Gene Environment

Question 1

What is an Autosomal Recessive Disorder?

Answer 1

Rare; mostly carriers; the abnormal allele is recessive

Must be homozygous to express the disease.
Usually appear in children-not parents
1/4 of offspring are affected.

Question 2

What are examples of autosomal recessive disorder?

Answer 2

CF, sickle cell, PKU

Question 3

What is the incidence parents will pass onto their offspring in Autosomal Recessive Disorders?

Answer 3

1/4 offspring will be affected.

Question 4

What happens if cosanguinity occurs with Autosomal Recessive Disorders?

Answer 4

Greatly increases the recurrence risk of the disorder. About double!!

Question 5

What is an Autosomal Dominant disorder?

Answer 5

Rare; expressed equally in males and females; Produces 50% chance of passing to offspring; Does not skip generations; Probability of passing never changes…always 50%.

Question 6

How do Autosomal Dominant Disorders occur?

Answer 6

Union of normal parent with Heterozygous parent.
When it passes to children; half of offspring will be heterozygous and express the gene; the other half will not express it.

Question 7

Which disorder never changes the probability of passing 50% off to offspring?

Answer 7

Autosomal Dominant

Question 8

What is occurring if there is no family history but a child presents with an Autosomal Dominant Disease?

Answer 8

New Mutation

Question 9

What is a Sex linked Disorder?

Answer 9

Caused by genes located on Sex Chromosomes.

Question 10

Why are Sex linked disorders usually termed X linked?

Answer 10

The Y chromosome contains only a few dozen genes, so most sex-linked traits are located on the X chromosome so said to be X linked.

Question 11

What are examples of X linked disorders?

Answer 11

Hemophelia A, Duchenne Muscular Dystrophy

Question 12

What are traits of Sex Linked disorders?

Answer 12

Usually EXPRESSED in males because females have another X chromosome to mask the effect. Affected males can’t transmit to sons, only daughters.

Question 13

How does a female express a Sex Linked Disorder?

Answer 13

Females must inherit two copies of the abnormal recessive allele. (one from each parent) but Males only need one to express the phenotype.

Question 14

Why can a father never transmit an X linked chromosome to their son?

Answer 14

A father can only give a son the Y chromosome; so the trait can’t be passed bc it is dictated by the X chromosome.

Question 15

What is the most common mating type involved with X linked disorders?

Answer 15

Combination of carrier female with a normal male. Will usually result in carrier mother passing onto to 50% of offspring.

Question 16

What happens when an affected father mates with a normal mother in X linked disorders?

Answer 16

The sons will be normal bc the father can’t pass the X linked disorder; All daughters will be heterozygous carriers.

Question 17

What happens when an affected father mates with a carrier mother in an X linked disorder?

Answer 17

The daughters will be half heterozygous and half homozygous carriers. Half the sons will be normal and the other half will be affected.