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MENDEL AND THE GENE IDEA

MENDEL AND THE GENE IDEA. Unit 3 - Chapter 14. Gregor Mendel Augustinian, Teacher and Scientist 1822 - 1884. Born in Heinzendorf Moravia in what is now the Czech Republic. Received agricultural training

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MENDEL AND THE GENE IDEA

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  1. MENDEL AND THE GENE IDEA Unit 3 - Chapter 14

  2. Gregor MendelAugustinian, Teacher and Scientist1822 - 1884 • Born in Heinzendorf Moravia in what is now the Czech Republic. • Received agricultural training • Entered the Augustinian Monastery of St. Thomas at Br?nn (now Brno) at the age of 22 and was ordained to the priesthood in 1847. • Taught science in secondary school fot the next 20 years • Performed experiments in the monastery garden which were to result in his discovery of the basic laws of heredity. His findings were published in 1866. Using the garden peas for his subject, Mendel's studies in "plant hybridization" proved the existence of paired elementary units of heredity (now called genes) and established the statistical laws governing them. • Subsequent scientists have refined his conclusions and discovered the system of particulate heredity by units or genes.

  3. WHY PEA PLANTS? • He already knew a lot about plants • Pea plants come in many varieties, so many traits can be studied • Pea plants have “perfect” flowers – both sex organs in the same flower. This gave him complete control over the plant mating

  4. STYLE CARPEL

  5. Characteristics • Eye Color • Eye shape • Skin Color • Skin type / texture • Hair Color • Hair type/ texture • Shape of mouth • Length of nose • Nostril size • Height of cheekbones • Jawbone width

  6. Blue-eyed Brown-eyed Attached Lobe Unattached Lobe Widow’s Peak Traits

  7. Homologous chromosomes, genes, alleles

  8. Genetic Crosses • The hybridization (mating) of two traits of one characteristics For example: Blue-eyed man mates a brown-eyed woman OR White-flowering pea plant mated with a purple-flowering pea plant

  9. Genetic Crosses, cont’d • Monohybrid – only traits of one characteristic are compared • Dihybrid – traits of two characteristics are compared

  10. Genetic Terminology • Dominant – an allele that expresses itself instead of it homologue • Recessive – an allele that is silent, or whose homologue is expressed • Homozygous – having two identical alleles of the same gene • Heterozygous – having two different alleles of the same gene • Genotype – the genetic (allelic) makeup of an organism • Phenotype – the expression of the alleles (This is a result of genotype) • True breeding – when the trait in question has been observed for many generations (pure bred)

  11. The 7 Characteristics Mendel Chose

  12. Experimental Method

  13. Number of heterozygous chromosome pairs This is a constant (number of homologues) Some Basics Before We Move Along The Generations • P = Parental generation • F1= First Filial or 1st generation of offspring • F2 = Second Filial or 2nd generation of offspring How does one determine what kind of gametes will be formed? 2n This formula can only be applied to non-linked genes.

  14. Independent Segregation of Alleles

  15. The Punnett Square Reginald C. Punnett, inventor of the Punnett Square

  16. Mendel’s Monohybrid cross

  17. Mendel’s Dihybrid cross

  18. Mendel’s Test Cross When Mendel did not know the genotype of an individual expressing a dominant trait, he did a test cross by crossing the individual with a homozygous recessive for the trait.

  19. Recessively Inherited Diseases in Humans • The disease occurs only if the individual inherits 2 recessive alleles from his parents • If the individual has only one recessive allele, he is not affected, but is considered a “carrier” Examples: Tay Sach’s, Cystic Fibrosis, Sickle-cell anemia

  20. Dominantly Inherited Diseases in Humans • The individual needs only one harmful allele to be affected • Lethal diseases inherited in this manner are less common because its effects are obvious (except for Huntington’s Disease – nervous system degeneration – due to its late onset in life at ~age 45) • Examples of Non-lethal diseases: Achondroplasia (dwarfism)

  21. When are Punnett Squares not useful? When only two pairs of genes are involved, you can solve the problems with Punnett squares. With three or four or more pairs of genes, the phenotype distribution begins to resemble a bell-shaped curve; then it's easier to estimate or "eye-ball" predictions.

  22. Discussed in next chapter Other Patterns of Inheritance • Incomplete dominance • Co-dominance • Pleiotropy • Epistasis • Polygenic Inheritance • Sex-Linked Inheritance (X-linked)

  23. Incomplete Dominance This is when one allele is “silent” and the other allele cannot produce the complete effect on its own.

  24. Co-Dominance (Multiple Alleles)

  25. Pleiotropy When one gene causes multiple effects: Sickle Cell Anemia

  26. Epistasis When one gene at one locus alters the Phenotypic expression of another gene at a different locus

  27. POLYGENIC INHERITANCE This is when the phenotype is affected by more than one pair of genes. This affects other characteristics like skin color, shoe size and intelligence Today, scientists have actually located 3 genes that play a role in eye color determination.

  28. GENETIC TESTING AND COUNSELING • Carrier Recognition • Fetal Testing - Amniocentesis - Chorionic Villus Sampling (CVS) • Newborn Screening

  29. THE END

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