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Mendelian Genetics

Explore Mendel’s work on single-gene inheritance, gene expression, genome, genotype, and phenotype in an informative guide on Mendelian genetics. Learn about Mendel’s observations, rediscovery, and Laws of Heredity. Uncover the significance of dominant and recessive alleles, homozygous and heterozygous traits, and the laws of dominance, segregation, and independent assortment. Discover the foundation of modern genetics through Mendel’s groundbreaking research on pea plants.

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Mendelian Genetics

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  1. Mendelian Genetics

  2. Genetics • Genetics: The study of heredity. • Trait: A heritable characteristic. • Gene: • a portion of DNA that determines a characteristic • Composed of nucleotides • Locus = location on chromosome • 2 per characteristic on autosomes

  3. Single Gene Inheritance Patterns • Allele: • sequence of genetic material occupying the same gene locus on homologous chromosomes • Or…alternative forms of the same gene

  4. Single Gene Inheritance • Genome: set of all genes necessary to specify an organism’s characteristics • Genotype: listing of all genes present • Phenotype: the way alleles express themselves – i.e. what you see

  5. Pea Soup? • Experiments done by Gregor Mendel using garden pea plants helped demonstrate how traits are inherited. • A purebred individual receives the same characteristics from both parents. • A hybrid individual receives different forms of a trait from each parent.

  6. Gene Expression • Dominant allele: masks effect of other alleles • Recessive allele: masked by dominant alleles • Homozygous: 2 identical alleles • Heterozygous: 2 different alleles Recessive alleles are not less likely to be inherited, however they must be homozygous to be expressed.

  7. Mendel’s Laws of Heredity • Gregor Mendel: 1822-1884 • Followed one trait at a time. • Used highly visible traits; therefore easy to track his research. • Since pea plants self-pollinate, may develop plants that are homozygous for many traits - Pure Line.

  8. Mendel Rediscovered • Mendel’s work was not recognized during his life; his unpublished studies were “resurrected” in the early 1900’s. • His work is remarkable in that he did not know anything about genes, much less chromosomes, yet was able to reason the existence of alleles through his careful observations and recording of data. This is real science.

  9. Mendel’s observations • Mendel observed 7 traits of pea plants, alone and in various combinations: • Flower Color • Flower Position • Pea Color • Pea Shape • Pea Pod Color • Pea Pod Shape • Height of Pea Plant

  10. Mendel’s Laws of Heredity • Mendel artificially pollinated plants to produce crosses and documented results. • All offspring were identical to parents – unexpected finding. • Crosses of offspring yielded: 3/4 showed phenotype of dominant gene.

  11. Mendel’s Laws of Heredity • Law of Dominance: when an organism has 2 different alleles for a given trait, the allele that is expressed is considered dominant. The other allele is recessive.

  12. Mendel’s Laws of Heredity • Law of Segregation: when gametes are formed by a diploid organism, the alleles that control a trait separate from one another into different gametes, retaining their individuality.

  13. Mendel’s Laws of Heredity • Law of Independent Assortment: Members of one gene pair separate from each other independently of the members of other gene pairs.

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