AQA Additional Science Biology - Inheritance

Taken from the AQA Science Revision Guide, just thought I'd share it on here anyway :)

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B2.6 Inheritance
6.1 Cell Division and Growth
Cell Division is necessary for the growth of an organism or for repair if tissues are damaged.
Mitosis results in two identical cells being produced from the original cell.
A copy of each chromosome is made before the cell divides and one of each chromosome goes
to each new cell.
Mitosis results in two new cells each identical to the parent cell. The new cells are for
either growth or replacement.
Key Points
Body cells need to divide to produce new cells for growth or repair
Mitosis is the type of cell division which produces identical new cells.

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B2.6 Inheritance
6.2 Stem Cells
Stem cells are unspecialised. They can develop (differentiate) into many different types of
specialised cell. Stem cells are found in the embryo and in adult bone marrow.
Many embryonic stem cells that we carry research out on are from aborted embryos, or are
`spare' embryos from fertility treatment. This results in ethical issues and much debate, as it can
be argued that you are destroying life to obtain these stem cells for research.…read more

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B2.6 Inheritance
6.3 Cell Division in Sexual Reproduction
Cells in reproductive organs, e.g. testes and ovaries, divide to form sex cells (gametes).
Before division, a copy of each chromosome is made. The cell now divides twice to form four
gametes (sex cells). This type of cell division is called meiosis.
Each gamete has only one chromosome from the original pair. All of the cells are different from
each other and the parent cell.…read more

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B2.6 Inheritance
6.4 From Mendel to DNA
Gregor Mendel was a monk who worked out how characteristics were inherited. His ideas were
not accepted for many years.
Genes are short lengths of DNA (deoxyribonucleic acid), which make up chromosomes and
control our characteristics.
Genes code for combinations of specific amino acids, which make up proteins.
Key Points
Gregor Mendel worked out how characteristics are inherited.
Genes make up the chromosomes, which control our characteristics.…read more

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B2.6 Inheritance
6.5 Inheritance in action
Human beings have 23 pairs of chromosomes, one pair of sex chromosomes. Females
are XX and males are XY.
Genes controlling the same characteristic are called alleles.
If an allele `masks' the effect of another it is said to be `dominant'. The allele where the
effect is `masked' is said to be `recessive'.
For example, the allele for brown eyes is dominant to the allele for blue eyes.…read more

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B2.6 Inheritance
6.6 Inherited Conditions in Humans
Huntington's disease is a disorder of the nervous system. It is causes by a dominant allele, so
even if only one parent has the disease it can be inherited by a child.
Cystic fibrosis is a disorder of the cell membranes. It is caused by a recessive allele so parents
may be carriers (Cc). Only if both parents are either carriers or have the disorder does the child
inherit it.…read more


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