CHAPTER 15:
THE CHOMOSOMAL BASIS OF INHERITANCE
•
Chromosome theory of inheritance- a basic principle in biology stating that gens are located on chromosomes and that the
behavior of chromosomes during meiosis accounts for inheritance patterns
•
Thomas Hunt Morgan did an experiment with fruit flies (
Drosophilia
melanosaster
). This species only has 4 chromosomes.
He did experiments by breeding them, and looking for mutations. He found that the white eyed mutations occurred on the
Y chromosome.
•
Wild
type
- the phenotype for a character most commonly observed in natural populations, such as red eyes in fruit flies
•
Mutant
phenotypes
- due to alleles assumed to have originated as mutations in the wild type
•
Linked
genes
- genes located on the same chromosome that tend to be inherited together in genetic crosses
•
Genes are not assorting independently in real life
•
Crossing over unlinks linked genes
•
Genetic
recombination
- general term for the production of offspring with combinations of traits that differ from those
found in either parent
•
Parental
types
- offspring that have the same phenotype as one of the parents
•
Recombinant
types
- offspring that have a different phenotype than the parents
•
When 50% of all offspring are recombinants, there is 50% frequency of recombination
•
Recombination frequencies depend on the distances between genes on a chromosome. The farther apart two genes are, the
higher the probability that a crossover will occur between them and therefore the higher the recombination frequency.
•
Distances between genes are expressed in map units. 1 map unit = 1% recombination frequency
•
Chromosomal systems of sex determination
o
Humans adhere to
the X-Y system
: In mammals, the sex of an offspring depends on whether the sperm cell contains
an X chromosome or a Y. Short segments at either end of the Y chromosome are the only regions that are
homologous with the corresponding regions of the X. These homologous regions allow the X and Y chromosomes in
males to pair and behave like homologous chromosomes during meiosis in the tests.
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- Spring '07
- Cusic
- Thomas Hunt Morgan
-
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