Topic 7 - Genetics

Question 1

Definition of an allele

Answer 1

An alternative form of a gene

Question 2

Definition of a genotype

Answer 2

The genetic constitution of an organism

Question 3

Definition of a phenotype

Answer 3

The expression of the genetic constitution and its interaction with the environment

Question 4

Definition of codominant

Answer 4

Both alleles are expressed in the phenotype

Question 5

What are homologous chromosomes

Answer 5

A pair of chromosomes that contain the same gene loci, but may contain different alleles

Question 6

What is the phenotype ratio for monohybrid inheritance

Answer 6

3:1 consists of RR, rr, Rr and rR

Question 7

What is the expected ratio for dihybrid inheritance

Answer 7

9:3:3:1 includes RRYy, RRYY, rryy and rrYY

Question 8

Codominance examples

Answer 8

Blood types
O is recessive and A/B are codominant

Question 9

What is a sex linked gene?

Answer 9

A gene that is on a sex chromosome (X mainly)

Question 10

What are autosomal chromosomes?

Answer 10

Chromosomes 1-22 (not X and Y)

Question 11

Why are males more likely to suffer from sex-linked disorders?

Answer 11

Males have both X and Y chromosomes therefore only need one recessive allele to express the disease phenotype
Females have X and X therefore need 2 recessive alleles

Question 12

Pedigree charts and how to prove recessive/dominance?

Answer 12

Dominance - parents have the condition but child does not. Parents are carriers of the recessive allele. Child is homozygous recessive.
Recessive - parents do not have the condition but the child does. Parents are carriers of the recessive allele.

Question 13

How to prove/disprove sex linkage?

Answer 13

Father and daughter with difference in phenotypes
If the allele is dominant, father passes the condition to the daughter (inherits the fathers X chromosome)

Question 14

What statistical test is commonly used in genetics?

Answer 14

Chi-squared
It’s categorical data

Question 15

The observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios. Suggest why.

Answer 15

Small sample
Fusion of gametes is random

Question 16

What is epistasis?

Answer 16

When one gene affects or masks the expression of another gene

Question 17

What is the ratio for dihybrid epistasis?

Answer 17

9:4:3

Question 18

The two types of epistasis

Answer 18

Gene 1 = E which is dominant and pigment x e which is recessive and no pigment
Gene 2 = B which is dominant black fur x b which is recessive brown fur

ee (no pigment) is yellow and masks the B and b

Question 19

Hardy-Weinberg Equations

Answer 19

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

Question 20

What assumptions are made by the Hardy-Weinberg principle

Answer 20

No mutations arise
No selection - alleles are equally passed on to the next generation
Random mating
Large population

Question 21

Define gene pool

Answer 21

Range of different alleles existing for a particular locus within a population

Question 22

Define allele frequency

Answer 22

Proportion of a certain allele within a gene pool, expressed as a decimal or percentage

Question 23

Which letters in the Hardy-Weinberg equation represents what?

Answer 23

p = dominant allele
q = recessive allele
2pq = heterozygous

Question 24

What is speciation

Answer 24

Evolution of a new species from an existing species

Question 25

What is genetic drift?

Answer 25

Random fluctuations in allele frequencies. It increases the occurrence of speciation (more in smaller populations).

Question 26

What is Allopatric Speciation

Answer 26

Population becomes geographically isolated into two areas

Question 27

What is Sympatric Speciation

Answer 27

Population in the same area that become reproductively separated

Question 28

Inversion mutation

Answer 28

Occurs during crossing-over in meiosis
DNA of a single gene is cut in two places, the cut portion is inverted 180° then rejoined to the same place within the gene
Result in non-functional proteins

Question 29

Duplication mutation

Answer 29

A whole gene/section is repeated so that two copies appear on the same chromosome
Mutation is not harmful

Question 30

Translocation mutation

Answer 30

Section of a gene is cut off and attaches to a separate gene
The cut gene is now non-functional