Mendel's First Law - Law of Segregation

1. Gene exists in alternative forms; which are different versions of the genes that impart the same characteristics. For an example; the gene that specifies the hair color can be (B) for black or (b) for blonde.
2. For each trait/characteristic an organism inherits two alternative forms of that gene, one from each parent. Alternative form of a gene is referred to as alleles. In Mendel’s experiment with the pea plants, he crossed pea plants with green pods (GG – also referred to as true breeding green pod plant) with ones with yellow pods (gg – also referred to as true breeding yellow pod plant ) the resulting offspring’s all had (Gg – heterozygous) genotypes.
3. Paired alleles for each characteristic will segregate during gamete formation. As a result each gamete will contain only one allele for each gene. Thus allowing combination of maternal and paternal alleles during fertilization. . For example, the sex cell for the green pod plant has a single (G) allele and the sex cell for the yellow pod plant has a single (g) allele. After fertilization the resulting F1 plants will have two alleles (Gg).
4. If two alleles differ, then the dominant allele will be expressed and seen in the phenotype of the organism over the allele encoding the recessive trait. In the case of Green and yellow pod plants we can observe that the green color gene (G) is dominant over yellow (g). Therefore plants with the genotype (Gg) will contain green colored pods. But it should be highlighted here that not all traits have the dominant-recessive relationship. Like in the case of Human blood types where A and B are codominant while O is recessive. Codominance or incomplete dominance results in the intermediate from.

References:

Mendelain inheritance. (n.d.). Retrieved July 12, 2007, from Website: http://en.wikipedia.org/wiki/Law_of_segregation