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Chapter 11 Genetics

Chapter 11 Genetics. Gregor Mendel. Used pure breed pea plants to understand inheritance Used self pollination to cross breed Pollen from the male part of the pea plant fertilizes the female egg of the same flower. Cross Pollination. Cross Pollination

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Chapter 11 Genetics

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  1. Chapter 11 Genetics

  2. Gregor Mendel • Used pure breed peaplants to understand inheritance • Used self pollination to cross breed • Pollen from the male part of the pea plant fertilizes the female egg of the same flower

  3. Cross Pollination • Cross Pollination • Mendel cut away the male parts of the plant and then dusted pollen from another plant on the flower • Seed that come from cross-pollination inherit all of the characteristics from two parents

  4. Genes and Dominance • A trait is a specific characteristic that varies from one individual to another • The chemical factors that determine traits are called genes • The different forms of a gene are called alleles • Video Clip!!

  5. Mendel’s Work • Mendel crossed two pure breed plants with different forms of the same trait • One plant was tall and one plant was short (trait: plant height) • The offspring plants were called hybrids • Hybrids are the offspring of crosses between parents with different forms of a trait

  6. Principle of Dominance • The principle of dominance states that some alleles are dominant and others are recessive • An organism with a dominant allele for a specific trait will always show that form of the trait. • An organism with a recessive allele for a specific trait will only show that form only when the dominant allele for that trait is not present.

  7. Segregation is the separation of alleles during gamete formation Gametes are specialized cells involved in sexual reproduction Segregation

  8. Probability and Punnet Squares • Principle of probability can be used to predict the outcomes of genetic crosses. • Probability is the likelihood that a particular event will occur. • Probability can predict the outcome of genetic crosses because alleles segregate randomly.

  9. Punnet Squares • These can be used to predict and compare the genetic variations that will result from a cross. T T T t

  10. Punnet Square, cont. • Homozygous – TT or tt, organisms that have two identical alleles for a particular trait. • Heterozygous – Tt, organisms that have different alleles for the same trait

  11. Phenotype – physical characteristics, • TT = tall, Tt = tall, tt = short • Genotype – genetic makeup, TT, Tt, tt. T t T t Ratios: Phenotype- 3 Tall: 1 Short Genotype- 1 TT: 2Tt: 1tt

  12. Probabilities Predict Averages • Probabilities predict the average outcome of a large number of events. • Probability cannot predict the precise outcome of an individual event

  13. Mendelian Genetics • Mendel found that the gene controlling seed shape did not affect the gene controlling seed color. • Principle of Independent Assortment • Genes for different traits can segregate independently during the formation of gametes

  14. Independent Assortment accounts for the many genetic variations observed in plants, animals, and other organisms Independent Assortment

  15. Beyond Dominant and Recessive Alleles • Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes.

  16. Incomplete Dominance • One allele is not completely dominant over the other. • The heterozygous phenotype is somewhere between two homozygous phenotypes

  17. Codominance • Both alleles contribute to the phenotype. • For Example: In chickens, the allele for black feathers is codominant with the allele for white feathers. These chickens will have both black and white feathers.

  18. Multiple Alleles/Polygenic Traits • Multiple alleles are when there is more than two possible alleles that exist for each trait in a population. Example: blood type (A, B, AB, O) • Polygenic traits are traits that are controlled by 2 or more genes. Example: variations in human skin color; height

  19. Meiosis • The daughter cells (haploid) produced contain only HALF of the number of chromosomes as the original parent cell (diploid). • How does this happen? Meiosis is a process of reduction division—that is, the number of chromosomes is cut in half. No replication occurs.

  20. Meiosis

  21. During meiosis I, chromosomes pair up with their corresponding homologous pair chromosomes. They form a tetrad. These tetrads exchange alleles and form new allele combinations in a process known as crossing-over. Video Clip!! Crossing-over

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