Biology 3.2 Chromosomes (YouTube)

• Genes are the basic units of heredity and affect organisms.
• Genes can change due to environmental factors and the process of inheritance.
• A genome is the complete set of genes for a species.
• Chromosomes carry genes in a linear sequence that is shared by members of a species.
• In prokaryotic cells, chromosomes are stored as a single chromosome consisting of circular DNA molecule suspended in cytoplasm and free to move about within the cell, this area is referred to as a nucleoid.
• Prokaryotic chromosomes are free of proteins unlike eukaryotic chromosomes, this lack of proteins in prokaryotic cells is essential for allowing the large chromosome to fit within the small prokaryotic cell.
• The presence of protein structures in prokaryotic cells would allow there to be a structure to the chromosome, but a lack of protein structures allows prokaryotic cell DNA to be supercoiled, which means to be twisted into a small and compact shape.
• The small and compact shape of prokaryotic cell DNA allows it to fit comfortably within the cell even though the chromosome strand is much longer than the cell itself.
• Some prokaryotic cells also have plasmids, which are small circular DNA molecules that contain only a few genes and are capable of self-replication, plasmids are not naturally found in eukaryotic cells.
• A zygote is a cell that can copy itself and develop into an organism.
• There are two types of chromosomes in humans: heterosomes and autosomes.
• Sex in humans is determined by a pair of sex chromosomes, which are heterosomes.
• A human female possesses a chromosome pair of XX, both of which have genes that code for female sex characteristics.
• Males have one X chromosome inherited from their mother and one Y chromosome inherited from their father.
• The presence of the Y chromosome in a human is what leads to the human developing male sex characteristics.
• If the sperm cell from the father is carrying the X chromosome, the resulting offspring will be a female.
• If the sperm from the father is carrying Y chromosome, the resulting offspring will be a male.
• It is the haploid from the father that determines the sex of the offspring in all cases.
• The female egg will carry an X chromosome.
• The remaining chromosomes that do not determine your sex are called autosomes.
• To organize the chromosomes of a species, a model must be present, known as a karyogram.
• The karyogram model shows homologous pairs in descending length order with sex chromosomes shown at the end.
• Carygrams are used to determine the sex of humans and if that human might have Down Syndrome.
• Before the baby is born, the karyogram can be created and analyzed for abnormalities to determine the sex of the baby.
• The sex chromosome must be identified to identify Down Syndrome.
• Plasmids allow the sharing of genetic material between bacterial cells, this sharing of genetic material can allow bacteria to evolve within a generation, the exchange occurs through a process called conjugation where the sex pili of the bacteria with the plasmid links with another bacteria cell, the plasmid is copied within the first cell and passed to the second cell.
• The last chromosomes in the karyogram show a long X chromosome and a shorter Y chromosome, indicating that the person is genetically male.
• The number of chromosomes in a species is a characteristic feature of members of a particular species, meaning that species with different diploid chromosome numbers will not produce viable offspring.
• There are some cases where species of different diploid numbers can reproduce, such as a horse and a donkey who can create a mule, but the offspring will be left unable to reproduce, defining these species as separate.
• The number of chromosomes does not indicate a more complex organism, as evidenced by the comparison of diploid chromosomes of humans compared to dogs, where dogs have 78 chromosomes and humans have 46.
• Genome size does not show a valid indication of genetic complexity when comparing the genome of a human to a canopy plant, as the canopy plant has 50 times more base pairs than humans but is not 50 times more complex.
• Viruses and bacteria tend to have very small genomes, while prokaryotes typically have smaller genomes than eukaryotes, and sizes of plant genomes can vary dramatically due to the capacity for plant species to self-fertilize and become polyploid.
• John Kerens developed his method for photographing chromosomes while they are uncoiled, a process called autoradiography, using cells grown in radioactive thymodyne, a chemical that reacts with the chromosomes and makes them radioactive.
• Radioactive chromosomes are placed on a photographic plate and placed in silver bromide solution, causing the silver in the solution to turn into an insoluble substance that can then be viewed through an electron microscope.
• The visual through the electron microscope shows the insoluble silver that has reacted as little black dots with a clear visual of uncoiled chromosomes, and the length can be measured.
• Plasmids are essential in bacteria in building immunity to antibacterial drugs, there are usually one of two plasmids per chromosome in prokaryotic cells but for some smaller plasmids the number can be up to 50.
• The number of plasmids within the prokaryotic cell influences the strength of the plasmid-borne characteristic, especially for antibacterial resistance.
• The structure of eukaryotic cells differs from prokaryotic cells due to the proteins used as a structure for DNA.
• Eukaryotic chromosomes are linear DNA molecules associated with histone proteins.
• Histone proteins create a compact structure for more efficient storage of DNA.