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Chapter 5B

Basic. Genetics. Chapter 5B. Gregor Mendel. Famous pea plant study Mendelian genetics “Father of Genetics”. Mendelian Genetics. Began with 34 varieties of pea seeds Chose 7 sets of opposing characteristics Chart, page 135. The Importance of Peas. Self-pollination vs.

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Chapter 5B

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  1. Basic Genetics Chapter 5B

  2. Gregor Mendel • Famous pea plant study • Mendelian genetics • “Father of Genetics”

  3. Mendelian Genetics • Began with 34 varieties of pea seeds • Chose 7 sets of opposing characteristics • Chart, page 135

  4. The Importance of Peas Self-pollination vs. Cross-pollination

  5. Mendelian Genetics • P1: the original parent generation • F1: first filial generation; offspring of the P1 generation • F2: second filial generation; offspring of the F1 generation

  6. If we consider your parents to be the P1 generation, which generation are you? • 1. P1 • 2. P2 • 3. F1 • 4. F2

  7. Mendel's Concepts The concept of unit characteristics Factors occur in pairs.

  8. Genes occur in pairs because diploid organisms have • 1. daughter chromosomes. • 2. homologous pairs of chromosomes. • 3. gametes.

  9. Mendel's Concepts The concept of dominant & recessive

  10. Dominant trait • A trait that is expressed and masks the expression of the other trait • Examples on page 113

  11. Recessive trait • A trait which, when in the presence of a dominant trait, is not expressed

  12. Language of Genetics Problems • Capital letters (T) = dominant • Lowercase letters (t) = recessive • A, a; B, b; R, r; etc.

  13. Mendel's Concepts The concept of segregation

  14. A cell forms gametes during which process? • 1. Mitosis • 2. Meiosis • 3. Cytokinesis • 4. Fertilization

  15. Genetic Terminology

  16. Phenotype • The physical expression of an organism’s genes • Examples: tall, short, black Genotype • The genetic make-up of an individual; the genes it has • Examples: Tt, AA, bb

  17. Locus • The site on a chromosome where a particular gene is located Allele • One of a pair of genes that has the same position on homologous chromosomes • Examples: T or t

  18. Homozygous • When both alleles in a cell are the same • Examples: tt, TT, BB, bb Heterozygous • When both alleles in a cell are NOT the same • Examples: Bb, Tt

  19. Monohybrid cross • A genetic cross dealing with only one set of characteristics Punnett square • A diagram used to show the possible gamete combinations from a genetic cross

  20. Incomplete Dominance

  21. Incomplete Dominance • Both alleles are expressed, but neither one is dominant. • KEY: a blending of the traits • Example: • When red snapdragons are crossed with white snapdragons, the resulting offspring are pink.

  22. Cw Cw Cr Cr 1st generation CrCw CrCw CrCw CrCw

  23. Cr Cw 1 : 2 : 1 Cr Cw 2nd generation Genotypic: _________ CrCr CrCw Phenotypic: _________ 1 : 2 : 1 CrCw CwCw

  24. Human example • Brachydactyly

  25. Codominance • Two alleles for a gene are both expressed. • KEY: both alleles are expressed with no blending. • Example: • In horses, red hair + white hair = roan (red and white hairs).

  26. Multiple Alleles • One of several alleles can be at a given locus • Example: human blood types (A, B, AB, O)

  27. Human Blood Types Dominant Alleles IA and IB Recessive Allele i

  28. IAIAtype A blood IA itype A IB IBtype B IB itype B IA IB type AB ii type O

  29. Suppose a woman who has type AB blood marries a man who is heterozygous for blood type A. What blood types might their children have?

  30. IA IB IA i type AB x heterozygous type A IA IA IA IB IA i IB i

  31. Dihybrid Crosses • Genetic crosses dealing with TWO characteristics at the same time • Example: green/yellow peas AND tall/short pea plants

  32. Mendel’s Concept of Independent Assortment • The segregation of one set of alleles during gamete formation is not affected by another set.

  33. Multiple Gene Interaction • Sometimes two or more genes working together result in a single trait. • Examples: many human traits such as hair color and skin color

  34. Sex-Linked Traits

  35. Two Types of Chromosomes • Autosomes • non-sex-determining chromosomes • humans = 22 pairs • Sex chromosomes • XX = female • XY = male

  36. X X X Y Female = XX Male = XY XX XX XY XY

  37. Sex-Linked Traits • Some genes are carried on the sex chromosomes. • The X and Y chromosomes are not homologous.

  38. Sex-Linked Traits • Males inherit more sex-linked disorders because they only have one gene for the trait. • If there is a defective gene on X, there wouldn’t be a normal gene on Y to counteract it.

  39. Sex-Linked Traits • Indicated with a superscript above the X and Y chromosomes • Example: • X H X h • X H Y

  40. Human Examples • Red-green colorblindness • Hemophilia • Lack a blood chemical that allows for blood clotting

  41. XH XH normal female XH Xh carrier female A heterozygous female that does not have the disease, but she does carry the gene for the trait Xh Xh hemophiliac female XH Y normal male Xh Yhemophiliac male

  42. XH Xh XH Y carrier female x normal male XH XH XH Xh XhY XHY

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