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Chapter 4: Problem 13

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

Expert verified
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

01

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.
02

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.
03

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
04

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.
05

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.

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Most popular questions from this chapter

Pigment in the mouse is produced only when the \(C\) allele is pres- ent. Individuals of the ce genotype have no color, If color is present, it may be determined by the \(A\) and \(a\) alleles. AA or Aa results in agouti color, whereas aa results in black coats. (a) What \(\mathrm{F}_{1}\) and \(\mathrm{F}_{2}\) genotypic and phenotypic ratios are obtained from a cross between \(A A C C\) and aace mice? (b) In the three crosses shown here between agouti females whose genotypes were unknown and males of the aacc genotype, what are the genotypes of the female parents for each of the following phenotypic ratios? (1) 8 agouti (2) 9 agouti (3) 4 agouti 8 colorless 10 black \(\quad 5\) black 10 colorless

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