Transcript Slide 1
Genetics Review Heterozygous vs. Homozygous Review Homozygous Heterozygous Tt Yy Ff rr QQ GG Ss hh PP mm Bb Ll dd Genotype vs. Phenotype B = brown eyes b = blue eyes What would the genotype be for an individual who is heterozygous? What would the phenotype be for an individual who is heterozygous? If a person has blue eyes, what is their genotype? Step-by-step guide to Punnett Squares -Punnett squares are used to predict the results of a genetic cross -For a monohybrid cross, you will start with a four-square Punnett square: -Then place the alleles of the parents on the outside of the square example cross: Tt x tt (tall x short) tt t t T T t t Tt -Next...fill in the boxes: 1. 3. 2. 4. -Now, summarize the results: Genotypes: Tt tt Phenotypes: tall short 50% or 1/2 50% or 1/2 50% or 1/2 50% or 1/2 Practice Question #1 Let's say that in seals, the gene for the length of the whiskers has two alleles. The dominant allele (W) codes long whiskers & the recessive allele (w) codes for short whiskers. a) What percentage of offspring would be expected to have short whiskers from the cross of two long-whiskered seals, one that is homozygous dominant and one that is heterozygous? b) If one parent seal is pure long-whiskered and the other is short-whiskered, what percent of offspring would have short whiskers? Answers to Practice Question #1 A) B) Practice Question #2 In purple people eaters, one-horn is dominant and no horns is recessive. Draw a Punnet Square showing the cross of a purple people eater that is hybrid for horns with a purple people eater that does not have horns. Summarize the genotypes & phenotypes of the possible offspring. Answers to Practice Question #2 genotypes: phenotypes: Question 1 (5) Which of the following represents the phenotype of an organism? A) BB B) brown eyes C) homozygous dominant D) monohybrid Question 2 (5) If you crossed two heterozygous organisms, what percentage of the offspring would be homozygous recessive? A) 25% B) 50% C) 75% D) 100% Question 3 (5) Which of the following genotypes is homozygous dominant? A) Bb B) bB C) bb D) BB Question 4 (5) If you cross two heterozygous brown-eyed people, what percentage of the offspring would have brown eyes? A) 25% B) 50% C) 75% D) 100% Question 5 (5) In a Punnett square, what do the letters in the inner boxes represent? A) the mom B) the dad C) the actual offspring D) the expected offspring Vocabulary Review one of each allele for a trait monohybrid the trait that is hidden (in heterozygous) the genetic makeup of an organism genotype a cross showing one trait dihybrid the physical appearance of the trait heterozygous homozygous dominant the trait is expressed in both hetero and homozygous two of the same alleles for a trait recessive phenotype a cross showing two traits