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Chromosomes to DNA
Transcript of Chromosomes to DNA
Thomas Hunt Morgan Embryologist to study Fruit flies called Drosophila melanogaster.
Wild Type is normal, Mutant phenotype is the new type.
They showed Sex-Linked inheritance. Sex-linked genes
are traits that are
carried on the X
Who shows it? MALE Women can show it, but they have to have two
copies of the recessive or mutant type. Women have two sex chromosomes, but they only need one to work. The original embryonic cell tells the rest of the cells it makes which one they will use. The other X becomes inactive and triggers a gene to RNA and cover it. These creates a Barr Body that stays close to the nuclear envelope. Human Examples:
Duchenne Muscluar Dystrophy
Hemophilia There are however linked genes... These are genes that are on the same chromosomes and are only separated by, what? Crossing over causes Genetic Recombination... Do I really need to explain what that means? Alfred Sturtevant took Morgan's calculations of how often the wild and mutant types showed. By using these percentages, they could see how close and in what order the genes were from each other. Sturevant called the spacing map units, but they were later called centimorgans to honor his protegee.
THESE DO NOT actually show the true location, just how the genes are related to each other! Other methods allowed us to make cytogenetic maps, or the ability to see gene locations in relations to the bands we see through the microscope. Other Disorders:
caused by Nondisjuction
monosomic or trisomic The karyotypes we worked with last chapter were examples, do you remember which was which? This is very common in the plant kingdom... Polyploidy -
like triploidy or tetraploidy 4n 6n Chromosomal alterations
Translocations Cri du chat: mentally retarded with a cry like a cat. Types of cancers are caused by this... The last chromosomal factor is genomic imprinting, with is the phenotype is infleunced by what sex they come from. Griffith: Oswald Avery Hershey and Chase Rosalind Franklin