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Mendelism: The Basic Principles of Inheritance Asmarinah.

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1 Mendelism: The Basic Principles of Inheritance Asmarinah

2 Gregor Johann Mendel ( ) explained how the characteristics of organism are inherited His ideas was published under: “Experiment in Plant Hybridization” His discoveries coined a new term to describe the study of heredity: genetics (Greek word, meaning: to generate

3 Mendel’s Law (consist of 3 part) 1. The Principle of Dominance “In heterozygote, one allele may conceal the presence of another” -Dominant and recessive forms are called alleles (Greek word meaning: of one another) - Alleles are alternate forms of a gene

4 2. The Principle of Segregation “In a heterozygote, two different alleles segregate from each other during the formation of gametes” Both of Mendel’s law I and II, it can be explained by monohybrid crosses

5 Mendel crossed tall vs dwarf pea plant: -Tall male vs dwarf female -Dwarf male vs tall female Monohybrid crosses

6 Explanation: - Two reciprocal crosses gave same result: tall plant - Dwarf characteristic seemed disappeared in the progeny -After self-fertilization, result: tall and dwarf plant (with ratio of approximately 3 : 1) -Hybrids carried a latent factor for dwarfness and expression factor for tallness  latent factor: recessive expression factor: dominant

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8 - Each trait is controlled by a hereditary factor that existed in two forms, one dominant and the other recessive - These factor are now called genes, a word coined by Wilhelm Johannsen (1909) -Each of reproductive cell (or gamete) contain only one copy of a gene for each trait. A particular gamete could have either the recessive or dominant allele for a given trait, but not both. -Consequently, one of the alleles that governed each trait is inherited from female parent and the other allele is inherited from male parent

9 Important conclusion from Mendel’s experiment:  Genes come in pairs -The parental strain carried two identical copies of a gene  diploid - During the production of gametes, these two copies are reduced to one, so that its carry a single copy of a gene  haploid - The hybrid between father factor and mother factor (zygot) would inherit two different alleles, called heterozygot

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11 3. The Principle of Independent Assortment The alleles of different genes segregate or assort, independently of each other  it can be explained by dihybrid crosses Aim of dihybrid crosses  To see if the two seed trait (color and texture) are inherited independently Each trait is controled by a different gene segregating two alleles, and two genes are inherited independently

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13 Application of Mendel’s Principles It can be used to predict the outcome of crosses, by 3 alternative methods: 1.The Punnet Square Method 2.The Forked-line Method 3.The Probability Method

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15 Mendelian Principle in Human Genetics Application of Mendel’s principle in human genetics is limited The genetic analysis of human heredity depends on family records  pedigree

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17 Pedigree Convention


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