Genetics

Genetics is the study of the inheritance of Characteristics

• Which of the following do you think are characteristics?

• Hair colour Eye Colour

• Sporting ability Piercings

Inheritable characteristics

• Many physical characteristics such as eye colour and shape of ears were inherited from your parents

• The instructions for these inherited characteristics were carried in the two cells that made you the egg and sperm

Examples of inherited characteritics

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Chromosomes + Genes

• The nucleus of each sex cell (gamete) contains 23 thread like structures called Chromosomes

• Chromosomes are made of protein + DNA

• These chromosomes carry genes

• Genes are chemicals found on chromosomes that pass on information from parents to children

• When an egg and sperm cell fuse (each has 23 chromosomes) they give the individual they are creating 46 chromosomes

• One set comes from the mother the other from the father

• Each characteristic will be controlled by a pair of genes

• If the gene from the sperm is brown eyes and the gene from the egg is brown eyes then the child will have brown eyes

• If the gene from the sperm is for blue eyes and the gene from the egg is for blue eyes then the child will have blue eyes

• If the gene from the sperm is for blue eyes and the gene from the egg is for brown eyes one of the genes is usually stronger and this one is the one that will be seen in the child

• This stronger gene is called the dominant gene

• The weaker gene is called recessive• Brown eyes are dominant over blue eyes

• A big letter is used to show the dominant gene while a small letter is used to show a recessive gene

• If b represents eye colour then B is for brown eyes and b is for blue eyes

Think of this example

• A sperm meets an egg• The sperm has the gene B for brown hair• The egg has the gene b for blonde hair• What colour hair will the child have?

H h

• If this child marries a man with blonde hair what colour hair could their child have?

Bb + bb

Bb bb

Brown Blonde

• The dominant gene is the one that appears in the child when two different genes are controlling a characteristic

• The recessive gene does not appear in the child when two different genes are controlling a characteristic