What is Genetics?

I. Heredity & Genetics The passing of traits from parent to offspring Traits are controlled by genes, so therefore, GENETICS is the study of how traits are inherited through the action of alleles

II. ALLELES Are ONE FORM of a gene (there can be more than one form) Sex cells have one form of a gene on their chromosomes Body cells have two forms or ALLELES for a single gene (you got one from Mom and one from Dad) One may be dominant over another. If this happens, the dominant gene is the one expressed. If not, the recessive trait is expressed.

III. DOMINANT AND RECESSIVE A Dominant trait will always be expressed and will “mask” a recessive trait A recessive trait can only be expressed if there are no dominant alleles present.

Example: Eye color—Brown color is dominant and blue is recessive Example: Eye color—Brown color is dominant and blue is recessive. - A person can have a brown allele and a blue allele but still have brown eyes because the brown allele is dominant and “hides” the blue allele.

Example: R= dominant r = recessive Generally, dominant alleles are represented with a capital letter, and recessive alleles are represented with a lowercase letter. Example: R= dominant r = recessive

The alleles present in the organism are referred to as its genotype The alleles present in the organism are referred to as its genotype. For example, BB, Bb, or bb. The PHYSICAL trait that shows, regardless of genotype is called a phenotype. For example, Blue or Brown Eyes.

IV. GREGOR MENDEL First known geneticist and “father of genetics” Was an Austrian monk and was born in 1822 Did most of his genetic studies on pea plants He made careful observations, and strictly adhered to the scientific method

He performed cross-pollination by becoming the pollinator himself, and controlling which plants mixed. Some traits Mendel worked with were shape of pea and it’s pod, color and shape of seeds, plant height, flower position and flower color.

VI. Using a Punnett Square In Punnett squares, dominant traits are represented with a CAPITAL letter, and recessive traits represented by a LOWER CASE letter. -Take for example, eye color. Choose to represent eye color with the letter b. Big B or “B” for dominant and little b or “b” for recessive.

Each organism is represented by TWO letters, one for each allele. “Purebred” species have two of the same allele (trait).This is called homozygous. For example: BB or bb. Species with two different alleles would have two different “letters” and by called “heterozygous”. For example: Bb

Steps for using the Punnett square: One parent’s alleles (genotype) go along the top, one allele above each box. The other parent’s alleles go down the side. One allele next to each box. You fill in the squares with the alleles that are in front of that box. Example:

Steps for using the Punnett square: Let’s say the parents are Bb and Bb(the same genotype). What would be their phenotype? Brown Eyes So you would predict: 1/4 offspring to be BB, or Brown Eyes 2/4 or 1/2 to be Bb, or Brown Eyes and 1/4 to be bb or Blue eyes B b BB Bb bb B Color in the boxes where the offspring would have brown eyes. *What is the chance the offspring would have brown eyes? __/4 boxes or % b

Practice Problem #1 Predict the fur color of the offspring of a white heterozygous hamsters and a brown homozygous hamster. White is dominant. Brown is recessive. Use the letter “F”.

Practice Problem #2 Predict the offspring of 2 white homozygous cats. Black is dominant over white. Use the letter “B”.

Practice Problem #3 Predict the offspring of 2 Grey Heterozygous rats. Gray is dominant over white, which is recessive. Use the letter “G”.