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Journal: Use punnett squares to answer the following questions. Use your notes and punnett practice from last class for help. 1. Cross a heterozygous brown furred male with homozygous recessive white furred female. a. What percentage of offspring will be brown? b. What percent will be white? c. What is the ratio of brown to white? d. What percentage of offspring will be BB? e. What percentage of offspring will be Bb? f. What percentage of offspring will be bb? g. Which is dominant brown fur or white? h. Give an example of a genotype from this scenario. i. Give an example of a phenotype from this scenario. • In pea plants, purple flowers are dominant over white flowers. Cross a homozygous dominant plant with a homozygous recessive plant. What percentage of offspring will be purple? What percent will be white? • Cross two offspring produced in #3. What are the genotypes and phenotypes produced? Express this in ratios and percentages. GENETICS DAY 3 DIHYBRID CROSSES & EXCEPTIONS TO MENDELIAN GENETICS DIHYBRID CROSSES • Cross involving two pairs of alleles. Uses 16 boxes • EX: round seeds R are dominant over wrinkled seeds (r). Yellow seeds (Y) are dominant over green seeds (y). – Parent generation = RRYY x rryy • F1 generation produces all dominant traits. – RrYy • F2 generation produces a mix of traits – RrYy x RrYy •Ratio is 9:3:3:1 EXCEPTIONS TO MENDELIAN GENETICS • INCOMPLETE DOMINANCE • Neither allele is completely dominant • Both alleles combine equally to give a new trait. • Called hybrids • EX: red flower crossed with white flower produces pink flower. • CODOMINANCE • Both alleles are expressed • EX: cross a black chicken with a white chicken, offspring will be black and white checkered. DAILY QUIZ #3 1. Cross out quiz #3 on the front of your quiz sheet. 2. On the back of your quiz sheet, complete the following dihybrid cross: GgRr x GgRr JOURNAL #3 • John has red hair and blue eyes. His two brothers and one sister have brown hair and brown eyes. Explain how this is possible. Use punnett squares to show how he might have inherited each trait.
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