Exam #5: Review

Question 1

Allele Heterogeneity

Answer 1

• Different mutations in the same gene cause different phenotypes
• Beta-Thalassemia

Question 2

Locus Heterogeneity

Answer 2

• Mutations in different genes cause the same phenotype

- Albinism

Question 3

Modifier Genes

Answer 3

The individual genetic background modifies the phenotype

Question 4

Proband

Answer 4

The particular person being reported on

Question 5

Polymerase Chain Reaction

Answer 5

Molecular biology lab technique used to amplify DNA

1) Denaturation= DNA is denatured by heating to make two separate strands
2) Annealing= premade primers/ oligonucleotides anneal to a specific sequence on each strand to be amplified
3) Elongation= heat stable DNA polymerase replicates the DNA between the primers

Question 6

Mnemonic for Bolts

Answer 6

SNoW DRoP

Southern= DNA 
Northern= RNA 
Western= Protein

Question 7

Southwestern Blot

Answer 7

Identifies DNA-binding proteins

Question 8

Microarrays

Answer 8

• Thousands of nucleic acid sequences are arranged in grids on glass or silicon i.e. “chip”
• DNA or RNA probes are hybridized to the chip
• Scanner detects complimentary binding
• Used to detect SNPs or CNV

Question 9

ELISA

Answer 9

Used to detect the presence of either a specific antigen (direct/ sandwich) or antibody (indirect) in a patient’s blood

Question 10

Direct/ Sandwich ELISA

Answer 10

• Uses a test antibody to see if a specific antigen is present in the patient’s blood
• A second antibody is coupled to a color-generating enzyme to detect the antigen/primary antibody

Question 11

Indirect ELISA

Answer 11

• Uses a test antigen so see if a specific antibody is present in the patient’s blood
• A secondary antibody coupled to a color-generating enzyme is added to detect the first antibody

Question 12

FISH

Answer 12

• Fluorescent DNA or RNA probe binds to a specific gene site of interest on a chromosome
• Used for localization of genes & direct visualization of anomalies (micodeletions)
• Fluoresce= gene present, No Fluoresce= NOT present

Question 13

Karyotyping

Answer 13

• Process in which metaphase chromosomes are stained, ordered, & numbered according to morphology, size, arm-length, and banding pattern.
• Can be performed on blood, bone marrow, amniotic fluid, or placental tissue.
• Used to diagnose chromosome imbalances

Question 14

Codominance

Answer 14

• Both alleles contribute to the phenotype of the heterozygote
• E.g. Blood groups

Question 15

Variable Expressivity

Answer 15

• Phenotype varies among individuals with the same genotype

- E.g. NF-1

Question 16

Incomplete penetrance

Answer 16

• Not all individuals with mutant genotype show the mutant phenotype
• E.g. BRCA1 gene mutations do not always result in breast or ovarian cancer

Question 17

Pleiotropy

Answer 17

• One gene contributes to multiple phenotypic effects

Question 18

Anticipation

Answer 18

• Increased severity or earlier onset of disease in succeeding generations
• Trinucleotide repeat disorders (Huntington’s Disease)

Question 19

Loss of Heterozygosity

Answer 19

• 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
• E.g. Retinoblastoma (Two-Hit Model)

Question 20

Dominant Negative Mutation

Answer 20

• Exerts a dominant effect. A heterozygote produces a nonfunctional altered protein that also prevents the normal gene product from functioning.
• Collagen proteins

Question 21

Linkage Disequilibrium

Answer 21

• Tendency for certain alleles at 2 linked loci to occur together more often than expected by chance in a population

Question 22

Mosaicism

Answer 22

• Presence of genetically distinct cell lines in the same individual. Arises from mitotic errors after fertilization.
• Somatic mosaicism= mutation propagates through multiple tissues or organs
• Gonadal= mutation only in egg or sperm cells

Question 23

Uniparental Disomy

Answer 23

• Offspring receives 2 copies of a chromosome from 1 parent & no copies from the other
• Uniparental is eUploid (normal #, not aneuploid)
• Consider in an individual manifesting a recessive disorder when only one parent is a carrier

Question 24

Hardy-Weinberg Equation

Answer 24

p^2 + 2pq + q^2= 1

Question 25

Hardy-Weinberg Assumptions

Answer 25

• No mutation occurring at the locus
• Natural selection not occurring
• Completely random mating
• No net migration

Question 26

Imprinting

Answer 26

• At some loci, only one allele is active
• The alternate allele is inactivated by methylation, or “imprinted”
• Disease results when there is a mutation or deletion of the active gene

Question 27

Prader-Willi Syndrome

Answer 27

• Paternal gene is deleted/ mutated (chromosome 15)

- Results in hyperphagia, obesity, intellectual disability, hypogonadism, & hypotonia

Question 28

AngelMan Syndrome

Answer 28

• Maternal gene is deleted/mutation (chromosome 15)

- Results in inappropriate laughter, seizures, ataxia, & severe intellectual disability

Question 29

Autosomal Dominant Inheritance

Answer 29

• Often due to defects in structural genes (but also signaling, growth differentiation, & development)
• Many generations affected
• Both males & females affected

Question 30

Autosomal Recessive Inheritance

Answer 30

• 25% of offspring from 2 carrier parents are affected
• Often enzyme deficiencies
• Usually seen in only one generation
• Increased risk with consanguineous families

Question 31

X-Linked Dominant Inheritance

Answer 31

• Transmitted through both parents
• Mothers transmit to 50% of daughters
• Fathers transmit to all daughters but NO sons

Question 32

X-Linked Recessive Inheritance

Answer 32

• No male-to-male transmission
• Sons of heterozygous mothers have a 50% chance of being affected
• Commonly more severe in males

Question 33

Mitochondrial Inheritance

Answer 33

• Transmitted only through the mother

- All offspring of affected females may show signs of disease