Mendelian Genetics

Question 1

What is Mendel’s first law?

Answer 1

Alternative versions of a gene account for variations in inherited characters

Question 2

What is Mendel’s second law?

Answer 2

Each character is independently inherited during gamete formation - each pair of alleles of a given gene are independently inherited from alleles at a different gene locus

Question 3

Causes of deviations from Mendelian ratios

Answer 3

Epistasis
Incomplete dominance
Co-dominance
Co-dominance and multiple alleles
Lethal alleles

Question 4

What is the difference between co-dominance and incomplete dominance?

Answer 4

In co-dominance heterozygote expressed in both forms - offspring looks like both parents at once
Incomplete dominance the heterozygote forms an intermediate phenotype - looks like a blend of both parents

Question 5

What is pleiotropy?

Answer 5

When one gene influences 2 or more phenotypic traits

Question 6

What is allelic heterogeneity?

Answer 6

A similar phenotype produced by different alleles of the same gene

Question 7

What is locus heterogeneity?

Answer 7

A similar phenotype is produced by mutations at different gene loci

Question 8

What is incomplete penetrance?

Answer 8

Not all individuals carrying a deleterious gene express the associated trait

Question 9

What is linkage?

Answer 9

When particular gene loci are inherited jointly

Question 10

Who discovered linkage?

Answer 10

Bateson and Punnet

Soon after 1900

Question 11

What is recombination frequency?

Answer 11

A measure of how often recombination occurs between genes, measured as the fraction of offspring that inherit recombinant proteins

Question 12

What is recombination frequency measured in?

Answer 12

centiMorgans (cM)

Question 13

How do recombination frequencies determine where genes are relative to each other on a chromosome?

Answer 13

Recombination is less likely between genes that are closer, because there is less DNA between them

Question 14

Why don’t gene mapping recombination frequencies always add up to 100%?

Answer 14

Double crossing over can occur

Question 15

What is another name for a sex chromosome?

Answer 15

Allosome

Question 16

What is X inactivation?

Answer 16

The inactivation of one of the two copies of the X chromosome in all female mammals. Happens during embryonic development

Question 17

What does the inactivated X chromosome become?

Answer 17

It condenses into a compact object called a Barr body. Most of its genes aren’t expressed and it lies alongside the nuclear envelope

Question 18

Why does X-inactivation not cause colourblindness?

Answer 18

The X chromosome is inactivated on a cell-by-cell basis - any daughter cell from one of the original embryonic cells will have the same X chromosome inactivated. As the eye comes from several different cells, some will have one X chromosome inactivated whilst others will have the other one inactivated

Question 19

How is mitochondrial DNA transcribed?

Answer 19

Like in prokaryotic cells with the production of polycistronic RNA (multiple genes on a single RNA molecule)