Genetic Variance

Question 1

Define pure breeding

How do you know if an organism is pure breeding

Answer 1

Pure breeding organisms show no variation in the particular characteristic being studied

This is achieved by either producing offspring via self fertilisation Or by breeding with others with identical characteristics

Test cross the offspring, with another individual that is homozygous recessive (the phenotype for this organism could only be the recessive trait so they are easy to spot) If any of the offspring of this mate pairing produce offspring with the recessive trait then the original organism you were testing must be heterozygous and not ‘purebred’

Question 2

What is pedigree analysis

Answer 2

Pedigree analysis is a way of illustrating inheritance patterns. It is a good way to follow the inheritance of genetic disorders through generations

Symbols are used to represent males, females etc. For traits of interest, symbols can be shaded to indicate individuals carrying the trait.

Individuals are designated by their generation number
and then their order number in that generation.

Question 3

What is a pedigree chart?

Answer 3

A pedigree chart is a diagram that shows the occurrence and appearance or phenotypes of a particular gene or organism and its ancestors from one
generation to the next,

Question 4

What is incomplete dominance

give an example

Answer 4

Incomplete dominance occurs when neither allele
dominates the other. When both alleles are present
in the heterozygous genotype, both contribute to
produce a phenotype that is an intermediate blend of
the genetic information. Three different phenotypes
may occur. Upper and lower case letter for alleles are still used even though neither allele is dominant

Examples of incomplete dominance include flower
color in snapdragons (right) and sweet peas, where red
and white flowered plants cross to produce pink flowered plants.

Question 5

What is co-dominance

give an example

Answer 5

Co-dominance occurs when both alleles are equally dominant. When both alleles are present in the heterozygous genotype, they are both expressed in the phenotype. Three different phenotypes may occur. Red and blue roans occur in cattle and horses

Pure breeding red (RR) x pure breeding white (WW) produces all Roan (RW) offspring. The coat is a
mixture of red and white hairs, gives an overall blotchy coat.

Question 6

What is multiple alleles

give an example

Answer 6

Multiple alleles occur when genes have more than two different alleles – though an individual will only have two of the alleles in their genotype.

The inheritance of blood groups shows multiple alleles (expressed as complete dominance and co-dominance). Three different alleles (IA,IB and i) exist for what is known as the ABO blood grouping. IA and IB are co-dominant; both are completely dominant to i.

Question 7

What is lethal alleles

give an example

Answer 7

Lethal alleles occur when a mutation results in an allele that produces a non-functional version of an essential protein. If an individual inherits a lethal combination of mutated alleles, it will die before or shortly after birth.

Exceptions occur when the expression of the allele is delayed until after reproductive maturity, as occurs in Huntington disease.
In other cases (e.g. Manx cats), the allele mutation results in a viable heterozygote with a recognizable phenotype.
Recessive lethal alleles are fatal only in the homozygote since their effect is masked in the heterozygote carrier.