G&E: Inheritance

Question 1

Gene

Answer 1

A sequence of bases on a DNA molecule that codes for a protein, which results in a characteristic.

Question 2

Allele

Answer 2

A different version of a gene.

Question 3

Genotype

Answer 3

The genetic constitution of an organism - the alleles an organism has.

Question 4

Phenotype

Answer 4

The expression of the genetic constitution and its interaction with the environment - an organism’s characteristics.

Question 5

Dominant

Answer 5

An allele whose characteristics appears in the phenotype even when there’s only one copy.

Shown with a capital letter.

Question 6

Recessive

Answer 6

An allele whose characteristics only appears in the phenotype if two copies are present.

Shown by lower case letters.

Question 7

Codominant

Answer 7

Alleles that are both expressed in the phenotype - neither one is recessive.

Question 8

Locus

Answer 8

The fixed position of a gene on a chromosome.

Alleles of a gene are found at the same locus on each chromosome.

Question 9

Homozygote

Answer 9

An organism that carries two copies of the same allele.

Question 10

Heterozygote

Answer 10

An organism that carries two different alleles.

Question 11

Carrier

Answer 11

A person carrying an allele which is not expressed in the phenotype but that can be passed on to offspring.

Question 12

Are humans diploid or haploid organisms?

Answer 12

Diploid

Question 13

How many alleles do gametes have?

Answer 13

One allele.

Question 14

How can you predict the genotypes and phenotypes of the offspring produced if two parents are crossed?

Answer 14

Genetic diagrams.

Question 15

Monohybrid inheritance

Answer 15

The inheritence of a characteristic controlled by a single gene.

Question 16

Describe sickle-cell anaemia and the alleles involved:

Answer 16

Codominant alleles.

Homozygous + normal haemoglobin = no disease

Homozygous + sickle haemoglobin = disease + all blood cells are sickle-shaped

Heterozygous = sickle-cell trait

Question 17

F₁

Answer 17

First generation from parents

Question 18

F₂

Answer 18

Offspring of first set of offspring.

Question 19

What is the phenotypic ratio for:

• monohybrid
• homozygous dominant x homozygous recessive

Answer 19

F₁ = all heterozygous offspring

F₂ = 3 : 1 (dominant: recessive)

Question 20

What is the phenotypic ratio for:

• dihybrid?
• homozygous dominant x homozygous recessive?

Answer 20

F₁ = all heterzygous offspring

F₂ = 9 : 3 : 3 : 1

dominant both : dominant 1st recessive 2nd : recessive 1st dominant 2nd : recessive both.

Question 21

What is the phenotypic ration for:

• codominant?
• homozygous for one allele x homozygous for the other allele?

Answer 21

F₁ = all heterzygous offspring

F₂ = 1 : 2 : 1

Question 22

In what scenarios might you not get the expected phenotypic ratio?

Answer 22

Because of sex linkage, autosomal linkage or epistasis.