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Ch. 2 - Transmission Genetics
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
All textbooksSanders 3rd EditionCh. 2 - Transmission GeneticsProblem 41c
Chapter 2, Problem 41c

Humans vary in many ways from one another. Among many minor phenotypic differences are the following five independently assorting traits that (sort of) have a dominant and a recessive phenotype: (1) forearm hair (alleles F and f )—the presence of hair on the forearm is dominant to the absence of hair on the forearm; (2) earlobe form (alleles E and e)—unattached earlobes are dominant to attached earlobes; (3) widow's peak (alleles W and w)—a distinct 'V' shape to the hairline at the top of the forehead is dominant to a straight hairline; (4) hitchhiker's thumb (alleles H and h)—the ability to bend the thumb back beyond vertical is dominant and the inability to do so is recessive; and (5) freckling (alleles D and d)—the appearance of freckles is dominant to the absence of freckles. In reality, the genetics of these traits are more complicated than single gene variation, but assume for the purposes of this problem that the patterns in families match those of other single-gene variants.
If a couple with the genotypes Ff Ee Ww Hh Dd and Ff Ee Ww Hh Dd have children, what is the chance the children will inherit the following characteristics?


all recessive traits

Verified step by step guidance
1
Step 1: Understand the problem. The question asks for the probability that the children inherit all recessive traits. This means the child must inherit the recessive allele for each of the five traits: forearm hair (f), earlobe form (e), widow's peak (w), hitchhiker's thumb (h), and freckling (d).
Step 2: Recognize that the parents are heterozygous for all traits (Ff Ee Ww Hh Dd). For each trait, the probability of passing on a recessive allele (f, e, w, h, d) from one heterozygous parent is 1/2.
Step 3: Since the traits are independently assorting, the probabilities for each trait can be multiplied together to find the overall probability of inheriting all recessive traits. Use the formula: P(all recessive traits) = P(f) × P(e) × P(w) × P(h) × P(d).
Step 4: Substitute the probabilities for each trait into the formula. For each trait, the probability of inheriting the recessive allele from both parents is (1/2) × (1/2) = 1/4. Therefore, the overall probability is (1/4) × (1/4) × (1/4) × (1/4) × (1/4).
Step 5: Simplify the expression to find the final probability. The result will represent the chance that the children inherit all recessive traits.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Mendelian Genetics

Mendelian genetics is the study of how traits are inherited through generations based on the principles established by Gregor Mendel. It involves understanding dominant and recessive alleles, where dominant alleles mask the expression of recessive ones. This framework helps predict the probability of offspring inheriting specific traits based on parental genotypes.
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Descriptive Genetics

Punnett Square

A Punnett square is a diagram used to predict the genetic makeup of offspring from two parents. By organizing the possible gametes from each parent, it allows for the visualization of potential genotype combinations. This tool is essential for calculating the probabilities of inheriting specific traits, such as the recessive traits in the given question.
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Chi Square Analysis

Independent Assortment

Independent assortment is a principle stating that alleles for different traits segregate independently of one another during gamete formation. This means that the inheritance of one trait does not influence the inheritance of another, allowing for a variety of combinations in offspring. Understanding this concept is crucial for analyzing the inheritance patterns of multiple traits simultaneously.
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Gamete Genetics and Independent Assortment
Related Practice
Textbook Question

A pure-breeding fruit fly with the recessive mutation cut wing, caused by the homozygous cc genotype, is crossed to a pure-breeding fly with normal wings, genotype CC. Their F1 progeny all have normal wings. F1 flies are crossed, and the F2 progeny have a 3:1 ratio of normal wing to cut wing. One male F2 fly with normal wings is selected at random and mated to an F2 female with normal wings. Using all possible genotypes of the F2 flies selected for this cross, list all possible crosses between the two flies involved in this mating, and determine the probability of each possible outcome.

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Textbook Question

Humans vary in many ways from one another. Among many minor phenotypic differences are the following five independently assorting traits that (sort of) have a dominant and a recessive phenotype: (1) forearm hair (alleles F and f )—the presence of hair on the forearm is dominant to the absence of hair on the forearm; (2) earlobe form (alleles E and e)—unattached earlobes are dominant to attached earlobes; (3) widow's peak (alleles W and w)—a distinct 'V' shape to the hairline at the top of the forehead is dominant to a straight hairline; (4) hitchhiker's thumb (alleles H and h)—the ability to bend the thumb back beyond vertical is dominant and the inability to do so is recessive; and (5) freckling (alleles D and d)—the appearance of freckles is dominant to the absence of freckles. In reality, the genetics of these traits are more complicated than single gene variation, but assume for the purposes of this problem that the patterns in families match those of other single-gene variants.

