Sheet 7

Question 1

What are risk genes?

Answer 1

Genes that increase the risk of developing a multifactorial disease but are not a direct cause of the disease

Question 2

What is the proband?

Answer 2

The first person in a family to receive genetic counseling and/or testing for suspected hereditary disease (may or may not be affected)

Question 3

What is the unit of inheritance?

Answer 3

The gene

Question 4

What is the gene’s locus?

Answer 4

The location of a gene on a chromosome

Question 5

What are alleles?

Answer 5

Alternative forms of a gene at a particular locus

Question 6

An individual’s genotype (genetic composition) at a particular locus is defined by:

Answer 6

the nature of the alleles

at that locus. (Homozygous vs. heterozygous)

Question 7

What are compound heterozygous alleles?

Answer 7

When both alleles of a gene harbor mutations, but the mutations are different (some are nonsense,
others are missense…)

Question 8

What is an example of compound heterozygous alleles?

Answer 8

Cystic fibrosis

Question 9

What are Gregor Mendel’s laws of inheritance?

Answer 9

1) Law of Unit Inheritance
2) Law of Segregation
3) Law of Independent Assortment

Question 10

What does the Law of Unit Inheritance state?

Answer 10

That parental characteristics do not blend because there is a unit of inheritance. Mendel’s “units” are now known as genes or alleles.

Question 11

What does the Law of Segregation state?

Answer 11

That the two alleles at a particular locus segregate into different gametes.

Question 12

What does the Law of Independent Assortment state?

Answer 12

Alleles at different loci are transmitted independently of each other.

Question 13

What is an exception to the Law of Independent Assortment?

Answer 13

Linkage

Question 14

What are some autosomal dominant diseases?

Answer 14

1) Familial hypercholesterolemia
2) Huntington disease
3) Neurofibromatosis type I (NF1)
4) Myotonic dystrophy
5) Marfan syndrome
6) Achondroplasia (Dwarfism)

Question 15

The mutation rate increases with:

Answer 15

Paternal age

Question 16

What causes Huntington’s?

Answer 16

Gradual degeneration of parts of the basal ganglia (responsible for motor control).

Question 17

What is myotonic dystrophy?

Answer 17

A type of muscular dystrophy, a genetic disorder that impairs muscle function.

Question 18

What are the symptoms of myotonic dystrophy?

Answer 18

1) Gradually worsening muscle loss and weakness
2) Cataracts
3) Intellectual disability
4) Heart conduction problems

Question 19

What causes Neurofibromatosis (NF type I)?

Answer 19

Mutations that can cause the Schwann cells in an affected individual’s nervous system to grow into tumors (PNS tumors) called neurofibromas, which appear as café-au-lait colored spots or bumps under the skin

Question 20

Which diseases display variable expressivity?

Answer 20

1) Myotonic dystrophy

2) Neurofibromatosis (NF type I)

Question 21

What is Familial hypercholesterolemia (FH)?

Answer 21

A genetic disorder characterized by high cholesterol levels.

Question 22

People heterozygous for Familial hypercholesterolemia (FH) may have:

Answer 22

Increased LDL and coronary heart disease at the middle age

Question 23

People homozygous for Familial hypercholesterolemia (FH) may have:

Answer 23

Severe coronary heart disease in childhood

Question 24

Which form of Familial hypercholesterolemia (FH) is more common?

Answer 24

Heterozygous

Question 25

What is Marfan syndrome?

Answer 25

An inherited disorder that affects connective tissue (Pleiotropy)

Question 26

What are the symptoms of Marfan’s syndrome?

Answer 26

1) Tall and thin with disproportionately long arms, legs, fingers, and toes
2) Faulty connective tissue can weaken the aorta, and the high pressure of blood leaving the heart can cause the wall of the aorta to bulge out forming an aortic aneurysm, which is life-threatening
3) Myopia (This happens since the connective tissue defect can affect the cornea, lens, and growth of the eye, and cause lens subluxation (dislocation))

Question 27

Which diseases display onset variability?

Answer 27

1) Myotonic dystrophy

2) Marfan’s syndrome

Question 28

When you u deal with an individual with an autosomal dominant disorder, suppose that this individual is __(homozygous/heterozygous) unless otherwise indicated.

Answer 28

Heterozygous

Question 29

What are the features of autosomal dominant inheritance?

Answer 29

1) Vertical transmission: direct transmission from grandparent to parent to child without skipping
generations.
2) Both sexes affected in 1:1 ratio (it’s an autosomal pattern of inheritance).
3) Both sexes may transmit the trait
4) Heterozygotes much more common and seriously affected than homozygotes
5) May see variable expressivity and variable age of onset
6) May be due to new mutation (spontaneous)
7) Gene product is usually a structural (non-enzymatic) protein