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Basic Principles of Heredity

Basic Principles of Heredity. Packet #18. Mendel. Vocabulary Word Introduction. Heredity Transmission of genetic information from parent to offspring Genetics The science of heredity Studies both genetic similarities and genetic variation. Vocabulary II. Genes Located on the chromosome

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Basic Principles of Heredity

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  1. Basic Principles of Heredity Packet #18

  2. Mendel

  3. Vocabulary Word Introduction • Heredity • Transmission of genetic information from parent to offspring • Genetics • The science of heredity • Studies both genetic similarities and genetic variation

  4. Vocabulary II • Genes • Located on the chromosome • Composed of DNA • Locus • The location of a gene on the chromosome • Allele • Different form, of a particular gene, that is located at a specific locus on a specific chromosome • Allele is used when investigation two or more forms of a particular gene

  5. Allele

  6. Mendel’s Laws • When Mendel carried out his research, the processes of mitosis and meiosis had not yet been discovered. • Principle of Segregation • During meiosis, the alleles for each locus, separate from each other • When haploid gametes are formed, each contain only one allele for each locus • Segregation of alleles is a direct result of homologous chromosomes separating during meiosis

  7. Mendel’s Laws • Principle of Independent Assortment • The random distribution of alleles, of different loci, into gametes • Results in recombination • The presence of new gene combinations not present in the parental (P) generation. • Independent assortment occurs because there are two ways in which two pairs of homologous chromosomes can be arranged at metaphase I of meiosis. • The orientation of homologous chromosomes on the metaphase plate determines the way chromosomes are distributed into haploid cells.

  8. Mendel’s Laws

  9. Mendel’s Laws

  10. Mendel’s LawLaw of Independent Assortment

  11. Vocabulary III • Dominant Allele • May mask the expression of the other allele known as the recessive allele • There must be two alleles present • Recessive Allele • May only be expressed when paired with another recessive allele

  12. Homozygous vs. Hetereozygous • Homozygous Dominant • Two identical alleles that are in a dominant state • Homozygous Recessive • Two identical alleles that are in a recessive state • Hetereozygous • Two different alleles • One dominant • One recessive

  13. Genotype vs. Phenotype • Genotype • Composition of a specific region of DNA, in an individuals genome, that varies within a population • The allele composition found within a cell • Allows the expression of the phenotype • Phenotype • The physical effect of a particular genotype.

  14. Genotype vs. Phenotype

  15. Punnett Square • Punnett Square • A diagram used in the study of inheritance • Shows the result of random fertilization in genetic crosses.

  16. Solving Genetics ProblemsTest/Monohybrid/Dihybrid Cross • Monohybrid Cross • A cross, between parents (P generation), involving ONE allele • Test Cross • A cross between individuals of an unknown genotype and a homozygous recessive individual • Still involving ONE allele • Dihybrid Cross • A cross, between parents (P generation), involving TWO alleles. • The first generation of offspring • F1 generation • First filial • The second generation of offspring • F2 generation • Second filial

  17. Punnett Square • Example #1 • Sex determination • Sex is determined by sex chromosomes • X & Y • The Y chromosome determines male sex in most species of mammals • The Y chromosome contains the SRY gene • Sex reversal on Y gene

  18. Punnett Square • Example #2 • Monohybrid cross

  19. Punnett Square • Example #3 • Test Cross

  20. Punnett Square • Example #4 • Dihybrid cross

  21. Blood Groups

  22. Multiple Alleles • Three, or more alleles, can potentially occupy a particular locus. • A diploid individual any two of the three alleles • A haploid individual, or gamete, has only one

  23. Blood Groups II

  24. Rh Factor • Determines whether someone has positive or negative blood • A protein antigen that is on the surface of blood cells and if that antigen is present, the individual is positive • A+; B+; O+; AB+ • If the antigen is not present, then the individual is negative • A-; B-; O-; AB-

  25. Rh Factor II • If an RH-negative mother is exposed to blood from an Rh-positive fetus, the mother’s blood will produce antibodies that will attack the blood of the fetus--potentially killing the unborn child. • This is why, blood types should be determined before having children • If, the male and female are negative, and positive, the mother must receive medication to prevent her immune system from attacking the child.

