7.1 Inheritance

Question 1

Define genotype

Answer 1

Genetic make up of an organism

Question 2

Define phenotype

Answer 2

• The effect of the environment on the genotype
• observable characteristics

Question 3

Define alleles

Answer 3

Different versions of the same gene

Question 4

Define codominant

Answer 4

Both alleles are expressed in the phenotype of an organism

Question 5

What are sex linked genes?

Answer 5

Genes located on the sex chromosomes (X or Y)

Question 6

What is epistasis?

Answer 6

• 2 genes, 2 alleles each
• 1 gene locus masks or modifies the effect of another in the phenotype

Question 7

What is autosomal linkage?

Answer 7

• 2 genes, 2 alleles each
• both genes located on the same chromosome

Question 8

Why are sex linked diseases more common in males than females?

Answer 8

• males are XY and females are XX
• males only have one allele present so it’s always expressed
• disease masked in females, they need 2 recessive alleles to have disease but males only need 1 recessive allele

Question 9

What are dihybrid crosses?

Answer 9

• genetic cross with 2 genes showing the inheritance of 2 traits each with 2 alleles
• eg round seeds and wrinkled seeds

Question 10

What is a monohybrid cross?

Answer 10

1 gene, 2 alleles

Question 11

What are multiple alleles?

Answer 11

• 1 gene with 3 or more alleles
• represent as phenotype ^superscript allele

Question 12

Why are the observed phenotypic ratios not the same as the expected ratios?

Answer 12

• Small sample size
• Random fusion/fertilisation of gametes
• linked genes
• epistasis
• lethal genotypes

Question 13

Why is a recessive allele with harmful effects able to reach a higher frequency in a population than a dominant allele?

Answer 13

• recessive alleles can be carried by individuals without showing effects
• organisms that are carriers are more likely to reproduce
• therefore recessive alleles are more likely to be passed on