Genetics

Cells are controlled by the nucleus, which contains all the DNA (the molecule that controls everything about the organism.).
DNA is arranged into chromosomes (they look like an X). Another way to say this is that the chromosome is made up of DNA.
Segments of DNA are called genes. Genes control traits.

During sexual reproduction, traits are passed when sex cells (egg and sperm) from parents join together to make a new organism (offspring). Each sex cell (egg or sperm) contains one-half of the genetic material needed to create a new organism.

***This means that even though you might resemble one parent more than the other, you still have HALF of your genetic information from your biological mom and the other half from your biological father.***

Genes and Alleles

Genes that control a trait come in pairs.
Each half of that gene pair is called an allele.
One allele comes from the father. One allele comes from the mother. Together they make one gene for the offspring.
Alleles of one trait are represented as single letters (ex: G or g).
Genes are represented as a combination of two alleles (GG, Gg, or gg).

Genotype vs. Phenotype

Genotype—the set of genes carried by the organism represented by a two letter combination (BB, Ff, hh, Nn, LL, rr, etc)
Phenotype—the physical expression of the genes...what you actually see about the organisms (blue eyes, brown hair, purple flowers, 6 legs, etc).
The genotype will determine the phenotype. In other words, the set of genes will cause a specific trait to be shown.

Heterozygous vs. Homozygous

A genotype may be Homozygous (aka Purebred) - the organism has two copies of the same allele in its genotype (HH, hh).

A genotype may be Heterozygous (aka Hybrid) - the organism has two different alleles in its genotype (Hh).

Dominant vs. Recessive

If the genotype of an organism has a capital letter, the phenotype (appearance) of the trait will be Dominant. (Dd, DD-both of these genotypes will have dominant phenotypes)
If the genotype of an organism does not have a capital letter, the phenotype (appearance) of the trait will be Recessive. (dd-this genotype will have a recessive phenotype)
Heterozygous organisms have both a dominant allele and recessive allele (Bb). They will show the dominant phenotype, but they will be carriers of the recessive gene, so the recessive phenotype may show up in their children. It is as if the dominant allele hides the recessive allele.

Page updated

Report abuse