Variation, Inheritance & Evolution
Meiosis
eiosis is the formation of four non-identical cells from one cell. Cells in the
M
reproductive organs divide by meiosis to form gametes.
- G
ametes only have one copy of each chromosome so when two fuse they
regain the correct amount
1. It duplicates its genetic information so there are 96 pairs of
chromosomes, the pairs of join together
2. The first division - the pairs are pulled apart so each one only has one
of each chromosome (46 pairs)
3. The second division - the chromosomes are pulled apart again (23
pairs)
4. This leaves four gametes each with a single set of chromosomes.
- They are genetically different because the chromosomes get
shuffled when they are separated
Sexual and Asexual Reproduction
Sexual reproduction:
- Gametes are the scientific name for sex cells
- Gametes in animals are the sperm cell (in males) and the egg cell (in
females)
- Gametes in flowering plants are pollen (in males) and the egg cell (in
females)
- Gametes are formed by meiosis (the formation of four non-identical cells
from one cell)
normal cell has 46 chromosomes (23 pairs). In each pair, there is one
A
chromosome from each parent. Each gamete contains 23 chromosomes and
when they fuse during fertilisation. So. . . the genetic information from each
parent is mixed, producing a variation in the offspring.
Asexual reproduction:
sexual reproduction involves one parent with no gametes joining. It happens
A
using the process ofmitosis, where two identicalcells are formed from one cell.
There is no mixing of genetic information. It leads to clones, which are genetically
identical to each other and the parent.
, Advantages & Disadvantages of Sexual and Asexual Reproduction
Sexual Reproduction Asexual Reproduction
Advantages 1 . SURVIVAL there is variation 1 . ONE PARENT is needed
in offspring which can lead to and less energy is used than
better survival if there is an sexual reproduction because
environmental change the organisms don’t have to
2. NATURAL SELECTION since find a mate
they can survive better they 2. FASTER
are more likely to breed 3. IDENTICAL offspring can
successfully and pass on the be favourable under certain
adapted characteristics conditions
3. SELECTIVE BREEDING we
can produce animals with
desirable characteristics to
produce offspring (eg. large)
Disadvantages 1 . MUCH SLOWER than 1 . CAN’T COPE WELL WITH
asexual and lots more energy CHANGE they don’t adapt
is needed throughout the because they are all identical
process so they will struggle to
2. TWO PARENTS means survive in new conditions
organisms have to find a mate
ome organisms can reproduce both sexually and asexually depending on their
S
circumstances
● Malaria
○ when it’s on a mosquito it reproduces sexually
○ when it’s on a human it reproduces asexually
● Some fungus
○ fungus releases spores which grow into new fungus
○ when the spores asexually it is the result of a fungus that’s very good
at survival
○ when the spores reproduce sexually it is often the response to an
unfavourable environmental change in hope of increasing the
survival chance
DNA and the Genome
NAstands for deoxyribonucleic acid. It’s the chemicalthat all of the genetic
D
material in the cell is made up of.
Ageneis a small section of DNA found on chromosomes - a triplet of bases that
codes for a specific protein. Each gene codes for a particular sequence of amino
acids, together a chain of amino acids can join to make a protein
Meiosis
eiosis is the formation of four non-identical cells from one cell. Cells in the
M
reproductive organs divide by meiosis to form gametes.
- G
ametes only have one copy of each chromosome so when two fuse they
regain the correct amount
1. It duplicates its genetic information so there are 96 pairs of
chromosomes, the pairs of join together
2. The first division - the pairs are pulled apart so each one only has one
of each chromosome (46 pairs)
3. The second division - the chromosomes are pulled apart again (23
pairs)
4. This leaves four gametes each with a single set of chromosomes.
- They are genetically different because the chromosomes get
shuffled when they are separated
Sexual and Asexual Reproduction
Sexual reproduction:
- Gametes are the scientific name for sex cells
- Gametes in animals are the sperm cell (in males) and the egg cell (in
females)
- Gametes in flowering plants are pollen (in males) and the egg cell (in
females)
- Gametes are formed by meiosis (the formation of four non-identical cells
from one cell)
normal cell has 46 chromosomes (23 pairs). In each pair, there is one
A
chromosome from each parent. Each gamete contains 23 chromosomes and
when they fuse during fertilisation. So. . . the genetic information from each
parent is mixed, producing a variation in the offspring.
Asexual reproduction:
sexual reproduction involves one parent with no gametes joining. It happens
A
using the process ofmitosis, where two identicalcells are formed from one cell.
There is no mixing of genetic information. It leads to clones, which are genetically
identical to each other and the parent.
, Advantages & Disadvantages of Sexual and Asexual Reproduction
Sexual Reproduction Asexual Reproduction
Advantages 1 . SURVIVAL there is variation 1 . ONE PARENT is needed
in offspring which can lead to and less energy is used than
better survival if there is an sexual reproduction because
environmental change the organisms don’t have to
2. NATURAL SELECTION since find a mate
they can survive better they 2. FASTER
are more likely to breed 3. IDENTICAL offspring can
successfully and pass on the be favourable under certain
adapted characteristics conditions
3. SELECTIVE BREEDING we
can produce animals with
desirable characteristics to
produce offspring (eg. large)
Disadvantages 1 . MUCH SLOWER than 1 . CAN’T COPE WELL WITH
asexual and lots more energy CHANGE they don’t adapt
is needed throughout the because they are all identical
process so they will struggle to
2. TWO PARENTS means survive in new conditions
organisms have to find a mate
ome organisms can reproduce both sexually and asexually depending on their
S
circumstances
● Malaria
○ when it’s on a mosquito it reproduces sexually
○ when it’s on a human it reproduces asexually
● Some fungus
○ fungus releases spores which grow into new fungus
○ when the spores asexually it is the result of a fungus that’s very good
at survival
○ when the spores reproduce sexually it is often the response to an
unfavourable environmental change in hope of increasing the
survival chance
DNA and the Genome
NAstands for deoxyribonucleic acid. It’s the chemicalthat all of the genetic
D
material in the cell is made up of.
Ageneis a small section of DNA found on chromosomes - a triplet of bases that
codes for a specific protein. Each gene codes for a particular sequence of amino
acids, together a chain of amino acids can join to make a protein
