Chapter 4: Part 2 Flashcards
Name 2 examples of X-linked Recessive Genetic Disorders
- Red-green colorblindness
- Hemophilia A
Red-green colorblindness
- inability to see green and red colors
- if a man inherits an X with a LOF allele from his mother (like red-green colorblindess), he will AUTOMATICALLY have the trait
Hemophilia A
- inability to form blood clots
Normal phenotypes in X-linked recessive genetic disorders
- Female:
X_N X_N (2 normal alleles)
X-lof X_N (1LOF, 1 normal) - Male:
X_N Y
Affected phenotypes in X-linked recessive genetic disorders
- Female:
X-lof X-lof (2 LOF alleles, one from each parent) - Male:
X-lof Y (1 LOF allele from mother)
(males more likely since only have 1 “X;” affected sons are usually born to unaffected mother, thus trait skips generations, criss cross patterns)
(females not often affected, if at all)
Hemizygous in Males
- cannot be homozygous or heterozygous, only hemizygous for genes on X, only one X chromosome
Criss cross patterns
- sex-linked genes/characters transmitted from fathers to daughters, or from mothers to sons
- X-linked inheritance
- character inherited to new generation through the carrier of the previous generation
Why are all X-linked recessive alleles never passed from father to son?
- males have 1 X and 1 Y chromosome
- females carry only 2 X chromosome
- So, an X chromosome must be inherited from the mother (since it is all she carries), and only the Y chromosome can be inherited from the father (so genes are from both parents)
Why are all daughters of affected fathers carriers?
- father: X-lof, Y
- female must receive 2 X chromsome, and 1 must be from each parent
- since one from both parents and 1 guaranteed to be X-linked recessive, daughters will have X-lof trait covered by X from mother
Quantitative Trait
- a measurable phenotype that depends on the genotype and the enviornment(epigentic modification)
- can vary among individuals over a range to produce continuous distribution of phenotypes
What does complex genetics grow from in quantitative traits?
- genetic linkage
- pleiotropy
- X-linked recessive inheritance dosage compensation
- QTL(quantitative trait locus mapping)
What does enviormental influences grow from in quantitative traits?
- chromatin modification vis methylation
- norms of reaction
-missing heritability - could branch off from QTL(quantitative trait locus) mapping from epistasis
Norm of reaction plots
- demonstrate that the environment alone can cause phenotypic change [for an identical genome]
Plasticity
- same genome leads to different phenotype in different enviornment
Canalized
- same genotype leads to the same phenotype in ANY environment (opposite of plasticity)
Epigenetics
- a change in the functional OUTPUT of a genomic locus
In the ABSENCE of sequence variation/mutation
Describe the importance of thee methyl group in epigentics
In DNA, the base C (cytosine) can be methylated or de-methylated
Enzymes in cells add or remove methyl groups (DAMM methylases)
DNA constantly switches between euchromatin and heterochromatin based upon methylation state
CPG islands
- hundreds of rows of cytosine/guanine
- concentrate where methyl groups come on and off
- on/off switch
The himalayan allele
- C^h
- temperature sensitive
- dark pigment produced by C protein product ONLY at cold temperatures
- generates “points at cold extremities- the permissive temperature, demethylated(ON) in cold temperatures
-the body core is too “hot” ( non-Permissive) so there is no color, methylated (OFF) in warm temperatures - in cats and rabbit
- environment changed phenotype, but genome still the same in each cell!!
