Download Definitions

From “Continuing Biology” Meg Bayley, David Layzell
Definitions for:
Mendelian Genetics
(Biology 3.3)
To revise, cover the right-hand side of the table with a sheet of paper and move down the left column
seeing which words you already know the definitions of (slide the paper down a word at a time to
check). Tick these ones off, and concentrate on the others until you have learnt them all. Then cover
the left-hand side of the table and have a go at writing the words to match the definitions!
If a word on the right-hand side is in bold, there is a definition for it elsewhere in the table.
The shaded words are less important.
Allele
Autosome, autosomal
Carrier
Codominance
Collaboration
Complementary genes
Dihybrid cross
Dominance
Duplicate genes
Epistasis
F1
F2
Gametes
Genotype
Heterozygous
Homozygous
Incomplete dominance
Lethal gene
Linked genes
Map distance
Modified Mendelian ratio
Monohybrid cross
Multiple allele
P
Penetrant gene
Phenotype
Pleiotropy
Polygene
Recessive
Sex chromosome
Sex linked gene
Supplementary gene
Test cross
Alternate forms of a gene at a particular locus
A non sex chromosome
When a person has the gene, but does not show the disease
When both alleles are active, e.g. the A and B blood group alleles
Where both produce a phenotype that could not be produced by
each acting independently (9 : 3 : 3 : 1 ratio)
Where both genes are needed to produce a phenotype (9 : 7 ratio).
(Not specifically in the new prescription)
A cross between 2 genes (4 alleles)
An allele is dominant if the phenotype is expressed when
heterozygous
When either gene by itself produces the same phenotype and only
the homozygous recessive is different (15 : 1 ratio). (Not specifically
in the new prescription)
Where one gene acts on or affects another gene. I.e. an umbrella
term for any type like collaboration and complementary genes
as well as supplementary genes.
The first generation (children)
The second generation (grandchildren)
Sex cells (sperm, pollen, eggs)
The gene arrangement, e.g. Bb, RrTt
A genotype with different alleles, e.g. Aa
A genotype with the same alleles, e.g. AA or aa
When only one allele is active, eg. the white allele in snapdragon
flowers
A gene that (usually when homozygous) is fatal to the organism,
e.g. the roan gene in horses. The offspring is aborted or dies young
Genes on the same chromosome
The distance between two linked genes on a chromosome
When the classical 3 : 1 or 9 : 3 : 3 : 1 ratio is not found, e.g. the 2 :
1 in the roan horse cross (lethal gene) or complementary,
collaboration, duplicate and supplementary genes
A cross between one gene pair (2 alleles)
Where there are more than two alleles, e.g. there are 3 blood group
alleles
Parent generation
When a gene is expressed regardless of the environment
The physical expression of the genotype
When a gene has more than one function, e.g. the roan gene in
horses
Where one trait is controlled by more than one gene, e.g. human
height and skin colour
The recessive allele is only expressed when homozygous
In humans, the X and Y chromosomes
A gene found on one of the sex chromosomes
Where one gene controls the expression of another (9 : 4 : 3)
A cross with the homozygous recessive. It is used to determine the
phenotype of the organism crossed