The Contribution of Mendel
Demonstrated that inherited characteristics are carried by discrete units that are reassorted in each generation.
Pea Plant Experiment
Performed experimental crosses with pure bred pea plants
Pea Plant Experiment
Discovered that first generation offspring all showed only one of two alternative traits.
Example: Pure breeding tall crossed with pure breeding short produced ALL tall.
MENDEL’S SEVEN F1 CROSSES ON PEA PLANTS
Pea Plant Experiment
Mendel allowed first generation offspring to self-pollinate. Discovered that the trait which had disappeared in the first generation reappeared in ¼ of the plants in the second generation. Example: Self-fertilizing tall plants produced ¾ tall plants and ¼ short plants
Dominant
Characteristics that appeared in the entire F1 generation and 75% of the F2 or “second filial” generation “Overshadows” recessive traits
Recessive
Characteristics that did not appear in the F1 generation, but reappeared in 25% of the F2 generation Is “overshadowed” by dominant trait
Mendel’s Law of Segregation
The hypothesis that every individual carries pairs of factors for each trait and that the members of the pair separate during the formation of gametes
Alleles
The different forms of a gene. Chromosomes are made up of DNA DNA is made up of genes Genes are made up of alleles Example of Gene:
gene for flower color
Example of Allele:
purple or white version of the gene
A pair of homologous chromosomes. Each chromosome carries a gene for a trait, eye color. The chromosome on the left carries the allele for brown eyes, whereas the chromosome on the right carries the allele for blue eyes. During meiosis, each homolog will go to a different cell; the genes will segregate.
Which allele does this gamete carry?
Which allele does this gamete carry?
The Principle of Independent Assortment
Of all possible allele combinations, only one of the alleles for the given trait can be passed to the offspring and it is done completely at random.
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