New cells are needed to
replace old ones, repair
damaged tissue, grow,
etc, but they much have the
same genetic material
They have a nucleus containing
genes (some DNA). Different forms
of genes are alleles. Genes are
grouped in chromosomes.
46 chromosomes in a nucleus. 23
pairs. One from a pair is inherited
from father and one from mother.
Gametes have only one of each pair
Mitosis
two identical
cells
Same chromosomes
asexual
no genetic variation
Produces copies
of chromosomes
then cell divides
eg, skin
Differentiation
In embryos cells
are unspecialised
(stem cells)
Some genes are
switched on to
specialise certain cells
and differentiate them
In adult animal cells
differentiation has already
occured so mitosis is
common yet plants can still
differentiate making them
easy to clone
Cell Division in Sexual Reproduction
Meiosis
ova made in
ovaries. Sperm
in testes
Chromosomes are copied, cell
divides twice leaving 4 sex cells
with half the chromosomes
Introduces variety
random
chromosome
areas
Fertilisation
more variety as
they each have
23
chromosomes
which pair
Meiosis then Mitosis
Variation
Asexual = no variation
sexual = variation
Stem Cells
The Function
egg and sperm fuse to form a zygote (a
single cell). This divides to form a ball of
cells (embryo). The inner cells of this ball
are stem cells which will differentiate
bone marrow
is a stem cell
They are needed for diseased or injured tissue
Using Stem Cells
Spinal injuries cause paralysis
Embryonic stem
cells can be cultured
and differentiated into
the right cells
We may be able to grow whole organs
Problems with Stem Cells
Some embryonic stem
cells come from abortions,
some from fertility treatment
which may cause ethical
issues
Human rights
Slow, difficult,
expensive and
hard to control
May cause cancer
The Future
There are stem cells in the umbilical
cord blood solving ethical issues
new ways of growing
adult stem cells, and
have even grown
tracheas.
Theraputic cloning uses
adult cells to clone an
embryo of themselves,
From Mendel to DNA
Mendel's discoveries
Born 1822 worked
in a monestry
cross bred peas
Found a pattern in the characteristic of offspring
considered
dominant
genes
DNA
Chromosomes
are made up of
long chain of
DNA and are
found in nuclei
Double
helix
structure
Genes are a small
section of DNA
Carries
instructions to
make the
proteins that form
cell structures
include enzymes to
control cell chemistry
The Genetic code
DNA is made of
4 different
chemicals
grouped into 3s. Each 3 is an amino acid
A gene is
made of
hundreds of
thousands of
these bases
The order of
bases controls
the order of
amino acids to
make protein.
A mutation in a base
will change the whole
protein structure
DNA fingerprinting
DNA is
unique to
you
UNLESS
YOU HAVE
AN
IDENTICAL
TWIN
Both developed
from one cell
Your DNA
can be used
to identify
you.
Your DNA pattern
is more similar to
relatives. You can
get your pattern
from bodily fluids
Can be used for
crimes and DNA
tests in parenting
Inheritance in action
How inheritance
works
Sex Chromosomes
XX is female, XY is male
Genes have different alleles
which result in a different protein
Most characteristics
are controlled by a
number of genes but
some are only 1.
You get dominant and
recessive alleles
Genetic terms
Homozygous - two
identical alleles (DD,dd)
Heterozygous
- an individual
with different
alleles (Dd)
Genotype -
the genetic
makeup of an
individual
Phenotype -
physical
appearance
(dimples)
Family Trees
Can be used for
tracing genetic
changes
Can track diseases
Inherited conditions in humans
Polydactyly
When a baby
has excess
fingers or toes
Caused by a
dominant allele
If 1 parent has it,
you have a 50%
chance as half
the gametes have
the fault. If they
are homozygous,
you have no
chance
Cyctic Fibrosis
Organs get
clogged by mucus
Treatment =
physiotherapy
and antibiotics
Caused by a
recessive allele
must be
inherited by
both parents
Carriers have
both alleles but
no symptoms
because the
dominant is
healthy
The Genetic Lottery
When an egg
and sperm
combine it is up
to luck which
alleles combine
Use a
punnet
square
Curing Genetic Disease
Scientists hope genetic
engineering will be the
answer as they can cut out
faulty alleles and replace
them with healthy ones
Genetic tests show people
what faulty alleles they have
and the probability of children
having them
They can then decide whether they
want a family. It raises ethical issues