Coordinated Science 2

Genetics

The study of heredity in biology is called Genetics. Heredity is the passing of traits to offspring; from it's parents or ancestors.

A quick note: that the offspring acquire/become predisposed to the characteristics of it's parent cell/organism. And that the variations exhibited by individuals can build up over time and cause a species to evolve.

Some important Vocabulary:

Phenotype - physical characteristics; height, color, texture, etc.
Genotype - genetic makeup; particular set of genes
Allele - are 2 forms of a gene; the one that masks the other is called dominant and the alternative is the recessive.
Homozygous - the same alleles of the gene are on both homologous chromosomes; YY or yy
Heterozygous - 2 different alleles are in the gene's position on the homologous chromosomes; Yy

When doing a test cross, such as a Punnett Square, there are 2 possible crosses to predict.

Mono-hybrid: only looking at 1 particular trait in an organism. Such as the one to the right
Di-hybrid: looking at 2 traits in an organism. Such as the example below.

The above Punnett Square is of a di-hybrid cross, in which you are looking at 2 different traits.

Round and Yellow = dominant
Wrinkled and Green = recessive

Co-Dominance And Incomplete Dominance

Both are results of a cross between 2 organisms, but the traits of the organisms differ.

Co-dominance is a cross between organisms with 2 different phenotypes and results offspring with a 3rd phenotype, in which both of the parental traits appear.

Incomplete Dominance is a cross between organisms with 2 different phenotypes and the result is offspring with a 3rd phenotype that is a blending of the parental traits.

The above picture is an example of Incomplete Dominance, which results in a combined phenotype displayed in the offspring. The picture shows, a red flower and a white flower producing offspring that are pink. Red + White = Pink, so it's incomplete.

The picture is an example of Co-dominance, in which both of the parental traits appear. In the picture, 2 parents have 2 different blood types; Dad = AO and the Mom = BO. They have 4 children and only 1 displays the characteristics of co-dominance. One of their daughters has the blood type, AB, which is a combination of the parents blood types.

Gregor Johann Mendel was a famous Austrian monk and scientist, who lived from 1822 - 1884. He is known as the
"Father of Genetics" for his study of inheritance traits in pea plants, showing these inheritances followed certain laws. He also devised fundamental tool called the "Test Cross".

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Test Cross

Is an experimental cross of 2 organisms;

One has a dominant phenotype and an unknown genotype
Another has a homozygous recessive genotype and phenotype

An example of a Test Cross, would be using a Punnett Square, like the one above. Punnett Squares are used to predict the likelihood that a cross will produce a particular trait.

The above cross is between 2 purple flower with purple, being the dominant trait and white the recessive.