Chromosomal Theory of Inheritance

Concept: Chromosomal Theory of Inheritance


Concept: Morgan's Experiments and Sex-Linkage


Concept: Dosage Compensation and X-Inactivation


Concept: Recombination and Genetic Maps


Chromosomal Theory of Inheritance Additional Practice Problems

Independent assortment of chromosomes is a result of 

A. the random nature of fertilization of ova by sperm.

B. the random separation of the sister chromatids to the two daughter cells during anaphase II.

C. the random orientation of each homologous pair at the metaphase I.

D. the relatively small degree of homology shared by the X and Y chromosomes.

E. all of the above

Watch Solution

Which of the following statements is TRUE of linkage?

A. All of the traits that Mendel studied - seed color, pod shape, flower color, and others - are due to genes linked on the same chromosome.

B. Crossing over has a low chance of separating genes that are located very close together on the same chromosome.

C. The farther two genes are apart on a chromosome, the lower the probability that a crossover will occur between them.

D. Linked genes are found on different chromosomes.

E. The observed frequency of recombination of two genes that are far apart from each other has a maximum value of 100%.

Watch Solution

In cats, black fur color is caused by an X-linked allele, the other allele at this locus causes orange color. The heterozygote is a tortoiseshell. What kinds of offspring would you expect from the cross of an orange female and a black male?

A. orange females, black males

B. orange females, orange males

C. tortoiseshell females, orange males

D. tortoiseshell females, black males

E. black females, orange males

Watch Solution

The state of having more than two sets of chromosomes is called _____.

A. aneuploid

B. dominant

C. non-disjunction

D. polyploid

E. autosomal

Watch Solution

Which ofthe following is required for chromatin to condense into the 30nm fiber?

A. histone H1

B. chromosomal scaffolding proteins

C. histone tails extending from the nucleosome

D. histone H1 & histone tails extending from the nucleosome.

Watch Solution

Cinnabar eyes is a sex-linked recessive characteristic in fruit flies. If a male having cinnabar eyes is crossed with a wild-type female, what percentage of the F1 males will have cinnabar eyes?

A. 0%

B. 25%

C. 50%

D. 75%

E. 100%

Watch Solution

Protein function is subject to post-translational regulation. Which of the following amino acids is enriched in histones and is modified through methylation or acetylation?

A. A

B. B

C. C and D

D. D

Watch Solution

Human sex chromosomes, X and Y, _____.

A. Have the same loci

B. carry the same number of genes

C. are homologous only at the pseudo-autosomal regions

D. only carry sex genes

Watch Solution

Color-blindness is an X-linked recessive disorder. Mike is color-blind. His wife, Meg, is homozygous for the normal color vision allele. Using Punnet squares, derive and compare the genotypic and phenotypic ratios expected for the offspring of this marriage.

If they have eight children, how many of them would you expect to be color-blind?

Watch Solution

A man homozygous for sickle cell disease (an autosomal recessive disease, i.e. not sex linked) who has normal vision marries a woman heterozygous for sickle cell disease who is colorblind (a recessive X-linked condition). What is the chance that a child (of either sex) born to them will have both sickle cell disease and be colorblind.

A. 0

B. 1/2

C. 3/8

D. 1/4

E. 1/8

Watch Solution

A true-breeding red-eye female is crossed with a white-eye male, you expect _____ red eye females that are heterozygous (consider in your % the number of males and females)

A. 25%

B. 50%

C. 100%

D. 0%

Watch Solution

In Drosophila melanogaster, the white-eye mutation is _____ and is represented as _____ for a white eye female.

A. gender-linked recessive; w+w+

B. gender-linked dominant, ww

C. gender-linked dominant, w+w+

D. gender-linked recessive, ww

Watch Solution

Queen Victoria of England was believed to have been a carrier for Hemophilia. She married Prince Albert who was not a hemophiliac. Their chances of having a male heir to the throne who was not a hemophiliac were?

A. 100%

B. 0%

C. 25%

D. 50%

Watch Solution

Predict the frequency of progeny genotypes for the cross: XAXaBb x XaYbb.

