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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…

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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…

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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.…

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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…

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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…

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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…

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