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Handout: Human Genetics
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Handout: Human Genetics


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  • 1. Human Genetics
  • 2. Genetic Terms
    • A Gene is a specific region of DNA that directs the synthesis of a specific product. That product controls one or more specific traits.
    • Diploid cells have two copies of each gene, and the two copies segregate from each other during gametes formation.
    • Alleles are the different molecular forms of a gene.
    • Wild-type alleles are the most common form of a gene. The less common forms are referred to as Mutant alleles.
  • 3. Genetic Terms
    • Dominant alleles – the allele whose phenotype would dominate in a heterozygote (Aa).
    • Recessive allele – the allele whose phenotype would be dominated over in a heterozygote.
    • Heterozygote – two alleles of the same gene are not identical (Aa).
    • Homozygote – two alleles of the same gene are identical (AA).
    • Genotype – refers to the genetic make up of an individual.
    • Phenotype – refers to the outward appearance of an individual.
  • 4. More Genetic Terms
    • Crossing over during meiosis results in genetic recombination.
    • Independent assortment refers to the random alignment and assortment of each pair of homologous chromosomes during Meiosis I.
    • Abnormal changes in the structure of chromosomes and changes in chromosome number are referred to as mutations.
  • 5. Autosomes and Sex Chromosomes
    • Sex Chromosomes are types of chromosomes that, in certain combinations determine a new individual’s sex. (X and Y in humans)
      • Homologous pairs are usually not the same in length and shape.
    • Autosomes are all of the other chromosomes, which are the same in both sexes.
      • Homologous pairs are usually the same length and shape.
  • 6. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 XX (or XY) centrifugation Obtain cells and arrest them in metaphase with colchicine
  • 7. Sex Determination
    • Evidence has shown that every normal egg produced by a human female has one X chromosome and that half of the sperm cells produced by a male carry an X chromosome and half carry a Y chromosome.
  • 8. eggs sperm female (XX) male (XY) X X Y X XX XY XX XY X X Y X x x
  • 9. Sex Determination
    • If an X-bearing sperm fertilizes an X-bearing egg, the new individual will develop into a female.
    • If a Y-bearing sperm fertilizes an X-bearing egg, the new individual will develop into a male
    • The X chromosome carries 2,062 genes.
    • The Y chromosome carries only 330 genes.
      • However one of these genes is the master gene for male sex determination.
  • 10. The SRY Gene
    • A gene on the Y chromosome called SRY ( S ex determining R egion of chromosome Y ) is the master gene for male sex determination.
    • If a functional copy of this gene is present, testes form. If a functional copy is absent, ovaries form.