principles of genetic inheritance

Question 1

Autosomal dominance?

Answer 1

one copy of a dominant mutant allele in one of the autosomes is enough to express the gene

Question 2

Autosomal recessive?

Answer 2

one mutant allele means the person is a carrier; two mutant alleles means the person will display the condition

Question 3

X-linked recessive-?

Answer 3

always are expressed in Males since they only have one X chromosome. Females will be carriers unless they possess both recessive alleles (DMD)

Question 4

X-linked dominant?

Answer 4

when the mutation is on the father’s X chromosome all daughters will express the condition. Father to son X transmission is not possible.

no carriers

Question 5

Leber’s hereditary optic neuropathy (LHON)

?

Answer 5

Point mutation affecting NADH dehydrogenase

Degeneration of retinal ganglion cells

Question 6

mitochondrial disorders?

Answer 6

Affected mother will pass on mitochondrial DNA to all children

LHON

MERRF

MELAS

Question 7

MERRF?

Answer 7

mutation in gene encoding tRNA for lysine

disrupts synthesis of cytochrome c oxidase

Question 8

MELAS?

Answer 8

Affects many body systems, CNS, and muscles

Stroke & dementia

Lactic acidosis

Single point mutation, can’t use pyruvate

Question 9

Nondisjunction?

Answer 9

too many or too few chromosomes

Question 10

Polyploidy?

Answer 10

complete set of extra chromosomes

Question 11

Aneupolid?

Answer 11

missing or addition individual chromosomes

Question 12

Uniparetal Disomy?

Answer 12

: two chromosomes inherited from same parent, parent specific imprinting

Question 13

Genomic Imprinting:?

Answer 13

• one allele is inactive

- silencing thru methylation of 5’ end of gene

Question 14

Prader Willi syndrome?

Answer 14

Deletion of a region on chromosome 15

Paternal gene imprinted: Prader Willi Syndrome
Short, hypotonia, small hands/feet, obesity, mild to mod intellectual disability

Maternal gene imprinted: Angelman syndrome
Severe intellectual disability, seizures, ataxic gait

Question 15

Klinefelter syndrome?

Answer 15

47XXY

Varying degrees of cognitive behavior, primary hypogonadism (Low T), small testes, gynecomastia, tall, infertile, can have more chromosomes

Question 16

Turner Syndrome?

Answer 16

45, XO

infertile, webbed neck, no cognitive defects

Question 17

Down’s syndrome?

Answer 17

trisomy 21

Most common, increased with maternal age, due to translocations
Cardiac defects, duodenal atresia

Question 18

Patau Syndrome

Answer 18

trisomy 13

Severe developmental abnormalities, perinatal death within 1 week( <13% survive to 10yo)
CNS, kidney issues, heart

Question 19

Edwards Syndrome:?

Answer 19

Triomy 18

Abnormal development, perinatal death within 1 year (<10% of live births survive to 10yo)
Microencephaly, small mouth

Question 20

Uniparental disomy

Answer 20

Individual received two copies of a chromosome or part of a chromosome from one parent and none from them other

Often asymptomatic, unless the only chromosome given has imprinted genes

Question 21

. Genomic imprinting

Answer 21

certain genes are expressed only from the mother or father.

Imprinted alleles are silenced thtough methylation of 5’ end; gene expressed only from non-imprinted allele

Imprinting is epigenetic, involves methylation and histone mods of egg/sperm cells

Question 22

chromosomal mutations? what are the 4 types

Answer 22

Inversion

Duplication

Translocation

deletion

Question 23

karyotyping?

Answer 23

Technique that allows determination of the number, size, and gross structure of metaphase chromosomes

Does not provide information at molecular level

Question 24

Neurofibramatosis?

Answer 24

variable expressivity, cafe du lait spots, tumor like growths

caused by inactivating mutant of NF-1 gene

Question 25

retinablastoma?

Answer 25

penetrance, autosomal dominant, genotypes dont match phenotypes often

Microdeletions in chromosome 13 cause defect in RB gene.
In hereditary form: one copy of RB gene is mutated or lost, leading to higher risk of cancer
Good second copy of gene is damaged due to somatic mutation
Cells lose control of G1 checkpoint

Question 26

Marfan Syndrome?

Answer 26

Affects the connective tissue, subsequently many different systems

variable expressivity

Question 27

Reduced/ Incomplete Penetrance: ?

Answer 27

Frequency a gene manifests: penetrance

-not all people with genotype will have phenotype

Question 28

Variable expressivity: ?

Answer 28

• range of phenotypes in patients with specific genotype

- neurofibromatosis/marfan

Question 29

Locus Heterogeneity:

Answer 29

• trait caused by mutations at genes in different locations

- ”osteogenesis imperfecta” chromosome 7,17

Question 30

Heteroplasmy

Answer 30

.Presence of more than one type of mitochondrial DNA

Symptoms don’t develop until adulthood because these mutant mitochondrial alleles must undergo many cell divisions before presenting

Question 31

Polygenic

Answer 31

more than one gene affects phenotype

Question 32

Multifactorial:

Answer 32

environmental factors affect trait too

-recurrence risk if higher, especially if more than one family member affected

Question 33

Liability of distribution:

Answer 33

If you pass threshold, you have disease

Question 34

Pyloric stenosis:?

Answer 34

more common in males

-least affected sex transmits condition more

Question 35

Postaxial Polydactyly method of inheritance?

Answer 35

autosomal dominant

Question 36

Tyrosinase-Negative Albinism method of inheritance?

Answer 36

autosomal recessive

Question 37

Duchenne Muscular Dystrophy method of inheritance?

Answer 37

X-linked Recessive

Question 38

Hypophosphatemia method of inheritance?

Answer 38

X-linked Dominant