- The form of the trait that masks the other in the F1 is dominant (S). The trait that disappears in the F1 is recessive (s). • For a given trait, a parent can be either homozygous with two identical alleles or heterozygous with two different alleles. • According to Mendel’s law of segregation, a parent can only donate one allele of the two alleles per gamete. • Because of the law of segregation, when two heterozygotes are crossed, three different genotypes and two different phenotypes result. This process results in recombination.

- In the experiment on the left, the true-breeding plants in the parental generation are homozygous (have two identical alleles for a given trait). The smooth-seed plant is designated SS and the wrinkled-seed plant is designated ss. - The smooth-seed plant can only contribute an S allele and the wrinkled-seed plant can only contribute an s allele to the F1 offspring. The resulting F1 offspring are heterozygous (have two different alleles for a given trait), having the designation Ss. The F1 plants display the smooth-seed trait. - The trait that masks the other in the F1 generation is the dominant trait. The one that disappears is the recessive trait - The genotype is the allelic composition of the trait in question. The phenotype is the physical manifestation of the trait. The chart on the left shows all of the possible genotypes that may result in the F2 generation and the resulting phenotypes. The chance of two independent events can be determined by multiplying the probability of their separate occurrences together. Because each sperm or egg type has a 1/2 probability of occurring, the probability of each genotype occurring is 1/2 X 1/2 = 1/4. For example the probability of a sperm containing an S allele is 1/2. The probability of an egg containing an S allele is 1/2. The probability of the events co-occurring, resulting in an SS offspring, is 1/2 X 1/2 = 1/4. - Three genotypes and two phenotypes are possible. Note that the SS and Ss genotypes have the same phenotype. The ratio of smooth to wrinkled seeds is 3:1. The genotypes occur in a 1:2:1 ratio.

- According to the law of segregation, each parent can only donate one allele of the two per gamete. Because the F1 plants are heterozygous they can contribute two different kinds of gametes to the F2 offspring. The sperm may contain either an S or s allele. Similarly the egg may contain either an S or s allele. There is a 50% likelihood for each gametic contribution. - For a heterozygous cross, there are four possible combinations (shown on the left). The probability for each combination occurring is 1/4 (= 1/2 X 1/2).

Which of the following statements is true?

- The dominant trait will be the phenotype of the individual if it has one dominant gene and one recessive gene.

9.1.4 Mendel's Conclusions: Segregation and Recombination Flashcards by Irina Soloshenko

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9.1.4 Mendel's Conclusions: Segregation and Recombination Flashcards

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