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Transcript
Genetics The Study of Heredity Cell Division Cells Divide for two reasons: 1. Growth 2. Reproduction The Cell Has a nucleus Nucleus contains: 1. Chromosomes: carries and protects the DNA. 2. A single strand of DNA: blueprint of life (carries the code) Chromosomes with DNA Chromosomes Human cells have 23 pair (46 total) Camels 35 pair Porcupines 17 pair Dogs 39 pair Leopard frog 13 pair Fruit fly 4 pair Potatoes 24 pair Human Karyotype Mitosis Cell division for growth One cell copies its DNA (chromosomes) Grows and expands The two strands of DNA (inside chromosomes) to opposite sides of cell. Cell membrane splits dividing cytoplasm. 1 cell to 2 cells Mitosis Meiosis Cell division for reproduction Forms sperm and egg Chromosome numbers half. (Haploid) Mitosis occurs Then the two cells split again splitting chromosome pairs. 1 cell to 2 cells to 4 repro. cells. Meiosis History of Genetics Gregor Mendel Priest in monastery in Central Europe Studied Pea Plants Why? 1. Have many traits that occur in only two forms (alleles): Stems are either tall or short (not medium). 2. Produce many offspring quickly. (Gave Mendel LOTS of data.) Mendel’s Experiments Studied 7 traits: height, seed shape, seed color, seed coat color, pod shape, pod color, and flower position. Mendel always started with PUREBRED plants. Purebred: always produces offspring with the SAME trait as the parent. Mendel’s Pea Plants Experiments Continued Mendel crossed (bred) plants with opposite alleles of a trait Tall plant x short plant Parents are called P generation. Offspring are called f1 The offspring WERE ALL TALL! What happed to the short? Mendel crossed the f1 generation (selfpollinated) New offspring: f2 75% Tall, 25% short How did the shortness return? Alleles Dominant Allele: ALWAYS shows up when it is present. Recessive Allele: Trait is not seen if a dominant allele is present, but is seen w/out D.A. Using Symbols in Genetics We use letters to describe alleles (traits) Dominant Allele: capital letter (T=tall) Recessive Allele: lower case (t=short) Letters of a trait must MATCH example (B=blue, b=red) Shortness? Mendel’s cross: TT (purebred Tall) x tt (purebred Short) f1 gets ONE allele from each parent. ONE T(tall) and ONE t (short) Genotype (the genes): Tt Phenotype (how it looks): Tall FOR ALL OFFSPRING OF THIS CROSS! Why did the shortness come back? This cross was Tt (tall) x Tt (Tall) Of 4 offspring; 1 would be TT (tall) 2 would be Tt (tall) 1 would be tt (short) Are you confused yet? Punnett Squares Help us see the outcomes of genetic crosses. Tt(tall) x Tt(tall) Parent Alleles here. T T t t Tall Tall TT Tt Tall short tt Tt Combine to get offspring alleles! Genotype vs. Phenotype Genotype: the genes (the letters: TT, Tt, tt) Phenotype: what it looks like (tall or short) Genotypes: Phenotypes: 1TT 3 Tall 2Tt 1 Short 1tt Ratio of phenotypes- 3:1 Tall: Short Punnett Problems-make the Punnett squares! 1. Round peas (R) is dominant and Wrinkled peas (r) is recessive. If we crossed a Round (Rr) plant with a Wrinkled (rr) plant and there were 4 offspring how many would be wrinkled? Round? 2. A green pod (G) is dominant to a yellow pod (g). If we crossed a green pod (Gg) with a green pod (GG) and there were 4 offspring how many would be green? How many yellow? 3. A yellow seed (Y) is dominant to a green seed (y). If we cross a yellow seed (Yy) with a yellow seed (Yy) and there are 8 offspring how many will be yellow? How many will be green?