GENES - Inheritance Flashcards
What is a gene
A sequence of bases on a DNA molecule that codes for a protein (polypeptide),
which results in a characteristic, e.g. a gene for eye colour.
What is an allele
A different version of a gene. 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 — they code for different
versions of the same characteristic. They’re represented using letters, e.g. the allele for brown eyes (B) and the allele for blue eyes (b).
What is a genotype
The genetic constitution of an organism — the alleles an organism has, e.g. BB, Bb or bb for eye colour
What is a phenotype
The expression of the genetic constitution and its interaction with the environment — an organism’s characteristics, e.g. brown eyes
What is a dominant
An allele whose characteristic appears in the phenotype even when there’s only one copy. Dominant alleles are shown by a
capital letter. E.g. the allele for brown eyes (B) is dominant — if a person’s genotype is Bb or BB, they’ll have brown eyes
What is a recessive
An allele whose characteristic only appears in the phenotype if two copies are present. Recessive alleles are shown by a lower
case letter. E.g. the allele for blue eyes (b) is recessive — if a person’s genotype is bb, they’ll have blue eyes
What is a codominant`
Alleles that are both expressed in the phenotype — neither one is recessive, e.g. the alleles for haemoglobin.
What is a locus
The fixed position of a gene on a chromosome. Alleles of a gene are found at the same locus on each chromosome in a pair
What is a homozygote
An organism that carries two copies of the same allele, e.g. BB or bb.
What is a heterozygote
An organism that carries two different alleles, e.g. Bb.
What is a carrier
A person carrying an allele which is not expressed in the phenotype but that can be passed on to offspring.
what do genetic diagrams show
the Possible Genotypes of Offspring
what type of organism are humans
Humans are diploid organisms (we have two sets of chromosomes) so we have two alleles for each gene.
what do gametes contain
Gamet es (sex cells) contain only one allele for each gene. When gametes from two parents fuse together,
the alleles they contain form the genotype of the offspring produced.
what re the two types of genotype at the locus
. At each locus, the genotype can be
homozygous or heterozygous.
