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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 11b
Chapter 2, Problem 11b

Black skin color is dominant to pink skin color in pigs. Two heterozygous black pigs are crossed.
What is the probability that the first and second offspring will have black skin?

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Step 1: Identify the genetic makeup of the parents. Since both pigs are heterozygous for black skin color, their genotype is Bb, where 'B' represents the dominant allele for black skin and 'b' represents the recessive allele for pink skin.
Step 2: Set up a Punnett square to determine the possible genotypes of the offspring. Place one parent's alleles (B and b) along the top of the square and the other parent's alleles (B and b) along the side.
Step 3: Fill in the Punnett square by combining the alleles from the top and side. The resulting genotypes will be: BB (homozygous dominant), Bb (heterozygous), Bb (heterozygous), and bb (homozygous recessive).
Step 4: Determine the phenotypic ratio from the Punnett square. Since 'B' is dominant, both BB and Bb will result in black skin, while bb will result in pink skin. The phenotypic ratio is 3:1 (3 black : 1 pink).
Step 5: Calculate the probability of both the first and second offspring having black skin. Since the probability of one offspring having black skin is 3/4, multiply this probability by itself for two independent events: \( \frac{3}{4} \times \frac{3}{4} \).

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Key Concepts

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

Dominant and Recessive Traits

In genetics, traits are often categorized as dominant or recessive. A dominant trait, such as black skin color in pigs, will express itself in the phenotype even if only one allele is present. In contrast, a recessive trait, like pink skin color, requires two copies of the recessive allele to be expressed. Understanding this distinction is crucial for predicting offspring traits.
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Variations on Dominance

Punnett Square

A Punnett square is a diagram used to predict the genetic makeup of offspring from a particular cross. By organizing the alleles of the parents, it allows for the visualization of possible combinations in the offspring. In this case, crossing two heterozygous black pigs (Bb x Bb) will help determine the probabilities of black and pink skin color in their offspring.
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Chi Square Analysis

Probability in Genetics

Probability in genetics refers to the likelihood of certain traits being passed from parents to offspring. When calculating the probability of specific traits, such as the likelihood of both offspring having black skin, one must consider the outcomes from the Punnett square. For two heterozygous parents, the probability of each offspring being black can be calculated and then combined for multiple offspring.
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Related Practice
Textbook Question

Black skin color is dominant to pink skin color in pigs. Two heterozygous black pigs are crossed.

What is the probability that their offspring will have pink skin?

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Textbook Question

The dorsal pigment pattern of frogs can be either 'leopard' (white pigment between dark spots) or 'mottled' (pigment between spots appears mottled). The trait is controlled by an autosomal gene. Males and females are selected from pure-breeding populations, and a pair of reciprocal crosses is performed. The cross results are shown below.

    Cross 1:  P₁: Male leopard x male mottled

             F₁: All mottled

             F₂: 70 mottled, 22 leopard

    Cross 2:  P₁: Male mottled x female leopard

             F₁: All mottled

             F₂: 50 mottled, 18 leopard

In the F₂ progeny from both crosses, what proportion is expected to be homozygous? What proportion is expected to be heterozygous?

Textbook Question

The dorsal pigment pattern of frogs can be either 'leopard' (white pigment between dark spots) or 'mottled' (pigment between spots appears mottled). The trait is controlled by an autosomal gene. Males and females are selected from pure-breeding populations, and a pair of reciprocal crosses is performed. The cross results are shown below.

    Cross 1:  P₁: Male leopard x male mottled

             F₁: All mottled

             F₂: 70 mottled, 22 leopard

    Cross 2:  P₁: Male mottled x female leopard

             F₁: All mottled

             F₂: 50 mottled, 18 leopard

Propose two different genetic crosses that would allow you to determine the genotype of one mottled frog from the F₂ generation.

Textbook Question

Black skin color is dominant to pink skin color in pigs. Two heterozygous black pigs are crossed.

If these pigs produce a total of three piglets, what is the probability that two will be pink and one will be black?

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Textbook Question

A male mouse with brown fur color is mated to two different female mice with black fur. Black female 1 produces a litter of 9 black and 7 brown pups. Black female 2 produces 14 black pups.

What is the mode of inheritance of black and brown fur color in mice?

Textbook Question

A male mouse with brown fur color is mated to two different female mice with black fur. Black female 1 produces a litter of 9 black and 7 brown pups. Black female 2 produces 14 black pups.

Choose symbols for each allele, and identify the genotypes of the brown male and the two black females.