Genetic Diseases - not finished

Question 1

What are the characteristics of monogenic traits?

Answer 1

• Only one pair of genes is involved
• Follows Mendel’s law

Question 2

What are the characteristics of polygenic traits?

Answer 2

• Many genes are involved, and the contribution of each gene to the traits may vary
• Traits have Gaussian distributions

Question 3

Describe silent mutations

Answer 3

• They affect DNA & mRNA by replacing a letter with another one that will code for the same amino acid
• They do not affect protein function & expression

Question 4

Describe missense mutations

Answer 4

• They change an amino acid
• This change affects the entire amino acid sequence

Question 5

Describe nonsense mutations

Answer 5

• adds a premature stop codon
• leads to an incomplete, nonfunctional protein

Question 6

Describe the mechanism and outcome of insertions/deletions

Answer 6

• Bases inserted / deleted in multiples of 3 causes the insertion or deletion of an amino acid
  – sequence can sometimes still function like it originally did
• Bases inserted / deleted NOT in multiples of 3 causes a frameshift mutation
  – Codes for incorrect amino acids, makes a completely different protein

Question 7

Define loss of function

Answer 7

mutated protein with no activity, no expression at all

Question 8

Describe gain of function

Answer 8

mutated proteins with abnormal activity
EXAMPLE - oncogenes

Question 9

Describe negative phenotypes

Answer 9

Inhibition of the activity of the unmutated protein expressed from the normal allele

Question 10

Describe the autosomal dominant inheritance pattern

Answer 10

• 50/50 chance for each child to get the trait
• Same probability for male & female children
• No carriers
• Typically, there is a delayed age of onset

Question 11

List some examples of autosomal dominant genetic disorders

Answer 11

Huntington disease
Marfan syndrome

Question 12

Describe the autosomal recessive inheritance pattern

Answer 12

• If both parents are carriers…
  25% chance of non-carrier child
  50% chance of carrier child
  25% chance of affected child
• If one parent is affected
  All children will be carriers (if not affected)
• Same probability for male & female children
• Typically, early age of onset
• More uniform symptoms compared to autosomal dominant

Question 13

List some examples of autosomal dominant genetic disorders

Answer 13

Phenylketonuria
Tay-Sachs disease,
All inborn errors of metabolism

Question 14

List some common characteristics of X-linked genetic disorders

Answer 14

Generally men are affected and women are carriers
(Women have 2 X chromosomes and Men have 1)

Question 15

Describe the X-linked dominant inheritance pattern

Answer 15

• Embryonic lethal for…
  Males with mutated x gene (xY)
  Homozygous Females (2 mutated, xx)
• Affected mother (heterozygous, xX)
  Sons AND daughters
  50/50 chance of being affected or normal
• Affected father (heterozygous, xY)
  Daughters are 100% affected (xX)
  Sons are 100% normal (xY)

Question 16

Describe the X-linked recessive inheritance pattern

Answer 16

• Female heterozygotes are carriers
• All males who receive recessive gene are affected, never carriers
• Carrier Mother
  Daughters are 50% affected & 50% carrier
  Sons are 50% normal & 50% affected
• Affected Father
  Daughters are 100% carriers
  Sons are 100% normal

Question 17

List some examples of X-linked recessive genetic disorders

Answer 17

Color blindness
Hemophilia A

Question 18

List some examples of X-linked dominant disorders

Answer 18

Fragile X syndrome

Question 19

Explain the concept of penetrance

Answer 19

• The PERCENTAGE of ppl with a certain genotype that ALSO express the associated phenotype
• Complete penetrance
  100% of ppl with a certain genotype express the associated phenotype
• Incomplete penetrance
  LESS THAN 100% of ppl with a certain genotype express the associated phenotype

Question 20

Explain the concepts of expressivity

Answer 20

• The DEGREE to which a certain genotype is expressed as a phenotype by a person with the genotype
• Sometimes a certain genotype will ALWAYS express the phenotype to the same degree
• Variable expressivity
  A range of symptoms can be expressed by people with the same genotype
  (Mild → debilitating)