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  • Created on: 15-05-14 19:13
Preview of Inheritance

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DNA structure
- DNA molecule= deoxyribonucleic acid, made up of two strands of nucleotide, double helix shape
- Four nitrogenous bases: adenine (A), thymine (T), cytosine (C), guanine (G)
- Between two strands of nucleotides, adenine always paired with thymine (AT), and cytosine
always paired with guanine (CG). Bases held together by hydrogen bonds
- Chromosome = long piece of DNA that contains the genes. Each human cell contains 23
homologous (containing DNA code for the same gene) pairs of chromosomes
- Diploid cell (2n) = contains 2 sets of chromosomes (N.B. di)
- Only gametes are haploid (n) (=HAlf the number of chromosomes found in body cell of organism)
A labelled nucleotide
- Used for: growth, repair, cell replacement, asexual
- Occurs in shoot tip and root tip in plants
- In animals, all cells divide by mitosis (except gametes), e.g.
Liver cells, skin cells
- Karyotype = photo of chromosomes from one cell
- First 22 pairs of human chromosomes = autosomes
- 23rd pair of human chromosomes determines gender
- Stages of mitosis using non-human example:
1. Nucleus contains 2 chromosomes
2. PROPHASE- Chromosomes shorter, thicker (visible)
and DNA replicates (chromosomes copied). Nuclear
membrane breaks down
3. METAPHASE- Chromosomes line up along equator of
cell + spindle fibres attach at centromere
4. ANAPHASE- Spindle fibres contract chromatids
pulled apart towards poles of the cell
5. TELOPHASE- Nuclear membrane reforms around each
set of chromosomes. Cytoplasm starts to divide
6. CYTOKINESIS- Cell splits 2 genetically identical cells
each containing same number of chromosomes as
parent cell (diploid)

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Meiosis (aka. Reduction division)
- During sexual reproduction 2 haploid gametes fuse
to make 1 diploid zygote. Gametes haploid or zygote
would have double the number of chromosomes
- Same as mitosis up to (and including) stage 3
4.The pairs of chromosomes are separated
and pulled to opposite ends of the cell
5.The chromatids separate and are pulled to
opposite ends of the cell. The cytoplasm divides
(2nd division)
6.Chromosomes no longer in matching pairs. 4
gametes formed.…read more

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Huntington's disorder- caused by dominant allele (written as H). Symptoms develop in middle age
and include: short-term memory lapses, mood changes, lack of concentration and slight,
uncontrollable muscle movements
Pedigree chart example
Square = boy, circle = girl, blue = sufferer, white = no symptoms (could be carrier too in this case
as sickle cell anaemia is recessive)
- Allele- one specific form of a gene (e.g.…read more


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