7.1 Inheritance

Question 1

Genotype

Answer 1

The genotype is the genetic constitution of an organism.

Question 2

Phenotype

Answer 2

The phenotype is the expression of the genotype and its
interaction with the environment.

Question 3

Alleles

Answer 3

Random mutation can result in new alleles of a gene.
Genetic diversity is the number of different alleles of genes in a
population - there may be many alleles of a single gene in a population.
An individual inherits alleles from their parent or parents.
A change in the allele frequency of a population is
evolution.
Alleles may be dominant, recessive or codominant.
In a diploid organism, the alleles at a specific locus may be either
homozygous or heterozygous.

Question 4

Genetic diagrams

Answer 4

You have to use fully labelled genetic diagrams (Punnett squares) to interpret, or predict, the results of:
* monohybrid and dihybrid crosses involving dominant, recessive and codominant alleles
* crosses involving sex-linkage, autosomal linkage, multiple alleles and epistasis.

Question 5

Chi-squared

Answer 5

Genetic diagrams give you expected phenotypic ratios.

You have to use the chi-squared test to compare the ‘goodness of fit’ of observed phenotypic ratios with expected phenotypic ratios. If chi squared results in a p value of 0.05 or lower, then there is a significant difference between the observed phenotypic ratios and the expected phenotypic ratio, meaning the assumptions made in producing the Punnet square were incorrect.

Question 6

Codominance

Answer 6

Two different alleles at the same locus are both expressed in the phenotype.

Question 7

Autosomal linkage

Answer 7

If two genes have their loci on the same chromosome, they are said to be autosomally linked (an autosome is any chromosome that is not a sex chromosome).

A dihybrid cross genetic diagram assumes the gametes have been produced by normal meiosis, including independent assortment and crossing over.

The alleles of two genes that are autosomally linked are not separated by independent assortment, although they may be separated by crossing over (the further apart the two loci are from each other on the chromosome, the more likely they are to be separated by crossing over) therefore the observed ratio will be not a a ‘good fit’ to the expected ratio.