INHERITANCE & SURVIVAL

Inheriting features

Key definitions

GENE

A part of a chromosome which controls a specific feature of an individual.

Key definitions

ALLELE

Different forms of a gene, e.g. the gene for eye colour may include and blue allele and a brown allele.

Key definitions

DOMINANT

An allele which is expressed (switched on) while another allele is switched off. Usually identified as a capital letter, e.g. R.

Key definitions

RECESSIVE

An allele which is not expressed (switched off) while another allele is switched on. Usually identified as a lower case letter, e.g. r.

Key definitions

HOMOZYGOUS

An individual who has inherited two identical alleles, e.g. RR or rr

Key definitions

HETEROZYGOUS

An individual who has inherited two different alleles, e.g. Rr or Rr

Key definitions

GENOTYPE

A description of the genes an individual carries, e.g. your genotype may be RR, rr, or Rr

Key definitions

PHENOTYPE

A description of the feature an individual shows, e.g. your phenotype may be tongue roller or non-tongue roller.

The inheritance of eye colour

A person with the genes BB will have brown eyes.

A person with the genes bb will have blue eyes.

A person with the genes Bb will have brown eyes.

The inheritance of eye colour

In a person with the genes Bb only the effect of gene B shows.

The effect of gene B dominates the effect of gene b.

Gene B is dominant to gene b.

Gene b is recessive to gene B.

B is the gene for brown eyes b is the gene for blue eyes

B is the gene for brown eyes b is the gene for blue eyes

ParentsBB bbBody cell in father

with a pair of genes for brown eyes

Body cell in mother with a pair of genes for blue eyes

B is the gene for brown eyes b is the gene for blue eyes

ParentsBB bbBody cell in father

with a pair of genes for brown eyes

Body cell in mother with a pair of genes for blue eyes

Gametes

B is the gene for brown eyes b is the gene for blue eyes

ParentsBB bbbody cell in father

with a pair of genes for brown eyes

body cell in mother with a pair of genes for blue eyes

Gametes

B Beach sperm has a gene for brown eyes

B is the gene for brown eyes b is the gene for blue eyes

ParentsBB bbbody cell in father

with a pair of genes for brown eyes

body cell in mother with a pair of genes for blue eyes

Gametes

B Beach sperm has a gene for brown eyes

b b each ovum has a gene for blue eyes

B is the gene for brown eyes b is the gene for blue eyes

ParentsBB bbbody cell in father

with a pair of genes for brown eyes

body cell in mother with a pair of genes for blue eyes

Gametes

B Beach sperm has a gene for brown eyes

b b each ovum has a gene for blue eyes

At fertilization

There are 4 possible ways of joining a sperm to an ovum

B is the gene for brown eyes b is the gene for blue eyes

ParentsBB bbbody cell in father

with a pair of genes for brown eyes

body cell in mother with a pair of genes for blue eyes

Gametes

B Beach sperm has a gene for brown eyes

b b each ovum has a gene for blue eyes

At fertilization

There are 4 possible ways of joining a sperm to an ovum

B

B

B is the gene for brown eyes b is the gene for blue eyes

ParentsBB bbbody cell in father

with a pair of genes for brown eyes

body cell in mother with a pair of genes for blue eyes

Gametes

B Beach sperm has a gene for brown eyes

b b each ovum has a gene for blue eyes

At fertilization

There are 4 possible ways of joining a sperm to an ovum

B

B

B is the gene for brown eyes b is the gene for blue eyes

ParentsBB bbbody cell in father

with a pair of genes for brown eyes

body cell in mother with a pair of genes for blue eyes

Gametes

B Beach sperm has a gene for brown eyes

b b each ovum has a gene for blue eyes

At fertilization

There are 4 possible ways of joining a sperm to an ovum

B

B

b b

B is the gene for brown eyes b is the gene for blue eyes

ParentsBB bbbody cell in father

with a pair of genes for brown eyes

body cell in mother with a pair of genes for blue eyes

Gametes

B Beach sperm has a gene for brown eyes

b b each ovum has a gene for blue eyes

At fertilization

There are 4 possible ways of joining a sperm to an ovum

Bb BbBb Bb

B

B

b b

B is the gene for brown eyes b is the gene for blue eyes

ParentsBB bbbody cell in father

with a pair of genes for brown eyes

body cell in mother with a pair of genes for blue eyes

Gametes

B Beach sperm has a gene for brown eyes

b b each ovum has a gene for blue eyes

At fertilization

There are 4 possible ways of joining a sperm to an ovum

Bb BbBb Bb

B

B

b b

All the children of this F1 generation have genotype Bb and phenotype brown eyes

Parentsfather with brown eyes

mother with brown eyes

Gametes

At fertilization

ParentsBb Bbfather with brown

eyesmother with brown eyes

Gametes

At fertilization

ParentsBb Bbfather with brown

eyesmother with brown eyes

Gametes

B b B b

At fertilization

ParentsBb Bbfather with brown

eyesmother with brown eyes

Gametes

B b B b

At fertilization

B

b

B b

ParentsBb Bbfather with brown

eyesmother with brown eyes

Gametes

B b B b

At fertilization

BB BbBb bb

B

b

B b

ParentsBb Bbfather with brown

eyesmother with brown eyes

Gametes

B b B b

At fertilization

BB BbBb bb

B

b

B b

A child who inherits the genes BB will have brown eyes

A child who inherits the genes Bb will have brown eyes

A child who inherits the genes bb will have blue eyes

ParentsBb Bbfather with brown

eyesmother with brown eyes

Gametes

B b B b

At fertilization

BB BbBb bb

B

b

B b

A child who inherits the genes BB will have brown eyes

A child who inherits the genes Bb will have brown eyes

A child who inherits the genes bb will have blue eyes

In the F2 generation the ratio of brown eyed children to blue eyes will be 3 to 1

The work of Gregor Mendel

Just over 100 years ago a monk called Gregor Mendel tried to discover how characteristics are inherited.

For one of his experiments Mendel used pea plants which are either tall or dwarf (short)

The work of Gregor Mendel

Flowers on tall plants were pollinated with pollen from tall plants.

Flowers on dwarf plants were pollinated with pollen from dwarf plants.

The seeds were collected. The seeds were planted. If all the new plants looked

the same as the parent plants they were pure breeding (true breeding)

The work of Gregor Mendel Using these pure breeding

plants he pollinated flowers on a tall plant with pollen from a dwarf plant.

The plants grown from these seeds were called the F1 generation.

All the F1 were tall, tallness was the dominant gene.

The F1 were called hybrids because they inherited different characteristics from each parent.

The work of Gregor Mendel

Mendel then pollinates one hybrid flower from the F1 with the pollen from another hybrid F1 flower.

The seeds were grown into the F2 generation.

The work of Gregor Mendel

Three quarters of the flowers in the F2 generation were tall.

One quarter of the F2 were dwarf.

The dwarfness reappeared in the F2 generation.

Dwarfness was the recessive characterisitic.

The work of Gregor Mendel