inheritance definitions

Question 1

gene

Answer 1

A gene is a section of DNA, that codes for a specific protein / polypeptide / RNA molecule.

Question 2

genotype

Answer 2

The genetic constitution of an organism. All the alleles that an organism possesses.

Question 3

Gene pool

Answer 3

All the alleles within an interbreeding population (at a specific time).

Question 4

Population

Answer 4

All the individuals of the same species that occupy the same area/ habitat at the same time.

Question 5

Phenotype

Answer 5

The organism’s phenotype is the expression of its genetic constitution and its interaction with the environment (i.e. its physical appearance).

Question 6

Allele

Answer 6

Different version / forms of the same gene.
May be dominant, recessive, or codominant.
Alleles of the same gene are formed by different types of mutations

Question 7

Multiple alleles

Answer 7

More than 2 alleles for the same gene. This produces a hierarchy of dominance.

Question 8

Locus

Answer 8

Different alleles for the same gene are found at the same position on the homologous chromosome; this position is referred to the locus of that gene.

Question 9

Homozygous

Answer 9

Most organisms are diploid, i.e. they have two copies of each chromosome and therefore two copies of a gene.
If the two copies of a gene are the same allele, the organism is said to be homozygous.

Question 10

Heterozygous

Answer 10

If the two copies of a gene are different alleles.
Normally, when an organism has two different alleles (heterozgous), one of the alleles is expressed in the phenotype and the otheris not. The phenotype is
not a mixture of the two. e.g. if a person has an allele for brown eyes and one for blue eyes, only brown eye colour will be seen.

Question 11

Dominant allele

Answer 11

If an allele is dominant, it will always be expressed in the phenotype regardless of whether an organism’s genotype is homozygous or heterozygous.

Question 12

Recessive allele

Answer 12

If an allele is recessive, it will only be expressed in the phenotype if the genotype is homozygous.

Question 13

Codominant alleles

Answer 13

Equally expressed within the phenotype.

Question 14

Diploid

Answer 14

Adult cells (Somatic) are normally diploid; they have two copies of a gene.
These may be the same (homozygous) or different (heterozygous).

Question 15

Haploid

Answer 15

During sexual reproduction, the adults produce gametes e.g., sperm and egg.
These are produced through meiosis and the gametes are haploid, i.e., they only have one copy of a gene.

Question 16

Genetic crosses

Answer 16

These diagrams show the way in which alleles are passed from one generation to the next. The allele is represented by a letter. The letter normally refers to the phenotype of the dominant allele (e.g. R would be used to represent an allele that codes for a red pigment in flowers)
The
DOMINANT allele is represented by an uppercase letter.

. R
The recessive allele is represented by a lowercase letter…

If an individual is described as true- bred or pure - bred, it indicates that it is homozygous RR or rr.
P is used to indicate a parental generation
F1 generation refers to the offspring of the parents
F2 generation refers to the offspring of the F1 generation