Patterns of Inheritance (Part 1)

Question 1

Define Gene:

Answer 1

Sequence of DNA that codes for a protein, including regulatory regions

Question 2

Define locus:

Answer 2

Location of gene on chromosome

Question 3

Define allele

Answer 3

Different forms (versions) of a gene

Question 4

Define polymorphism:

Answer 4

Multiple forms (alleles) of a gene in population

Question 5

Define homozygote:

Answer 5

Possess same allele at a locus

Question 6

Define heterozygote:

Answer 6

Possess different alleles at a locus

Question 7

Define Dominant

Answer 7

Require only one copy of the mutation to produce disease

Question 8

Define recessive

Answer 8

Requires TWO copies of the mutation to produce disease

Question 9

An allele is one of the alternate forms of a gene that occur at a ___.

Answer 9

Locus

Question 10

Define recurrence risk

Answer 10

Probability of the offspring of a couple will express the genetic disease.

• For single gene disorders, it does not depend on the number of previously affected/ unaffected offspring.

Question 11

Recurrence risk depends on what?

Answer 11

Mode of inheritance of a disease

Question 12

Define proband:

Answer 12

The AFFECTED INDIVIDUAL in the family who has approached the physician for consultation.

Question 13

Define monozygotic twins

Answer 13

• Arise as a result of fertilization of a single zygote.

- Possess identical genes

Question 14

Define dizigotic twins

Answer 14

• Arise as a result of fertilization of two ova

- Genetically share about 50% genes (sibling)

Question 15

Autosomal dominant disorders manifest in which state?

Answer 15

Heterozygous

Question 16

What are the characteristics of Autosomal Dominant disorders when looking at pedigree?

Answer 16

• Affected children receive disease causing gene from affected parent.
• Skipped generations NOT common (Vertical inheritance)
• Males and females are affected with equal frequency
• Male to male transmission is seen

Question 17

How is the affected parent depicted as for autosomal dominant disorder? Normal parents?

Answer 17

Affected parent: Aa

Normal parent: aa

Question 18

For a autosomal dominant disorder, if children have one affected parents, and one normal parent, what is the recurrence risk?

Answer 18

50% risk to the next offspring regardless of the sex of the child.

(Note: Recurrence risk does NOT depend on the number of previously affected children. It remains the same for every new child born to the couple… 50%)