Single-Gene Inheritance

Question 1

Triangle pedigree symbol

Answer 1

pregnancy terminated spontaneously or not

Question 2

Diamond pedigree symbol

Answer 2

unspecified sex

Question 3

Double horizontal line in pedigree

Answer 3

consanguinity

Question 4

brackets

Answer 4

adopted child (into has dashed line) (out of is solid line)

Question 5

Proband arrow

Answer 5

marks the one who instigates the disease of study in the family

Question 6

What is a compound heterozygote?

Answer 6

genotype with 2 different mutant alleles at one locus

Question 7

What is haploinsufficiency

Answer 7

One allele is not enough to overcome the loss of function of the other

Question 8

What are the characteristics of autosomal recessive inheritance?

Answer 8

1. Disease in homozygote
2. Appears in more than one sibling of proband, but not in parents or offspring
3. Male and females are equally affected
4. Parents are asymptomatic
5. Parents may be consanguineous
6. Risk to each sibling of the proband is 25%

Question 9

Coefficient of inbreeding (F)

Answer 9

Proportion of loci at which a person is homozygous by descent= 1/2 x coefficient of relationship

Question 10

Coefficient of relationship

Answer 10

proportion of genes two related individuals have in common (1/2)^n

Question 11

Degree of relationship (n)

Answer 11

corresponds to the # of uninterrupted line segments connecting

Question 12

Coefficient of relationship

Answer 12

(1/2) ^n where n is degree of relationship= the probability of inheriting the same allele from a common ancestor

Question 13

Coefficient of inbreeding

Answer 13

(F) =(1/2)(coefficient of relationship)

Question 14

What are the characteristics of an autosomal dominant disease?

Answer 14

1. Manifests in heterozygote
2. Seen in every generation if not lethal
3. Unaffected family members not likely to transmit to offspring
4. Males and females equally affected
5. Child of affected parents have 1 in 2 chance of inheriting

Question 15

Qualifications of a dominant mutant allele

Answer 15

1. Haploinsufficiency: the normal gene copy does not produce sufficient quantities of normal gene product for functions of the organism
2. The product of inactive mutant gene interferes with normal gene function
3. Product of mutant gene acquires new function
4. The affected gene is a tumor suppressor

Question 16

X-linked Recessive Disease Characteristics

Answer 16

1. Incidence higher in males
2. Heterozygous females are usually unaffected
3. Transmitted from an affected male to 50% of his grandsons through daughters
4. Males never transmit it to their sons (only give normal Y chromosome)

Question 17

X-linked Dominant Inheritance Characteristics

Answer 17

1. Affected mothers have a 50% chance of transmitting disorder to son or daughter
2. Affected fathers have affected daughters but no affected sons (Y chromosome healthy)
3. Affected females may have milder expression of phenotype

Question 18

When a mutation occurs in the course of development then only that part of the body derived from the mutant cell may ultimately be affected

Answer 18

Somatic Mosaicism

Question 19

When a mutation affects germ cells, the parents may be negligibly affected but multiple offspring may have uniform disease

Answer 19

Germline mosaicism

Question 20

Prader Willi syndrome

Answer 20

Occurs from a microdeletion on Chromosome 15 arm q (PWS gene) inherited from the father (mother’s is silenced). Form of genomic imprinting gone wrong. Symptoms: obesity, hypogonadism, small hands, short stature, mental retardation.

Question 21

Angelman syndrome

Answer 21

Occurs from a microdeletion on Chromosome 15 arm q (AS gene) inherited from the mother (father’s is silenced). Form of genomic imprinting gone wrong. Symptoms: wide stance and arm position, short stature, mental retardation, spasticity, and seizures.

Question 22

Mitochondrial inheritance follows which principles?

Answer 22

1. Replicative segregation through random distribution of mitochondria among daughter cells; if the proportion of diseased mito that are passed on exceed threshold=disease
2. Reduced penetrance
3. Variable expression
4. Pleiotropy (copy # above threshold varies in different tissues affected by mutation)
5. Mosaicism