A gene is a unit of inheritance. It is a small segment of DNA that controls the production of one polypeptide that determines a characteristic
Alleles are different form of the same gene
Homozygous (RR/rr)
heterozygous (Rr)
Female XX, male XY
Mutation is a sudden, random change in the structure of a gene or in the number of chromosomes in the nucleus.
Gene mutation
albinism : people with albino allele (recessive) cannot produce a pigment for skin,hair and eye colour. They are sensitive to sunlight and easily sunburnt.
sickle cell anemia : gene controlling haemoglobin is affected. The mutated gene is recessive causing red blood cell to be sickle shaped which can interfere with the oxygen carrying property of red blood cells
Chromosome mutations
Down syndrome : humans normally have 46 chromosomes. Down syndrome people have 47 (extra chromosome 21)
Factors increasing rate of mutation
chemicals (eg: tar)
radiation ( eg: ultraviolet light, X-rays)
What is a gene?
A gene is a unit of inheritance that controls the production of one polypeptide determining a characteristic.
What is the difference between dominant and recessive alleles?
A dominant allele expresses itself in both homozygous and heterozygous conditions, while a recessive allele expresses itself only in homozygous condition.