non mendelian inheritance week 8

Question 1

what is incomplete penetrance

Answer 1

where you have environmental factors and genetic modifiers

Question 2

what is genomic imprinting

Answer 2

• variation depending on which parent you inherit a gene from
• there are some regions of the genome which are imprinted and in those only one of the two copies of the gene are active and the other is switched off
• so you can have maternally expressed genes or paternally expressed genes
• either mum or dad chromosome is switched off

Question 3

how is gene is chromosome in genomic imprinting switched off

Answer 3

through methylation

Question 4

switching off of gene in genomic imprinting is called what

Answer 4

epigenetic modification

Question 5

what is extranuclear inheritance

Answer 5

where you have mitochondria mutations

Question 6

what is anticipation phenomenon

Answer 6

where the signs/symptoms of a genetic condition tend to become more severe and/or appear at an earlier age as the disorder is passed on from one generation to the next

Question 7

what is complex inheritance

Answer 7

• multigenic risk

- where you have multiple genes working together

Question 8

what are the mechanisms of non-mendelian inheritance

Answer 8

• incomplete penetrance
• genomic imprinting
• extranuclear inheritance
• anticipation phenomenon
• complex inheritance

Question 9

what is penetrance

Answer 9

the frequency of which a trait is manifested by individuals carrying the gene

• cystic fibrosis has high penetrance
• BRCA1/2 breast (70-80%), ovarian (50/20%)

Question 10

what are genetic modifiers

Answer 10

• genes that have small quantitative effect on the level of expression of another gene
• defined as genetic variants that can modify the phenotypic outcome of the primary disease-causing variant

Question 11

what are the mechanisms of imprinting disorders

Answer 11

- deletions 
  if you have a deletion of your maternal copy of a maternally expressed gene then you would end up with no working copy whereas if you have deletion of parental copy of maternally expressed gene then it won't matter
- point mutations 
- imprinting errors
- uniparental disomy

Question 12

what is uniparental disomy

Answer 12

where you end up with two copies of one parent’s chromosomes

Question 13

in uniparental disomy what is trisomy rescue

Answer 13

• one gamete has 2 chromatids from one parent, the other gamete has 1 chromatid from one parent
• therefore zygote has three chromatids
• then there is nondisjunction and 2 somatic cells produced, one is normal (copy from each parent) and then the other has uniparental disomy

Question 14

in uniparental disomy what is monosomy rescue

Answer 14

• one gamete has one chromatid from parent and the other gamete has no chromatids at all
• then the zygote only has one chromatid
• then duplication occurs and the somatic cell has uniparental disomy

Question 15

in uniparental disomy what is mitotic error

Answer 15

• starts off as normal, each gamete has one chromatid from each parent
• so zygote is normal
• the recombination occurs in some cells leading to partial uniparental disomy and non-disjunction or duplication happens in other cells leading to uniparental disomy

Question 16

what is mitochondrial inheritance

Answer 16

• maternal inheritance
• circular form
• higher mutation rate than the nuclear genome

Question 17

why does mitochondrial inheritance have a higher mutation rate

Answer 17

• lack of efficient DNA repair system
• lack of protective proteins such as histones
• damaged by reactive oxygen species such as free radicals

Question 18

what is homoplasmy

Answer 18

uniform mitochondrial DNA

no mutations

Question 19

what is heteroplasmy

Answer 19

two or more mitochondrial DNA

mutations present

Question 20

what could anticipation phenomenon be due to

Answer 20

triplet repeat expansion

increasing repeats or triplets of nucleotides due to slippage