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Mendel’s 1 st Law

Mendel’s 1 st Law. The Law of Segregation Members of a pair of alleles for a given trait are separated when gametes are formed. Mendel’s 2 nd Law. The Law of Independent Assortment

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Mendel’s 1 st Law

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  1. Mendel’s 1st Law • The Law of Segregation • Members of a pair of alleles for a given trait are separated when gametes are formed

  2. Mendel’s 2nd Law • The Law of Independent Assortment • When two or more pairs of characteristics are considered at one time, each pair shows dominance and segregation independently of the other • Eg. A plant that is heterozygous for two pairs of alleles, TtRr, can form four types of gametes: • TR, Tr, tR, and tr

  3. Incomplete Dominance • There are instances in nature where strict dominance did not apply • In snapdragons, crossing of white-flowered plant with red-flowered plant produces pink-flowered plants

  4. Incomplete Dominance • Dominance: • The dominant allele (A) can hide the expression of a recessive allele (a) in a heterozygous condition • Incomplete Dominance: • Different alleles of a gene are expressed in the heterozygous condition to produce an intermediate phenotype • When neither gene is completely dominant over the other

  5. Having two RR genes produce enough red pigment to make red flowers Having only 1 R genes produce only enough red pigment to make pink flowers

  6. Co-dominance • Two alleles expressed at the same time • One parent is homozygous red (RR) and the other homozygous white (rr) • Offspring (Rr) is a blend red and white

  7. Co-dominance • Each individual hair is either completely white or completely red • NOT intermediate in colour • Neither allele dominates the expression of the other

  8. Blood Type • Human blood types show co-dominance • Possible blood types: • A, B, AB, and O • Blood type is determined by a pair of alleles • There are 3 different alleles (A, B, O) that may be found at the locus on either of the homologous chromosome • Multiple allelism

  9. Blood Type • Alleles for A = IA • Alleles for B = IB • Alleles for O = i • IA and IB are co-dominant over i

  10. Sex Linkage • Human sex is determined by X and Y chromosomes • Male = XY • Female = XX • Any gene on the X chromosome, whether dominant or recessive, is expressed in males • Traits controlled by genes on the X chromosome are called X-linked traits

  11. X-Linked Disorders • Colourblindness • Muscular Dystrophy • Hemophilia • Fragile X Syndrome

  12. Punnett Square • Use X’s and Y’s to represent male and female • Use superscript letters to designate the alleles • Eg.

  13. In fruit flies, the allele for eye colour is located on the X chromosome, where red eyes is dominant to white eyes. Show the cross of a heterozygous red-eyed female and a white eyed male.

  14. Quest on Friday • Out of 40

  15. Importance of cell division • Stages of cell division • mitosis • Prophase,metaphase,anaphase, telophase • Know diagrams and descriptions • Meiosis • Crossing over • Stages • location

  16. Problems with meiosis • non disjunction • Aneuploidy • Monosomy, trisomy • Chromosomal Mutations • Deletion, Duplication, Inversion, Translocation

  17. Sexual vs Asexual reproduction • Advantages and disadvantages of both • Types of asexual reproduction • Diagrams and descriptions

  18. Mendel & experiments • Mendel’s Phenotypes vs Genotypes  ratios F1 and F2 generation • Homozygous vs heterozygous • Law of independent assortment and law of segregation

  19. Punnettsquares • Incomplete dominance • Co dominance • Multiple alleles • Sex linked traits

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