A1. Genetic Terms

Question 1

Genes and alleles
A gene is …
You can have one or more versions of the same gene. These different versions are called alleles. There can be many different alleles of a single ____, but most plants and animals, including humans, only carry two alleles of each gene, one from each parent. The order of bases in each allele is slightly different - that’s because each allele codes for ___________ _________ __ ___ _____ ______________. Alleles are represented using letters.

Answer 1

A gene is a sequence of bases on a DNA molecule that codes for a protein (polypeptide) which results in a characteristic.
You can have one or more versions of the same gene. These different versions are called alleles. There can be many different alleles of a single gene, but most plants and animals, including humans, only carry two alleles of each gene, one from each parent. The order of bases in each allele is slightly different - that’s because each allele codes for different versions of the same characteristic. Alleles are represented using letters.

Question 2

Loci
Humans are ___________organisms. This means we have two copies of each chromosome, one from each parent. It’s why we have two alleles of each gene. The allele of each gene is found at a fixed position, called a ______, on _____ _____________ __ _ _____.

Answer 2

Humans are diploid organisms. This means we have two copies of each chromosome, one from each parent. It’s why we have two alleles of each gene. The allele of each gene is found at a fixed position, called a locus, on each chromosome in a pair

Question 3

Genotype
The genotype of an organism is its ________ ______________, or put another way, the ____________ _________ an organism has. This could be a list of all its _________but usually it’s just the ________for one characteristic at a time.

Answer 3

The genotype of an organism is its genetic constitution, or put another way, the different alleles an organism has. This could be a list of all its alleles but usually it’s just the alleles for one characteristic at a time.

Question 4

Phenotype
The phenotype of an organism is …

This just means ….

Answer 4

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 its genes and the effect the environment has on its genes.

Question 5

Dominant and recessive alleles
A ___________allele is always expressed in the ______________, even when there’s only ____ copy of it. Dominant alleles are shown by a _________ ________. Recessive alleles are those with characteristics that only appear in the phenotype if ____copies are present. They’re shown by lower case letters.

Answer 5

A dominant allele is always expressed in the phenotype, even when there’s only one copy of it. Dominant alleles are shown by a capital letter. Recessive alleles are those with characteristics that only appear in the phenotype if two copies are present. They’re shown by lower case letters.

Question 6

Codominant alleles are …

Answer 6

alleles that are both expressed in the phenotype because neither one is recessive. They are said to be codominant alleles.

Question 7

Homozygous and heterozygous
At each locus in a diploid organism, the __________can be homozygous or heterozygous. If an organism carries two copies of the same _______, it’s said to be homozygous at that locus. If an organism carries two __________alleles for a gene, then it’s heterozygous.

Answer 7

At each locus in a diploid organism, the genotype can be homozygous or heterozygous. If an organism carries two copies of the same allele, it’s said to be homozygous at that locus. If an organism carries two different alleles for a
gene, then it’s heterozygous.

Question 8

Tip: An organism can be _______________at one locus and _______________at another.

Answer 8

Tip: An organism can be homozygous at one locus and heterozygous at another.