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Introduction to Genetics Who was Gregor Mendel? • He was known as the “FATHER OF GENETICS” • He discovered how traits were inherited Genetics: The study of heredity, how traits are passed from parent to offspring or x = or Mendel’s Peas • Mendel did his study on pea plants • Pea plants have many traits (tall/short, purple flowers/white flowers) • Pea plants can be self-fertilized or cross-fertilized • Mendel crossed (bred) tall pea plants with short pea plants. Predict what the offspring were like. Tall x Short ? Mendel allowed the F1 plants to self-pollinate Types of Plants 1.True-Breeding - these plants always create plants that look like themselves 2.Hybrids – offspring of truebreeding plants Tall x Short = Hybrid Dominance Some traits are dominant over others. Tall x Short = all tall offspring (hybrids) *Tall is the dominant trait * Short is recessive Genes and Alleles Mendel discovered that each trait is controlled by two factors (alleles) Genes – factors that determine your traits There are three basic kinds of genes: –Dominant - A gene that is always expressed and hides others –Recessive - A gene that is only expressed when a dominant gene isn’t present –Codominant - Genes that work together to produce a third trait GENOTYPE - what genes, letters, the organism has (TT, Tt, tt) PHENOTYPE - what it looks like (tall or short) Dominant and Recessive Genes • A dominant gene will always mask a recessive gene. • A “widows peak” is dominant, not Widows Peak having a widows peak is recessive. • If one parent contributes a gene for a widows peak, and the other parent doesn’t, the offspring will have a widows peak. Punnett Square - A tool we use for predicting the traits of an offspring • Shows all of the possible combinations of alleles from the parents Alleles: different forms of the same gene • Organisms have two alleles for each gene (one from each parent) – Letters are used as symbols to designate genes – Capital letters are used for dominant genes – Lower case letters are used for recessive genes – Genes always exist in pairs Ex) Tall pea plants x short pea plants (TT) (tt) genotype TALL SHORT T T t tT tT t tT tT offspring 100% tall (tT) Ex) Tall pea plants x tall pea plants (tT) (tT) genotype TALL TALL T t T TT tT t tT tt offspring ¾ tall – 75% ¼ short – 25% All organisms have two copies of each gene, one contributed by the father, the other contributed by the mother. Homozygous – same alleles (TT, tt) Heterozygous – different alleles (tT) A Widows Peak, dominant, would be symbolized with a capital “W”, while no widows peak, recessive, would be symbolized with a lower case “w”. Father - No Widows Peak - w Mother - Has a Widows Peak - W For the widows peak: WW - has a widows peak Ww - has a widows peak ww - no widows peak Homozygous dominant Heterozygous Homozygous recessive Since Herman has no widows peak, he must be “ww”, since Lilly has a widows peak she could be either “WW” or “Ww” Definitely ww Either Ww or WW Homozygous recessive Heterozygous Homozygous dominant We can use a “Punnet Square” to determine what pairs of genes Lilly has • A Punnet Square begins with a box 2 x 2 Assume Lilly is heterozygous Ww Assume Herman is homoozygous recessive ww • One gene is called an “allele” W w w Ww ww w Ww ww • One parents pair is split into alleles on top, the other along the side • Each allele is crossed with the other allele to predict the traits of the offspring Notice that when Lilly is crossed with Herman, we would predict that half the offspring would be “Ww”, the other half would be “ww” Half “Ww”, Heterozygous, and will have a widows peak Half “ww”, Homozygous, and will not have a widows peak W w w Ww ww w Ww ww Genetics Another possibility is that Lilly might be “WW”, homozygous dominant. Assume Lilly is homozygous dominant WW W Assume Herman is homoozygous ww W w Ww Ww w Ww Ww Notice that all the offspring are heterozygous and will have a widows peak So which is true? Is Lilly homozygous dominant (WW) or is she heterozygous (Ww)? W w W W w Ww ww w Ww Ww w Ww ww w Ww Ww If Lilly were heterozygous, then 1/2 of their offspring should have a widows peak, 1/ shouldn’t 2 If Lilly were homozygous, all of their children will have a widows peak W w W W w Ww ww w Ww Ww w Ww ww w Ww Ww Recall that Herman and Lilly had another offspring, Marylin. She had no widows peak, therefore, Lilly must be heterozygous. Hair color is a perfect example of a trait Prince Charming is blond Snow White has dark hair What color hair should their children have? Hair color is different from widows peak, no color is truly dominant. – Brown and blond are the two, true traits – Homozygous conditions produce either brown or blond hair – Heterozygous conditions produce red hair For Snow White to have brown hair she must be homozygous dominant, “BB”, a blond Prince Charming must be homozygous recessive, “bb”. B B b Bb Bb b Bb Bb All the offspring from Prince Charming and Snow White will therefore be heterozygous, “Bb”, and since hair color is codominant….. all their children will have red hair. +