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Mendel - • The expression of the trait that results in...

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Mendel's first law: Law of Segregation Mendel did not formulate his conclusions as laws or principles of genetics, but later researchers have  done so. Restating and using modern, standardized terminology, this is the information that  developed and expanded from his early experiments. Inherited traits are encoded in the DNA in segments called  genes , which are located  at particular sites (  loci , singular  locus ) in the chromosomes. (Genes are Mendel's  “factors.”)  Genes occur in pairs called  alleles , which occupy the same physical positions on  homologous chromosomes; both homologous chromosomes and alleles segregate during  meiosis, which results in haploid gametes.  The chromosomes and their alleles for each trait segregate independently, so all  possible combinations are present in the gametes.
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Unformatted text preview: • The expression of the trait that results in the physical appearance of an organism is called the phenotype in contrast to the genotype , which is the actual genetic constitution. • The alleles do not necessarily express themselves equally; one trait can mask the expression of the other. The masking factor is the dominant trait, the masked the recessive . • If both alleles for a trait are the same in an individual, the individual is homozygous for the trait, and can be either homozygous dominant or homozygous recessive. • If the alleles are different—that is, one is dominant, the other recessive—the individual is heterozygous for the trait. (Animal and plant breeders often use the term “true-breeding” for homozygous individuals.)...
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