Chromosomal Inheritance I

Question 1

X Inactivation in Female Mammals

Answer 1

One of two X chromosomes in each cell is randomly inactivated during embryonic development
-discovered by Mary Lyon (lyonization)

Question 2

Mosaic

Answer 2

when a female is heterozygous for a particular gene located on the X chromosome
Ex: tortoiseshell cat

Question 3

parental-type offspring

Answer 3

offspring have phenotypes of parents

Question 4

recombinant offspring

Answer 4

offspring have different phenotype than parents

Question 5

What is the frequency of recombination for unlinked genes?

Answer 5

50%

Question 6

For any two genes that are perfectly linked on a chromosome…

Answer 6

recombination is not observed

Question 7

How does linkage influence inheritance?

Answer 7

Morgan’s fly experiment:
-body color and wing size are usually inherited together in specific combinations (parental phenotypes) bc the genes are on the same chromosome
-non-parental phenotypes were also produced, which argued that the genes were linked on the chromosome (but linkage was incomplete)
-Morgan proposed that some process must sometimes break the physical connection between genes on the same chromosome (crossing over of homologous chromosomes)

Question 8

Crossing over

Answer 8

when homologous chromosomes cross over each other and share genetic information to produce new allele combinations, leading to separation of chromatids that produce recombinant gametes

Question 9

Will there be more recombination between the A and B loci or between B and C?

Answer 9

A and B because they are further apart on the chromosome segment than B and C

Question 10

Recombination frequency

Answer 10

a measure of the distance between genes

Question 11

The ______________ the frequency of recombination between two genes, the ____________ genetically distant the genes are from each other

Answer 11

higher, more

Question 12

What is the maximum frequency of observed recombinants?

Answer 12

50%
-At this frequency, the genes are assorting independently as if they were on 2 diff. chromosomes

Question 13

(# recombinant progeny/total progeny) x 100 = ?

Answer 13

distance between the two loci on the genetic map (% recombination)

Question 14

Will recombination frequency be less than or greater than 50% if genes are on the same chromosome?

Answer 14

less than 50%

Question 15

How many pairs of chromosomes do Drosophila flies. have?

Answer 15

4

Question 16

Difference between physical map and and genetic maps?

Answer 16

-linear order of genes is identical
-physical –> base pairs
-genetic –> relationships between genes

Question 17

Genome-Wide Association Study (GWAS)

Answer 17

experimental design used to detect associations between genetic variants and traits in samples from populations
-relies on genetic linkage between genetic markers (SNPs) and disease-associated alleles

Question 18

Manhattan plot

Answer 18

a graphical presentation of DNA variants that may be associated

Question 19

Insights from GWAS

Answer 19

-proportion of variance explained by each individual variant is small (schizophrenia: 108 loci, height 700 loci)
-each individual carries several alleles that increase and several alleles that decrease the trait or disease risk
-the effect size of most risk to loci is small

Question 20

Factors that affect success of GWAS

Answer 20

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