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1

Genetic variation originates from ___.

Heritable DNA mutations

2

What are the four general patterns of inheritance?

1. Sex-linked (encoded on X or Y chromosome)

2. Autosomal (encoded on numeric chromosomes)

3. Recessive (both alleles must be affected for the phenotype to be conferred)

4. Dominant (a single mutant allele confers a phenotype)

3

Draw the following pedigree symbols:

1. Male

2. Female

3. Unspecified sex

4. # of children of a certain sex

5. Affected

6. Nonpenetrant carrier (may manifest disease)

7. Obligate carrier (will not manifest disease)

8. Proband

9. Deceased

10. Marriage/union

11. Divorced

12. Consanguinity

13. Monozygotic twins

14. Dizygotic twins

15. Twins, unknown zygosity

16. Pedigree with generations and individuals numbered

17. Still birth

18. Adopted into family

19. Adopted out of family

20. Consultand

21. Spontaneous abortion

22. Miscarriage

23. No offspring

24. Multiple unions

25. Pregnancy (with information)

26. Termination of pregnancy

4

What is the genetic constitution of an individual or locus?

Genotype

5

What is the outward characteristics of an individual or gene product?

Phenotype

6

What is one of the alternative versions of a gene or DNA sequence at a given locus?

Allele

7

What is the position occupied by a gene on a chromosome?

Locus

8

What is a genotype with identical alleles at a given locus?

Homozygote

9

What is a genotype with different alleles at a given locus?

Heterozygote

10

What is a genotype with a single allele for a given chromosome segment?

Hemizygous

11

What is a genotype with two different mutant alleles at one locus?

Compound heterozygote

12

What is an alternate genotype present in a population at >1% frequency?

Polymorphism

13

What is the proportion of individuals manifesting disease?

Penetrance

14

What is the extent to which a mutation exhibits a phenotype?

Expressivity

15

What results from different mutations at one locus?

Allelic heterogeneity

16

What results from mutations at different loci?

Locus heterogeneity

17

What occurs when the same mutations manifest differently among individuals?

Phenotypic heterogeneity

18

What type of inheritance manifests only when there is no healthy allele present (for single gene disorders)?

Recessive inheritance

19

Individuals carry ___ recessive alleles that are lethal in homozygotes.

1-5

20

What is an example of a recessive disease?

Sickle cell anemia

21

What are the major characteristics of autosomal recessive inheritance?

1. Only displayed in homozygotes

2. Appears in more than one sibling of the proband, but not in parents, offspring, or other relatives (in other words, there is clustering among siblings and absence in ancestors)

3. Males and females are affected equally

4. Parents are asymptomatic carriers

5. Parents may be consanguineous

6. The recurrence risk for siblings = 1/4

7. Carrier risk of unaffected siblings of proband = 2/3

22

What is a relationship resulting from common ancestry which increases the chance that both parents carry the same mutant allele?

Consanguinity

23

Risk of recessive genetic disease is affected by ___, ___, and ___.

Consanguinity; inbreeding; population carrier frequency

24

How is the degree of relationship to the proband calculated?

Degree of relationship = n = # of uninterrupted lines between proband and target

25

What is the coefficient of inbreeding of a child and what does it equal?

F = 1/2(proportion of alleles in common); this is the probability a child will receive both alleles for a particular gene from the same ancestor (one from mother, one from father); the proportion of loci at which a person is homozygous or identical by descent

26

What is the proportion of alleles in common?

(1/2)^n

27

If a person is inbred through more than one line of descent, how is F calculated?

Sum F

28

___ disorders exhibit a phenotype despite presence of a healthy allele.

Dominant

29

What are the features of autosomal dominant inheritance?

1. For single gene disorders, a pheontype is dominant if it manifests in the heterozygote.

2. If not lethal, the phenotype is found in every generation.

3. The child of an affected parents has 1/2 risk of inheriting the disease trait. 

4. Unaffected family members are unlikely to transmit the disease to offspring.

5. Males and females are usually equally affected.

30

A mutant allele is dominant in what 5 instances?

1. Haploinsufficieny: the single normal copy produces an insufficient quantity of the normal gene product for the requirements of the organism.

2. Dominant negative effect: the product of the inactive mutant interferes with the function of the normal gene product

3. Simple gain of function: the product of the mutant gene acquires a new or enhanced function

4. Affected gene is a tumor suppressor, resulting in a predisposition to cancer that is inherited as a dominant trait because even a single cell losing the function of the other allele is enough to cause cancer.

5. Codominance: a trait is defined by two alleles that each exhibit a phenotype