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MENDEL & GENETICS Peas, Peas, Peas, Peas Studying Mendel’s Peas (Sing to tune of “Eating Goober Peas”) Gregor Mendel • 1822-1884 • Austrian monk • High school science teacher • Discovered laws of inheritance Gregor Mendel • Studied pea plants • Easy to study • Many traits only have 2 forms • 7 different traits • • • • • • • Stem height Seed shape Seed color Seed coat color Pod shape Pod color Flower position A Closer Look at Pea Traits • Stem Height • 2 forms • Tall stems • Short stems • All traits have 2 forms, a dominant & a recessive 2 types of Alleles (forms of a trait) • Dominant allele • Always shows up if present • Recessive allele • May be present but masked if paired with a dominant allele • Only shows up if paired with another recessive alleles Examples of common traits • Tongue rolling • Can roll tongue - dominant • Can’t roll tongue - recessive • You have 2 alleles for this trait Where do your alleles come from? • One from mom • One from dad What does this mean? • If you can roll your tongue, you have either • 2 dominant alleles Or • 1 dominant and 1 recessive What does this mean? • If you can’t roll your tongue, you have • 2 recessive alleles MENDEL & GENETICS PART 2 CHROMOSOMES & YOUR CELLS Where do they come from? Chromosomes & Body cells • All cells have chromosomes • Number of chromosomes for an organism is unique • Humans - 46 chromosomes • Dogs - 78 chromosomes • Silkworms - 56 chromosomes How do they get there? • By mitosis, of course! • Remember - mitosis creates new cells that are identical to the original cell • So that means a cell with 46 chromosomes will create a new cell with 46 chromosomes! But what about our sex cells? • Sex cells are created through a process called meiosis • New cells have half the number of chromosomes • New cells are not identical to original cells Why is this important? • Remember, all organisms have a unique number of chromosomes • On offspring may not survive if the number of chromosomes is incorrect Why is this important? (con’t) • Think about how you were created, a sperm fertilized an egg. • The sperm donated half the chromosomes (23) • The egg donated the other half of the chromosomes (23) So why is it important that sex cells have half the number of chromosomes? Your turn to write an answer