Reproduction
Meiosis leads to non-identical cells being formed while mitosis leads to identical cells being
formed.
Sexual reproduction involves the joining (fusion) of male and female gametes: • sperm and
egg cells in animals • pollen and egg cells in flowering plants.
In sexual reproduction there is mixing of genetic information which leads to variety in the
offspring. The formation of gametes involves meiosis.
Asexual reproduction involves only one parent and no fusion of gametes.
There is no mixing of genetic information.
This leads to genetically identical offspring (clones). Only mitosis is involved.
Meiosis
Meiosis halves the number of chromosomes in gametes and fertilisation restores the full
number of chromosomes.
Cells in reproductive organs divide by meiosis to form gametes.
When a cell divides to form gametes: • copies of the genetic information are made • the
cell divides twice to form four gametes, each with a single set of chromosomes • all
gametes are genetically different from each other.
Gametes join at fertilisation to restore the normal number of chromosomes.
The new cell divides by mitosis. The number of cells increases. As the embryo develops
cells differentiate.
Knowledge of the stages of meiosis is not required.
DNA and the genome
The genetic material in the nucleus of a cell is composed of a chemical called DNA.
DNA is a polymer made up of two strands forming a double helix.
The DNA is contained in structures called chromosomes. A gene is a small section of DNA on
a chromosome.
Each gene codes for a particular sequence of amino acids, to make a specific protein.
The genome of an organism is the entire genetic material of that organism.
The whole human genome has now been studied and this will have great importance for
medicine in the future.
discuss the importance of understanding the human genome. This is limited to the: • search
for genes linked to different types of disease • understanding and treatment of inherited
disorders • use in tracing human migration patterns from the past.
Meiosis leads to non-identical cells being formed while mitosis leads to identical cells being
formed.
Sexual reproduction involves the joining (fusion) of male and female gametes: • sperm and
egg cells in animals • pollen and egg cells in flowering plants.
In sexual reproduction there is mixing of genetic information which leads to variety in the
offspring. The formation of gametes involves meiosis.
Asexual reproduction involves only one parent and no fusion of gametes.
There is no mixing of genetic information.
This leads to genetically identical offspring (clones). Only mitosis is involved.
Meiosis
Meiosis halves the number of chromosomes in gametes and fertilisation restores the full
number of chromosomes.
Cells in reproductive organs divide by meiosis to form gametes.
When a cell divides to form gametes: • copies of the genetic information are made • the
cell divides twice to form four gametes, each with a single set of chromosomes • all
gametes are genetically different from each other.
Gametes join at fertilisation to restore the normal number of chromosomes.
The new cell divides by mitosis. The number of cells increases. As the embryo develops
cells differentiate.
Knowledge of the stages of meiosis is not required.
DNA and the genome
The genetic material in the nucleus of a cell is composed of a chemical called DNA.
DNA is a polymer made up of two strands forming a double helix.
The DNA is contained in structures called chromosomes. A gene is a small section of DNA on
a chromosome.
Each gene codes for a particular sequence of amino acids, to make a specific protein.
The genome of an organism is the entire genetic material of that organism.
The whole human genome has now been studied and this will have great importance for
medicine in the future.
discuss the importance of understanding the human genome. This is limited to the: • search
for genes linked to different types of disease • understanding and treatment of inherited
disorders • use in tracing human migration patterns from the past.
