Genetics

Question 1

define and give example of codominance

Answer 1

both alleles contribute to phenotype of heterozygote;

ex: Blood groups A, B, AB

Question 2

define and give example of variable expressivity

Answer 2

phenotype varies among individuals w/ same genotype;

2 pts w/ neurofibromatosis type I (NF1) may have varying disease severity

Question 3

define and give example of incomplete penetrance

Answer 3

not all individuals w/ mutant genotype show mutant phenotype;
BRCA-1 gene mutations do not always result in breast or ovarian cancer

Question 4

define and give example of pleiotropy

Answer 4

one gene contributes to multiple phenotypic effects;

PKU causes many seemingly unrelated Sx, ranging from mental retardation to hair/skin changes

Question 5

define and give example of imprinting

Answer 5

differences in gene expression depend on whether mutation is of maternal or paternal origin;
Prader-Willi and Angelman’s Sx

Question 6

define and give example of anticipation

Answer 6

increased severity or earlier onset of disease in succeeding generations;
Huntington’s disease

Question 7

define and give example of loss of heterozygosity

Answer 7

patient inherits/develops a mutation in tumor suppressor gene, complementary allele must be deleted/mutated before cancer develops;
Rb and 2 hit hypothesis

Question 8

define dominant negative mutation

Answer 8

exerts dominant effect=> heterozygote produces nonfunctional altered protein that prevents normal gene product from functioning

Question 9

give example of dominant negative mutation

Answer 9

mutation of transcription factor in allosteric site => nonfunctioning mutant bind DNA, preventing wild type transcription factor from binding

Question 10

define and give example of linkage disequilibrium

Answer 10

tendency for alleles at 2 linked loci to occur together more often than expected by chance => varies in different populations

Question 11

define a mosaicism

Answer 11

occurs when cells in body differ in genetic makeup due to post-fertilization loss or change of genetic information during mitosis

Question 12

what is a germ line mosaic?

Answer 12

gonadal that when disease is not carried by parent’s somatic cells

Question 13

what is a mutation in embryonic precursor of bone marrow stem cell?

Answer 13

hematologic mosaic individual

Question 14

What is a chimeric individual derived from?

Answer 14

2 zygotes that subsequently fuse

Question 15

define locus heterogeneity

Answer 15

mutations at different loci can produce the same phenotype

Question 16

What diseases are associated w/ locus heterogeneity?

Answer 16

Marfan syndrome, MEN 2B, homocystinuria;
all cause marfanoid habitus;

albinism

Question 17

define heteroplasmy

Answer 17

presence of both normal and mutated mtDNA, resulting in variable expression in mitochondrial inherited disease

Question 18

define uniparental disomy

Answer 18

offspring receives 2 copies of a chromosome from 1 parent and no copies from the other parent

Question 19

what does heterodisomy (heterozygous) indicate?

Answer 19

meiosis I error

Question 20

isodisomy (homozygous) indicates what?

Answer 20

meiosis II error or post-zygotic chromosomal duplication of one of pair of chromosomes;
loss of other original pair

Question 21

most occurrences of uniparental disomy have how many chromosomes?

Answer 21

correct number of chromosomes w/ normal phenotype

Question 22

what is the hardy-weinberg population principle? what do the factors mean?

Answer 22

p^2 + 2pq + q^2 = 1=> if p + q=1 then=>

p^2=freq of homozygosity for allele p
q^2=freq of homozygosity for allele q
2pq=freq of heterozygosity (carrier freq w/ autosomal recessive disease)

Question 23

How can Hardy-weinberg principle be used for X linked diseases?

Answer 23

males = q

females = q^2

Question 24

what 4 things does the Hardy weinberg law assume?

Answer 24

• no mutation occurring at locus
• no selection for any of genotypes at locus
• completely random mating
• no net migration

Question 25

define imprinting

Answer 25

at same loci, only 1 allele is active; other inactive by methylation;
1 allele inactivated, deletion of active allele gives disease

Question 26

What allele is not expressed in prader-willi syndrome?

Answer 26

paternal allele not expressed

Question 27

what allele is not expressed in angelman’s syndrome?

Answer 27

maternal allele not expressed

Question 28

what causes prader-willi and angelman’s syndrome?

Answer 28

inactivation or deletion of genes on chromosome 15=> may be result of uniparental disomy

Question 29

What are Sx of prader willi syndrome

Answer 29

mental retardation;
hyperphagia;
obesity;
hypogonadism;
hypotonia

Question 30

what are Sx of angelman syndrome?

Answer 30

mental retardation, seizures, ataxia, inappropriate laughter

Question 31

characterize autosomal dominant

Answer 31

due to defects in structural genes => many generations of equal sex affected

Question 32

What is critical to diagnose autodomal dominant diseases?

Answer 32

family history

Question 33

characterize autosomal recessive disease

Answer 33

1/4 affected from carrier parents due to enzyme deficiencies usually only 1 generation

Question 34

characterize XLR genetics

Answer 34

heterozygous mothers have 50% chance of affection w/ no male to male transmission => females must be homozygous to be affected

Question 35

characterize XLD genetics

Answer 35

transmitted through both parents => male or female offspring affected whereas all female offspring of affected father affected

Question 36

what is a disease with XLD genetics

Answer 36

hypophosphatemic rickets => vit D resistant rickets resulting in increased phosphate wasting at proximal tubule w/ rickets like presentation

Question 37

characterize mitochondrial inheritance

Answer 37

transmitted only through mother => all offspring of affected females show signs of disease;

variable expression in population due to heteroplasmy

Question 38

what are mitochondrial diseases often due to?

Answer 38

failures in oxidative phosphorylation;

Question 39

how do mitochondrial myopathies present? what are they the result of?

Answer 39

result from mutations affecting mitochondrial function;
present w/ myopathy and CNS disease;
muscle biopsy shows ragged red fibers

Question 40

what type of disease is achondroplasia? define it

Answer 40

AD;

cell signaling defect of fibroblast growth factor