Intro

Question 1

Genes that determine cell identity and positioning during embryonic development

Answer 1

Homeobox (Hox) genes

Question 2

Number of genes humans have

Answer 2

20,000

Question 3

Silent substitutions

Answer 3

redundancy of genetic code

Question 4

Missense mutation

Answer 4

Produce change in single AA

Question 5

Nonsense mutation

Answer 5

Produce one of the stop codons in mRNA (causes termination)

Question 6

Frameshift

Answer 6

Result from addition or deletion of number of bases not a multiple of 3

Question 7

First demonstration that mutation in structural gene could cause AA sub in corresponding protein

Answer 7

Sickle cell (GAG to GTG)

Question 8

Incidence of newborns with single gene or chromosomal disorder

Answer 8

1:60

Question 9

Incidence of people under age 25 with genetic disorder

Answer 9

1:20

Question 10

Types of nontraditional inheritance

Answer 10

Microdeletion, imprinting, trinucleotide repeats

Question 11

Anticipation

Answer 11

severity increases and younger age of diagnosis as passed from generation to next

Question 12

Segregation

Answer 12

alleles are paired and each gamete normally receives one member of the pair

Question 13

Independent assortment

Answer 13

Gene pairs tend to segregate independently of each other

Question 14

Exception to independent assortment

Answer 14

Linkage

Question 15

Gene locus

Answer 15

specific location on chromosome

Question 16

Allele

Answer 16

alternative forms of a gene at given locus

Question 17

Allelic heterogeneity

Answer 17

different mutant alleles at the same locus produce an abnormal phenotype (ex: CF)

Question 18

Locus heterogeneity

Answer 18

Mutations at two or more loci cause similar phenotype (ex: retinitis pigmentosa, adult polycystic kidney disease, AD breast cancer)

Question 19

Adult polycystic kidney disease (APKD)

Answer 19

AD, progressive accumulation of renal cysts (also liver cysts, hypertension, cerebral aneurysms), caused by mutations in genes of PKD1 or PKD2

Question 20

Pleiotropy

Answer 20

single mutant allele can have widespread effects in different tissues or organ systems (ex: marfan syndrome with cardio, musculoskeletal, and ocular)

Question 21

Penetrance

Answer 21

proportion of individuals with mutant genotypes that express a mutant phenotype (range 0-1). Complete is 100%

Question 22

Expressivity

Answer 22

Variability in degree of phenotypic expression seen in different individuals with mutant genotype

Question 23

True dominant

Answer 23

Heterozygous expression is same as homozygous (ex: HD)

Question 24

Sex-limited/sex-influenced

Answer 24

expression is affected by sex of individual (ex: male pattern baldness)

Question 25

Codominant expression example

Answer 25

blood types

Question 26

AD inheritance

Answer 26

phenotype transmitted generation to generation, each gene carrier has 50% chance of passing each allele to each child, male to male transmission (ex: NF, Marfan, Achondroplasia, OI)

Question 27

NF1 facts

Answer 27

variable expressivity, AD, 100% penetrance, 50% de novo, neurofibromin maps to 17q

Question 28

major diagnostic criteria for NF1

Answer 28

six or more cafe-au-lait macules >5 mm prepubertal, >15 postpubertal; two or more neurofibromas of any type and on plexiform neurofibroma; freckling most often axillae or groin; optic glioma; two or more lisch nodules (iris hamartomas); pseudoarthroses; affected 1 degree relative

Question 29

Penetrance and expressivity are particularly relevant concerning disorders with autosomal dominant inheritance patterns. Your patient has been diagnosed with Osteogenesis imperfecta (OI) caused by variance in the COL1A1 and COL1A2 genes, where not all individuals develop symptoms in their lifetime and even among those with symptoms, some might be more severely affected than others. Your patient mentioned that their mother had the gene but has never had symptoms and that their grandfather carried the gene but had much more severe symptoms than they do.
Which of the following best describes Marfan syndrome

Answer 29

Incomplete penetrance and variable expressivity

Question 30

Noonan syndrome is a single-gene disorder that presents clinically with short stature,
craniofacial differences, ocular abnormalities, and cardiac malformations, among other
symptoms. Over 15 different genes are associated with Noonan syndrome, including PTPN11, BRAF, and NF1. Within the most commonly associated gene, PTPN11, there are multiple known pathogenic variants affecting different amino acids. Which of the following best describes heterogeneity among this condition

Answer 30

Allelic heterogeneity and locus heterogeneity