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Standard Biology Chapter 26 Inheritance of Traits

Standard Biology Chapter 26 Inheritance of Traits. Section 1 Genetics, How and Why. Genetics. Genetics: the study of how traits are passed from parent to offspring Mystery for a long time Now know traits are passed in sex cells. Chromosomes.

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Standard Biology Chapter 26 Inheritance of Traits

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  1. Standard Biology Chapter 26 Inheritance of Traits Section 1 Genetics, How and Why

  2. Genetics • Genetics: the study of how traits are passed from parent to offspring • Mystery for a long time • Now know traits are passed in sex cells

  3. Chromosomes • Nucleus found in center of cell which directs the cell’s activities • Chromosomes are found in nucleus • Chromosomes are thickened and easy to see • Remember, chromosomes are duplicated before cell reproduction

  4. Chromosomes • Two kinds of cells • Body cells- chromosomes in pairs (diploid) • Sex cells- single chromosomes (so ½ the number of chromosomes as body cells) (haploid)

  5. Genes on Chromosomes • Gene • Small section of chromosome that determines a specific trait; examples • Eye color • Wing shape • Chemical process • Humans have about 23,000 genes

  6. Genes on Chromosomes • Genes are arranged on a chromosome like beads on a necklace • Chromosomes are paired, so genes are paired (except sex cells)

  7. Passing Traits to Offspring Female egg • Traits are passes from parent to offspring in sex cells • Example: Ear Lobe Shape p. 548 A A AF F Child will have free ear lobes F Male sperm A= attached ear lobes F= free ear lobes

  8. Dominant and Recessive Genes • One trait dominates another like free dominates attached • Free=dominate and Attached=recessive • Mother is pure attached (AA) or homozygous recessive (homo means same) • Father is pure dominate (FF) or homozygous dominate • Child is one Free and one Attached (FA) or heterozygous (hetero means different)

  9. Traits of Plants and Animals

  10. When Both Parents are Heterozygous • If mother is heterozygous (FA), she can make F eggs and A eggs • If father is Heterozygous (FA), he can make F sperm and A sperm • How many combinations of traits in children as possible? Table 26-2 p. 551

  11. When Both Parents are Heterozygous • Mother’s eggs: F and A • Father’s sperm: F and A • Child: FF, FA, AF or AA • So four combinations of genes possible (although FA and AF are the same) • Child will have free ear lobes if FF, FA or AF • Child will have attached ear lobes if AA

  12. Standard Biology Chapter 26 Inheritance of Traits Section 2 Expected and Observed Results

  13. Punnett Square • Easy way to look at combinations of traits is with a Punnett Square • Letters used represent genes • Capital letters dominant • Lower case letters recessive • Trait’s letter based on dominant

  14. Punnett Square Example: Free ear lobes dominant F Attached ear lobes recessive f Homozygous recessive mother ff Homozygous dominant father FF Mother’s genes f f F Ff Ff Ff F Ff Father’s genes

  15. Punnett Square Example when parents are heterozygous: Mother’s genes F f F FF Ff Father’s genes ff f Ff

  16. Directions for Punnett Square • Draw a Punnett Square (4 boxes). Each box shows possible combination of genes in offspring. • Decide what genes will be in the sex cells of each parent. • Write mother’s genes on top; write father’s genes on side. • Copy the letters that appear at the top of the square into the boxes below each letter. • Copy the letters that appear at the side into the boxes next to each letter. • Look at the 4 small boxes in the Punnett Square, these are possible combinations in the offspring.

  17. Expected Results • Get from Punnett Square • What you expect to happen • Probability Expected Results

  18. Observed Results Expected Results • The numbers you actually get • They don’t match up exactly with what you expect • The greater the number of offspring, the closer you should get to the expected results. • Table 26-3 p. 557 Observed results when you count the pods of this one cross: 71 yellow pods and 24 green pods

  19. Mendel’s Work • Gregor Mendel • Father of Genetics • 1865 Austrian monk/teacher in Czech • Grew garden peas, came up with ideas about how traits are inherited • Counted 1000’s of traits in pea plants and conducted scientific investigations (applied math to science)

  20. Mendel’s Work • Traits he studied: • Plant height • Pod colorPod shape • Seed color • Seed shape • Flower color • Flower position • Always found 3 dominate to 1 recessive when heterozygous parents were crossed

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