Chapter 5.3 + 5.4 The Test Cross / Miltiple Alleles for one Gene ✓

Question 1

Define test cross

Answer 1

A test cross is a genetic technique where an individual with an unknown genotype for a dominant trait is crossed with an individual that is homozygous recessive for the trait.

Question 2

Explain how a test cross helps breeders determine the genotype of an organism.

Answer 2

It helps breeders determine the genotype of an organism by crossing it with a homozygous recessive individual (aa).
If all offspring show the dominant phenotype, the organism is homozygous dominant (AA).
If offspring show both dominant and recessive phenotype in a 1:1 ratio, the organism is heterozygous dominant (Aa). This allows breeders to identify the organisms genotype and predict traits in future generations.

Question 3

Define multiple alleles

Answer 3

The term given when three or more alleles of a gene exist among members of a population

Question 4

What is an example of multiple alleles?

Answer 4

the ABO blood group system because there is three alleles IA, IB, and i.

Question 5

Define discontinuous variation

Answer 5

Variation in a characteristic that shows two or just a few clearly distinct phenotype

Question 6

Why is the ABO blood group a discontinuous variation?

Answer 6

In the ABO blood group system, only four blood groups are possible - A, B, AB or O. You cannot have a blood group in between these four groups, so this is discontinuous variation.

Question 7

Draw a punnett square to show that a person with blood group AB cannot have children with blood group O

Answer 7

A person with blood group AB has the genotype IAIB while a person with blood group O has the genotype ii.
A cross between these two would produce offspring with blood group A or blood group B, but not blood group O.
Since the AB parent does not carry the i allele required for blood group O, they cannot have children with blood group O