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The cell contains the genetic material responsible for inherited characteristics.

The cell contains the genetic material responsible for inherited characteristics. The resemblances between offspring and parents of species that sexually reproduce is due to inherited characteristics called traits .

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The cell contains the genetic material responsible for inherited characteristics.

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  1. The cell contains the genetic material responsible for inherited characteristics. • The resemblances between offspring and parents of species that sexually reproduce is due to inherited characteristics called traits. • Some traits in the offspring are acquired from the environment while other traits are inherited from our parents through their genetic material. Early geneticists originally believed inherited traits were controlled by complex proteins. In 1953, Watson and Crick discovered the DNA model that is passed from generation to generation. What’s so genetically special about this baby nine-banded armadillo? It is one of four identical quadruplets. The fertilized egg of every nine-banded armadillo mother splits into four during her pregnancy.

  2. In eukaryotic cells, DNA is found in the nucleus.

  3. Human Karyotype • Human somatic (body) cells have 23 pairs of chromosomes (46 homologous chromosomes in total): • 22 autosomes (different sizes) • 1 sex (X or Y). • 2 m long if stretched out • Note that human gamete (sex) cells have only 23 chromosomes, but the zygote has 46 chromosomes after fertilization. • Each species has a different number of chromosomes.

  4. DNA Terminology: • During most of the cell cycle (interphase), the genetic material exists as long, invisible, tangled fibres of uncoiled DNA combined with proteins called chromatin. • As a cell prepares to divide, to keep the DNA sequence organized and protected, the chromatin is like a thread wrapped tightly around spools that are bead-shaped proteins called histones causing the chromatin to thicken and shorten and become chromosomes. • One unduplicated chromosome may also be called a chromatid. • One duplicated chromosome may also be described as two sister chromatids (one from the mother and the other from the father). • Sister chromatids are held together by the centromere.

  5. The Human Chromosome • Each chromosome is made of many small segments called genes located at specific positions on the chromosome called a locus (loci). • A gene is a unit of inherited material. • Genes coding for a trait that may be expressed and can be turned on and off are called exons. • These are separated by filler genes (“junk” DNA) called introns. • Alleles are the different versions of a gene.

  6. Loci, Genes, Alleles

  7. Genes: Exons and Introns

  8. rails rungs DNA (DeoxyriboNucleic Acid) • DNA is a nucleic acid macromolecule made of C, H, O, N, P that carries the genetic code for proteins that are the building blocks of life. • Except for identical twins, everyone’s DNA sequence is unique from everybody else’s. • Rosalind Franklin used X-ray crystallography and determined that DNA had a helix (spiral) shape. • Watson and Crick then created the double-helix (spiral staircase) model where the two “ladder supports” or “rails” are sugar-phosphate molecules and the “rungs” consist of pairs of nitrogenous bases.

  9. Nucleotide: • DNA is composed of two long polymer backbone chains of subunits called nucleotides. • Each nucleotide is made up of three parts: • a five carbon ring-shaped sugar called deoxyribose alternates with • a phosphate group composed of phosphorus and oxygen which is attached to • a nitrogenous base which define it as a purine or a pyrimidine.

  10. Nitrogenous Bases: • Thymine and Cytosine are pyrimidines. • Adenine and Guanine are purines. • Purines are complimentary to pyrimidines. • Due to the specific size and shape of these molecules, these complimentary nitrogenous bases form hydrogen bonds between each other. • A always pairs with T. • G always pairs with C. • If this pairing is disrupted or incorrect due to mutagens such as chemical toxins, radiation, bacteria and viruses, then mutations or errors can occur during interphase which is when DNA is replicated.

  11. Note that the resulting two strands arecomplementary,butdoes NOT mean that the two strands have the same DNA sequence! A T A A A T T T C C C G G G

  12. The two strands are anti-parallel where direction of polarity runs from 5’ to 3’.

  13. The Double Helix

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