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Transcript
Ch. 8 Heredity GLE 0707.4.3 Explain the relationship among genes, chromosomes, and inherited traits TB 234-240 What You’ll Learn… • Explain how traits are inherited • Identify Mendel’s role in history of genetics • Use Punnett Squares to predict the results of the crosses • Compare and contrast the difference between an individual’s genotype and phenotype Why You Need To Know It… • Heredity and genetics help explain why people are different I. Inheriting Traits 1. Heredity – passing of traits from parent to offspring A. What is Genetics? 1. Genes on chromosomes control organism’s form, function, and traits 2. Different forms of traits that make up a gene pair = alleles 3. Meiosis = pair of chromosomes separate, alleles also separate into different sex cells 4. Every sex cell has 1 allele for each trait 5. Study of how traits are inherited through interactions of alleles = science of genetics II. Mendel: Father of Genetics 1. Gregor Mendel a. Austrian Monk b. 1865- studied pea plants to predict possible types of flowers and fruits resulting from cross breeding c. 1st to trace on trait through several generations d. 1st to use math = probability to explain heredity http://www.brainpop.com/science/c ellularlifeandgenetics/heredity/ III. Genetics in a Garden 1. a. b. c. Mendel studied specific traits Crossed 2 plants with different expressions of that trait New plants all looked like one of the 2 parents New plants called hybrids = received different genetic information (Diff. Alleles) for a trait from each plant 2. Organism that always produces the same trait generation to generation = purebred EX: Tall plants that always produce tall plants = purebred III. Genetics in a Garden A. Dominant and Recessive Factors 1. Cross pollination- pollinate one trait with opposite trait Ex: Purebred tall plants with purebred short plants 2. Dominant Allele = trait that covers up/dominants other form of that trait Ex: Tall gene covered short gene in plants 3. Recessive Allele = trait that is covered by the dominant trait http://www.brainpop.com/health/geneticsgrowthanddevelop ment/genetics/ Dominant and Recessive Factors III. Genetics in a Garden B. Using Probability to Make Predictions 1. Probability- math that helps you predict the chance of something happening Ex: Coin toss – heads or tails – 50/50 chance 2. Mendel worked with a large number of plants – helped make predictions more accurate. Also increased the chances of seeing a repeatable pattern 3. Valid science conclusions need to be based on results III. Genetics in a Garden C. Punnett Squares 1. Letters represent dominant and recessive alleles 2. Uppercase letter = dominant allele 3. Lowercase letter = recessive letter 4. Letter – A code (genotype) = Genetic make-up 5. The way an organism looks or behaves is a result of genotype = phenotype Ex: Brown hair = phenotype of hair color = brown III. Genetics in a Garden D. Alleles Determine Traits 1. Most cells have 2 alleles for every trait 2. Alleles are located on chromosomes in nucleus of the cell 3. Organism with the same 2 alleles = homozygous trait EX: both tall alleles ( TT ) 4. Organism with that has 2 different traits EX: 1 tall and 1 short ( Tt ) 5. Mendel produced heterozygous hybrids for height = Tt III. Genetics in a Garden E. Making a Punnett Square 1. Letters representing 2 alleles from 1 parent are written along the top of the grid 2. Those of the 2nd parent are placed down the side of the grid (1 letter per section ) 3. Each square of the grid is filled with 1 allele donated by each parent 4. Letters represent genotypes of possible offspring that parents could produce T T T t III. Genetics in a Garden F. Principles of Heredity 1. Traits are controlled by alleles on chromosomes 2. An allele’s effect is dominant or recessive 3. When a pair of chromosomes separates during meiosis, the different alleles for a trait move into separate sex cells https://www.khanacademy.org/science/biology/heredit y-and-genetics/v/punnett-square-fun