Probability and Genetics Practice Problems

Probability is a measure of the likelihood of an event occurring. Which of the following statements is false about probability?

Albinism is an autosomal recessive disorder which means that only the homozygous recessive genotype will show the disorder. If a male carrier (Aa) crosses with an albino female (aa), then the ratio of unaffected and albino children will be:

Autosomal recessive traits pass from both parents onto their children. Albinism is an autosomal (not sex-linked) recessive trait. Both homozygous dominant (AA) and heterozygous dominant (Aa) individuals will exhibit a normal phenotype, while only homozygous recessive (aa) individuals will be albino. What is the probability that a child of a homozygous dominant father and a heterozygous mother will have albinism?

An X-linked genetic condition known as Duchenne muscular dystrophy (DMD) is characterized by progressive muscle weakness and degeneration as a result of alterations in a protein known as dystrophin, which aids in the preservation of muscle cells. What is the probability that each child will inherit DMD if an affected man marries a carrier woman?

In cattles, the polled (absence of horn) condition is dominant over horned, and the coat color is controlled by two codominant alleles. The genotype RR produces red coat color, RW produces roan, and WW produces white. A dairy farmer crossed a PpRW bull with a ppWW cow. What is the probability that the offspring of this cross will be polled white?

Bulldog dwarfism is a lethal genetic defect in which fetuses homozygous for the mutation in the ACAN gene have severe disproportionate dwarfism and are usually aborted around seven months of gestation. When two cattle that are heterozygous for the mutation are crossed, what is the probability that the offspring will be of the same genotype as the parents?

Which of the following supports the chromosome theory of heredity?

In a dihybrid cross between AaBb heterozygotes, what is the probability of the offspring genotype being AABB?

What is the probability that a child born to parents who are carriers for an autosomal recessive disorder will also be a carrier?

A couple has two children, both of whom have been diagnosed with cystic fibrosis, an autosomal recessive condition. They are expecting their third child and are concerned about the possibility of cystic fibrosis in their baby. They seek information from a genetic counselor. After discussing their family histories, the counselor said that they are both carriers of this recessive condition. What is the chance that the third child of the couple will be free of the condition?

Galactosemia is a disorder that affects how the body processes a simple sugar called galactose.  The signs and symptoms of galactosemia result from an inability to use galactose to produce energy. Researchers have identified several types of galactosemia. These conditions are each caused by mutations in a particular gene and affect different enzymes involved in breaking down galactose. There are 3 types of galactosemia. Type I, type II, and type III galactosemia are also called?

Galactosemia happens when there's a change (mutation) in the genes that make an enzyme that breaks down galactose. To have galactosemia, a child must inherit two galactosemia genes, one from each parent. If both the parents who were found to be galactosemia carriers are planning for a child, what will be the probability that the child will be a carrier, affected or healthy, respectively?

The autosomal recessive inheritance of galactosemia results in a lack of an enzyme necessary for adequate galactose degradation. Galactose accumulation becomes the substrate for enzymes that catalyze the polyol pathway of carbohydrate metabolism in galactosemic patients.  What is the possible reaction that the accumulated galactose undergoes?

A cross was performed between individuals of genotypes AaBbCcDd and AaBbCcDd. What is the probability that the offspring will have the same genotype as their parents?

A cross was performed between individuals of genotypes AaBbCcDd and AaBbCcDd. What is the probability that their offspring will have the genotype AABbCcDD?

A cross was performed between individuals of genotypes AaBbCcDd and AaBbCcDd. What is the probability that their offspring will have all the four recessive traits?

An unaffected female marries a man who is affected by an X-linked recessive trait. What is the probability that she will conceive an unaffected son? 

a. 0% 

b. 25% 

c. 50% 

d. 100%

If a man with an X-linked recessive trait marries a female who is an unaffected carrier, what is the probability that his daughter is a carrier of the trait?

A dominant X-linked trait is hypophosphatemic rickets. An individual with hypophosphatemic rickets marries a woman who is not genetically predisposed to the disorder. How likely is it that they have an unaffected daughter?

A woman who is heterozygous (Dd) for a dominant gene marries a man who is homozygous recessive. What is the probability of her first child inheriting the dominant allele?

