Day 4, Lecture 1 (Aug 25): Genetics IV: Modes of Inheritance

Question 1

Locus

Answer 1

• a specific position or location on a chromosome. Frequently, locus is used to refer to a gene

Question 2

Allele

Answer 2

• Alternate forms of a gene, or DNA sequence, at a given locus

Question 3

DNA Mutation and Polymorphism

Question 4

Genotype

Answer 4

• The genetic makeup of an individual

Question 5

Phenotype

Answer 5

The clinical or behavioral presentation of a genetic

variation in an individual

Question 6

Mendelian Disease

Answer 6

• Disease results form a single mutant gene and is often inherited in a (simple) recognizable pattern
  
  • Can be autosomal or X-linked
  • “dominant” if phenotypically expressed in heterozygotes and “recessive” if clinically manifest in homozygotes
• The type of Mendelian disease is deduced by constructing a pedigree and analyzing the pattern of transmission of the trait within the family

Question 7

heterozygosity

Answer 7

The presence of different alleles at a given locus/gene

Question 8

Compound Heterozygote

Answer 8

• the presence of two different mutant alleles at a particular gene locus, one on each allele of the pair

Question 9

Hemizygote

Answer 9

Males have a single X chromosome. Thus for most genes coded on the X-chromosome there is not a complementary allele. Males are thus hemizygous at these loci.

Question 10

Homozygote

Answer 10

If both alleles at a locus are identical,the individual is homozygous at that locus (a homozygote for that condition).

Question 11

Pedigree

Answer 11

A visual representation of family relationships, and aims to allow recognition of inheritance patterns

Question 12

Autosomal Dominant (AD) Inheritance

Answer 12

Question 13

Non-penetrance

Answer 13

• Lack of clinical expression of the mutant gene

Question 14

Variable expression

Answer 14

• Widely different clinical severity in carriers of the same mutation

Question 15

Gender-bias expression

Answer 15

• Widely different severity in males and females

Question 16

Possibilities of autosomal dominant inheritance? Like how could mutations causes problems for the organism?

Answer 16

• Haploinsufficiency
• Dominant-negative effect
• Gain-of- function
• Expansion repeat disorder

Question 17

Example of Loss-of-function effect caused by autosomal dominant mutation?

Answer 17

Question 18

Example of Dominant-negative effect caused by autosomal dominant mutation

Answer 18

Question 19

Example of Gain-of-function effect caused by autosomal dominant mutation

Answer 19

Question 20

Noonan Syndrome (NS)

Answer 20

• Inherited in an AD manner
• characterized by short stature, congenital heart defect, and developmental delay of variable degree. Other findings can include broad or webbed neck, unusual chest shape, characteristic facies, and ocular abnormalities

Question 21

Autosomal Recessive (AR) Inheritance

Answer 21

Question 22

Question 23

Example of autosomal Recessive inheritance

Answer 23

Question 24

X-linked Recessive Inheritance

Answer 24

Question 25

Example of X-linked Recessive inheritance

Answer 25

Question 26

How may females manifest an X-linked disease

Answer 26

Question 27

Mitochondrial Inheritance

Answer 27

Question 28

Factors affecting the manifestation of Mitochondrial Mutations

Answer 28

• Variable number of mitochondria per cell (2-100) and mtDNA chromosomes per mitochondria (5-10)
• Heteroplasmy:
  
  • Different cells/tissues may have varying numbers of mutant mtDNA
• Variable susceptibility of different tissues to defective oxidative phosphorylation caused by abnormal mitochondrial funciton

Question 29

Clues to identify modes of inheritance

Answer 29

Question 30

Recurrence Risks

Answer 30

Question 31

Variations in modes of inheritance

Answer 31