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 XX 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