B) Duchenne Muscular Dystrophy is caused by a recessive allele located on the X chromosor people experience progressive weakening and loss of skeletal muscle . How can,two unaffected (dominant) people have a child with Duchenne MD (recessive)? Show how in the Punnett square and explain below, square show Squar

To understand how two unaffected (dominant) individuals can have a child with Duchenne Muscular Dystrophy (DMD), we need to consider the inheritance pattern of the recessive allele responsible for DMD. Since DMD is caused by a recessive allele located on the X chromosome, it primarily affects males, as they have only one X chromosome. Females, having two X chromosomes, are typically carriers (heterozygous) and may not show symptoms.<br /><br />Let's denote the normal allele as "X^N" and the DMD allele as "X^d".<br /><br />### Step-by-Step Explanation:<br /><br />1. **Genotypes of the Parents:**<br /> - Both parents are unaffected but carriers: X^N X^d (female) and X^N Y (male).<br /><br />2. **Punnett Square:**<br /> - Female (X^N X^d) can produce two types of eggs: X^N and X^d.<br /> - Male (X^N Y) can produce two types of sperm: X^N and Y.<br /><br /> | | X^N (sperm) | Y (sperm) |<br /> |-------|-------------|-----------|<br /> | **X^N (egg)** | X^N X^N | X^N Y |<br /> | **X^d (egg)** | X^N X^d | X^d Y |<br /><br />3. **Possible Offspring:**<br /> - X^N X^N: Female, unaffected carrier.<br /> - X^N X^d: Female, unaffected carrier.<br /> - X^N Y: Male, unaffected.<br /> - X^d Y: Male, affected with Duchenne Muscular Dystrophy.<br /><br />### Explanation:<br />- In this scenario, there is a 25% chance (1 out of 4) that the offspring will be a male (X^d Y) and thus affected by Duchenne Muscular Dystrophy.<br />- The other possibilities are:<br /> - 75% chance of having an unaffected child (either X^N X^N or X^N Y for females or males).<br /> - 25% chance of having a carrier female (X^N X^d).<br /><br />### Conclusion:<br />Two unaffected carriers can have a child with Duchenne Muscular Dystrophy because each parent carries one copy of the recessive allele. When both parents are carriers, there is a 25% probability that a son will inherit the X chromosome carrying the DMD allele from both parents, resulting in the condition.