Question

Duchenne muscular dystrophy (DMD), marked by muscular degeneration, results from an \(\mathrm{X}\) - linked recessive gene. Thus, a female who is heterozygous for this gene and does not have the disease can be a carrier. What kind of offspring can you expect from a DMD-affected male and a carrier female? Can there be a carrier male?

Short answer

Explain your answer. Answer: No, there cannot be a carrier male in this situation. A carrier male would have the genotype X_dY, meaning they would also be affected by DMD since they only have one X chromosome, which contains the defective gene. In this scenario, males either have the affected genotype (X_dY) or the unaffected genotype (XY).

Step-by-step solution

Understand the genotypes of the parents

A DMD-affected male has the genotype X_dY, where X_d is the defective X chromosome. A carrier female has the genotype X_dX, where X is the normal X chromosome.

Set up a Punnett square

A Punnett square is a diagram that is used to predict the possible genotypes and outcomes of offspring from the cross of two genetic parents. To create our Punnett square, draw a 2x2 grid and write the possible gametes (reproductive cells) of the parents along the top and side of the grid. For the DMD-affected male, the gametes will be X_d and Y. For the carrier female, the gametes will be X_d and X.

Fill the Punnett square

Fill the boxes of the Punnett square by combining the gametes from each parent. This will give us the following combinations: - X_dX_d: affected female - X_dX: carrier female - X_dY: affected male - XY: unaffected male

Identify the offspring outcomes

Looking at the Punnett square, the following outcomes for the offspring are: 1. 50% chance of being an affected female (X_dX_d) 2. 50% chance of being a carrier female (X_dX) 3. 50% chance of being an affected male (X_dY) 4. 50% chance of being an unaffected male (XY) Keep in mind that this is a probability, so individual offspring may not follow these exact ratios, but with a large enough sample size, these ratios would be observed.

Analyze whether there can be a carrier male

A carrier male would have the genotype X_dY, meaning they would also be affected by DMD since they only have one X chromosome, which contains the defective gene. Therefore, there cannot be a carrier male in this situation.