What is the likelihood that a child would have two diseases if both parents are healthy yet carry the genes for both autosomal recessive disorders?

In pea plants, plant height, flower color, and pod color are governed by three independently assorting genes. The three genes have dominant and recessive alleles, with tall (T) dominant to short (t), axial flower (A) dominant to terminal (a), and green pod (G) dominant to yellow (g). If two pea plants that are heterozygous for all three genes are crossed, what is the probability that their offspring will have the genotype TtAaGg?

A dihybrid cross between pea plants with round yellow seed (RrYy) and wrinkled green seed (rryy) is performed. What is the probability of obtaining offspring with wrinkled yellow seeds?

If two parents are both heterozygous for a trait, what is the probability that their offspring will be homozygous recessive for that trait?

What is the probability of rolling a 6 on a fair die?

A jar contains 4 red balls and 6 green balls. What is the probability of drawing a red ball?

What is the probability of drawing a red card from a deck of cards?

What is the probability of flipping a coin and getting heads?

Sickle cell anemia is an autosomal recessive disorder. Suppose we use "a" to denote the recessive allele associated with this condition, which of the following crosses can produce offspring in which 50% are affected by this condition?

The following conditions can be caused by an autosomal dominant inheritance except:

If we cross a flower with a TtYyWW genotype to another flower with a ttYYWw genotype, what is the chance of producing heterozygous offspring for all three traits?

Hemophilia is a bleeding disorder that can be inherited from one of the parents or both. If the father has hemophilia and the mother is not a carrier of the hemophilia gene, each son has a 0% chance of inheriting the condition. However, each daughter has a 100% chance of being a carrier of the hemophilia gene. What type of inheritance pattern is shown by this condition?

Brachydactyly is a genetic condition in which there is a shortening of fingers and toes because of unusually short bones. Once the defective gene is present, this condition can be expressed phenotypically. What type of inheritance is illustrated by this condition?

Suppose we cross-pollinate white and red variants of Hibiscus rosa-sinensis. If they produce a pink variant, this event is referred to as:

If a pea plant with genotype AaBBCCdd is crossed with another pea plant with genotype AAbbCcDd, what is the probability of producing offspring with AABbCCdd or AaBbCcDd?

If we cross an organism with EeFFGg and eeFfGG genotypes, what is the probability of producing an EeFfGG genotype?

If we cross an organism with AaBBCC and AABbcc genotypes, what is the probability of producing an AABbCc genotype?

If a couple that is both heterozygous for Cystic fibrosis has five children, what is the probability of having at least one child affected by the disease?

A male is heterozygous for Phenylketonuria (PKU). If he marries a female that is also heterozygous for PKU and has four children, what is the probability of having at least one child affected by PKU?

In a dihybrid cross, if the two traits are completely linked, what is the expected phenotypic ratio of the offspring?

In a dihybrid cross between two heterozygous individuals, what is the probability of obtaining offspring with the recessive phenotype for one trait and the dominant phenotype for the other trait?

The fork-line method is a useful approach to tracking probabilities in a genetic cross. Which of the following scenarios does this method usually apply?

Mendel investigated the inheritance pattern of pea plants by counting the number of plants with certain traits in the progeny after doing crossing experiments. Considering this method, what type of probability did he use?

A cross of a white-eyed (bb) Drosophila and a red-eyed (Bb) Drosophila produces a total of 150 offspring. How many of these progeny are white-eyed?

If we cross two heterozygous parents with the same genotypes (BbCcDd), what is the probability of producing a progeny that has dominant phenotypes for all three traits?

If we cross two heterozygous parents with the same genotypes (BbCcDd), what is the probability of producing a progeny that has recessive phenotypes for all three traits?

A white straight-eared (WwEe) female rabbit is crossed with a brown droopy-eared (wwee) male rabbit. What is the probability of producing a brown rabbit?

A white straight-eared (WwEe) female rabbit is crossed with a brown droopy-eared (wwee) male rabbit. They can produce offspring with the following genotypes except:

A white straight-eared (WwEe) female rabbit is crossed with a brown droopy-eared (wwee) male rabbit. What is the probability of producing Wwee genotype?

