Chapter 5- Complicating Inheritance

Question 1

Factors influencing inheritance

Answer 1

Multiple Alleles
Codominance
Incomplete dominance
Penetrance
Heterogeneity
Mitochondial genes
Linkage

Question 2

Multiple Alleles

Answer 2

More than two forms of allele in population
Individual expresses at most two
Examples- ABO blood types and HLA Genes

Question 3

Codominance

Answer 3

Heterozygotes express both alleles
Example- ABO blood types

Question 4

Epistasis

Answer 4

Multiple gene interactions on phenotype

Question 5

Labrador Coat Phenotypes

Answer 5

Gene B controls melanin density
Dominant- black coat, recessive- brown
Gene E controls deposition
Dominant- Normal, recessive- None, yellow
Gene D controls melanin production
Dominant- Full, normal; recessive- dilute, silver

Question 6

Penetrance

Answer 6

Chance that an individual with a particular allele with display the phenotype
Reduced penetrance- Some individuals will no show symptoms
Autosomal dominant heritability

Question 7

Variable Expression

Answer 7

Expression of different degrees of the phenotype, varying severity
Will always show some symptoms
Causes- Environment, modifier genes, Allelic heterogeneity

Question 8

Allelic Heterogeneity

Answer 8

Many different mutations on same gene cause similar diseases

Question 9

Locus Heterogeneity

Answer 9

Mutations on different genes can cause similar diseases
Example- Polycystic kidney disease can result from mutations on chromosome 16 or 4

Question 10

Pleiotropy

Answer 10

Single genotype causes many phenotypic expressions
Impacts many bodily systems

Question 11

Phenocopy

Answer 11

Environmental influences cause traits that appear to be inherited

Question 12

Huntington’s Disease

Answer 12

Autosomal dominant progressive brain disorder
Mutation of Huntingtin (HTT) gene
Expansion of glutamine triplets cause misfolding and protein aggregation
Impair basal ganglia function
Defects in motor, cognitive, and psychiatric domains

Question 13

Mitochondrial Genome

Answer 13

Independent, unique
37 genes- 13 ETC, 2 rRNA, 22 tRNA
Many copies
Maternal inheritance
High mutation rate
Heteroplasmy

Question 14

Heteroplasmy

Answer 14

Copies of mitochondrial DNA are not identical
Segregation during cell division is random and unorganized
Phenotype is dependent on if mutant DNA is above threshold

Question 15

Mitochondrial Disease Pedigree

Answer 15

All children regardless of sex inherit DNA
Only develop symptoms if above threshold
Maternal transmission only

Question 16

Leber’s Hereditary Optic Neuropathy (LHON)

Answer 16

Sudden bilateral blindness ~27 years old
Reduced penetrance
Defects in NADH dehydrogenase

Question 17

Linked Genes

Answer 17

Close together loci that do not segregate independently
Inherited together as haplotype
Recombination rate less than 50%

Question 18

Genetic Mapping

Answer 18

1% recombination = 1 map unit
1 map unit = 1 centimorgan (cM)
Recombination frequency= recombinant progeny over total progeny

Question 19

Human Gene Mapping

Answer 19

Collect pedigrees of families with disease of interest
Analyze genetic markers throughout genome
Perform statistical analysis
Compared linked genes with pedigree data
Analyze linked gene functions for mechanism

Question 20

Genetic Statistical Analysis

Answer 20

LOD Scores
Odds genes are linked on the same chromosome
LOD score over 3 is significant

Question 21

Amyotrophic Lateral Sclerosis (ALS)
Lou Gehrig’s Disease

Answer 21

Progressive lethal motor neuron disease
Kills motor neurons in brain and spinal cord
Death by muscle atrophy and diaphragm paralysis
Familial mutations in SOD1 gene encoding CuZn superoxide dismutase
Abberant chemistry or protein aggregation causes cell death