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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
Parents
Body cell in father
with a pair of
genes for brown
eyes
BB
b is the gene for blue eyes
bb
Body cell in mother
with a pair of genes
for blue eyes
B is the gene for brown eyes
Parents
Body cell in father
with a pair of
genes for brown
eyes
Gametes
BB
b is the gene for blue eyes
bb
Body cell in mother
with a pair of genes
for blue eyes
B is the gene for brown eyes
Parents
body cell in father
with a pair of
genes for brown
eyes
BB
bb
Gametes
each sperm
has a gene for
brown eyes
B
b is the gene for blue eyes
B
body cell in mother
with a pair of genes
for blue eyes
B is the gene for brown eyes
Parents
body cell in father
with a pair of
genes for brown
eyes
b is the gene for blue eyes
BB
body cell in mother
with a pair of genes
for blue eyes
bb
Gametes
each sperm
has a gene for
brown eyes
B
B
b
b
each ovum has a
gene for blue eyes
B is the gene for brown eyes
Parents
body cell in father
with a pair of
genes for brown
eyes
b is the gene for blue eyes
BB
body cell in mother
with a pair of genes
for blue eyes
bb
Gametes
each sperm
has a gene for
brown eyes
At fertilization
There are 4
possible ways of
joining a sperm
to an ovum
B
B
b
b
each ovum has a
gene for blue eyes
B is the gene for brown eyes
Parents
body cell in father
with a pair of
genes for brown
eyes
b is the gene for blue eyes
BB
body cell in mother
with a pair of genes
for blue eyes
bb
Gametes
each sperm
has a gene for
brown eyes
B
b
B
At fertilization
There are 4
possible ways of
joining a sperm
to an ovum
B
B
b
each ovum has a
gene for blue eyes
B is the gene for brown eyes
Parents
body cell in father
with a pair of
genes for brown
eyes
b is the gene for blue eyes
BB
body cell in mother
with a pair of genes
for blue eyes
bb
Gametes
each sperm
has a gene for
brown eyes
B
b
B
At fertilization
There are 4
possible ways of
joining a sperm
to an ovum
B
B
b
each ovum has a
gene for blue eyes
B is the gene for brown eyes
Parents
body cell in father
with a pair of
genes for brown
eyes
b is the gene for blue eyes
BB
body cell in mother
with a pair of genes
for blue eyes
bb
Gametes
each sperm
has a gene for
brown eyes
B
b
B
each ovum has a
gene for blue eyes
b
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
Parents
body cell in father
with a pair of
genes for brown
eyes
b is the gene for blue eyes
BB
body cell in mother
with a pair of genes
for blue eyes
bb
Gametes
each sperm
has a gene for
brown eyes
B
b
B
each ovum has a
gene for blue eyes
b
At fertilization
There are 4
possible ways of
joining a sperm
to an ovum
b
B
B
Bb
Bb
b
Bb
Bb
B is the gene for brown eyes
Parents
body cell in father
with a pair of
genes for brown
eyes
b is the gene for blue eyes
BB
body cell in mother
with a pair of genes
for blue eyes
bb
Gametes
each sperm
has a gene for
brown eyes
B
b
B
each ovum has a
gene for blue eyes
b
At fertilization
There are 4
possible ways of
joining a sperm
to an ovum
b
B
B
Bb
Bb
b
Bb
Bb
All the children of this F1 generation have genotype Bb and phenotype brown eyes
Parents
father with brown
eyes
Gametes
At fertilization
mother with brown
eyes
Parents
father with brown
eyes
Gametes
At fertilization
Bb
Bb
mother with brown
eyes
Parents
father with brown
eyes
Bb
mother with brown
eyes
Bb
Gametes
B
At fertilization
b
B
b
Parents
father with brown
eyes
Bb
mother with brown
eyes
Bb
Gametes
B
B
b
b
B
At fertilization
B
b
b
Parents
father with brown
eyes
Bb
mother with brown
eyes
Bb
Gametes
B
B
b
b
B
At fertilization
B
b
BB
Bb
b
Bb
bb
Parents
father with brown
eyes
Bb
mother with brown
eyes
Bb
Gametes
B
B
b
b
B
At fertilization
B
b
BB
Bb
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
b
Bb
bb
Parents
father with brown
eyes
Bb
mother with brown
eyes
Bb
Gametes
B
B
b
b
B
At fertilization
B
b
BB
Bb
b
Bb
bb
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

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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

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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

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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