How many defective copies of a gene must someone inherit to

How many defective copies of a gene must someone inherit to express a disease caused by a dominant gene? How many defective copies of a gene must someone inherit to express a recessive disorder? What is the expected phenotypic ratio of affected to unaffected individuals for a dominant disorder?

Solution

Q. How many defective copies of a gene must someone inherit to express a disease caused by a dominant allele(not gene)?

Ans. One copy of allele one needs to inherit to express a disease caused by a dominant allele.

Q. How many defective copies of an allele (not gene) must someone inherit to express a recessive disorder?

Ans. Two defective copies of recessive allele one must inherit to express a recessive disorder.

Q. What is the expected phenotypic ratio of affected to unaffected individuals for a dominant disorder?

Ans. Expected phenotypic ratios for a dominant disorder:

[Let D is dominant allele causing disorder and d is recessive one]

case 1, A Homozygous dominant individual mates with a healthy partner, all F1 individuals would be infected.

case 2, A Heterozygous individual mates with a healthy partner, F1 individuals would have affected:unaffected phenotypic ratio = 1:1