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Understanding Test Crosses and Pedigrees in Genetics

This resource explores the concepts of test crosses and pedigrees, essential tools in genetics for determining an organism's genotype and mapping inheritance patterns. A test cross involves breeding an individual of unknown genotype with a homozygous recessive to reveal hidden traits. Pedigrees serve as visual family trees, illustrating genetic relationships and traits across generations. Examples with dogs and pea plants highlight how to determine genotypes and phenotypes, while specific questions delve into familial relationships portrayed in pedigrees.

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Understanding Test Crosses and Pedigrees in Genetics

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  1. Biology Genetics Test crosses & Pedigrees

  2. What is a Testcross? • Method used to determine an unknown organisms genotype • Involves crossing an unknown organism with a homozygous recessive • If any of the offspring are recessive, then the unknown parent had to carry recessive traits so was heterozygous.

  3. What is a pedigree? • Pedigrees: graphic representation of family tree • May be used if testcross cannot be made • Pedigree key: • = male • = female • = marriage • Children = connected to marriage by vertical life • = recessive male/female (bb) • = heterozygous ½ shaded, ½ unshaded

  4. Suppose in dogs, Long tongue (L) is dominant over short (l) and Short hair (H) is dominant over long hair (h). What gene combinations could be found in a dog that is LLHh? • LH, Lh • LH, lH, lh, Lh • LH only • In pea plants, round seeds (R) are dominant to wrinkled (r) and yellow seeds (Y) are dominant to green seeds (y). What is the phenotype of the box labeled A? (Hint: figure out the genotype first then phenotype.) a. Round, yellow b. Round, green c. Wrinkled, green A

  5. What relationship exists between Jim & Kay? • They are brother and sister • They are married • Jim is Kay’s uncle • What does a shaded circle represent? a. Female with a disease/disorder b. Female without a disease/disorder • What is Joe’s genotype? a. BB b. Bb c. bb • What must Tom’s genotype be? (Hint: Look at the genotypes of his two sons) • BB b. Bb c. bb

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