Week 3

Question 1

why are family studies important

Answer 1

determines if a disorder is hereditary
shows the method of transmission
allows genetic counselling for future chances
can sometimes provide a diagnosis

Question 2

what is the law of segregation

Answer 2

observation that each individual has two genes for each characteristic

and only one is passed down

this logic is explained to families

Question 3

what is mendelian diseases

Answer 3

single gene disorders

medical conditions caused by change in one or both copies of genes

Question 4

what is autosomal inheritance

Answer 4

trait or disorder
determined by gene on an autosome

Question 5

what is a sex linked inheritance

Answer 5

trait or disorder
determined by a gene on a sex chromosome

Question 6

what is pleiotropy

Answer 6

where a mutation is in a single gene

can cause two or more apparently unrelated effects

often in autosomal dominant diseases

Question 7

what is the autosomal dominant pattern of inheritance

Answer 7

50% chance of being affected

an affected individual has at least one affected parent

vertical transmission

Question 8

variable penetrance

Answer 8

proportion of individuals with the same genetic mutation who show symptoms of that disorder

Question 9

variable expressivity

Answer 9

range of signs and symptoms from genetic background and environment

Question 10

what is anticipation

Answer 10

where a disorder becomes more severe with each generation

caused by a triplet repeat expansion

Question 11

what is the autosomal recessive pattern of inheritance

Answer 11

homozygotes - needs two copies of the gene to be affected

transmission is normally in one generations siblings
horizontal transmission

Question 12

what is pseudodominance

Answer 12

where a single recessive gene is inherited
but is still expressed

this is the result of a deletion of a masking dominant gene

Question 13

what are genocopies

Answer 13

mutants at a different gene loci

have the same phenotype

double heterozygotes - where both parents are affected but the children are not

Question 14

what is an x linked recessive disease

Answer 14

one altered gene on the x chromosome

as males only have one chromosome - they are always affected

Question 15

x linked recessive disease chances

Answer 15

males always affected

mother is normally an unaffected carrier

daughters can be carriers

no male to male transmission

carrier females have a 25% chance of having an affected child

where father is affected - daughters will be carriers

Question 16

x linked dominant

Answer 16

dominant gene carried on the x chromosome

so males and females affected equally

Question 17

x linked dominant inheritance

Answer 17

depends on whether mother or father is the carrier

mother - 50% offspring

father - 100% daughters

Question 18

what is reduced or incomplete penetrance

Answer 18

autosomal dominant disorders with few or no abnormal clinical features

Question 19

variable expression

Answer 19

range of features indifferent individuals

Question 20

new mutations / de novo

Answer 20

trait appears without any family history

Question 21

homozygosity for autosomal dominant traits

Answer 21

usually in heterozygous state, rarely homozygous

can have different phenotypic effects

Question 22

compound heterozygosity

Answer 22

presence of two mutated alleles at a particular gene locus

Question 23

co dominance

Answer 23

where two alleles are expressed in the heterozygous state