Watch Solution

_____ is though to be composed of _____.

A. The active X chromosome; heterochromatin

B. A Barr body; euchromatin

C. The centromere; euchromatin

D. A telomere; euchromatin

E. All of the above are correct answers

F. None of the above is a correct answer

Watch Solution

Drosophila may be monosomic for chromosome 4, yet remain fertile. A recessive mutant for bent bristles is identified on chromosome 4. Determine the genotypes of the F1 and F2 progeny for the following crosses. The following cross is conductd of true-breeding adult flies: monosomic normal bristles x diploid bent bristles

Select the two F1 genotypes that will be produced from this cross.

A. _/b+

B. _/b

C. b/b

D. b/b+

E. b+/b+

Watch Solution

Normally in humans a mutant gene on the Y chromosome will be inherited in which of the following ways?

A. All of the daughters of a parent with the mutant gene will receive it but none of the sons will.

B. All of the sons of a parent with the mutant gene will receive it but none of the daughters will.

C. Half of the sons of a parent with the mutant gene will receive it and half will not; none of the daughters will receive it.

D. One-quarter of both the sons and daughters of a parent with the mutant gene will receive it and the rest will not.

E. Half of the sons and daughters of a parent with the mutant gene will receive it and half will not.

Watch Solution

You do a cross between a white curly haired mouse and a black straight-haired mouse. You do not know if these animals come from true breeding populations. The 16 F1 progeny are 8 white curly mice and 8 black straight-haired mice. The following are consistent with this data.

A. Black is dominant.

B. One of the mice was heterozygous for both curly/straight and white/black hair.

C. Both curly/straight and white/black are present together on the same chromosome.

D. All of the answers listed above are correct.

E. None of the answers listed above are correct.

Watch Solution

Red-green color blindness is a recessive sex-linked trait (i.e. it is on the X chromosome). If a color blind man marries a woman with normal vision, what are their children likely to be?

A. All the boys and all the girls will e color blind.

B. Half of the boys and none of the girls will be color blind.

C. Half of the girls and none of the boys will be color blind.

D. None of the children will be color blind.

E. None of the answers listed above are correct.

Watch Solution

Two parents of genotype AAcc, aaCC are crossed (i.e. AAcc x aaCC). Neither locus is sex-linked. The A and C loci are on different chromosomes. 

a) Give the expected resulting genotypic frequencies for F1 offspring.

b) Now give the expected genotypic frequencies for an F1 cross.

Watch Solution

In a species of snakes, two parents of genotype Aa are crossed together (Aa x Aa). The locus is not sex-linked.

Assume complete dominance of the alleles, with AA and Aa causing a jagged scale pattern, and aa causing a smooth scale phenotype.

Give the expected genotypic and phenotypic frequencies of the offspring.

Watch Solution

A black female cat (XBXB) and an orange male cat (XOY) were mated to each other ad produced a male cat that was calico. Which sex chromosomes did this male offspring inherit from its mother and father? Remember that the presence of the Y chromosome determines maleness in mammals.

Watch Solution

A mutation that causes a yellowing of leaves in snapdragon plants was discovered in the early 1900s. Plants with this condition, termed aurea, have less chlorophyll than green plants. Crosses between various combinations of green and aurea plantsyielded the following results:

green x green = all green

aurea x aurea = 2/3 green, 1/3 aurea

green x aurea = 1/2 green, 1/2 aurea

If the green allele is designated as G, and the aurea allele is designates as GA, assign genotypes to the phenotypes listed.




Watch Solution

Give the genotypes of the various individuals in the pedigree shown below (Figure 8.1). Show the alleles as superscripts to the X chromosomes, with H representing the normal allele and h the allele for hemophilia.

NOTE: Circles represent females, squares represent males, black squares represent hemophiliacs

Watch Solution

The following pedigree depicts the inheritance of a hereditary disease affecting the heart. What is the most likely mode of inheritance of this disease? Pay particular attention to individuals 10 & 11.