  26. Punnett Square • Example #5 • Blood Type Cross • We WILL NOT be doing Punnett Squares involving the Rhesus factor.

  27. Incomplete Dominance • Occurs when hybrids have an appearance between the phenotypes of the parental varieties. • The hetereozygote is intermediate in phenotype • Example • The color between red and white • Pink

  28. Incomplete Dominance

  29. Incomplete Dominance

  30. Punnett Square • Example • Incomplete Dominance

  31. Codominance • Situation in which the phenotypes of both alleles are exhibited in a heterozygote • Hetereozygote simultaneously expresses the phenotypes of both parents. • Example • Red Flower crossed with a White Flower • The child will display flowers with red and white spots • Both alleles are exhibited

  32. Punnett Square • Example # • Codominance

  33. Epistasis • Epistatis occurs when one gene alters the expression of another gene • The genes are independent of each other

  34. Epistasis

  35. Linkage • Each chromosome behaves genetically as if it consisted of genes arranged in a linear order • Linkage is the tendency for a group of genes, on the same chromosome, to be inherited together via crossing over • Therefore, groups of genes on the same chromosome are linked genes. • Independent assortment does not apply if two loci are linked close together on the same pair of homologous chromosomes. • Normally, they are passed on together. • However, recombination of linked genes can result from crossing-over during Prophase I of Meiosis I

  36. Linked vs. Unlinked • Recombination of unlinked genes = Independent Assortment of chromosomes • Recombination of Linked genes = Crossing Over

  37. Linkage II • Measuring the frequency of recombination between linked genes may provide an opportunity to construct a linkage map of a chromosome.

  38. Distinguishing Between Independent Assortment and Linkage(Linked Genes) • Perform a two-point test cross • One individual must be hetereozygous for the linked genes • One individual must be homozygous recessive for the both characteristics • Linkage is recognized when there is an excess of parental type offspring (majority) and a deficiency of recombinant type offspring are produced in the two-point cross.

  39. Two Point Cross • Parent #1 • BbVv • Grey with normal wings • Parent #2 • bbvv • Black with vestigial wings

  40. Linked Genes

  41. Two-Point Cross • Calculations • Parental Genotypes • 965 (42%) +944 (41%) = 1909 • 1909/2300 = 83% • Recombinant Genotypes • 206 (9%)+185 (8%) = 391 • 391/2300 = 17% • If independent assortment was to occur, the percentages would be 25% a piece. • The recombinants arose because of crossing over

  42. Gene Mapping • By measuring the frequency of recombination between linked genes, it is possible to construct a linkage map of a chromosome • This is how scientists were able to develop a detailed genetic map of Neurospora (fungus), fruit fly, the mouse, yeast and many plants that are particularly important as crops

  43. Sex-Linked Genetics • Sex is determined by sex chromosomes • X and Y • XX = female • XY = male • The X chromosome contains many important genes that are unrelated to sex determination • These genes are required for both males and females • A male receives ALL of his X-linked genes from his mother while a female receives her X-linked genes from both parents.

  44. Sex-Linked Genetics

  45. Female Mammals • Display Dosage Compensation • In females, only one of the two chromosomes is expressed in each cell • Equalizes the expression of x-linked genes for both genders. • The other allele is inactive • Seen as a dark-staining Barr body at the edge of the interphase nucleus. • A random event that occurs in each somatic cells • A female that is hetereozygous expresses one of the alleles in about half her cells and the other allele in the other half

  46. Dosage Compensation II • Mice and cats have several alleles that code for coat color on the x-chromosome. • Females that are hetereozygous for such genes may show patches of one color in the middle areas of the other color. • Variegation • Not always visible in other circumstances • May require special techniques

  47. Dosage Compensation

  48. Sex Linked Disorders

  49. X-Linked Recessive Disorder • Males will show this trait if they have the recessive allele on the X chromosome • Considered as hemizygous for the trait • Females will show this trait if they have the recessive allele on both X chromosomes • Homozygous recessive • Hemophilia • Inability to have clotting of blood • xh • Color blindness • xc

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