Intro

Question 1

How many copies of mitochodnrial DNA is in each cell>

Answer 1

Exists in thousands of copeis in each cell, so genes packed into cell cytoplasm

Question 2

Is mtDNA exon or intron

Answer 2

purely exon

Question 3

Homoplastic vs heteroplastic

Answer 3

Homospalistic indivdiuals- show genetically indetnical mtDNA in very cell

Hteroplastic individuals have a mix of genetically different mtDNA in their cells

Question 4

What is the cuase of mutifactoral (polygenic) disorders?

Answer 4

from interactions of genes at multiple loci and also may be influenced by environemtnal factors, sucha s mutagenic chemcials

Multfactorial genetic disorders do not follow Mendelain inhertiance

COMPLEX INHERITANCE

Question 5

genetic imprinting

Answer 5

if expression of a disease phenotype depends upon which parent passed along teh mutation

i.e. Huntington’s disease has an earlier onset when inherited from the father compared to the mother

Question 6

Penetrance

Answer 6

probability that a person witha particualr mutated gene will exhibit a phenotype (disease). Some alleles may show reduceds or incompelte penetrance.

Indivuals carrign that mutated gene have a reduced pehnotype

Question 7

complete penetrance

Answer 7

trait will be detected in everyone that has the mutation

Question 8

Expressivity

Answer 8

the range of phyiscal manifestions of the phenotype among indivuals with the same disease-causing genotype

Age-dependent onset and modification by other genes in teh indivdual’s genome will also modify the character of genetic disorders

Question 9

What is a proband

Answer 9

the family member who brings the disorder to medical geneticist, if he/she is affected by the diseases

Question 10

Consultant

Answer 10

an unaffected individual who may bring the disorder to the attention of a medical geneticist is known as a consultant

Question 11

What does it mean to be consanguineous

Answer 11

coupels who have more than one ancestor in common

Question 12

What are characterisitcs of Autosomal Dominant inheritance

Answer 12

1. phenotype detected in every generation, each affected person has an affected parent
2. Any child of an affected parent has 1 in 2 inheritance risk (50%)
3. Phenotypically normal family members do not transmit the mutant phenotype to their children
4. both genders are equally likely to transmit the phenotype to children of eithe rsex
5. A signifiant proportion of isoalted cases may be due to new mutations

Question 13

Characteristics of autosomal Recessive inheritnace

Answer 13

1. inherited through BOTH parents, who are asymptomatic (blue bull’s eyes)
2. Disease occurs only in homozygotess- no normal gene copy compensates for mutatn allele
3. Parents of an affected child are asymptomatic carriers of the mutant alleles
4. The risk for each proband sib is 1 in 4
5. Granparents (second degree relations; shaded gray with bulls’ eye notation) must hve possessed one copy of mutant allel that was passed on

Question 14

Characteristics of X-linked recessive inheritance

Answer 14

1. Phenotype is much higher in males than in females
2. heterozygous females are usually not affected, but some may express the condition with variable severity based upon X inactivation
3. Mutant gene is transmitted from affected man to his daughters (obligate carriers); any of his grandsons has 50% chance of inheriting the mutations
4. Mutant allel may be transmitted through a series of carrier females, and teh affected males in a kindred are related through the females
5. Never transmitted directly from father to son

Question 15

What clinical significance is associated with deletions

Answer 15

mental impairment
structural malformations
Cri-du Chat syndrome

Question 16

What is Mosaicism?

Answer 16

chromosomal aberration occurring after fertilization that produces a mixture of normal and abnormal cells

Cells may be somatic or germ cells

Mosaicism is not transferred to offspring unless it occurs in the germ line cells

Question 17

When is mosaicism transferred to offspring?

Answer 17

only when it occurs in the germ line cells

Question 18

What is a chimera>

Answer 18

individuals with contributions from more than one fertilized ovum

Question 19

What stage of mitosis are cells in when a “chormosome spread” is made from WBC

Answer 19

Metaphase

Question 20

What is a karyotype

Answer 20

sum of all chromosome information

Question 21

What are the two arms of a chromosome called?

Answer 21

short arm = p arm
long arm = q arm

position of the primary constriction of the chromosome (another name for centromere) defines whether the chromosome is meacentraic or acrocentenric

Question 22

Difference between metacentric vs acrocentric

Answer 22

Metacentric (2 substantial arms)

Acrocentric (one very tiney arm and one which contains almost all DNA)

Question 23

Which chromosomes are acrocentric?

Answer 23

13, 14, 15, 21, 22

Question 24

What is mosaicism?

Answer 24

non-disjunction can occur during mitosis during early embryogenesis

This yields a mosaic embryo, which is defined as arising from a single zygote and has more than one genotype

Mitotic non-disjunction may be observed b/c it “rescuses an original trisomic zygotic (which is suually lethal) by providing a normal cell line

Question 25

How can you determine the fraction of cells having each genotype?

Answer 25

variable, reflecting how early during embryogeneiss the mosaicism originated

Question 26

Why are females considered to be mosiacis

Answer 26

all normal females have roughly equal popluations of two genetically different cell types and are therefore a type of mosaic.

in roughly half the cells, paternal X chromosome has been inactivatd, and in the other half the maternal X chromosome is inactive

Question 27

What is a chimera

Answer 27

Composed of more than two cell-lines that originated form different zygotes, e.g. fraternal twins fused into one zygote

interspecies chimeras have also been produced experimentally