Principles of Genetic Inheritance

Question 1

What is a chromatid

Answer 1

one of two identical copies of chromosome

Question 2

What is a homologous chromosome?

Answer 2

a pair of chromosomes, almost the exact same, with order of the 4 loci being the same

Question 3

What is the difference between metacentric, submetacentric and acrocentric in autosomes?

Answer 3

Meta= centromere in middle of chromosome
Sub=centromere off from the middle
Acrocentric= one side has little to know information

Question 4

What is the karyotype?

Answer 4

An entire set of chromosomes, 46 in each diploid cells

Question 5

How do you determine the sex of a karyotype?

Answer 5

XX is female

XY is male

Question 6

What is lyonization (females)?

Answer 6

it is the inactivation of X, inactivated randomly, condensing the domain into a Barr body

Question 7

What is mosaicism and examples?

Answer 7

A condition in which cells from a patient have different genotypes and karyotypes. EX: down syndrome 46XX/47XX, Klinefelter syndrome 46XY/47XXY, Turner syndrome 46XX/45XO

Question 8

What is homologous recombination?

Answer 8

Where crossover exchange occurs and information from one chromosome is switched with info from another in meiosis

Question 9

What are important steps of mitosis and what is the product?

Answer 9

Interphase is where chromosomes are duplicated
One copy of each chromosome and half of cyotplasm split between two daughter cells.
Results in 2 identical diploid cells

Question 10

Differences between meiosis 1 and 2?

Answer 10

Meiosis 1 starts with diploid cells (homologs separated). Meiosis 2 starts with haploid cells and makes 4 gametes (chromatids separated)

Question 11

What are some mitotic errors?

Answer 11

polyploidy:extra set of chromosomes
Aneuploidy: cells missing or have addition chromosomes (trisomy/monosomy)

Question 12

What is nondisjunction and what does it form?

Answer 12

Nondisjunction occurs when homologous pair or single pair does not get separated, causing mono/trisomy

Question 13

What are translocations?

Answer 13

Where non-homologous chromosomes exchange genetic material, either in reciprical or robertsonian

Question 14

What is Klinefelter Syndrome?

Answer 14

a form of nondisjunction which leaves karyotypes with 47XXY

Question 15

What is Turner syndrome?

Answer 15

a karytype for a female with 45XO, leads to lack of puberty, ovarian issues, normal intelligence

Question 16

What is Trisomy 21?

Answer 16

Autosomal trisomy, 47XX+21, downsyndrome, due to translocation (robersonian) or age of mom

Question 17

What is trisomy 13?

Answer 17

Patau syndrome, 47XX+13,

Question 18

What is trisomy 18?

Answer 18

Edwards syndrome, 47XX+18

Question 19

What is genomic imprinting?

Answer 19

gene silencing by methylation near 5’ end

Question 20

What does it mean to be paternally imprinted, maternally?

Answer 20

Paternally imprinted (30 genes like this) means the paternal gene will be silenced and express the maternal gene, and vice versa

Question 21

What is Prader-Willi/Angelman Syndromes?

Answer 21

PW deletion of a region on paternal chrom 15, resulting in obesity, small hands and feel, shortness
Angel: Deletion of region on maternal chrom 15, resulting in severe intellect disabilities, seizures and ataxic gait

Question 22

What is uniparental disomy?

Answer 22

Related to nondisjunction and genomic imprinting: if 2 chromos are inherited from same parent (uniparental disomy) they will have parent specific imprinting

Question 23

Difference between genotype and phenotype?

Answer 23

Geno: inidividuals genetic makeup
Pheno: physical presentation

Question 24

Autosomal dominant inheritance?

Answer 24

One allele of gene need for expression. If unaffected cannot transmit the trait,
50% reccurent risk (Aa)

Question 25

Autosomal recessive inheritance?

Answer 25

2 alleles of gene needed for expression of trait. skips generations, 25% or less reccurent risk (aa)

Question 26

What is consanguinity and how does it affect autosomal recessive inheritances?

Answer 26

It is first cousin mating which cause an increase in expression of trait

Question 27

What is X-linked recessive and example?

Answer 27

disease is on X, males hemizygous, females hetero or homozygous.
Females give to all sons, 50 daughters
All daughters of affected males are heterozygous carriers
EX: Duchenne Muscular Dystrophy

Question 28

what is X-linked dominant (rare) and example?

Answer 28

Males w disease transmits to 100% females. Females to 50% of offspring.
EX: hypophosphatemia

Question 29

What is reduced penetrance?

Answer 29

The frequency a gene manifests itself is called penetrance. So if phenotype occurs in 90% of individuals who have the defect, 90% penetrance (reduced from 100)

Question 30

What is variable expressivity?

Answer 30

Describes the range of phenotypes that vary between individuals with a specific genotype EX: neurofibromatosis presents in many different shapes and colors

Question 31

What is locus of heterogeneity?

Answer 31

a single disorder or trait cause by mutations in genes at different chromosomal loci EX:Osteogenesis imperfecta

Question 32

Difference between gene and genotype frequencies?

Answer 32

Gene: specify the proportions of each allele in a population
Genotype: specify the proportions of each genotype in a population

Question 33

What is the hardy weinberg principle?

Answer 33

p^2 + 2pq + q^2=1

Question 34

Difference between nuclear and mtDNA?

Answer 34

Nuclear is in nucleus and has 2 copies per cell

mtDNA in mitochondria and has 100-1000 copies per cell, does not contain introns, inherited through maternal line

Question 35

For a mitochondrial disease to show, what needs to happen?

Answer 35

A threshold needs to be met, eg: 60% of mitochondria need to be diseased to show symptoms (MELAS)

Question 36

What increases recurrence risk?

Answer 36

more than one family member is affected
disease in proband, increases
environmental factors

Question 37

What is multifactorial inheritance?

Answer 37

is polygenic (many genes), environmental factors