Topic 7—A: Genetics- 1. Genetic terms

Question 1

Gene

Answer 1

• a sequence of bases on a DNA molecule that codes for a protein (polypeptide) which results in a characteristic

Question 2

Allele

Answer 2

A version of a gene

Question 3

How many alleles of each gene do most plants and animals only carry from each parent?

Answer 3

2 alleles of each gene

Question 4

Why is the order of bases in each allele different?

Answer 4

Because each allele codes for different versions of the same characteristic

Question 5

How are alleles represented?

Answer 5

By using letters

Question 6

Example of alleles

Answer 6

• different alleles for eye colour
• allele for brown eyes is B and the allele for blue eyes is b
• pea plants have a gene for seed shape
• allele for round seed is shown using an R and the allele for a wrinkled seed uses r

Question 7

What organisms are humans?

Answer 7

Diploid organisms

Question 8

Definition of diploid

Answer 8

• When a cell contains two copies of each chromosome (one from each parent)

Question 9

What is the reason we have 2 alleles for each gene?

Answer 9

• we have 2 copies of each chromosome

Question 10

Where is the allele of each gene found at?

Answer 10

• its found at a fixed position called a locus on each chromosome in a pair

Question 11

Definition of locus

Answer 11

• the position on a chromosome where a particular allele is found

Question 12

Genotype

Answer 12

• the genotype of an organism is its genetic constitution/ the different alleles an organism has
• This could be a list of all its alleles but usually its just the alleles for one characteristic at a time

Question 13

Examples of genotypes

Answer 13

• one person may have the genotype BB for eye colour and another person Bb
• One pea plant might have the genotype RR for seed shape and another pea plant rr

Question 14

Phenotype

Answer 14

• the phenotype of an organism is the expression of the genetic constitution and its interaction with the environment
• this just means what characteristics an organism has as a result of both of its genes and the effect the environment has on its genes

Question 15

Examples of phenotypes

Answer 15

• one person may have brown eyes and another may have blue eyes
• one pea plant may have round seeds and another may have wrinkled seeds

Question 16

Dominant alleles

Answer 16

• always expressed in the phenotype even when there is only one copy of it
• shown by a capital letter

Question 17

Recessive alleles

Answer 17

• those with characteristics that only appear in the phenotype if two copies are present
• shown by lower case letters

Question 18

Examples of dominant and recessive alleles

Answer 18

• allele for brown eyes, B, is dominant, so if a persons genotype is Bb or BB they’ll. have brown eyes. The allele for blue eyes, b, is recessive, so a person will only have blue eyes is their genotype is bb
• the allele for round seed shape, R, is dominant, so if a pea plant’s genotype is Rr or RR it will have round seeds. The allele for wrinkled seed shape, r, is recessive so a pea plant will only have wrinkled seeds if its genotype is rr

Question 19

Codominant alleles

Answer 19

Some alleles are both expressed in the phenotype because neither one is recessive
- there said to be codominant alleles

Question 20

Examples of codomiinant alleles

Answer 20

• horses can have alleles for white hair or coloured hair
• neither allele is recessive
• so a horse with one copy of each allele will have a roan coat.
• (a coat with a mixture of white hairs and coloured hairs)

Question 21

What can the genotype either be at each locus in a diploid organism?

Answer 21

• homozygous
• heterozygous

Question 22

Homozygous

Answer 22

When an organism carries two copies of the same allele at the same locus

Question 23

Heterozygous

Answer 23

When an organism carries two different alleles at the same locus

Question 24

Example of homozygous and heterozygous

Answer 24

• the genotype BB and bb are homozygous and the genotype Bb is heterozygous
• The genotype RR and rr are homozygous and the genotype Rr is heterozygous