phenotypic expression: *penetrance *expressivity gene expression often governed by genotype and...
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Phenotypic Expression:
*Penetrance
*Expressivity
Gene expression often governed by genotype and environment
Example:
if 9/10 of individuals carrying an allele express the trait, the trait is said to be 90% penetrant
*Onset of genetic expression
*Temperature
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Chapter 5: Sex Determination
Life cycles and reproductive modes
*Asexual reproduction
*Primary sexual differentiation
*Secondary sexual differentiation
*Unisexual, dioecious and gonochoric
*Bisexual, monoecious and hermaphroditic
*Alternation of generations
*Sexual reproduction
Some additional terms:
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Chlamydomonas
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Maize (Zea mays)
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Mutants of Maizetassel seed (ts)
silkless (sk)
barren stalk (ba)
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Caenorhabditis elegans (C. elegans)
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Review: Sexual Differentiation
Life cycles and reproductive modes
*Asexual reproduction – C.elegans hermaphrodite vegetative Chlamydomonas
*Alternation in cycles -Chlamydomonas
Maize
*Sexual reproduction – Chlamydomonas
C. elegans Maize
Humans
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X and Y Chromosomes: Early Studies
1906 Edmund B. Wilson
and Protenor
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X and Y Chromosomes: Early Studies
Wilson and Lygaeus
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X and Y Chromosomes: Early Studies
Terms:
Homogametic sex
Heterogametic sex
*The male is not always the heterogametic sex…
Examples:
Moths, butterflies, most birds, some fish, reptiles, amphibians, at least one species of plants
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Chromosome Composition in Humans
Karyotype
XX XY
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The Y Chromosome
Pseudoautosomal regions (PAR)
NRY
Testis Determining Factor (TDF)
*SRY – Sex determining region
Is the Y chromosome a “genetic wasteland”?
*Housekeeping genes
*Testis development and function
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SKALETSKY, et al. (2003) The male-specific region of the human Y chromosome is a mosaic of discrete sequence classes. Nature 423, 825 - 837
The Y Chromosome