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Chapter 15
The Chromosomal Basis of Inheritance
14
Biology
Undergraduate 2
09/22/2008

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Term
Chromosome Theory of Inheritance
Definition
1902

- mendelian genes have specific loci on chromosomes, and it is the chromosomes that undergo segregation and independent assortment
Term
Thomas Hunt Morgan
Definition
early 1900s

- proved that genes are located on chromosomes through his work with fruit flies

- first indication of sex-linked genes because only males had white eyes
Term
Why did Morgan use fruit flies?
Definition
• Easy to rear in lab
• Short generation time (approximately 10 days)
• Abundant offspring (100s per mating)
• Only 4 pairs of chromosomes
• Numerous mutation stocks now available
Term
Wild Type
Definition
- the normal phenotype for a character (the phenotype most common in natural populations)

example: fruit flies with red eyes
Term
Mutant Phenotypes
Definition
- traits that are alternatives to the wild type

- assumed to have originated as mutations in the wild-type allele

example: fruit flies with white eyes
Term
Linked Genes
Definition
- linked genes are located on the same chromosome and tend to be inherited together in genetic crosses

- probability of gene linkage is related to the space between the genes on the chromosome

- goes against Mendel's law of independent assortment
Term
genetic recombination
Definition
- the production of offspring with combinations of traits differing from those found in either parent

- identified by Morgan

mechanism: crossing over
Term
parental types
Definition
- offspring that inherit a phenotype identical to one of the parental phenotypes
Term
recombinant types
Definition
- offspring whose phenotypes are nonparental (do not match the phenotypes of either parent)
Term
crossing over
Definition
- the process that breaks the physical connection between genes on the same chromosome (one maternal and one paternal chromatid break at corresponding points and then are rejoined to each other?)

- allows for recombinant types

- the mechanism that Morgan purposed to support the idea of genetic recombination
Term
genetic map
Definition
- an ordered list of the genetic loci along a particular chromosome
Term
Recombination Frequency
Definition
- the frequency with which crossing over will occur depends upon the distance between the genes on a chromosome

- the farther apart two genes are, the higher the probability that a crossover will occur between them and therefore they will have a higher recombination frequency
Term
Sex-Linked Genes
Definition
- genes located on either sex chromosome

- historically related to genes inherited on the X-chromosome in humans
Term
polyploidy
Definition
- general term for the chromosomal alteration that causes an organism to inherit more than two chromosome sets

- common in the plant kingdom
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