Mendelian Genetics

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Mendelian Genetics

* Pea plants have several advantages for genetics.
* Pea plants are available in many varieties with distinct heritable features (characters) with different variants (traits). * Another advantage of peas is that Mendel had strict control over which plants mated with which. * Each pea plant has male

(stamens) and female
(carpal) sexual organs.
* In nature, pea plants typically
self-fertilize, fertilizing ova
with their own sperm.
* However, Mendel could also
move pollen from one plant
to another to cross-pollinate
plants.
* In a typical breeding experiment, Mendel would cross-pollinate (hybridize) two contrasting, true-breeding pea varieties. * The true-breeding parents are the P generation and their hybrid offspring are the F1 generation. * Mendel would then allow the F1 hybrids to self-pollinate to produce an F2 generation. * It was mainly Mendel’s quantitative analysis of F2 plants that revealed the two fundamental principles of heredity: the law of segregation and the law of independent assortment. 2. By the law of segregation, the two alleles for a characters are packaged into separate gametes * If the blending model were correct, the F1 hybrids from a cross between purple-flowered and white-flowered pea plants would have pale purple flowers. * Instead, the F1 hybrids

all have purple flowers,
just a purple as the
purple-flowered
parents.
* When Mendel allowed the F1 plants to self-fertilize, the F2 generation included both purple-flowered and white-flowered plants. * The white trait, absent in the F1, reappeared in the F2. * Based on a large

sample size, Mendel
recorded 705
purple-flowered F2
plants and 224
white-flowered F2
plants from the
original cross.
Vocab:
* Character –heritable feature
* Trait – each variant for a character
* True-breeding – plants that self-pollinate all offspring are the same variety *...
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