---Can result in Color blindness, muscular dystrophy, hemophilia.
Females inherit two X chromosomes (XX) However, one becomes inactivated. Inactive X condenses->Barr body. Barr bodies reactivate in ovarian cells. Prevent overexpression of X genes (dosage compensation)
Mosaic of cells with alternative active Xs--Patchiness of gene expressions. Ex: Toriseshell cats.
Usually located on same chromosome--Chromosomes passed along as a unit.
Expected ratio of phenotypes not found. Linked genes do not assor independently where one gene goes, so does the other.
Genetic recombination can still occur by crossing over can separate the linked genes.
•Recombinant % data can create gene map
•Space between genes: recombination %
–Genes far apart: increased recombination %
•Greater chance of crossing over separating genes
–Genes closer: decreased recombination %
•Lesser chance of crossing over separating genes
Homologous chromosomes do not separate
two of the same chromosome->one daughter cell
No chromosome-> other daughter cell
a result of nondisjunction. there is a wrong chromosome number in zygote.
fertilized egg is 2n+1
Alteration of individual chromosome structure
Mulitiple Sets of chromosomes=polyploidy
ex: Triploidy 3n; Tetraploidy: 4n
Can result from complete nondisjunction
-All chromosomes to one cell, none other
Not uncommon in plant kingdom
-results in speciation
Rare in higher animals
Some traits affected by parental source
--Different effect if gene from mother or father
--Vs. typically, alleles have equal effect
New imprinting with each generation
-Previous imprinting "overwritten" in gametes
Methylation (-CH3) of cytosine involved
-Additional functional group silences allele
One of many epigenic factors
Exhibit non-Mendelian inheritance patterns
Ex-DNA in mitochondria, plastids (plants)
Not distributed by rules of meiosis
Organelles with genes passed in cytoplasm
-Cytoplasm comes from egg (maternal)
Therefor, Genes of plastids are maternal only and genes of mitochondria are maternal only.