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Flashcards in Genetics Deck (59)
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Codominance

Both allele contribute to the phenotype of the hererozygote

1

Codominance example

Blood group, A,B,AB
Antitrypsin deficiency
HLA groups

2

Variable expressivity example

2 patients with NF1 may have varying disease severity

3

Variable expressivity

Phenotype varies among individuals with same genotype

4

Incomplete penetrance example

BRCA1 gene mutations do not always result in breast or ovarian cancer

5

Incomplete penetrance

Not all individuals with mutant genotype show the mutant phenotype

6

Pleiotropy

One gene contributes to multiple phenotypic effects

7

Pleiotropy example

Untreated phenylketonuria manifests with light skin, intellectual disability, musty body odor

8

Anticipation

Increased severity or earlier onset of disease in succeeding generations

9

Anticipation example

Trinucleotide repeat diseases (Huntington)

10

Loss of heterozygosity

If patient inherits or develops a mutation in a tumor suppressor gene, the complementary allele must be deleted/mutated before cancer develops. Not true of oncogenes

11

Dominant negative mutation example

Mutation of a transcription factor in its allosteric site. Nonfunctioning mutant can still bind DNA, preventing wild-type transcription factor from binding

12

Loss of heterozygosity example

Retinoblastoma and the 2-hit hypothesis
Lynch syndrome
Li-fraumeni syndrome

13

Dominant negative mutation

Exerts a dominant effect. A heterozygote producse a nonfunctional altered protein that also prevents the normal gene product from functioning

14

Mosaicism

Presence of genetically distinct cell lines in the same individuals. Arises from mitotic errors after fertilization

15

Somatic mosaicism

Mutation propagates through multiple tissues or organs

16

Linkage disequilibrium

Tendency of certain alleles at 2 linked loci to occur together more often than expected. Measured in population, not in a family, often varies in different populations

17

Gonadal mosaicism

Mutation only in egg or sperm cells. If parentts and relatives do not have the disease, suspect gonadal or germline mosaicism.

19

Locus heterogeneity (and exampl)

Mutations at different loci can produce a similar phenotype
example: Albinism

19

Heteroplasmy

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

20

Allelic heterogeneity

Different mutations in the same locus produce the same phenotype
example: β-thalassemia

22

Uniparental disomy (and types)

Offspring receive 2 copies of a chromosome from 1 parent and no copies from the other:
1. Heterodisomy (heterozygous)
2. Isodisomy (homozygous)

23

Hererodisomy (homozygous) pathophysiology

Meiosis 1 error

23

Uniparental is euploid or aneuploid

Euploid (correct number of chromosomes)

24

Isodisomy (homozygous) pathophysiology

Meiosis 2 error or postzygotic chromosomal duplication of one of a pair of chromosomes, and loss of the other of the original pair

25

Most common phenotype of uniparental disomy

Normal phenotype

26

Consider uniparental disomy in an individual:(when)

Recessive disorder when only one parent is a carrier

27

Hardy weinberg population
p and q are the frequencies of separate alleles

p^2+2pq+q^2=1..........p+q=1
q^2=frequency of homozygosity of q
p^2=frequency of homozygosity of p
2pq=frequency of heterozygosity (carrier frequency, if an autosomal recessive disease)

28

Frequency of X-linked recessive disease

Males:q
Females:q^2

29

Hardy-weinberg law assumptions include:

1. No mutations occuring at locus
2. Natural selection is not occuring
3. Completely random mating
4. No net migration