Mendelian Inheritance

Question 1

A red flower and a white flower make a pink flower. This is an example of

Answer 1

Codominance: both alleles get expressed; heterozygote is clinically distinguishable from either homozygote

Question 2

How is the ABO blood group an example of codominance?

Answer 2

A and B are codominant alleles –> AB phenotype

Question 3

Reduced Penetrance- what does it look like on a pedigree and what is it?

Answer 3

Looks like the disorder has “skipped” a generation.

The person carrying the gene would show NO signs of the disorder.

Question 4

Variable expressivity

Answer 4

The extent that the genetic disorder is clinically evident in an individual who carries the gene.

Usually in terms of severity, but the same gene may even cause a different phenotype in different family members(e.g. Schizophrenia and Bipolar disorder)

Question 5

NF, Waardenburg syndrome, and Marfan are examples of

Answer 5

Autosomal dominant disorders with variable expressivity - the severity varies

Question 6

Varying degrees of deafness, minor defects on neural crest structures, pigmentation changes

Answer 6

Waardenburg syndrome - autosomal dominant, variable expressivity

Question 7

Tall and thin; long arms, fingers, toes

Answer 7

Marfan’s syndrome: an autosomal dominant disorder that affects elastic fibers –> can lead to aortic dissection

Question 8

Cafe au lait spots indicates what disorder?

Answer 8

Neurofibromatosis (NF): autosomal dominant disordr caused by mutations in the NF gene that cause Schwann cells to grow into tumors called neurofibromas; some get much mroe severe symptoms than others (variable expressivity)

Question 9

New Mutation Rate- what is it and what is it sometimes associated with?

Answer 9

Individuals with autosomal dominant disorders may have no affected parents and may be the first in their family with the gene

sometimes associated with advanced paternal age. I

Question 10

Achondroplasia - what is it and what type of disorder is it?

Answer 10

Autosomal dominant disorder that prevents cartilage changing into bone –> dwarfism, limited range of motion, small fingers, macrocephaly, normal intelligence

Question 11

Osteogenesis Imperfecta - what type of disorder is it?

Answer 11

Autosomal dominant disorder (imperfect boen formaiton)

Question 12

Allelic/intralocus vs Locus/interlocus heterogeneity

Answer 12

Allelic/intralocus heterogeneity is when different mutations in a single gene can cause the same disorder

Locus/interlocus heterogeneity is when mutations in different genes can cause the same disorder

Question 13

Albinism is what type of disorder? It demonstrates what important genetic concept?

Answer 13

Autosomal recessive disorder

Can be caused by different genes (tyrosine positive or tyrosine negative), so it’s an example of heterogeneity

Question 14

Ethnicity of Disease

Answer 14

Especially for recessive diseases - more likely to carry same deleterious genes if parents are of the same ethnicity or are related.

Question 15

Sickle Cell Anemia, Tay Sachs, and most inborn errors of metabolism are _______ disorders, with the exception of

Answer 15

Autosomal recessive, except Hunter syndrome

Question 16

In autosomal recessive disorders, what do we assume about the parents of an affected child?

Answer 16

They’re both heterozygous carriers and are asymptomatic; may have consanguinity

UNLESS there’s uniparental disomy (2 copies of a chromosome came form the same parent)

Question 17

Lyon’s hypothesis in females

Answer 17

Primordial cell chooses which X to shut down and all daughter cells descending from that cell shuts down the same X chromosome –> The heterozygote is really a hemizygote because some cells wille express one allele, some the other

Question 18

Mosaicism

Answer 18

2 cell lines of different genotype are derived from the same zygote

Question 19

Sex limited traits

Answer 19

Autosomally transmitted, but expressed in only one sex

Ex) Precocious puberty

Question 20

Progressive muscle degeneration early in childhood; delays in sitting and standing in independently

Answer 20

Duchenne muscular dystrophy - an X-linked recessive disorder that causes alterations in the dystrophin protein that keeps muscle cells intact

Question 21

Hunter’s syndrome

Answer 21

X-linked recessive disorder (only metabolism disorder that is NOT AR)

Lysosomal storage disease that affects GAGs –> Thickened skull, ribs, vertebral abnormalities, hepatosplenomegaly, retardation

Question 22

• Trait appears in every generation - affected persons usually have an affected parent (new mutations are possible) – vertical pedigree pattern
• Recurrence risk is 50% for affected individual to produce affected offspring. Note: Male-to-male transmission can occur.
• Unaffected individuals do not transmit the disorder to their children

Answer 22

AD

Question 23

• Disorder appears in siblings of the family – horizontal pedigree pattern
  
  • May skip generations
• Recurrence risk is 25% that sibs of an affected individual will also be affected.
• Parents of affected individuals may be consanguineous.

Answer 23

AR

Both parents are obligate heterozygous carriers

Question 24

• Incidence of the disorder is much higher in males.
• Affected man gives it to all his daughters, and half his sons
  
  • All daughters of an affected male are carriers.
• Affected males related to one another through females.
• Carrier females may show variable expression of trait - depending on X- inactivation
• FATHER TO SON DOES NOT OCCUR

Answer 24

X-linked recessive disorder

Question 25

• Affected females are more common than affected males.
• Affected males have normal sons and no normal daughters.
• Affected females transmit the condition to one-half of their children.

Answer 25

X-linked dominant

Question 26

ectodermal dysplasia, Hunters, Fragile X, Duchene’s

are examples of

Answer 26

X-linked recessive

Question 27

Xg blood group; Vitamin D-resistant rickets are examples of

Answer 27

X-linked dominant

Question 28

What type of disorders DONT skip generations?

Answer 28

Autosomal domiannt and X-linked dominant

Question 29

“This disease can be inherited as AD, AR, or X-linked”

this is an example of

Answer 29

Heterogeneity - different genes can cause the same phenotype

Question 30

This unaffected patient has an affected sibling with an AR disorder. What do you immediately assume?

Answer 30

Parents are heterozygous, so the unaffected patient has a 2/3 chance of being a carrier.

Question 31

If you have an affected father and an affected son in an X-linked recessive example, then you KNOW

Answer 31

Tha the mother must have been a carrier