Foundations in Genetics Assessment 1

Question 1

allele

Answer 1

a version of a gene at a given locus

Question 2

locus

Answer 2

the position of a gene (or DNA sequence) on a chromosome

Question 3

allelic heterogeneity

Answer 3

different variants in the same gene may produce the same phenotype

Question 4

locus heterogeneity

Answer 4

variants in different genes may cause the same phenotype

Question 5

PKU

Answer 5

An example of allelic heterogeneity (multiple changes within the PAH gene have been linked to causing phenylketonuria)

Question 6

Sickle Cell Anemia

Answer 6

does not show allelic heterogeneity, almost always caused by the same variant in HBB gene

Question 7

Retinitis pigmentosa

Answer 7

lots of different locations on multiple genes can lead to the same phenotype

Question 8

pleiotropy

Answer 8

the same variant can lead to different phenotypes

Question 9

genotype

Answer 9

typically refers to the alleles at a particular locus on both homologs

Question 10

haplotype

Answer 10

when a person inherits both homologs from one parent as opposed to one homolog from each parent

Question 11

compound heterozygote

Answer 11

inherit a non-functional variant maternally, and a different non functional variant paternally

Question 12

autosomal dominant

Answer 12

one non-working gene is sufficient to cause the condition (mechanisms: dominant negative, haploinsufficiency)

Question 13

autosomal recessive

Answer 13

two non-working genes are required to cause the condition (loss of function)

Question 14

lethality in dominant homozygotes

Answer 14

typically having both non-functioning versions of the gene in dominant conditions is not feasible because the child usually dies before birth

Question 15

fitness

Answer 15

measure of the impact of a condition on reproduction (ratio of number of offspring of an affected individual who survive to reproductive age compared to number of offspring of unaffected individuals

Question 16

incomplete dominance

Answer 16

describes a condition/trait in which the phenotype is more severe in homozygotes

Question 17

codominance

Answer 17

a condition/trait in which both alleles show the associated phenotype at the same time

Question 18

pseudodominance

Answer 18

the inheritance of a recessive trait mimics a dominant pattern (one parent could also be a carrier)

Question 19

pedigree pattern of autosomal recessive conditions

Answer 19

parents are typically “normal” and have a child with a condition. Parents are carriers. Horizontal pattern in the pedigree

Question 20

autosomal dominant pedigree pattern

Answer 20

male to male transmission, every generation is impacted (vertical in pedigree)

Question 21

2/3 rule

Answer 21

two carrier parents, we know one is homozygous recessive so we eliminate that one and that leaves 2/3 risk of being a carrier.

Question 22

X-linked dominant inheritance in pedigrees

Answer 22

no male to male transmission, females passing it on roughly 50/50, males show more severe phenotypes

Question 23

x-linked male lethality

Answer 23

some rare x-linked conditions are expressed exclusively in women; at least one functional gene is necessary for embryonic development, so affected males will die before birth

Question 24

variable expressivity

Answer 24

phenotypes are expressed differently in each person

Question 25

reduced penetrance

Answer 25

not everyone with the disease-causing genotype will develop the phenotype. there is a risk factor, but not a guarantee

Question 26

sex limited

Answer 26

could have same genotype but only shows up in certain sexes

Question 27

sex influenced

Answer 27

both show up but maybe more extreme in one or the other

Question 28

germline mosaicism

Answer 28

mutation that occurs to a portion of the germ cells (ova or sperm). Some germ cells are normal and others are mutant forms

Question 29

somatic mosaicism

Answer 29

normal and abnormal cell lines within the cells of the body (may or may not include germline). Mutation will not be transmitted to offspring unless present in the germline

Question 30

genetic code is degenerative

Answer 30

64 codons code for 20 amino acids

Question 31

miRNA

Answer 31

micro RNAs that bind to mRNA and suppress expression

Question 32

pseudogenes

Answer 32

closely resemble working genes but do not code for anything; can make actual testing of a gene very difficult because it is so similar to the actual gene, variants in the pseudogene can cause confusion

Question 33

missense mutation

Answer 33

a variant that causes a change to the amino acid

Question 34

frameshift (fs)

Answer 34

variant that causes a shift in the reading frame of the codon

Question 35

nonsense

Answer 35

(*) when a mutation causes a stop codon instead of the original amino acid

Question 36

read through

Answer 36

stop codon is changed to a different amino acid

Question 37

splice site

Answer 37

mutation occurs at ends of introns or beginning of exons

Question 38

silent changes (synonymous)

Answer 38

when a variant still codes for the same amino acid

Question 39

missense variants leading to gain of function mutation

Answer 39

example: autosomal dominant pancreatitis caused by a pathogenic variant in the trypsin gene that causes it to become overly active and leads to a digestion of the pancreas