A. autosomal dominant

B. autosomal recessive

C. X-linked recessive

D. Y-linked

E. X-linked dominant

Watch Solution

What characteristic is exhibited by an X-linked trait?

a. Only females have the trait.

b. Males inherit X-linked traits from their paternal parent only.

c. Females inherit X-linked traits from their maternal parent only.

d. Males can inherit a gene for an X-linked trait from either parent but normally inherit it from their fathers.

e. Females can inherit a gene for an X-linked trait from either parent.

Watch Solution

All female mammals have one active X chromosome per cell instead of two. What causes this to happen?

a. attachment of methyl (-CH3) groups to the X chromosome that will remain active

b. activation of the XIST gene on the X chromosome that will become the Barr body

c. inactivation of the XIST gene on the X chromosome derived from the male parent

d. activation of the BARR gene on one X chromosome, which then becomes inactive

Watch Solution

Which approach to determining the likelihood of various genotypes occurring in the offspring of particular parents is easier for you-constructing a Punnett square, or using the product rule to calculate probabilities? 

Compare and contrast the inheritance patterns of autosomal recessive and autosomal dominant traits.

Watch Solution

What is the chromosomal theory of inheritance?

Watch Solution

Assume that white color (W) is dominant over yellow color (w) in corn. Perform a Punnett square for a cross where pollen from the anthers of a plant is heterozygous for color is placed on the pistil of a yellow-fruited plant. What are the genotypes and phenotypes you would expect to find from this cross?

Watch Solution

Sex chromosomes in birds are referred to as “W” and “Z”, with females being the heterogametic sex and males being homogametic for the Z chromosome. In chickens, the allele for feather color is Z-linked with black feathers dominant to red feathers. If a rooster that is heterozygous for black feathers mates with a red hen, what is the probability that their chicks will be red hens?

a. 1/4

b. 1/2

c. zero

d. 1/1

e. 1/18

Watch Solution

A woman with normal blood clotting factor had a hemophiliac father. If she begins a family with a man whose mother was a hemophiliac, then what is the probability that they will have a hemophiliac son and a hemophiliac daughter?

a. 1/2

b. 1/4

c. 1/8

d. 1/16

e. 1/64

Watch Solution

Assume moths have the same sex-determining system as humans. In a species of moth, red wings are caused by an X-linked allele; the other allele at this locus causes white wings. The heterozygote has "candy-cane" wings that are white with red stripes. What kinds of offspring would you expect from the cross of a red female and a white male?

a. white females; red males

b. candy-cane females; red males

c. red females; white males

d. white females; white males

e. candy-cane females; candy-cane males

Watch Solution

Assume fruit flies have the same sex-determining system as humans. Cinnabar eyes is an X-linked recessive characteristic in fruit flies. If a female having cinnabar eyes is crossed with a wild-type male, what percentage of the F1 males will have cinnabar eyes?

A) 50%

B) 0%

c) 75%

D) 100%

E) 25%

Watch Solution

A particular inherited abnormality in humans has been shown to be an X-linked recessive trait. In one family seeking professional help from a genetic counselor, the following information is known:

1. The mother shows the abnormality.

2. Their only child is a daughter who is normal.

i) If their next child is a son, what is the probability that he will show the abnormality?

ii) What is the probability that the next child born will be a daughter showing the abnormality?

Watch Solution

In chickens and other birds, the chromosomal basis of inheritance is the opposite of that in humans; i.e., in birds, ZZ homogametic individuals are males , and ZW heterogametic individuals are females .

In chickens, barred plumage is dominant to non-barred plumage; the gene is Z-linked.

Suppose that you were a poultry breeder and that you needed large numbers of  barred males and nonbarred females . Describe a breeding stock that you could assemble for this purpose, which would produce only barred males and nonbarred females.

Be certain that you show the genotypes of both the roosters and the hens in your breeding stock and also the genotypes of all the offspring that this stock will yield.

Watch Solution

You are given a mouse with short ears and a straight tail from a pure breeding strain and another mouse with long ears and a curly tail, also from a pure breeding strain. When you cross them the offspring all have short ears and straight tails. When you cross these offspring to one another the results in the next generation exhibit all four possible combinations of ear size and tail shape (short & straight, long & curly, short & curly, long & straight) with short and straight being the most common and long and curly being the least common.

