Genetic variation and genetic disorders

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4 FACTS...

1- Alleles are diffrent forms of a gene. 

2- alleles can be dominant or recessive.

3-polydactyl ( having exra fingers or toes) is caused by a dominant allele.

4- cystric fibrosis ( dicorder of the cell memeberanes) is caused by a reccesive alelle.

 gender determination (3 facts)...

1-human body cells have 23 pairs of chromosomes in the nuclues. one of these pairs controls the inheritance of a gender.

2- males have XY chromosomes.

3-females have ** chromosomes.

alleles (8 facts)...

1-some chracteristics are controlled by 1 single gene. E.G. eyecolour,shape of earlobe.

2-they are either dominnant or reccesive

3-the characteristic controlled by the dominant alle devlops if the allile is prent in one or bth chromosmes un a pair.

4- ressesive only devlops if the allele is present in both pairs.

5-brown eyes = dominant



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