Genetics

Question 1

What is a proband?

Answer 1

First person diagnosed in the pedigree

Question 2

Describe X linked recessive

Answer 2

Always expressed in male carriers
Females must be homozygous to be effected
Never father to son transmission

Question 3

Describe X linked dominant

Answer 3

Males with the disease transmit the trait only to females only
Females with the disease also transmit the trait to both males and females equally

Question 4

What is UPD?

Answer 4

Both chromosomes are inherited from one parent

Question 5

What is a Robertsonian translocation?

Answer 5

Long arm of two acrocentric chromosomes combined and the short arm is lost

Question 6

What is Turner syndrome?

Answer 6

45, XO (monosomy X -female)
Short stature, ovarian hypofunction, do not undergo puberty, infertile, webbed neck, low hairline, CV defects but no cognitive defects

Question 7

What is Klinefelter’s syndrome?

Answer 7

47, XXY
Varying degrees of cognitive social, behavioral and learning difficulties
Primary hypogonadism, small undescended testes, gynecomastia and tall stature

Question 8

What is trisomy 21?

Answer 8

Down’s syndrome
Most common and associated with increased maternal age
Cognitive impairment, increased nuchal translucency, cardiac defects, duodenal atresia, ventriculomegaly, absent nasal bone and short limbs

Question 9

What is trisomy 18?

Answer 9

Edwards syndrome (election age 18)
Microencephaly, malformed and low set Ears, small mouth and jaw, clEft lip/palatE, rocker bottom FEET, overlapped fingErs

Question 10

What is trisomy 13?

Answer 10

Patau (puberty 13)
Severe developmental abnormalities
Closely spaced/absent eyes, malformed ears, clenched hands and Polydatcyl, cleft lip/Palate

Question 11

What is reduced/incomplete penetrance?

Answer 11

The frequency of a gene manifesting itself
Not all individuals with a mutant genotype will express the mutant phenotype
Ex. Retinoblastoma penetrance is 90% bc 90% of people with the defect express the phenotype

Question 12

What is variable expressivity?

Answer 12

Describes the range of phenotypes that can vary in individuals with the same genotype
Ex. Two pts with neurofibromatosis or Marfan syndrome may have varying disease severity

Question 13

What is locus heterogeneity?

Answer 13

Mutations at different loci can produce a similar phenotype
Only one mutant locus needed for phenotype manifestation
Ex. Osteogenesis imperfecta

Question 14

What is osteogenesis imperfecta?

Answer 14

Brittle bone disease
Mutations in collagen genes on two loci in chromosomes 7 and 17
Either mutations exhibits similar phenotypes with varying severity
Ex of locus heterogeneity

Question 15

What is the Hardy Weinberg equation?

Answer 15

p2 + 2pq + q2 = 1
Or
p + q = 1

Question 16

What is consanguinity?

Answer 16

Mating with people in your family

Increase chance of producing offspring with rare autosomal recessive disorders

Question 17

What does polygenic mean?

Answer 17

Traits in which variations are thought to be caused by the combined effects of multiple genes

Question 18

What is multifactorial inheritance?

Answer 18

When environmental factors cause variation in the trait
Tend to follow a bell shaped distribution in populations
Below the threshold = normal
Above the threshold = affected by the disease

Question 19

What is fragile X syndrome?

Answer 19

X linked defect
Tri-nt repeat disorder (CGG)
eXtra large testes, jaw, ears
Intellectual disability