Non-Mendelian Inheritance
AP Biology
Non-disjunction
Failure of chromosome pairs to separate during meiosis
Results in gametes with too many or too few chromosomes
-Aneuploidy: abnormal # of a certain chromosome
-Polyploidy: more than 2 complete chromosome sets
An embryo needs at least one X chromosome to survive
Alterations of Chromosome Structure
Breakage of a chromosome can lead to four types of changes in chromosome structure:
Deletion removes a chromosomal segment
Duplication repeats a segment
Inversion reverses a segment within a chromosome
Translocation moves a segment from one chromosome to another
Barr Bodies
In body cells of females one X chromosome at random is turned off early in development; inactivated X
is called a Barr body
All the cells descended from that cell have the same X turned off
If female is heterozygous she becomes a mosaic—some areas have the dominant gene expressed, some
have the recessive
Ex: calico cats, patches of colorblindness
Genomic imprinting
-a small number of genes are stamped with a “memory” of which parent they came from.
-the information in certain genes is active only when it passes to a child through the sperm or the egg.
-About 200 genes are imprinted in mammals, ½ are active on the female chromosome and ½ on the
male chromosome
Both Prader-Willi and Angelman syndromes are caused by a deletion of the same segment of
chromosome #15.
Inheritance of Organelle Genes
Extranuclear genes are genes found in organelles in the cytoplasm
The inheritance of traits controlled by extranuclear genes depends on the maternal parent because the
zygote’s cytoplasm comes from the egg
The first evidence of extranuclear genes came from studies on the inheritance of yellow or white
patches on leaves of an otherwise green plant
These genes for leaf color are carried in the chloroplast DNA
Some diseases affecting the muscular and nervous systems are caused by defects in mitochondrial genes
that prevent cells from making enough ATP
Examples include: mitochondrial myopathy
Mutations in mitochondrial genes acquired during your lifetime can contribute to diabetes, Alzheimer’s
disease, and heart disease