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Chapter 12: Problem 28

The trait for widow鈥檚 peak can be considered a monoallelic dominant trait in humans. If a man with a widow鈥檚 peak and a woman with a straight hairline have a child together, what is the probability that the child will inherit the widow鈥檚 peak if you know that the father鈥檚 mother had a straight hairline? a. 0.25 b. 0.5 c. 0.75 d. 1

Short Answer

Expert verified
The probability is 0.5.

Step by step solution

01

Understand the trait inheritance

Widow's peak is a dominant trait. This means that an individual needs only one copy of the dominant allele (W) to express the trait. A straight hairline is recessive, meaning an individual needs two copies of the recessive allele (ww) to have a straight hairline.
02

Determine the father's genotype

Since the father has a widow's peak and his mother had a straight hairline, the father must have inherited the recessive allele (w) from his mother. Therefore, the father's genotype must be Ww.
03

Determine the mother's genotype

The mother has a straight hairline, which means her genotype must be ww.
04

Set up the Punnett square

Draw a Punnett square for the cross between the father's Ww genotype and the mother's ww genotype. List the father鈥檚 alleles (W and w) on the top and the mother鈥檚 alleles (both w) on the side.
05

Fill in the Punnett square

Fill in the Punnett square by combining the alleles from each parent. The resulting genotypes are: Ww, Ww, ww, and ww.
06

Calculate the probabilities

Out of the four possible genotypes, two are Ww and two are ww. Thus, there is a 50% chance (2 out of 4) for the child to inherit the widow鈥檚 peak (Ww).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

dominant and recessive traits
Genetic traits are characteristics that are passed from parents to offspring. These traits are determined by genes, which come in pairs, one from each parent. There are two types of alleles in these genes: dominant and recessive.
A dominant trait only needs one copy of the dominant allele to be expressed. For example, if 'W' is the dominant allele for a widow's peak, a person with either 'WW' or 'Ww' will have a widow's peak.
A recessive trait, on the other hand, requires two copies of the recessive allele to be expressed. For instance, if 'w' represents the allele for a straight hairline, then an individual will have a straight hairline only if they are 'ww'.
In the provided problem, the widow's peak (W) is the dominant trait, and a straight hairline (w) is the recessive trait. The interaction between these dominant and recessive traits determines the phenotype, which is the observable characteristic.
Punnett square
A Punnett square is a simple graphical way of predicting the genotypes of offspring from a particular cross. It helps you visualize the possible combinations of parental alleles and their associated probabilities.
To solve the exercise, we first identified the genotypes of the parents. The father has a widow's peak but also carries a recessive allele for a straight hairline (Ww). The mother has a straight hairline, representing a recessive genotype (ww).
The Punnett square for this cross looks like this:
  • Father's alleles: W and w
  • Mother's alleles: w and w

By combining these alleles, we can determine the possible genotypes of their children:
  • Ww (widow's peak)
  • Ww (widow's peak)
  • ww (straight hairline)
  • ww (straight hairline)

Hence, two out of four possible genotypes result in a widow's peak. This gives a 50% probability that the child will inherit the widow's peak (Ww).
genotype and phenotype
Genotype and phenotype are essential terms in understanding genetics.
The genotype refers to the genetic makeup of an individual, the combination of alleles they have. For example, 'Ww' and 'ww' are genotypes.
The phenotype is the visible expression of the genotype. In our case, a widow's peak or a straight hairline.
For instance:
  • Genotype 'Ww' produces a phenotype of a widow's peak because 'W' is dominant.
  • Genotype 'ww' produces a phenotype of a straight hairline because there are no dominant 'W' alleles to mask the recessive 'w'.

Understanding the difference between genotype and phenotype helps in predicting offspring traits using tools such as the Punnett square. By analyzing the genotypes of the parents, you can determine the potential genotypes, and thus phenotypes, of their children.

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Most popular questions from this chapter

Flower position in pea plants is determined by a gene with axial and terminal alleles. Given that axial is dominant to terminal, list all of the possible F1 and F2 genotypes and phenotypes from a cross involving parents that are homozygous for each trait. Express genotypes with conventional genetic abbreviations. a. F1: All AA-axial; F2: AA-Axial and aa-terminal. b. F1: All aa-terminal; F2: AA-Axial and Aaterminal. c. F1: AA-axial and Aa-terminal; F2: All AA-axial. d. F1: All Aa-axial; F2: AA-Axial, Aa-Axial, and aa-terminal.

What is the probability that a couple will have three daughters? a. \(\frac{1}{2}\) b. \(\frac{1}{3}\) c. \(\frac{1}{6}\) d. \(\frac{1}{8}\)

Can a human male be a carrier of red-green color blindness? a. Yes, males can be the carriers of red-green color blindness, as color blindness is autosomal dominant. b. No, males cannot be the carriers of red-green color blindness, as color blindness is X-linked. c. No, males cannot be the carriers of red-green color blindness, as color blindness is Y-linked. d. Yes, males can be the carriers of red-green color blindness, as color blindness is autosomal recessive.

Petunias can be blue, red, or violet. When a blue flower is crossed with a red flower, all the resulting flowers are violet. Two violet petunias are crossed. Which is the most probable result of the cross? a. 75% of the flowers are blue and 25% of the flowers are red. b. 50% of the flowers are blue and 50% of the flowers are red. c. 75% of the flowers are red and 25% are blue. d. 25% of the flowers are blue, 50% of the flowers are violet, and 25% of the flowers are red.

Petunias can be blue, red, or violet. When a blue flower is crossed with a red flower, all the resulting flowers are violet. When a violet flower is crossed with a red flower, about half of the flowers are violet and half are red. How do you characterize the color trait? a. complete dominance b. codominance c. incomplete dominance d. sex-linked
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