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Heredity

Heredity. The genetic passing of characteristics from parent to offspring Eye color Hair color and texture Facial features Height. It’s all in the DNA…. DNA – D eoxyribo N ucleic A cid Unique individual sequence of nucleotides Only identical twins have the same sequence Gene

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Heredity

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  1. Heredity The genetic passing of characteristics from parent to offspring • Eye color • Hair color and texture • Facial features • Height

  2. It’s all in the DNA…. • DNA – DeoxyriboNucleicAcid • Unique individual sequence of nucleotides • Only identical twins have the same sequence • Gene • A segment of DNA that codes for a protein • Humans are estimated to have 50,000 genes

  3. Chromosomes • DNA wrapped around proteins • Contain genes Humans have 46 chromosomes in somatic (body) cells That equals 23 pairs of chromosomes • the pairs are called: Homologous Chromosomes

  4. Homologous Chromosomes Pairs of chromosomes with the same genes on each individual in the pair Which means….. We have two copies of each gene Those copies of the genes are called alleles

  5. Where do we get our chromosomes? • We inherit 23 chromosomes from each parent But…somatic cells have 46 chromosomes…..if two somatic cells from our parents are put together that would be 96 chromosomes! • Gametes are the solution! • Sex cells (eggs and sperm) • Have 23 chromosomes • When two gametes are put together = 46 chromosomes! • Created during Meiosis – a reduction division

  6. Karyotype • A visualization of the chromosomes of a somatic cell. • Used as part of amniocentesis tests • Cells are “caught” with their chromosomes condensed and duplicated during prophase. • Chromosomes are matched by size • Can see chromosome disorders using a karyotype

  7. Special Names for the Number of Chromosomes • Diploid • A cell with a double set of chromosomes • All somatic cells are diploid • 46 chromosomes in humans • 2n • Haploid • A cell with a single set of chromosomes • All gametes are haploid • 23 chromosomes in humans • n

  8. Diploid Cells • Pair of chromosomes – 2n • Each individualof the pair has a copy of the same set of genes • We all have two alleles (copies) of a single gene • We got one allele from Mom and one from Dad

  9. Can’t use Mitosis to get a haploid cell! Meiosis • Cell division that reduces the number of chromosomes – Reduction Division • Involves two consecutive cell divisions called Meiosis I and Meiosis II

  10. Meiosis I • Interphase • Carrying out metabolic processes • Replicating DNA – condensing it into chrmosomes • Prophase I • Metaphase I • Anaphase I • Telophase I

  11. Prophase I • Chromosomes appear • sister chromatids are joined in the middle • Synapsis • Replicated homologous chromosomes pair up and form bonds • Crossing over • Chromosome segments are exchanged between homologous chromosomes • Results in greater genetic variation

  12. Metaphase I • Homologous chromosomes and their sister chromatids line up on the equator (middle) of cell • Spindle fibers attach

  13. Anaphase I • Homologous chromosomes separate • Sister chromatids go to the poles of the cell

  14. Telophase I • Sister chromatids reach poles • Only one of the original homologous chromosome pair (and it’s sister chromatid –the replicated DNA is still attached) are a part of this cell • Creates two haploid cells

  15. Meiosis II • During the Interphase between Meiosis I and Meiosis II –The DNA does not replicate • The cell undergoes another round of phases: • Prophase II • Metaphase II – sister chromatids line up on equator • Anaphase II – sister chromatids pull apart • Telophase II – 4 haploid cells all genetically different are created

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