Variation and Genetics

These cards will hold definitions for basic terms and explanations of the features covered in ths topic.

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  • Created by: Mz
  • Created on: 21-09-09 20:10

Variation - 1

Variation is the differences between members of the same species.

There are 2 causes of variation in a species :

  • inheritance/ genes
  • Enviroment
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Variation -2

Some characeristics are due to a combination of genes and enviroment.

Variation can be continuous and have a range of values.

It can also be discontinuous where data falls into discrete categories.

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Genetic / Enviromental or both?


  • Sex
  • Eye colour
  • blood group
  • hair colour
  • finger prints


  • Stamina


  • Weight
  • skin colour ect.
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Genes and Chromosomes

Nucleus - The part of a cell that contains genetic information

Gene - A small packet of information controlling a characteristic.

Cell - The basic building block of a living organism

DNA -The chemical from which chromosomes are made.

Chromosome - Thread like structure containing genes

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1. What are chromosomes?

1a. Chromosomes are fine threads that carry genes and DNA.

2. What are genes?

2a. Genes are parts of a chromosome whch controll the characteristics of every organ.

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3. What are genes made of?

3a. Genes are made of a small chemical called DNA.

4. What are Homologous pairs?

4a. Homologous pairs are pairs of chromosomes which have joined together.

5. Explain how a human gets 46 chromosomes?

5a. 23 chromosomes from the sperm and 23 chromosomes from the egg join to make 23 pairs of chromosomes or 46 single chromosomes

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Dominant and Recessive Genes

  • Some characteristics such as eye colour and the shape of the earlobe are controlled by a single gene. These genes may have different forms.
  • Different Forms of the same gene are called alleles.
  • The gene for eye colour has an allele for blue eye colour and an allele for a brown eye colour.
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Dominant and Recessive Genes

Alleles are Dominant or Recessive.

  • The characteristic controlled by a dominant allele develops if the allele is present on one or both chromosomes in a pair.
  • The characteristic controlled by a recessive allele develops if the allele is present on both chromosomes in a pair.

Eg. the allele for brown eyes is dominant, while the allele for blue eyes is recessive. An individual will only have blue eyes if they inherit two copies of the allele for blue eyes.

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