Extensions of Mendelian Genetics

Question 1

What is the phenotype ratio of a dihybrid cross of two heterozygous individuals?

Answer 1

9:3:3:1

Question 2

What is the product rule and when should it be used?

Answer 2

It is where we multiply the probabilities (fractions) of events together - (assume they are independent genes [not linked]).
It is used for independent events

Question 3

What is the sum rule and when should it be used?

Answer 3

It is where we add the probabilities (fractions) of events together.
This is used for mutually exclusive events (where it is an either or situation. eg. either a or b).

Question 4

What is the name for one gene that has many alleles?

Answer 4

polymorphic

remember each individual can only have 2 alleles though, one on each homologous chromosome

Question 5

What is incomplete dominance?

Answer 5

When F1 has an intermediate phenotype (a blend of the to phenotypes).
The offspring of this F1 phenotype will be one homozygous dominant (eg. red), two heterozygous (eg. pink), and one homozygous recessive (eg. white).

Question 6

What is co-dominance?

Answer 6

When both phenotypes exist/are displayed side by side in the organism.

Question 7

What are polygenic traits?

Answer 7

The phenotype is controlled by many genes that have an additive effect. Characteristics appear as continuous or quantitative (they add up to contribute to the whole. eg. skin colour determined by total number of colour producing alleles).

Question 8

What does the environment effect?

Answer 8

The phenotype. It can smooth differences among phenotypes so that the genotypes are no longer discreet.

Question 9

Can continuous traits have a simple genetic basis?

Answer 9

Yes