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Life Science Genetics Genetics The study of heredity, how traits are passed from parent to offspring or x = or Genetics Small sections of DNA are responsible for a “trait”. These small sections are called “Genes”. – Gene - A segment of DNA that codes for a specific trait – Trait - A characteristic an organism can pass on to it’s offspring through DNA Gene The study of heredity started with the work of Gregor Mendel and his pea plant garden Mendel was an Austrian Monk that lived in the mid 1800’s Mendel noted that the size of pea plants varied. He cross-bred these pea plants to find some surprising results. Mendel’s cross between tall pea plants yielded all tall pea plants. His cross between small pea plants yielded all small pea plants. X = X = Mendels’ cross between tall pea plants and small pea plants yielded all tall pea plants. x = Mendel then crossed these second generation tall pea plants and ended up with 1 out 4 being small. x = Mendel’s work led him to the understanding that traits such as plant height are carried in pairs of information not by single sets of information. The pairs are called alleles. They can be dominant or recessive. Genetics Types of genes: – Dominant - A gene that is always expressed and hides others. Stronger form of the trait. Written as a capital letter. (D) – Recessive - A gene that is only expressed when a dominant gene isn’t present. Weaker form of ones traits. Written in lower case. (d) – Alleles-One of the forms of a gene, may be dominant or recessive. (D or d) – Genes always exist in pairs. DD, Dd, dd Genetics All organisms have two copies of each gene, one contributed by the father, the other contributed by the mother. Homozygous - Two copies of the same gene (DD, dd) = purebred Heterozygous - Two different genes (Dd) = hybrid Dominant and Recessive Genes • • • • A dominant gene will always mask a recessive gene. “widows peak” = dominant (W) no “widows peak” = recessive (w) If one parent contributes a gene for a widows peak, and the other parent doesn’t, the offspring will have a widows peak. Widows Peak Genetics A Widows Peak, dominant, would be symbolized with a capital “W”, Mother - Has a Widows Peak - W while no widows peak, recessive, would be symbolized with lower case “w”. Father - No Widows Peak - w Genetics For the widows peak: WW - has a widows peak Ww - has a widows peak ww - no widows peak Homozygous dominant Heterozygous Homozygous recessive Genetics 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 Phenotype – an organisms appearance. Example: Brown eyes, Blue eyes Genotype – an individual’s combination of alleles for a trait. Example: BB, Bb, bb Genetics 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 Genetics 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 Genetics 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 Genetics 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 Genetics Recall that Herman and Lilly had another offspring, Marylin. She had no widows peak, therefore, Lilly must be heterozygous. Genetics So, back to the original question. What color hair will the offspring of Prince Charming and Snow White have? Genetics 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 Genetics For Snow White to have brown hair she must be homozygous dominant, “BB”, a blond Prince Charmin must be homozygous recessive, “bb”. B B b Bb Bb b Bb Bb Genetics 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. + Cell Division (Meiosis) 1. A process of cell division where the number of chromasomes is cut in half 2. Occurs in gonads (testes, ovaries, stamens, etc) 3. Makes gametes (sperm, ova, pollen, etc)