Principles of Genetic Inheritance

Question 1

Lyonization

Answer 1

Also called x-inactivation. When one x chromosome is randomly inactivated in a cell

Question 2

Translocations

Answer 2

non-homologous chromosomes will exchange genetic material- two types reciprocal or Robertsonian

Question 3

Robertsonian Translocation

Answer 3

Long arm of two acrocentric chromosomes combined, short arm typically is lost
EX- chrom 14 and chrom 21- the long arms of 14 and 21 will combine and the short arm will be lost.

Question 4

Reciprocal translocation

Answer 4

exchange of material between non homologous chromosomes

Question 5

Turner Syndrome

Answer 5

Genotype- 45, XO- has normal intelligence but will be short in stature, be infertile, 30% webbed neck, low hairline, most will not go through puberty without hormone therapy

Question 6

Klinefelter Syndrome

Answer 6

Genotype- 47, XXY- Some will have little to no sx. Primary hypogonadism (low T), tall in stature, infertile. Can be worse if there are more X chroms involved.

Question 7

Downs Syndrome

Answer 7

Genotype- 47 XX +21- Most common trisomy. Greater risk with older women.

Question 8

Patau Syndrome

Answer 8

Genotype- 47 XX +13- Severe developmental abnormalities and death results in about one week

Question 9

Edwards Syndrome

Answer 9

Genotype- 47 XX +18- Abnormal development, resulting in death about one year

Question 10

How many genes are known to be maternally imprinted?

Answer 10

70

Question 11

How many genes are known to be paternally imprinted?

Answer 11

30

Question 12

Genomic imprinting

Answer 12

Gene silencing through 5’ methylation of gene sequence- chromatin condensed and inactive. Can be inherited from parent to offspring

Question 13

Prader Willi- syndrome

Answer 13

Deletion of PWS and AS genes from paternal chromosome- result in short stature, hypotonia, small hands/feet, obesity and slight intelligence deficits

Question 14

Angelman Syndrome

Answer 14

Deletion of PWS and AS genes from the maternal chromosome- result in severe intellectual disability, seizures and ataxia

Question 15

Penetrance

Answer 15

frequency a gene manifest the phenotype

Question 16

Expressivity

Answer 16

Range of phenotypes given a particular genotype

Question 17

What is the difference in penetrance and expressivity?

Answer 17

Penetrance is either the phenotype is present or not while expressivity is a range of phenotypes.

Question 18

Locus heterogenity

Answer 18

single disorder, trait or pattern of traits that are caused by mutations of genes at different chromosome loci

Question 19

Mitochondria DNA

Answer 19

comes from the maternal line only- mutation rate is much higher since there are no repair mechanisms and higher damage present from O2 radicals

Question 20

Leber’s hereditary optic neuropathy

Answer 20

mitochondrial disorder- degeneration of retinal ganglion cells

Question 21

Mitochondrial encephalomyopathy, lactic acidosis, and

stroke-like episodes

Answer 21

Mitochondria disorder

Question 22

Polygenic

Answer 22

variations in phenotype are the result of many different genes working in tandem

Question 23

multifactoral inheritance

Answer 23

When the environment and multiple genes effect the outcome of the phenotype

Question 24

Threshold of liability

Answer 24

Some disorders that are multifactorial have a line that means the disorder will be expressed or not.

Question 25

What factors make recurrence of a multifactoral disorder more likely in a population?

Answer 25

1: if more than one member is affected
2: If expression in the proband is more severe
3: if the proband is of the less commonly affected sex
4: more closely related to the proband