Chapter 12
Mendel's Experiments and Heredity
By Boundless
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While working with pea plants, Gregor Mendel noticed that offspring were similar to their parent plants, which led him to some of the earliest theories about genetics.
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The garden pea has several advantageous characteristics that allowed Mendel to develop the laws of modern genetics.
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Mendel's crosses involved mating two true-breeding organisms that had different traits to produce new generations of pea plants.
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Mendel's experiments with peas revealed the presence of dominant and recessive traits in the filial generations.
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The rules of probability can be applied to Mendelian crosses to determine the expected phenotypes and genotypes of offspring.
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Genes exist in pairs within an organism, with one of each pair inherited from each parent.
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The observable traits expressed by an organism are referred to as its phenotype and its underlying genetic makeup is called its genotype.
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A Punnett square applies the rules of probability to predict the possible outcomes of a monohybrid cross and their expected frequencies.
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With the inclusion of incomplete dominance, codominance, multiple alleles, and mutant alleles, the inheritance of traits is complex process.
A gene present on one of the sex chromosomes (X or Y in mammals) is a sex-linked trait because its expression depends on the sex of the individual.
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Inheriting two copies of mutated genes that are nonfunctional can have lethal consequences.
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Mendel formed the Laws of Heredity (the Law of Segregation and the Law of Independent Assortment) from his pea plant experiments.
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In a heterozygote, the allele which masks the other is referred to as dominant, while the allele that is masked is referred to as recessive.
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Mendel's Law of Segregation states that a diploid organism passes a randomly selected allele for a trait to its offspring, such that the offspring receives one allele from each parent.
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Independent assortment allows the calculation of genotypic and phenotypic ratios based on the probability of individual gene combinations.
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Genes that are on the same chromosome, or "linked", do not assort independently, but can be separated by recombination.
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Epistasis occurs when one gene masks or interferes with the expression of another.