Genes are units of inheritance that determine the characteristic of an individual.
The characteristic of individuals that are controlled by genes include the colour and type of hair, types of ear lobes, being right-handed or left-handed and many more.
genes are found in long molecules called deoxyribonucleic acids (DNA).
DNA molecules are found in chromosomes.
Chromosomes are thread-like structures in the nucleus of a cell.
Each chromosome contains a long DNA molecule enveloped by protein.
Chromosomes exist in pairs, so do genes. Each pair of genes controls one characteristic of an individual.
Phenotype- characteristic which express
Genotype- a pair of allele
Dominant gene- genes that show their effects whenever they are present
Recessive gene-genes that only show their effects in the absence of dominant genes.
Dominant trait- characteristic which express when the present of dominant gene.
Recessive trait- characteristic which express when the absent of dominant gene.
Heterozygous alelle-different allele (H,h)
Homozygous alelle-same allele (H,H),(h,h)
MANDEL’S FIRST LAW:
Mandel’s First Law describes the monohybrid cross of a pea plant. When a dominant homozygous pure breed was cross by recessive homozygous pure bread the first generations have the same genotype which is heterozygous.
For example, the purple flower is dominant and yellow flower is recessive. A purple flower pure breed (PP) was cross by a yellow flower pure breed (pp). All the first generations were heterozygous (Pp) which express purple flower. This process is explained by the diagram below: