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Genetics

Genetics. Textbook Chapters 10-13 Review Book Topic 3. Mendelian Genetics. 1866 – Gregor Mendel (Austrian monk) Studied inheritance of traits in pea plants Easy to grow, breed, control “True breeding” – meaning they always produce offspring with only one form of a trait

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Genetics

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  1. Genetics Textbook Chapters 10-13 Review Book Topic 3

  2. Mendelian Genetics • 1866 – Gregor Mendel (Austrian monk) • Studied inheritance of traits in pea plants • Easy to grow, breed, control • “True breeding” – meaning they always produce offspring with only one form of a trait • Inheritance (heredity) – passing of traits onto the next generation • Known as the “father of genetics”

  3. Noticed that certain characteristics are passed onto offspring from generation to generation (traits) • Mendel controlled cross- pollination (breeding) between plants by removing the male organs from the flower • He then chose which plants reproduced

  4. Mendel called the parent plants the “P” generation • When crossing two “P” generation, the offspring produced were called the “F1” generation (hybrids) • By crossing two “F1” generation, Mendel could study if characteristics could skip generations • Creates the “F2” generation

  5. Mendel studied seven different traits • Seed color • Flower color • Seed pod color • Seed shape or texture • Seed pod shape • Stem length • Flower position

  6. After his experiments Mendel concluded: • There must be two forms of a trait • Each form is controlled by an allele • Allele – alternate form of a single gene passed on from generation to generation

  7. Dominant allele (A) – form of the trait that appears in the F1 generation (shown) • Doesn’t mean it is stronger or more present in the population • Ex. Polydactyly • Recessive allele (a) – form of the trait that is masked in the F1 generation (not shown)

  8. Traits are different forms of a single gene • Genes contain a segments of DNA which codes for a specific protein

  9. Law of Segregation • Homologous traits occur in pairs on homologous chromosomes • Separated from each other during gamete formation (Law of Independent Assortment) • Recombine at fertilization • One form of a trait is inherited from each parent

  10. Law of Dominance • Homozygous – an organism with two of the same alleles for a given trait (AA, aa) • Heterozygous – an organism with two different alleles for a given trait (Aa) • When heterozygous, the dominant trait will be observed

  11. Three forms of dominance: • Homozygous dominant – AA • Heterozygous – Aa • Homozygous recessive – aa

  12. Characteristics • The outward appearance does not always indicate which pair of alleles is present • Genotype – organism’s allele pairs (AA, Aa, aa) • Phenotype – observable characteristic of an allele pair (tall, short, green, yellow)

  13. It is possible for two organisms to have the same phenotype but different genotypes • The genotype and phenotype of an organism is called a genome

  14. Activity #1 • Genotype versus phenotype smiley face activity

  15. Punnett Squares (1900s) • Used to predict the possible offspring of a cross between two known genotypes • Each parent contributes one allele per square in the box

  16. Monohybrid cross – only the inheritance of one trait is being studied • Homozygous-homozygous • AA x AA • AA x aa • aa x aa • Homozygous-heterozygous • AA x Aa • aa x Aa • Heterozygous-heterozygous • Aa x Aa

  17. Dihybrid cross – inheritance of two or more different traits are being studied

  18. Test Cross • An individual of unknown genotype is mated with an individual showing the homozygous recessive trait • Unknown could be homozygous or heterozygous • Look at offspring produced to determine unknown genotype

  19. Law of Independent Assortment • Allele pairs are randomly separated independently during gamete formation (meiosis) • Different traits are inherited separately • Exception is gene linkage • Linked genes are inherited together

  20. Activity #2 • Punnett square practice worksheet

  21. Law of Probability • “Law of chance” • Inheritance of genes can be compared to flipping a coin • Probability = # of ways a specific event can occur # of total possible outcomes

  22. Activity #3 • Probability and Inheritance Lab

  23. Heredity BrainPop

  24. Exceptions to Mendel’s Laws • Incomplete dominance • Both alleles contribute to the phenotype • Heterozygote is an intermediate of two parent’s traits

  25. Codominance • No single allele is dominant • Both alleles expressed at same time

  26. Polygenic Inheritance • More than one gene can affect a single trait • Ex. Four genes are involved in eye color • Ex. Human height • Ex. Skin color

  27. Pleiotrophy • A single gene can affect more than one trait • Ex. Cystic fibrosis, sickle cell anemia

  28. Gene Interactions (epistasis) • Products of genes (proteins) can interact to alter genetic ratios • Ex. Coat color in mammals • Ex. Purple pigment in corn

  29. Environmental Effects • Genes may be affected by the environment • Ex. coat color in arctic fox or hares (rabbits) • Ex. Siamese cats

  30. Multiple alleles for one gene • Genes may have more than two alleles • Ex. blood type • A, B, O alleles • Types: A, B, AB, O • IAIA / IAi (A); IBIB / IBi (B); IAIB (AB); ii (O)

  31. Pedigrees • Diagram that shows the phenotypes of several generations in a family tree for a specific trait • Symbols used: • Female -  • Male –  • Shading indicates individual shows the trait • Marriage represented by horizontal line between • Offspring represented by vertical lines

  32. Applied Genetics • Selective Breeding • Humans breed animals/plants with certain traits to obtain offspring that have desired traits • Results in traits becoming more common in a breed

  33. Hybridization • Animals/plants are bred to form heterozygotes • Heterozygous advantage • Ex. Disease resistance, increased offspring variation, faster growth, higher fruit yield • Disadvantages: • Time consuming • Expensive • Careful selection of parents to produce correct combinations of traits in offspring

  34. Inbreeding • Two closely related organisms are bred to have the desired traits • Also to eliminate the undesired traits in future generation • Disadvantage – harmful recessive traits also can be passed on to future generations in homozygous recessive individuals

  35. Examples of Human Inbreeding • Ancient Egypt • Pharaohs married their sisters • Royal Europe • Royalty married within their family

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