Biology GCSE

Biologys GCSE 2012-2014

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Genes

Genes are found in our chromosomes, which parents pass down to offspring through their sex cells during reproduction. Different versions of the genes are called alleles, which determine properties such as eye colour, hair colour, and inherited disorders such as cystic fibrosis

The nucleus in cells controls its activities, the instructions of how an organism develops are found in the nuclei of its cells

Chromosomes are the structures found in the nucleus of most cells. They consist of DNA. A section of DNA that has a certain code for making a certain protein is called a gene. The proteins can be either structual proteins; such as the ones found in muscles and hair, or enzymes; such as proteases and otehr digestive enzymeschromosome, showing gene as section of DNA (http://www.bbc.co.uk/schools/gcsebitesize/science/images/cell_chrom_dna.jpg)

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Genes 2

Identical twins are genertically the same

An identical twin that take regular exercise will have a better muscle tone, so therefore the environment changes what we look like. All the differences seen in identical twins are due to the environment they live in, all their genes are the same

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Inheritence

When a sperm and egg come together, the fertilized egg contains 23 pairs of chromosomes. The sex chromosomes are responsible for the genes.

Human body cells contain 23 pairs of chromosomes, parents pass their genes to their offspring through their sex cells 

+ female sex cells are called ova

+ male sex cells are called sperm

Sex cells only contain one chromosome from each pair, therefore when the sex cells from ova and sperm join together it creates the 46 chromosomes, 23 pairs

Which chromosome you receive from each pair is entirely random, so different children in the same family will not look the same as they will receive different sets of chromosomes

Sex chromosomes can be seperated from its cell, if spread out on a microscope and magnified many times, longer chromosomes are X chromosomes, shorter ones are Y, females are XX, males are XY

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Determination of gender

When sex cells form, the sex chromosomes (XX and XY) are seperated, 

-all normal egg cells produced by a overy carry X chromosomes

-half the sperm carry X and half carry Y

a babys gender is determined by the sperm that fertilizes the egg cell

-if the sperm carrying the Y chromosome fertilizes the egg cell, the baby will be a boy, if i carries the X chromosome it will be a girl (XX or XY) 

The probability of the child being a boy or girl is 50:50

it is now possible to choose the gender of your child using IVF, although many people believe it is playing god or its not natural

Decisions like this are called values

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