A brown long-haired (BBcc) dog is crossed with a white short-haired (bbCC) dog. If one of the F1 progeny is crossed with another F1 progeny, which of the following genotypes has the highest frequency in the F2 progeny?

A brown long-haired (BBcc) dog is crossed with a white short-haired (bbCC) dog. If one of the F1 progeny is crossed with another F1 progeny, how many genotypes will be produced in the F2 progeny?

If a brown long-haired (BBcc) dog is crossed with a white short-haired (bbCC) dog, what will be the phenotype of their offspring?

If a brown long-haired (BBcc) dog is crossed with a white short-haired (bbCC) dog, what will be the genotype of their offspring?

If the male and female parents are heterozygous for a specific trait, what is the probability of getting a homozygous recessive offspring?

A male heterozygous for the cystic fibrosis (CF) mutation 'G542X' marries a female heterozygous for the CF mutation 'G551D'. The G542X mutation causes defective CFTR protein (an ATP- and phosphorylation-dependent chloride channel) production, while the G551D mutation causes defective regulation of CFTR protein. Determine the probability of the couple having an affected child.

The offspring obtained by crossing two different parents is called ______ and the offspring obtained by crossing the first filial generation is called ______.

Phenylketonuria has an autosomal recessive inheritance. A quadruplet was born to a newlywed couple, and phenylketonuria was discovered in one of the children. Genetic counseling is recommended for the parents of the affected infant. It would be important to inform them that:  

Epistasis determines the Labrador retriever's coat color. B denotes black pigment, b denotes brown pigment (recessive), and the expression of the B locus is controlled by the E locus. Which of the following is inaccurate?

Which of the following statements about mutations in the mitochondrial DNA is true?

Based on the cloning and analysis of the star-branching enzyme, what could be the foreign sequence that disrupted the normal coding sequence of the mutant gene?

What is the effect of the absence of starch-branching enzyme on the pea plant?

In Mendel's experiment, he selected contrasting pairs of traits to be studied. After mating the parental generation, what did he observe in the F1 results?

What is the genotype of an F1 gamete if it undergoes self-fertilization and produces the following F2 genotypes:

    AA: 1/4
    Aa: 1/2
    aa: 1/4

Which of the following statements about the First Filial (F1) Generation is considered false?

Mendel's principles also apply to the inheritance of multiple traits as demonstrated by the trihybrid cross.  If an F1 AabbCc serves as a parent in a trihybrid cross, the following are the resulting gametes except:

Smooth and yellow-seeded peas are dominant over wrinkled and green-seeded peas. If we cross a smooth (Rr) and green-seeded (yy) pea with a round (Rr) and yellow-seeded (Yy) pea, what is the probability of producing smooth-seeded peas?

The phenomenon where a type of inheritance in which two alleles of the same gene are both expressed in the same degree within an organism is called:

Smooth and yellow-seeded peas are dominant over wrinkled and green-seeded peas. If we cross a smooth (RR) and yellow-seeded (Yy) pea with a wrinkled (rr) and green-seeded (yy) pea, what are the two resulting genotypes of the offspring?

Smooth and yellow-seeded peas are dominant over wrinkled and green-seeded peas. If we cross a smooth (RR) and yellow-seeded (Yy) pea with a wrinkled (rr) and green-seeded (yy) pea, what are the resulting phenotypes of the offspring?

The purple (P) flowers dominate over the white (p) flowers. If we cross two heterozygous parents, what will be the resulting genotypic ratio of the offspring?

A geneticist cross-fertilized the different pea plants that differ in only one character to produce F₁ offspring. He then allowed the F₁ to self-fertilize to raise the F₂ generation. The following ratios were then obtained from a large F₂ generation: 

P. 50/48   Tall, short 

Q. 78/26  Tall, short 

R. 99/0    Tall, short 

S. 0/77    Tall, short

Assuming that the allele for tallness (T) is dominant over the allele for shortness (t), identify the option that includes the offspring with both parents being heterozygous for one trait.

If curly fur (C) is dominant over straight fur (c), and the coat color black (B) is dominant over the color brown (b) in dogs, determine the probability of puppies with curly fur and a black coat color when two BbCc parent dogs are crossed.

