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The Human Genome and Chromosomal Basis of Heredity and Chromosomal Disorders. Chromosomes were found to be the bearer of genetic factor. Ömer Faruk Bayrak. WHAT IS GENE?. 2005. 2003. DNA Double Helix, Watson & Crick Nature, 1953. Human genome Project.
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Chromosomes were found to be the bearer of genetic factor
Ömer Faruk Bayrak
DNA Double Helix,
Watson & Crick
Human genome Project
Inactivation of different X genes
Nucleic acids first called “nuclein” because they were isolated from cell nuclei by F. Miescher in 1869
(1) a Phosphate group
(2) a five – carbon sugar (or Pentose), and
(3) a cyclic nitrogen containing compound called a base.
In RNA, the sugar is ribose (thus ribonucleic acid).
Cytosine, thymine, and uracil are single-ring base called Pyrimidines.
After publishing their model, W&C made a hypothesis for the replication of DNA.
a. Hydrogen bonds break, and the two strands separate.
b. Each strand now serves as a template for a new complimentary strand.
c. Nucleotides are connected and the daughter DNA molecules are formed.
- Once hydrogen bonds begin to break, replication bubbles begin to form at points along the DNA strand.
- Bubbles form at sites called origins of replication.
- DNA replication proceeds in both directions from the origin of replication.
(one chromosome = one molecule)
(visible evidence for chromosomes)
- histone H2A
- histone H2B
- histone H3
- histone H4
The DNA molecule is
wound one and three
fourths turns around a
(confirmed by DNase digestion)
- G1 = pre-DNA synthesis
- S = DNA synthesis
- G2 = post-DNA synthesis
- M = mitosis: cell division occurs by precise steps which distribute one set of chromosomes to each of two daughter cells
-Stages of Mitosis-
*Chromosomes decondense until they are no longer visible. *Cytokinesis follows.
<Simplified overview of meiosis>
*The behavior of a single pair of
*Each chromosomes already
consists of two chromatids,
joined at a single centromere.
- Chromosomes duplicate in S phase
- Homologous chromosomes pair: 4 strands of chromatids align
- Homologous chromosomes are pulled to either pole of the cell at anaphase
- Cell division occurs in the absence of chromosome duplication
- Sister chromatids separate at anaphase as in mitotic division
Two Pairs of Homologous Chromosomes
* No cross-over between sister chromatids.
* Random genotype formation in a gamete
genetically haploid (n)
What mechanisms would result in cytogenetic abnormalities?
Relate Down syndrome and the nonseparation of chromosomes
Describe how chromosomes can be damaged and the consequential effects
Explain how a “jumping gene” can affect other genes.
Use a microscope to observe different shapes and lengths of chromosomes
N = A B C:
2N = AA BB CC:
N = A B C:
3N = AAA BBB CCC
Horse + donkey mule
N = 63
Though people with Down syndrome have lifetimes that are shorter than average, they can live to middle age or beyond.
Click here for some effects of chromosomal translocations…
Some copy themselves and jump to new locations in our DNA where they affect adjacent genes. In their new location they can disrupt a gene completely, or subtly change the way it exerts its effects in the cell. This can have both positive and negative consequences.
Click here if you want to learn more…