If you wanted to test for linkage which of the following types of mice would you use in a test cross with the second generation?

a. homozygous for straight tail and short ear

b. homozygous for curly tail and long ear

c. homozygous for short tail and long ear

d. homozygous for curly tail and short ear

e. heterozygous for both

Watch Solution

The pair of unmatched chromosomes in humans: 

a. Are the sex chromosomes

b. Are the "X" and "Y" chromosomes

c. Determine sex (gender) of humans

d. Contain different genes

e. All are correct

Watch Solution

In humans, the sex of a child is determined by: 

a. The sex chromosome in the egg

b. The number of autosomes in the sperm

c. The number of autosomes in the egg

d. The sex chromosome in the sperm


Watch Solution

People who have a single X chromosome are female, while those with XXY sex chromosomes are males. In order to be a female a human: 

a. Must have two X chromosomes

b. Cannot have a Y chromosome

c. Must have one X chromosome

d. Must have one Y chromosome

e. Cannot have an X chromosome

Watch Solution

The Y chromosome is: 

a. Larger than the X chromosome

b. Contains more genes than the X chromosome

c. The same size as the X chromosome

d. Smaller than the X chromosome

e. Genetically identical to the X chromosome

Watch Solution

The X chromosome is: 

a. Larger than the Y chromosome

b. Smaller than the Y chromosome

c. The same size as the Y chromosome

d. Genetically identical to the Y chromosome

e. Both A and D are correct

Watch Solution

The chromosomal designation for a human female is: 

a. XYY

b. XY

c. YY

d. XX

e. None are correct

Watch Solution

The chromosomal designation for a human male is: 

a. XX

b. XO

c. XY

d. YY

e. XXX

Watch Solution

A male expresses an X-linked recessive disorder only if he inherits these alleles from both parents. 

a. True

b. False

Watch Solution

X-linked recessive disorders affect more females than males.

a. True

b. False

Watch Solution

Linkage maps are diagrams of nitrogen base sequences on DNA. 

a. True

b. False

Watch Solution

Thomas Hunt Morgan chose to work with fruit flies in part because they have a short life cycle and large number of offspring. 

a. True

b. False

Watch Solution

A Barr body is: 

a. An inactive Y chromosome

b. An inactive autosome

c. An active X chromosome

d. An active Y chromosome

e. An inactive X chromosome

Watch Solution

A male expresses: 

a. Only the dominant alleles on his X chromosome

b. Both the dominant and recessive alleles on his X chromosome

c. Only the homozygous recessive alleles on his X chromosome

d. None of the alleles on his X chromosome

e. None of these are correct

Watch Solution

Diagrams of gene order and spacing on chromosomes are: 

a. Karyotypes

b. Phenotypes

c. Linkage maps

d. Genotypes

e. Metabolic maps

Watch Solution

Recombinant chromosomes have a mix of paternal and maternal alleles due to:

a. Random fertilization

b. Linkage

c. Independent assortment

d. Crossing over

e. Mutation

Watch Solution

Linked genes, by definition, are genes that:

a. Are found on the same chromosome

b. Have no alleles

c. Are found in the same species

d. Have more alleles than usual

e. Are alleles that are found in different daughter cells

Watch Solution

The most common phenotype or allele for a gene in a population is referred to as: 

a. The wild type

b. The dominant population

c. The recessive population

d. The P generation

e. The F1 generation

Watch Solution

In humans, alleles are inherited from: 

a. Females only (moms)

b. Males only (dads)

c. Males and females (one allele from each parent)

d. Males and females (two alleles from each parent)

e. None are correct

Watch Solution

Could a colorblind man pass his gene for colorblindness on to his sons?

Show the cross or crosses to support your answer.

What would be the genotype of a wife (for this man) that would produce only normal visioned sons? Show the cross or crosses to support your answer.

Could this man find a wife that would result in daughters that would not carry the gene for color blind vision? Show the cross or crosses to support your answer.

Watch Solution