A geneticist cross-fertilized two pea plants and obtained the following F1 progeny. 

Round seeded =77, wrinkled seeded= 77 

The allele for roundness, "R", is completely dominant over the allele for wrinkledness, "r". What is the probability of having a homozygous round offspring from a cross between F1 round and wrinkled?

When a homozygous dominant pea plant with blue flower (BB) is cross-bred with a homozygous recessive pea plant with white flower (ww), What is the expected ratio of the genotype BB and Bw in the F2 progeny?

Organisms that can pass specific traits to all their offspring when interbred are called:

Albinism is a rare genetic disorder where a person does not have the usual amount of melanin pigment. Mr. X is suffering from albinism, whereas Mrs. X is normal, but her father was albino. What is the probability of their next child being normal? (Note: The allele for normal is "A" and for albino is "a" and albino is a recessive genetic disorder) 

black (B) and wide (D) eyes are dominant over blue (b) and narrow (d) eyes. If the mother has blue and wide (bbDD) eyes and the father has black and narrow (Bbdd) eyes, what is the probability of producing BbDd genotyped offspring?

A hybrid plant with a pink (Rr) flower is produced by a plant with red (RR) and white (rr) flowers. What is the expected phenotypic ratio when the hybrid plant with pink is crossed with the recessive parent with white flowers?

Round pea seeds (R) are dominant over wrinkled seeds (r). If breeding a round-seeded pea plant and a wrinkle-seeded pea plant yields 100% round-seeded plant, what are the genotypes of the offspring?

The punnet square shown below is constructed by self-crossing the dihybrid with the genotype RrYy. What percentage of offspring is recessive for both gene pairs? 

What is the probability that the offspring of a trihybrid crossing between AaBbCC and AABbCc will be AABbCc?

In heterozygous pea plants (Pp), what is the probability (Pp x Pp) that the offspring will be homozygous recessive?

If one of the parental genotypes is homozygous recessive for a specific trait, what genotype can the other parent have if all of their offspring are heterozygous?

A test cross is used to identify the genetic makeup of an organism. Why can't we utilize phenotypes to determine the dominant traits?

Achondroplasia is a condition in which the changing of cartilage to bone is prevented. It follows an autosomal dominant pattern of inheritance and affected individuals are characterized by dwarfism. Which of the following is true about autosomal dominant disorders such as Achondroplasia?

When two independent events are occurring simultaneously, like in a dihybrid cross, then the ratio of each joint phenotypic combination can be calculated by multiplying their individual probabilities. This statement is true for:

In pea plants, the height of pea plants, seed color, and seed shape are three independent events. The individual probabilities of the outcome of a cross between pea plants that are heterozygous for one particular trait are given as follows:

1. The probability of the pea plant being tall is 3/4, and that it is short is 1/4. 

2. The probability of the pea plant having a round seed is 3/4 and having a wrinkled seed is 1/4. 

3. The probability of the pea plant having a yellow seed is 3/4 and having a green seed is 1/4. 

Two pea plants that are heterozygous for all three of the above traits are brought into the same cross. Calculate the probability of having a pea plant that is tall in height and has a seed with a yellow color and wrinkled shape. 

Cystic fibrosis is a hereditary disease. It is due to a gene defect that interferes with how salt and water enter and exit cells. This can lead to a buildup of thick, sticky mucus in the body's tubes and passages, notably the lungs and digestive system, along with recurring infections. What is the probability of having a child that is affected by cystic fibrosis if both parents are carriers (Cc) for cystic fibrosis? (Note: The normal allele is "C" and the allele for cystic fibrosis is "c".)

Regarding the sum rule and product rule of probability, which of the following is true?

Geneticists use Punnett squares to predict the genotypic or phenotypic probabilities of various genetic crosses. Which genotype belongs to the "X" and "Y" in the lower boxes of the illustration below?

Sickle-cell anemia is a type of disorder that is caused by recessive genes in the autosomal chromosome. It is only expressed when the individual has:

Albinism is a genetic defect that affects the production of melanin in the body. In most cases, albinism has parents that do not show symptoms of the condition. People who have an affected gene but are not showing any symptoms are called: