. What is the most basic distinction between these terms?

Answer 19 • Incomplete dominance describes the relationship between 2 alleles of a single gene, whereas epistasis relates to the genetic relationship between 2 genes and the respective alleles of each.

Question 20 Andalusian chickens with the genotype CBCB are black, those with the genotype CWCW are white, and those with the genotype CBCW are gray. What is the relationship between the CB and CW alleles?

Answer 20 • The relationship between the alleles is one of incomplete dominance.

Mendelian Genetics