Chromosomal Inheritance II

Question 1

Insights from GWAS

Answer 1

1. On average, the proportion of variance explained by each individual variant is small
2. Each individual carries several alleles that increase and decrease the trait or disease risk

Question 2

Factors that affect success of GWAS

Answer 2

1. how many loci affecting the trait segregate in the population
2. joint distribution of effect size and allele frequency at those loci (I.e. genetic architecture)
3. experimental sample size

Question 3

Missing heritability mystery

Answer 3

We know that 80-90% of variance in height is explained by genetics but the alleles identified that determine height only explain 20% (same is true for many other genetically complex traits)

Question 4

Nondisjunction

Answer 4

pairs of homologous chromosomes do not separate normally during meiosis, resulting in one gamete receives two of the same type of chromosome and another gamete receives no copy

Question 5

Nondisjunction in meiosis I

Answer 5

n+1 (2)
n-1 (2)

Question 6

Nondisjunction in meiosis II

Answer 6

n+1
n-1
n (2)

Question 7

Aneuploidy

Answer 7

Results from the fertilization of gametes in which nondisjunction occurred and results in monosomic (2n-1) and trisomic (2n+1) individuals

Question 8

Down Syndrome (Trisomy 21)

Answer 8

-aneuploid condition that results from three copies of chromosome 21
-1/830 children
-the frequency of Down Syndrome increases w/ the age of the mother

Question 9

Patau Syndrome (Trisomy 13)

Answer 9

Symptoms: serious eye, brain, circulatory defects as well as cleft palate
-children rarely live more than a few months

Question 10

Edward’s Syndrome (Trisomy 18)

Answer 10

Almost every organ system affected
-children generally do not live more than a few months

Question 11

Trisomy X (XXX)

Answer 11

healthy and fertile, usually cannot be distinguished from normal female except by karyotype, slightly taller than average

Question 12

Klinefelter Syndrome (XXY)

Answer 12

unusually small testes, sterile, breast enlargement, other feminine body characteristics

Question 13

Monosomy X (singular X chromosome)

Answer 13

-only known viable monosomy in humans
-phenotypically female but sterile due to lack of female organ maturation

Question 14

XYY

Answer 14

healthy and fertile, tend to be taller than average

Question 15

Accessory chromosomes

Answer 15

chromosomes that are not essential for survival
-show high mutation rates, the acquisition of foreign genes, copy number polymorphisms, and frequent rearrangements (evolve fast)

Question 16

Core chromosomes

Answer 16

chromosomes that carry essential genes that encode housekeeping functions such as cellular metabolism and reproduction (evolve slowly)

Question 17

Polyploidy

Answer 17

a condition in which an organism has more than two complete sets of chromosomes
-common in plants

Question 18

Triploidy

Answer 18

3 complete sets of chromosomes, either miscarriage or death within the first year of life

Question 19

Developmentally Programmed Polyploidy

Answer 19

-polyploidy increases the metabolic capacity of a tissue
-Hepatocytes and placental trophoblast giant cells (TGCs): provide nutrients and metabolites
-Megakaryocytes: stockpile of components needed to generate platelets

Question 20

Chromosome Structure Alterations

Answer 20

-Deletion: deletes a segment
-Duplication: repeats a segment
-Inversion: reverses a segment within a chromosome
-Translocation: moves a segment from one chromosome to a non-homologous chromosome

Question 21

Cri du Chat

Answer 21

-specific deletion in chromosome 5
-small head w/ unusual facial features, severe intellectual disabilities, and a cry that sounds like the mewing of a distressed cat
-individuals usually die in infancy or early childhood

Question 22

Chronic Myelogenous Leukemia

Answer 22

-translocation between chromosome 9 and 22
-translocated chromosome 22 = Philadelphia chromosome
-causes cancer by activating a gene involved in control of cell cycle

Question 23

Genomic Imprinting

Answer 23

-silencing genes through DNA methylation
-only affects a small fraction of mammalian genes
-most imprinted genes are critical for embryonic development
-not expressed early in fetal development
-reprogrammed in the germ line of the adult, who could be either male or female

Question 24

What is an exception to standard Mendelian Inheritance?

Answer 24

Mitochondria and plastids

Question 25

Extranuclear/Cytoplasmic genes

Answer 25

genes in mitochondria or plastid genomes

Question 26

What is inheritance controlled by in mitochondria and plastids?

Answer 26

depends on the maternal parents bc the zygote’s cytoplasm comes from the egg

Question 27

Evidence of extranuclear genes

Answer 27

yellow or white patches on leaves of an otherwise green plant
-phenotype of offspring only matched the maternal parent