Transcript Document
Genetics Standard S7L3: Recognition of how biological traits are passed on to successive generations Genetics The study of heredity, how traits are passed from parent to offspring or x = or The study of heredity started with the work of Gregor Mendel and his pea plant garden Heredity is study of passing traits from parents to offspring. 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. -Carrying the information are chromosomes. -Chromosomes are made up of sections called genes. -Genes are made up of DNA EQ: What were Mendel’s experiments with inherited traits? • 1st Generation Plants • 1st group of offspring from cross-pollination • Dominant Trait • Trait observed in the 1st generation when parents with different traits are bred • Recessive Trait • Trait that reappears in the 2nd generation after disappearing in the 1st generation when parents with different traits are bred • Mendel’s 2nd Experiment • Recessive trait did not show up as often as the dominant trait • Expressed as a ratio DNA D.N.A. - Deoxyribonucleic Acid Molecule made of: 1. Deoxy Sugar 2. Combination of four nitrogen bases Either: a. Guanine b. Cytocine c. Thymine d. Adenine The sum total of combinations that these four bases are capable of creating are greater than all the stars visible in the night time sky DNA • Nitrogen bases pair up – Cytosine & Guanine – Thymine & Adenine • Pairing creates a ladder shape • Angle of bonds creates a twist Ladder and Twist produces the famous “Double Helix” DNA Cell • DNA resides in all cells – Inside the nucleus • Each strand forms a chromosome Nucleus DNA DNA DNA is found in all living cells – It controls all functions inside a cell – It stores all the genetic information for an entire living organism – Single cell like an amoeba – Multi cell like a human 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 Genetics Hair color is a perfect example of a trait What color hair should their children have? Prince Charming is blond Snow White has dark hair Genetics 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 Genetics Dominant and Recessive Genes • A dominant gene will always mask a recessive gene. • A “widows peak” is dominant, not 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. Widows Peak Genetics Punnet Square - A tool we use for predicting the traits of an offspring – 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 Genetics 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 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 Heterozygous - Two different genes 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 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. + EQ: How are genes and alleles related to genotype and phenotype? • Phenotype • An organism’s appearance • Hides the nondominant alleles • Genotype • Entire genetic makeup of an organism • The combination of genes for one or more traits 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)