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Standard Biology Chapter 26 Inheritance of Traits

Delve into the realm of genetics, exploring the inheritance of traits and the mechanisms through which characteristics are passed from parents to offspring. Unravel the mysteries of chromosomes, genes, dominant and recessive traits, and discover the significance of Punnett squares in predicting offspring traits.

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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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