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Biology Unit 2.7 - Cell Division and
Inheritance
- Cell Division
- In body cells the chromosomes are normally
found in pairs. Body cells divide by mitosis
- The chromosomes contain the genetic information
- When a body cell divides by mitosis...
- Copies of the genetic material are made
- Then the cell divides once to form two
genetically identical body cells
- Then the cell divides once to form two
genetically identical body cells
- Copies of the genetic material are made
- Mitosis occurs during growth or to
produce replacement cells
- Body cells have
two sets of
chromosomes; sex
cells have only one
- Cells in
reproductive
organs divide
to form
gametes
- The type of cell
division in which a
cell divides to form
gametes is called
meiosis
- The type of cell
division in which a
cell divides to form
gametes is called
meiosis
- When a cell
divides to form
gametes...
- Copies of the genetic
information are made
- Then the cell divides
twice to form four
gametes, each with a
single set of
chromosomes
- Then the cell divides
twice to form four
gametes, each with a
single set of
chromosomes
- Copies of the genetic
information are made
- When gametes join at
fertilisation, a single body cell
with new pair of
chromosomes is formed. A
new individual then develops
by this cell repeatedly
dividing by mitosis
- Most types of animal cells differentiate at an early stage
whereas many plant cells retain the ability to differentiate
throughout life. In mature animals, cell division is mainly
restricted to repair and replacement
- Cells from human embryos and adult bone marrow, called stem cells,
can be made to differentiate into many different types of cells. E.g. nerve
cells
- Human stem cells have the ability to
develop into any kind of human cell.
- Treatment with stem cells may be able to
help conditions such ad paralysis
- The cells of the offspring produced by asexual
reproduction are produced by mitosis from the
parental cells. They contain the same alleles
as the parents.
- In body cells the chromosomes are normally
found in pairs. Body cells divide by mitosis
- Genetic Variation
- Sexual reproduction gives rise to variation
because, when gametes fuse, one of each
pair of alleles comes from each parent
- In human body cells, one of the 23 pairs of chromosomes carries the genes that determine sex. In females
the sex chromosomes are the same (XX); in males the sex chromosomes are different (XY)
- Some characteristics are controlled by a single gene. Each
gene may have different forms called alleles
- An allele that controls the development of a
characteristic when it is present on only one of the
chromosomes is a dominant allele
- An allele that controls the development of
characteristics only if the dominant allele is
not present is a recessive allele
- Chromosomes are made
up of large molecules of
DNA which has a double
helix structure
- A gene is a small section of DNA
- Each gene codes for particular combination of amino acids
which make a specific protein
- Each gene codes for particular combination of amino acids
which make a specific protein
- Each person (apart from identical twins) has
unique DNA. This can be used to identify
individuals in a process known as DNA
fingerprinting
- Sexual reproduction gives rise to variation
because, when gametes fuse, one of each
pair of alleles comes from each parent
- Genetic Disorders
- Some disorders are inherited
- Polydactyl - having extra fingers or toes - is
caused by a dominant allele of a gene and can
therefore be passed on by only one parent who
has the disorder
- Cystic fibrosis (a disorder of cell membranes)
must be inherited from both parents. The
parents may be carriers of the disorder
without actually having the disorder
themselves. It is caused by a recessive allele
of a gene and can therefore be passed on by
parents, neither of whom has the disorder
- Embryos can be screened for the
alleles that cause these and other
genetic disorders
- Some disorders are inherited
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