BIOL 1001 Lecture 10: Chapter 10 Part 2 of 2
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Testcross is the breeding of an organism of unknown genotype with a homozygous recessive organism. According to the law of independent assortment, genes for different characters are inherited independently of each other. The parental crosses that mendel did in his earlier experiments involved parental varieties that differed in a single trait (i. e. , monohybrid crosses) In later experiments, mendel crossed parental varieties that differed at two characters: dihybrid cross. Yellow (y__) is dominant to green (yy) (smooth yellow ball ) x ( wrinkled green ball ) F1 ssyy (dominant trait yellow & smooth) By using plants that were true-breeding (homozygous) for two different characters, mendel tested how the traits for these characters segregated. He hypothesized that the two characteristics would either segregate together (null hypothesis), or they would segregate independently (alternative hypothesis). If genes segregated together then the f2 will show a 3:1 phenotype. Combinations from sy and sy gametes if genes segregated together :