Genetics Terms

Genes - Segments of Dna which code for proteins There are different forms of genes. Each “form” of the same gene is called an allele.

Gene- segment of DNA that codes for a certain protein/trait Allele- different forms of the same gene (ex: white or purple)

Examples: Gene for Hitchhiker's Thumb: Gene for earlobe shape: Allele for Hitchhiker’s Thumb Allele for Non-Hitchhiker’s Gene for earlobe shape: Allele for attached earlobes Allele for detached earlobes

Each organism receives 2 alleles for each gene: 1 from mom 1 from dad

Complete dominance When a trait exhibits complete dominance, one allele is dominant over the other. The non-dominant trait is called the recessive allele. NOTE  Dominant does NOT mean more common. Dwarfism is a dominant trait and is not more common. We represent dominant alleles with capital letters. We represent recessive alleles with lower case letters. Example: E = Widow’s peak e = Straight hair-line

How many dominant alleles do you need for the dominant trait to be shown? How many recessive alleles do you need for the recessive allele to be shown?

Rules of inheritance Dominant traits only need 1 dominant allele to be visible. EE = widow’s peak Ee = widow’s peak (only need 1 capital E) Recessive traits need 2 recessive alleles to be visible. ee = straight hairline

How would you define heterozygous and homozygous?

Homozygous= 2 of the same allele; either 2 dominant or 2 recessive Terms to know Homozygous= 2 of the same allele; either 2 dominant or 2 recessive Also called purebred Examples: TT cc dd YY Heterozygous = 2 different alleles Examples: Bb Hh Ll Rr Also called hybrid

Purebred Homozygous BB bb

HYBRID Bb Ff Gg

Homozygous or heterozygous? Purebred -when the same traits are seen generation after generation Hybrid- when the traits seen in the offspring are different than the parent generation Homozygous or heterozygous?

Homozygous or heterozygous? Mom Dad Homozygous or heterozygous? Child

How would you define genotype & phenotype?

Phenotype- physical or visible characteristics Genotype- genetic composition of alleles

Definitions Genotype = organism’s allele combinations (always 2 letters) Examples: GG, Tt, bb Phenotype = organism’s physical appearance Think PHENO = PHYSICAL Examples: Tall, short, round peas, wrinkled peas

Phenotype or Genotype? Green eyes Widow’s Peak Aa Tail length Attached earlobes GG Ff tt

GENOTYPE PHENOTYPE BB Bb White fur In one species of wild cat, black fur is dominant to white fur. Fill in the chart in your notes. GENOTYPE PHENOTYPE BB Bb White fur

Mendel’s Experiment Gregor Mendel crossed (bred) pea plants to study how traits are passed to offspring. Cross Terms P – parent generation F1 – offspring of P generation F2- offspring of F1 generation

Mendel’s Laws 1. The Law of Dominance: In a cross between contrasting homozygous individuals, only one form of the trait will appear in the F1 generation - this trait is the dominant trait.

2. The Law of Segregation: during the formation of gametes, alleles responsible for a trait separate; one allele is receive from each parent (in gametes).

3. The Law of Independent Assortment: - alleles responsible for different traits are distributed to gametes (and thus the offspring) independently of each other

21. Lupe grows pea plants in her garden 21. Lupe grows pea plants in her garden. The pea plants have flowers that can be either purple or white, with purple color being dominant to white color. The peas produced by Lupe's pea plants can also be either round or wrinkled, with round peas being dominant to wrinkled peas. Lupe crosses two pea plants that are heterozygous for both traits. If a gamete from this cross receives a dominant allele for flower color, how does this influence the probability of the gamete receiving a dominant allele for pea shape? (Assume that the genes for flower color and pea shape follow the law of independent assortment.)         

Decreases probability Gamete can’t receive the allele Lupe crosses two pea plants that are heterozygous for both traits. If a gamete from this cross receives a dominant allele for flower color, how does this influence the probability of the gamete receiving a dominant allele for pea shape? No effect Decreases probability Gamete can’t receive the allele Increases probability

A. No effect! Because the alleles sort independently into gametes, they do not affect the reception of the second allele.

A Punnett Square is a tool used to predict the offspring from a cross. Uses the laws of probability Probability- describes how likely it is that an event will occur Each outcome is equally likely to occur despite previous outcomes Each allele combination is equally likely to occur because the alleles sort independently

When crossing 2 heterozygotes with complete dominance, you get the following ratios always: 1:2:1 Genotypic 1 Homozygous dominant (25%) 2 Heterozygous (50%) 1 homozygous recessive (25%) 3:1 Phenotypic 3 dominant phenotype (75%) 1 recessive phenotype (25%) Mendelian Ratios B b BB Bb bb

Test Cross We use a test cross when we have an organism with an unknown genotype and we cross it with a homozygous recessive organism.

- Blue = dominant - Yellow = rec - Blue = dominant - Yellow = rec. Results from testcross: 50% blue 50% yellow

Heterozygous Homozygous b B Bb bb b B Bb

Monohybrid Crosses Looks at only 1 characteristics/gene Basically, all the problems we’ve been doing b B Bb bb