Intro to Genetics

Question 1

Examples of unifactorial diseases

Answer 1

Duchenne muscular dystrophy
Haemophillia
Phenylketonuria

Question 2

Polygenic inheritance

Answer 2

Phenotype is determined by variants of many genes at diff loci, each allele exerting a small additive effect

Question 3

Traits showing continuous distribution

Answer 3

Determined by interplay of many alleles at diff loci but influenced by environmental factors

Question 4

Multifactorial

Answer 4

Phenotype results from the interaction of environmental (incl in utero environment) and genetic factors

Question 5

Heritability

Answer 5

The proportion of variance in a characteristic attributed to genetic factors for a given pop.

Question 6

Concordant

Answer 6

If both twins have same trait (incl complex disease phenotypes)

Question 7

Discordant

Answer 7

If only one twin has the disease

Freq. of concordance is compared for mz and dz twins

Question 8

Concordance rates in multifactorial traits

Answer 8

Degree of concordance in mz twins exceeds that seen in dz twins but is <100% as a result of diff environmental contributions

Question 9

When are concordance rates the same in mz and dz twins

Answer 9

When the disease is caused directly by environmental factors

Question 10

What do family and twin studies measure

Answer 10

Heritability

Heritability estimates can vary over times and between populations

Question 11

What does the liability threshold model explain

Answer 11

Why we see family clustering for polygenetic and multifactorial traits e.g. heart disease and psychiatric disorders

Question 12

Examples of autosomal dominant and autosomal recessive monogenic

Answer 12

Huntingtion disease

Hereditary haemochromatosis

Question 13

Huntington disease

Answer 13

Classic single gene disorder
Inherited as autosomal dominant trait and underlying mutation has v. high penetrance - the chance that a carrier of the mutation (genotype) will eventually express the disease phenotype too

Question 14

Mutation leading to Huntington’s

Answer 14

Expansion to CAG codon –> expressed as glutamine in the proteins AA sequence
Altered protein is toxic and causes progressive degeneration of the basal ganglia

Question 15

Altered protein in Huntington’s

Answer 15

Altered protein is toxic and causes progressive degeneration of the basal ganglia and cerebral cortex’s resulting in a range of neurological symptoms
Toxic-gain of function phenotype —> degeneration

Question 16

Transmission of Huntington’s

Answer 16

Pedigree shows vertical transmission

Question 17

Anticipation

Answer 17

Age of onset decreases w/ successive generations

Seen in several neurological disorders caused by mutations that involve expansions of trinucleotide repeats

Question 18

Hereditary haemochromatosis

Answer 18

Used by absorption of too much dietary iron –> accumulates in organs such as liver and heart
Patients have accumulated large iron stores that damage essential organs by the time they are symptomatic so patients present w/ a host of life threatening disease manifestations e.g. liver cancer

Question 19

Treatment of HH

Answer 19

Venesection

Question 20

Venesction

Answer 20

Removal of blood - done through phlebotomy needle and leg

Question 21

Causes of HH

Answer 21

Single nucleotide polymorphisms/ point mutation resulting in change in codons for AA 63 or 282

Question 22

What are recessive genetic diseases usually associated with

Answer 22

Mutations that result in loss of normal protein function

Question 23

How does the centromere divide the chromosome

Answer 23

Into the short (p) arm and the longer (q) arm

Question 24

Classification of centromeres

Answer 24

Done according to the position of the centromere and relative lengths of the p and q arms

Metacentric
Sub metacentric
Acrocentric

Question 25

Metacentric

Answer 25

Centromere located midway

Question 26

Sub metacentric

Answer 26

Centromeres placed slightly away from centre

Question 27

Acrocentric

Answer 27

Centromere placed quite near one end of the chromosome

Question 28

Telomere

Answer 28

End of chromosome

Question 29

Isoforms

Answer 29

A single gene encodes for two or more isoforms through alternative splicing

Question 30

Alternative splicing

Answer 30

Transcripts from coding sequences can be cut up and re-joined in many ways

Question 31

Why can protein and transcript isoforms occur

Answer 31

Alternative initiation and termination sites for gene expression —> far fewer coding-genes than potential transcripts and protein sequences

Question 32

Why is plasticity in genome important

Answer 32

For tissue spp gene expression