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Mendel & Meiosis

Mendel & Meiosis. 2011. Gregor Mendel – Just the Facts. 1822 – 1884 “Father of Genetics” Studied pea plant inheritance at an Austrian monastery. Why pea plants? They only have seven chromosomes They grow quickly & traits can be easily observed. Possible Traits of Pea Plants.

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Mendel & Meiosis

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  1. Mendel & Meiosis 2011

  2. Gregor Mendel – Just the Facts • 1822 – 1884 • “Father of Genetics” • Studied pea plant inheritance at an Austrian monastery. • Why pea plants? • They only have seven chromosomes • They grow quickly & traits can be easily observed

  3. Possible Traits of Pea Plants • Seed Shape – Round or wrinkled • Seed color – yellow or green • Seed coat color – gray or white • Pod shape – smooth or constricted • Pod color – green or yellow • Flower position – axial or terminal • Plant height – tall or short

  4. Mendel’s Conclusions • Conclusion #1: The Principle of Dominance – • Mendel concluded that some forms of a gene or trait are dominant over other traits, which are called recessive. • A dominant trait will mask or hide the presence of a recessive trait. • Ex: Tall vs. Short pea plants in book; Yellow vs. green peas in our demonstration today. • ALSO CALLED: Mendel’s First Law of Inheritance

  5. Mendel’s Conclusions, cont’d… • Conclusion #2 – The Principle of Segregation • Mendel concluded that when forming sex cells, the paired alleles separate so that each egg or sperm only carries one form of the allele. • The two forms of the allele come together again during fertilization. • Ex: Tall x Tall – giving us 3 tall: 1 short; Yellow vs. Green – giving us 3 yellow: 1 green • HOW THE ALLELES SEPARATE IS RANDOM! • ALSO CALLED: Mendel’s Second Law of Inheritance • Mendel's Laws of Inheritance 1 & 2

  6. Mendel’s Conclusions, cont’d… • Conclusion #3 – The Principle of Independent Assortment • Mendel concluded that each pair of alleles segregates independently during the formation of the egg or sperm. • What this means is: offspring can possess combinations of genes that neither parent possesses. • ALSO CALLED: Mendel’s Third Law of Inheritance

  7. Some Important Vocabulary • Haploid (n)– a cell with one copy of each chromosome (half the number needed for life) • Diploid (2n) – a cell with two copies of each chromosomes (one from mom + one from dad) 23 46

  8. Meiosis – Why? • Meiosis – a cell division that produces gametes with half the number of chromosomes. 46 23 46 23 92 46

  9. Meiosis – Where? • Meiosis occurs in the reproductive organs – • It happens to reproductive cells! (Egg & Sperm)

  10. Meiosis – Number of Divisions • Two divisions – • Meiosis I • Meiosis II • Total of 8 stages (4 each – PMAT)

  11. Meiosis: The Basics • Parent Cell

  12. Interphase I • DNA Replication

  13. Meiosis I • Prophase I – Crossing-over occurs • Crossing-over = the exchange of genes between homologous chromosomes. • Homologous Chromosomes Separate • End Result:

  14. Interphase II • No need for chromosomes to make a copy, they are already there!  • Cell just “hangs out”

  15. Meiosis II • Chromatids (copies) separate • Four new cells are formed. • Each contains half the original number of chromosomes as the original cell.

  16. Mitosis Vs. Meiosis

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