General Genetics/Basics of Heredity

Heredity is basically the passage of traits from a P ( parental) generation onto its offspring. Genetics is intimately related to reproduction and a knowledge of reproduction will facilitate your learning of genetics.

Reproduction
Reproduction is continuation of life. What reproduction does is transmit the hereditary information found in all cells of an organism, namely DNA. There are 2 types of reproduction, asexual and sexual. Asexual reproduction is the propagation of a single organism. That organism recreates itself and all its offspring are identical to it. Sexual reproduction promotes change and requires 2 organism to fuse gametes ( reproductive cells with genetic information) to create offspring that are different from their parents.

Genetic information is packaged into a unit known as a chromosome. A chromosome is made up mostly of DNA and proteins that make up its structure. Chromosome is a very general term. Humans have X shaped chromosomes, e. coli has a circular chromosome known as a plasmid. From these chromosomes and through DNA cells can construct an entire organism. It is a very efficient and elegant system that oversees the life of all organisms from tiny cells to humans.

In sexual reproduction, 2 organisms fuse gametes to make up the genetic information for their offspring. Examples of gametes are sperm and eggs. Gametes each contain half the genetic information their parents had. This means they are haploid ( haploid - half ploid) is represented by 1n. To be useful you need 2 gametes to fuse and a make a diploid ( di, two ploid) zygote ( 2n). From the zygote will be born the organism.

Chromosomes
Chromosomes are the carriers of genetic information. Most mammalian organisms have an arrangement of diploid chromosomes. They exist in pairs, carrying homologous genetic information. That is they carry different versions of the same thing. Let's say there was a plant with only 1 pair of chromosomes. One chromosome has the allele for blue stem color and the other chromosome has an allele for green stem color (an allele is a subunit of a chromosome, its an alternate version of a gene -in this case stem color). In the end, only one of these alleles are expressed ( more on this later) but they are both present in this organism.