In Exercises 21-28, find the probability and answer the questions.

X-Linked Genetic Disease Men have XY (or YX) chromosomes and women have XX chromosomes. X-linked recessive genetic diseases (such as juvenile retinoschisis) occur when there is a defective X chromosome that occurs without a paired X chromosome that is not defective. In the following, represent a defective X chromosome with lowercase x, so a child with the xY or Yx pair of chromosomes will have the disease and a child with XX or XY or YX or xX or Xx will not have the disease. Each parent contributes one of the chromosomes to the child.

c. If a mother has one defective x chromosome and one good X chromosome and the father has good XY chromosomes, what is the probability that a son will inherit the disease?

검증된 단계별 안내

Step 1: Understand the genetic inheritance. The mother has one defective x chromosome (x) and one good X chromosome (X), while the father has good XY chromosomes. Sons inherit one X chromosome from their mother and one Y chromosome from their father.

Step 2: List all possible combinations of chromosomes for a son. Since the son inherits the Y chromosome from the father, the possible combinations for the son are xY (defective X from the mother) or XY (good X from the mother).

Step 3: Determine the probability of each combination. The mother has a 50% chance of passing on the defective x chromosome and a 50% chance of passing on the good X chromosome. The father always contributes the Y chromosome.

Step 4: Identify the condition for the son to inherit the disease. The son will inherit the disease if he has the xY chromosome pair, which occurs when the mother passes on the defective x chromosome.

Step 5: Calculate the probability. Since the mother has a 50% chance of passing on the defective x chromosome, the probability that the son will inherit the disease is 50% or 0.5.

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주요 개념

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X-Linked Inheritance

X-linked inheritance refers to the pattern of genetic transmission of traits or diseases that are associated with genes located on the X chromosome. In this case, males (XY) are more likely to express X-linked recessive diseases because they have only one X chromosome. If the X chromosome inherited from the mother carries a recessive allele for a disease, the son will express that disease since he does not have a second X chromosome to mask the effect.

Probability in Genetics

Probability in genetics involves calculating the likelihood of inheriting specific traits based on the genetic makeup of the parents. In this scenario, the probability of a son inheriting the disease can be determined by analyzing the combinations of chromosomes contributed by each parent. The mother, with one defective X chromosome, has a 50% chance of passing on either her defective or normal X chromosome to her son.

Punnett Square

A Punnett square is a diagram used to predict the genetic outcomes of a cross between two parents. It helps visualize the possible combinations of alleles that offspring may inherit. In this case, constructing a Punnett square with the mother's X chromosomes (X and x) and the father's XY chromosomes will clarify the probability of the son inheriting the defective X chromosome and thus the disease.