Inheritance is the transmission of genetic information from generation to generation.

• Chromosomes: Located in the nucleus of cells.
  • Thread-like structures of DNA, carrying genetic information in the form of genes.
• Gene: Short length of DNA found on chromosome, that codes for a specific protein.
  • e.g., Structural protein such as collagen found in skin cells, enzyme or hormones.
• Allele: Different versions of a particular same gene.
  • e.g., THE ABO gene for all blood group type has three alleles: $I^A,I^B,I^O$
    • Alleles give all organisms their characteristics.

TL;DR | Cell contains chromosome, chromosome contains DNA, DNA contains alleles of genes, Genes are made up from bases.

Chromosomes

Sex is determined by an entire chromosome pair.

Female have the XX Sex Chromosomes; Males have the XY Sex Chromosomes.

As only males can pass on the Y chromosome, he is responsible for determining the sex of child.

— The inheritance of sex can be shown using a genetic diagram: Punnett Square.

Haploid & Diploid Cells

All humans have 23 different chromosomes in each cell.

In most body cells, excluding gametes, we have two copies of each chromosome — 23 x (2 Pairs) = 46 chromosomes. | Diploid

The gametes have only one copy of each chromosome, meaning they only have a total of 23 chromosomes in each gamete cells. | Haploid

Mitosis

Mitosis is a type of cell division.

When cells, excluding gametes, divide, their chromosomes double beforehand. 46 * 2 = 92

This ensures when cell splits into two, each new cell still has two copies of each chromosome, ensuring it is still diploid. This is called Mitosis. 92 ÷ 2 = 46

Defined: Nuclear division giving rise to genetically identical cells.

Importance: All cells in the body excluding gametes are produced by mitosis of zygote.