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Mendelian Genetics and Gene Concepts

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  • Blending hypothesis

    The idea that genetic material from two parents blends together in offspring, producing a uniform mixture.

  • Particulate hypothesis

    Genes retain their separate identities through generations and can be separated again, as shown by Mendel's pea plant experiments.

  • True-breeding

    Organisms that produce offspring identical to themselves when self-pollinated or crossed with the same genotype.

  • Mendel's Law of Segregation

    Two alleles for a heritable character separate during gamete formation, so each gamete carries only one allele.

  • Dominant allele

    An allele that determines the organism's appearance when present, masking the effect of a recessive allele.

  • Recessive allele

    An allele that has no noticeable effect on the organism's appearance when paired with a dominant allele.

  • Genotype vs. Phenotype

    Genotype is the genetic makeup; phenotype is the observable physical or physiological traits.

  • Homozygous

    Having two identical alleles for a particular gene (e.g., PP or pp).

  • Heterozygous

    Having two different alleles for a particular gene (e.g., Pp).

  • Testcross

    Crossing an organism with a dominant phenotype but unknown genotype with a homozygous recessive individual to determine the unknown genotype.

  • Law of Independent Assortment

    Alleles of different genes assort independently during gamete formation, applying to genes on different chromosomes or far apart on the same chromosome.

  • Incomplete dominance

    Heterozygous phenotype is intermediate between the two homozygous phenotypes.

  • Codominance

    Both alleles are fully expressed in heterozygotes, such as in ABO blood groups.

  • Multiple alleles

    More than two allelic forms of a gene exist in a population, e.g., ABO blood group alleles.

  • Pleiotropy

    One gene influences multiple phenotypic traits, such as the sickle-cell gene affecting blood and other organs.

  • Epistasis

    One gene affects the expression of another gene, as seen in Labrador coat color inheritance.

  • Polygenic inheritance

    Multiple genes contribute to a single phenotypic character, producing quantitative variation, e.g., human height.

  • Environmental impact on phenotype

    Phenotype can be influenced by environmental factors in addition to genotype, leading to multifactorial traits.

  • Pedigree analysis

    A chart used to track inheritance patterns of traits in humans and other organisms across generations.

  • Recessively inherited disorders

    Disorders that appear only in individuals homozygous for the recessive allele, e.g., cystic fibrosis and albinism.

  • Dominantly inherited disorders

    Disorders caused by dominant alleles, such as achondroplasia and Huntington's disease.