16. Intro to Genetics

  Today we started learning about genetics. This unit is very similar to the Hardy Weinberg principle we learned. For every inherited trait (features) of an organism (all traits are inherited through meiosis or mitosis), there must be an unique type of gene in the DNA to provide instruction to determine the features, and those genes are called "alleles". If one allele overrides another in the organism, the allele is called dominant allele, and the other allele is called recessive allele. For example, if the allele for black hair for human is dominant, and allele for blond hair is recessive, a man with heterozygous alleles will have black hair, but the allele for blond hair is in the man as well. Therefore we say that the genes shown on the surface is phenotype, and the genes inside the organism is genotype.

 
    This diagram shows an example of monohybrid cross. In the diagram, T is the dominant allele and t is the recessive allele. If the father and mother are both heterozygous, the ratio of genotypes would be 1 homozygous dominant: 2 heterozygous: 1 homozygous recessive. The ratio of phenotypes would be 3 dominant: 1 recessive.

  This diagram shows an example of dihybrid cross with 2 traits. In the diagram, A & B are the dominant alleles and a & b are the recessive alleles. If the parents are AABB and aabb, all the F1 generation are heterozygous for both traits. Through self-pollination, the F1 generation will breed the next generation (F2), which has a phenotypic ratio of 9 dominant/dominant: 3 dominant/recessive: 3 recessive/dominant: 1 recessive/recessive.

- Andy Liu '15