Using Punnett Squares to Solve Genetics Problems Topics

Using Punnett Squares to Solve Genetics Problems Topics for today: What is a genetics problem? Alleles, Dominance, Meiosis Gregor Mendel Punnett squares Solving genetics problems

Vocabulary List Dominant Characteristic Recessive Variations Gene Parents Allele Offspring Genotype Cross Phenotype Offspring ratios Trait Sex chromosome Independent assortment Sexual reproductions Homozygous Asexual reproduction Heterozygous

Traits and variation What are traits and some examples of traits? Discontinuous variation vs continuous variation Your turn: What are examples of discontinuous and continuous variation in humans

What is a genetics problem Chromosomes and genes Dominant and Recessive alleles Terms to know: Genotype and Phenotype Homozygous and Heterozygous Your turn: Why are the mechanics of meiosis important in studying genetics?

Gregor Mendel (1822 -1884) Austrian monk “Father of genetics” Studied several traits in pea plants Noticed that some traits could be skipped on one generation but reappear in later generations

Punnett Squares Parents have two genes, one on each chromosome. During meiosis, those genes are randomly separated so each gamete has only one copy of each gene. There are four possible combinations of offspring Your turn: Why are there three purple but only one white offspring?

Punnett Squares Your Turn: What is the Phenotype ratio? What is the Genotype ratio? Are there really only 4 offspring?

Nidoran Genetics

Nidoran Genetics Horns are a dominant trait over no horns. Make a cross between two Nidorans, both heterozygous for horns. If only one baby Nidoran is born, what is the chance that it will have a horn? If it has a horn, what is the chance that it is a carrier of the no-horn gene?

Practice Question 1 Make the following crosses Homozygous dominant Nidoran male with horns crossed with a homozygous recessive Nidoran female without horns. Homozygous dominant female Nidoran with a heterozygous male. Heterozygous female Nidoran mated with a male Nidoran with out horns. For each scenario answer the following questions: What is the genotype ratio? What is the phenotype ratio? Have all possible genotypes and phenotypes been expressed?

Practice Question 2 Nidoran Spots The gene for dark spots (S) is dominant to light spots (s) I have a Nidoran Male with dark spots but I don't know if it is homozygous or heterozygous. What sort of female could I mate my Nidoran with to see what alleles it has for spots? Why would this be the best choice? Draw a Punnet square to show the cross. If we had a litter of 10, how many dark and light spotted Nidorans would you expect if the male was homozygous? Heterozygous?