law of dominance- when two pairs of contrasting characters are brought together in a gamete one of them is manifested. the character which is expressed is dominant and the one that remains masked recessive
law of segregation- when a pair of two contrasting characters are brought together in a gamete, one character is dominant and the other is recessive, in the first generation they are segregated as 3:1
law of independent assortment- when a pair of two contrasting characters are brought together in a gamete, the distribution of each pair of characteristics is independent of the other
in a monohybrid cross, the phenotype of the offspring is all red but in the second generation, it is 3:1. however, the genotypic ratio is 1:3:1
for a dihybrid cross, the phenotype of the offspring is in the ratio 9:3:3:1.
| gene | it is the unit of heredity which is passed on from generation to generation and determines particular traits |
|---|---|
| allele | it is two different forms of the same character, which both occupy the same position on a homologous chromosome and affecting the same character |
| homozygous | when two alleles in a offspring are identical to each other ex- Rr |
| heterozygous | when the two alleles in the pair of chromosomes are identical to each other ex- rr, RR |
| dominant | when two contrasting characters are brought together in an offspring the character that is expressed is the one that is coined as dominant |
| it is the allele that influences the appearance of the phenotype even in the presence of an alternate allele | |
| recessive | it is the trait that will only be manifested if two identical alleles compose a pair of chromosomes |
| mutation | it is the chemical change in the gene which can be inherited |
| variation | it is a result of crossing over which leads to genetic diversity and enables us to differentiate between two individuals of the same race |
| phenotype | it is the physical appearance of an organism which is controlled by genetic composition |
| genotype | it is the genetic composition of an organism |
sex determination in humans
XX- female
XY- male
sex linked inheritance
x linked- haemophilia and colour blindness.
if only one X has carries the gene it can be covered by the dominant X, so therefore that particular offspring would only be a carrier of the gene, which would be expressed if it forms an offspring with a partner having the same disorder.