Principles of Genetic Inheritance

Question 1

Describe lyonization.

Answer 1

Also called X-inactivation. Females have two X chromosomes, so one is inactivated at random. Example: calico cats

Question 2

Define mosaicism.

Answer 2

Two or more populations of cells with different genotypes in an individual who developed from a single fertilized egg. Results from errors in cell division.

Question 3

What is the the most common karyotype for Down Syndrome and what are its symptoms?

Answer 3

47, XX, +21. Varying degrees of cognitive ability, cardiac defects, duodenal atresia

Question 4

What is the the most common karyotype for Klinefelter Syndrome and what are its symptoms?

Answer 4

47XXY. Infertility, hypogonadism, tall stature.

Question 5

What is the most common karyotype for Turner Syndrome and what are its symptoms?

Answer 5

45XO. Short stature, infertility, webbed neck, ovarian hypofunction.

Question 6

What is the difference between embryonic stem cells and adult stem cells?

Answer 6

Embryonic stem cells are pluripotent (undifferentiated) and can become any cell type. Adult stem cells are differentiated in accordance to the tissues which they reside.

Question 7

Mutations in what gene/subunit of hemoglobin is a common cause of RBC related disease?

Answer 7

HBB gene, which encodes for beta-globin

Question 8

What are the main differences between mtDNA and DNA?

Answer 8

mtDNA is smaller, circular, contains no introns, has a much higher mutation rate, and is inherited exclusively through the maternal line.

Question 9

What is encoded by mtDNA?

Answer 9

rRNAs, tRNAs, and proteins for OxPhos

Question 10

What is the difference between somatic cell mitosis and stem cell mitosis?

Answer 10

Stem cell divide asymmetrically during mitosis, resulting in one stem cell and one daughter cell

Question 11

What is the order of the steps in mitosis?

Answer 11

Interphase, prophase, metaphase, anaphase, and telophase

Question 12

Define polyploidy and aneuploidy.

Answer 12

Polyploidy: cells contain a complete set of extra chromosomes in a cell (common in plants). Aneuploidy: cells contain a missing or additional individual chromosomes (monosomy, trisomy).

Question 13

What is a hemizygous allele?

Answer 13

The diseased allele on the X chromosome in males

Question 14

Why is the mutation rate in mtDNA ~10 times higher than DNA?

Answer 14

No DNA repair mechanisms and damage from free oxygen radicals.

Question 15

Describe Leber’s Hereditary Optic Neuropathy (LHON).

Answer 15

Degeneration of retinal ganglion cells caused by 3 pathogenic mtDNA point mutations affecting NADH dehydrogenase.

Question 16

Describe Myoclonic Epilepsy and Ragged Red Fibers (MERRF).

Answer 16

Caused by mutation in mtDNA gene encoding for the tRNA for lysine, which disrupts the synthesis of cytochrome-c oxidase. Can lead to issues in muscle movement.

Question 17

Describe Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like episodes (MELAS).

Answer 17

Most common maternally-inherited mitochondrial disease. Affects brain, nervous system, and muscles. Can lead to stroke and dementia.

Question 18

Describe genomic imprinting.

Answer 18

An epigenetic process that involves the methylation and histone modification of egg or sperm cells during their formation while the genetic sequence is unchanged. Only one allele is transcriptionally active. Imprints remain active throughout the lifespan of the individual somatic cells. Imprints are erased and new ones are set during meiosis.

Question 19

What is uniparental disomy (UPD)?

Answer 19

UPD is a phenomenon when an individual receives two copies of a chromosome or part of a chromosome from one parent and no copies from the other parent.

Question 20

What causes Prader-Willi and Angelman Syndromes?

Answer 20

Deletion of a region of chromosome 15.

Question 21

What is the difference between Prader-Willi and Angelman Syndromes?

Answer 21

Prader-WIlli: Paternal chromosome 15 deletion. Short stature, obesity, moderate intellectual disability, hypotonia. Angelman: Maternal chromosome 15 deletion. Severe intellectual disability, seizures, ataxic gait.

Question 22

What is the karyotype for Edwards Syndrome and what are its symptoms?

Answer 22

47, XX +18. Microencephaly, low-set ears, cleft lip, rocker bottom feet. 95% die in utero.

Question 23

What is the karyotype for Patau Syndrome and what are its symptoms?

Answer 23

47, XX +13. Clenched hands, ploydactyl, closely spaced/absent eyes.

Question 24

What is reduced penetrance? Give an example.

Answer 24

When the phenotype is not displayed in 100% of individuals inheriting the genetic defect. Example: Retinoblastoma

Question 25

What is variable expressivity? Give two examples.

Answer 25

Describes the range of phenotypes that vary between individuals with a specific genotype. Examples: Neurofibromatosis, Marfan Syndrome

Question 26

What is locus heterogeneity? Give an example.

Answer 26

Single disorder, trait, or pattern of traits caused by mutations in genes at different chromosomal loci. Example: Osteogenesis imperfecta

Question 27

What is the Hardy-Weinberg equation?

Answer 27

Question 28

What is Pyloric Stenosis and how does the occurance differ between males and females?

Answer 28

Muscular hypertrophy between stomach and duodenum. Five times more common in males than females. Males need less risk genes to show disease; females need more risk genes.