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Presentation on theme: "Genetics."— Presentation transcript:

1 Genetics








9 1866- published findings on plant breeding and inheritance
Gregor Mendel “Father of Genetics” 1866- published findings on plant breeding and inheritance (During American Civil War) Not discovered until early 1900s

10 Keys to Success Used “True-Breeding” pea plants (“purebreds”)
Always produce offspring with only one form of a trait Studied only 1 characteristic at a time Analyzed data mathematically

11 Pea Plant Reproduction
Self-pollination Pollen fertilizes egg cells on same flower 1 parent Cross-pollination Pollen from flower of one plant fertilizes egg cells on another plant 2 parents

12 Mendel controlled breeding by cross-pollinating
To prevent self-pollination, Mendel removed male parts from a flower and dusted the flower with pollen from a different pea plant

13 Genetics: The science of heredity Heredity: The biological inheritance of traits from parent to offspring

14 Genetics used for: Preventing & treating diseases Developing tougher plants to increase food production

15 Generations F1 generation F2 generation
P generation: parent generation “true - breeding” F1 generation First generation of offspring F2 generation Second generation produced when f1 generations are crossed

16 Allele The different forms of a gene 2, 3, or even 12 possible alleles per gene

17 Dominant Form of the gene that is expressed Capital letter: T

18 Recessive Form of a gene (allele) that is only expressed in homozygous state Lowercase letter: t

19 Homozygous 2 identical alleles for the same trait Homozygous dominant: TT Homozygous recessive: tt

20 Heterozygous 2 different alleles for the same trait Tt : dominant trait will be expressed Also called a “hybrid”

21 Genotype Genetic make-up of an organism The “letters” Tt or TT or tt Aa or AA or aa

22 Phenotype Physical expression of a trait Ex: Tall or Short

23 Examples: TT = genotype Tall = phenotype tt = genotype Short = phenotype

24 Law of segregation The two alleles for each trait separate during meiosis So, for each gene, an organism receives one allele from each parent - during fertilization

25 Part 2

26 Seed Color P generation cross: (“true - breeding”)
Yellow peas x Green peas F1 generation: All yellow F2 generation: 6022 yellow : 2001 green 3 yellow : 1 green

27 Monohybrid cross Use a Punnett square to cross 2 hybrids: Yy x Yy
What are the possible genotypes? What is the genotypic ratio? What is the phenotypic ratio?

28 Law of Independent Assortment
Genes on separate chromosomes sort independently during meiosis Alleles for seed shape separate independently from seed color alleles So, seed shape is not connected to seed color

29 Dihybrid cross A Special type of two - factor cross YyRr x YyRr
(heterozygous for both traits) You will always find the same phenotypic ratio. What is this ratio?

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