Biology 1 Spring Semester 2015 Heredity Biology 1 Spring Semester 2015

Standard 7: Heredity Objectives: complete a punnett square with the parents already determined (B) Given the phenotypes or genotypes of two parents, be able to analyze the possible outcome of monohybrid genetic cross. (P) Upon completion of a monohybrid cross, the student can demonstrate understanding that the results of that cross are the probabilities of specific traits an organism could inherit. (P)

Genetics video….. Let's Explore the World of Genetics

Origin of Genetics Gregor Mendel Genetics- the study of biology that focuses on heredity So what is heredity? Heredity- the passing of traits from parents to offspring

Mendel’s Results

Where to begin…. DNA of course! DNA holds segments of genes that hold the genetic traits of that individual. It’s important to know that there are two parts to every trait. Those parts are called alleles. So in sexual reproduction, the female passes down one allele for every trait and so does the male.

Inheritance of Genes The offspring inherits one allele from it’s mom and one allele from its dad for every trait. Parent Parent YY Meiosis yy gametes Y Y y y Yy

Rules of Inheritance Each parent gives one allele to its offspring that can either be dominant or recessive depending upon what the parents alleles are. Dominant- expressed form of the trait Recessive- not expressed when the dominant form of the allele is present (hidden) When two alleles join together during fertilization, the offspring has inherited a random combination of the parents’ alleles for that trait.

Using letters to practice knowing the difference between dominant and recessive alleles: 1st- let’s pick a trait…. A person’s height. 2nd- Understand that the gene for height has two alleles (one allele inherited by mom and one from dad) Since scientists know that tallness is dominant to shortness we will use the capital letter “T” for dominant We will use the lowercase letter “t” for recessive

Now that we know what letters to use, we need to understand how to characterize the trait: Homozygous- two alleles of a trait present are the same (both dominant- TT or both recessive- tt) Ex. A plant with dominant alleles for tallness(TT) is called homozygous dominant. So the plant will be tall. Ex. A plant with both recessive alleles for shortness is called homozygous recessive. So the plant will be short.

Characterizing the trait, cont. Heterozygous- the alleles of a trait are different- (One is dominant and the other is recessive- Tt) Ex. A plant with a dominant allele and a recessive allele for tallness is heterozygous and will express the tall trait.

More vocab---difference between what’s in the genes and what you actually see… Genotype- the set of alleles that an individual has for a characteristic Ex. I have two dominant alleles for tongue rolling, so my genotype is TT Phenotype- the physical characteristics that an individual displays Ex. The fact that you can see the tongue rolled.

More examples…. Genotype Phenotype Ex. I am heterozygous for a widows peak, so my genotype is Ww. Phenotype Ex. The fact that you can see the widows peak. (or not see it!)

Let’s practice the difference between: homozygous/heterozygous and dominant/recessive in a genetic cross. Mendel used pea plants so let’s use those traits.

What if we crossed….. (use the chart on pea plants and remember to use the letter for the one that is dominant.) 1. Two plants that are heterozygous for green pods. Genetic cross: _____X_____ 2. Cross a homozygous tall plant with a short plant. Genetic cross: ______X______ 3. Cross a plant that is heterozygous for round seed shape with a plant that has wrinkled seeds. Genetic Cross: ______X______

What are the outcomes of those crosses? Remember that it is random for what ever allele the parents pass down for a trait. So there needs to be a way to determine the possible outcomes for the individual offspring. Glad you asked…. We use a Punnett Square!

Studying Genetics Punnet squares- a diagram that predicts the outcome of a genetic cross by considering all possible combinations of gametes in the cross 1.write the gametes of one parent at the top of the square 2.write the gametes of the other parent at the side of the square 3. combining the alleles in each box 4. determine the genotypic and phenotypic ratio

Let’s practice!

Monohybrid Cross Genetic Cross: ______X______ Genotypic Ratio: _______________ Phenotypic Ratio: