Key area 2.4 - Variation and inheritance

Question 1

What is variation ?

Answer 1

Differences that occur between individual members of a species

Combining genes from two parents contributes to variation within a species

Question 2

Name and describe the two types of variation

Answer 2

Discrete

Is where measurements fall into distinct groups

It’s single gene controlled

Examples :

Wing length
Seed shape
Ear lobe type
Eye colour

Continuous

A characteristic will have a range of values between a min and a max

It’s Polygenic

Examples

Body mass
Length of index finger
Milk yield
Body length of trout
Resting heart rate

Question 3

What is polygenic inheritance ?

Answer 3

It means they are controlled by many genes that act together

Polygenic characteristics show continuous variation

Question 4

Describe alleles

Answer 4

Alleles are different forms of the same gene

A gene controls the characteristics of an organism

Question 5

Name and describe both types of traits

Answer 5

Diploid organisms have two copies of every gene, alleles can’t be dominant or recessive

Dominant

Dominant alleles always show up in the appearance of an organism, even if only one copy is present

Recessive

Recessive alleles only show up in the appearance of an organism if there are two copies present in the genotype

Question 6

What is genotype and phenotype ?

Answer 6

Genotype

The alleles an organism carries for a particular characteristic

Example

TT, Tt or tt

Phenotype

The physical feature of a characteristic

Example

Blue eyes or brown eyes

Tall or short

Question 7

What is homozygous and heterozygous ?

Answer 7

They are used to describe the set of alleles an organism possesses for one gene - its genotype

If alleles are the same the organism is homozygous ( TT tt)

If the alleles are different the organism is heterozygous ( Tt )