If a couple with the genotypes Ff Ee Ww Hh Dd and Ff Ee Ww Hh Dd have children, what is the chance the children will inherit the following characteristics?


the same phenotype as the parents

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Textbook Question

Humans vary in many ways from one another. Among many minor phenotypic differences are the following five independently assorting traits that (sort of) have a dominant and a recessive phenotype: (1) forearm hair (alleles F and f )—the presence of hair on the forearm is dominant to the absence of hair on the forearm; (2) earlobe form (alleles E and e)—unattached earlobes are dominant to attached earlobes; (3) widow's peak (alleles W and w)—a distinct 'V' shape to the hairline at the top of the forehead is dominant to a straight hairline; (4) hitchhiker's thumb (alleles H and h)—the ability to bend the thumb back beyond vertical is dominant and the inability to do so is recessive; and (5) freckling (alleles D and d)—the appearance of freckles is dominant to the absence of freckles. In reality, the genetics of these traits are more complicated than single gene variation, but assume for the purposes of this problem that the patterns in families match those of other single-gene variants.

If a couple with the genotypes Ff Ee Ww Hh Dd and Ff Ee Ww Hh Dd have children, what is the chance the children will inherit the following characteristics?


four dominant traits and one recessive trait

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Textbook Question

Alkaptonuria is an infrequent autosomal recessive condition. It is first noticed in newborns when the urine in their diapers turns black upon exposure to air. The condition is caused by the defective transport of the amino acid phenylalanine through the intestinal walls during digestion. About 4 people per 1000 are carriers of alkaptonuria.

Sara and James had never heard of alkaptonuria and were shocked to discover that their first child had the condition. Sara's sister Mary and her husband, Frank, are planning to have a family and are concerned about the possibility of alkaptonuria in one of their children.

The four adults (Sara, James, Mary, and Frank) seek information from a neighbor who is a retired physician. After discussing their family histories, the neighbor says, 'I never took genetics, but I know from my many years in practice that Sara and James are both carriers of this recessive condition. Since their first child had the condition, there is a very low chance that the next child will also have it, because the odds of having two children with a recessive condition are very low. Mary and Frank have no chance of having a child with alkaptonuria because Frank has no family history of the condition.' The two couples each have babies and both babies have alkaptonuria.


The couples are worried that one of their grandchildren will inherit alkaptonuria. How would you assess the risk that one of the offspring of a child with alkaptonuria will inherit the condition?

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Textbook Question

Humans vary in many ways from one another. Among many minor phenotypic differences are the following five independently assorting traits that (sort of) have a dominant and a recessive phenotype: (1) forearm hair (alleles F and f )—the presence of hair on the forearm is dominant to the absence of hair on the forearm; (2) earlobe form (alleles E and e)—unattached earlobes are dominant to attached earlobes; (3) widow's peak (alleles W and w)—a distinct 'V' shape to the hairline at the top of the forehead is dominant to a straight hairline; (4) hitchhiker's thumb (alleles H and h)—the ability to bend the thumb back beyond vertical is dominant and the inability to do so is recessive; and (5) freckling (alleles D and d)—the appearance of freckles is dominant to the absence of freckles. In reality, the genetics of these traits are more complicated than single gene variation, but assume for the purposes of this problem that the patterns in families match those of other single-gene variants.

If a couple with the genotypes Ff Ee Ww Hh Dd and Ff Ee Ww Hh Dd have children, what is the chance the children will inherit the following characteristics?


the genotype Ff EE Ww hh dd

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Textbook Question

In chickens, the presence of feathers on the legs is due to a dominant allele (F), and the absence of leg feathers is due to a recessive allele (f). The comb on the top of the head can be either pea-shaped, a phenotype that is controlled by a dominant allele (P), or a single comb controlled by a recessive allele (p). The two genes assort independently. Assume that a pure-breeding rooster that has feathered legs and a single comb is crossed with a pure-breeding hen that has no leg feathers and a pea-shaped comb. The F₁ are crossed to produce the F₂. Among the resulting F₂, however, only birds with a single comb and feathered legs are allowed to mate. These chickens mate at random to produce F₃ progeny. What are the expected genotypic and phenotypic ratios among the resulting F₃ progeny?

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