Important terms:

1. Aneuploidy à Failure of segregation of chromatids during cell division cycle resulting in
    the gain or loss of a chromosome(s), called aneuploidy.
2. Polyploidy à Failure of cytokinesis after telophase stage of cell division results in an increase in a whole set of chromosomes in an organism and this phenomenon is known as polyploidy. This condition is often seen in plants.
3. Heterosis à When hybrid shows superiority over parents.
4. Trisomyà When an additional copy of a chromosome is present (2N + 1)
5. Monosomy à When one chromosome of any pair of chromosomes is absent. (2N – 1)
6. Polygenic trait à The trait which is controlled by three or more than three genes is polygenic.

For example: Human skin color is controlled by AABBCC alleles. AABBCC is for dark and aabbcc is for light color.

7. Pleotrophy → When a single gene exhibit multiple characters is Pleotrophy. Example: Phenyl Ketonuria. Here a single gene manipulation causes many disorders like skin color changes, hair loss, mental retardation and change in Pigmentation.
8. Homozygous →When both alleles of a gene are same, then individual is homozygous. For example; TT or tt , one pair  is fully dominant and other  pair is fully recessive.
9. Heterozygous →When both alleles of individual are dissimilar, then individual is called heterozygous. For example; Tt, here one allele is dominant and other is recessive.
10.  Dominant → The phenomenon where one allele expresses itself even at the presence of other allele.
11.  Recessive → The phenomenon where an allele expresses itself when other dominant allele is absence, but remains invisible in others presence.