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Mendel's Laws of Heredity

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Jeff Kriske

on 28 April 2011

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Transcript of Mendel's Laws of Heredity

Mendel's Laws of Heredity Who was Gregor Mendel? An Austrian Monk who studied heredity in the 1800s. First to predict how traits are transferred
from parent to offspring. The Experiment Why peas? Peas reproduce sexually, producing male and female sex cells called gametes. When the male and female gametes unite, fertilization occurs. The fertilized cell is called a zygote. When pollen transfers from the male reproductive organ to the female reproductive organ, pollination occurs. In peas, both male and female reproductive organs are in the same flower and surrounded by petals. Because of this, Mendel could control which plants were bred together. Mendel took pollen from one plant and dusted it onto another. This is called cross-pollination. Then What? Mendel picked tall pea plants from populations of plants that had always been tall. He did the same with the short plants. He then crossed the tall plants with the short plants to create hybrids. Hybrids are the offspring of parents that have different forms of a trait, such as tallness and shortness. Pea Plants: The First Generation
The offspring of one tall plant and one short plant grew to be tall, as though the short plant never existed! The Second Generation
Mendel then allowed the tall plants from the first generation to self-pollinate. Three-fourths of the plants in this second generation grew tall, while the remaining one-fourth were short. So what does it all mean? Mendel concluded that each organism has two factors that control each of its traits. Those factors are called genes, which are located on chromosomes. Different gene forms are called alleles. One allele is inherited from the mother and one from the father. The Rule of Dominance
Dominant traits are observable in the offspring, masking the recessive trait.
Recessive traits are the traits that disappear.
In Mendel's experiment, tall is the dominant trait. Short is the recessive. The Law of Segregation
Every individual has two alleles of each gene and when gametes are produced, each gamete receives one of these alleles. During fertilization, these gametes randomly pair to produce four combinations of alleles. Two organisms can look the same but have different allele combinations. The way an organism looks is called its phenotype. An organism's allele combination is called its genotype. If an organism has two identical alleles, it is homozygous. For instance, a true-breeding tall plant that had two alleles for tallness (TT) would be homozygous for the height trait. TT=dominant homozygous
tt=recessive homozygous If an organism has two different alleles for a trait, it is heterozygous. A tall plant with one allele for tallness and one for shortness (Tt) is heterozygous. But wait, there's more! Mendel's Dihybrid Crosses Di=2.
Mendel took true-breeding pea plants with round yellow seeds and crossed them with true-breeding wrinkled green seeds. First generation: All round, yellow seeds.
Second generation produced four different
kinds of seeds:
1. Round Yellow
2. Round Green
3. Wrinkled Yellow
4. Wrinkled Green Law of Independent Assortment:
Genes for different traits are inherited independently of each other.
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