Download Special Topics in Heredity

AP BIOLOGY
CHAPTER 15 notes
Mapping genes
Crossing
over happens more often to certain alleles
that are far away from each other on the chromosome
The distance is designated by the number of map
units separating the two genes.
Example of mapping genes
http://www.biology.lsu.edu/webfac/jcl
arkin/genetics2153/GENET10.pdf
Multiple Gene effects
•
Pleiotropy: The ability of one gene (one protein) to affect an
organism in many ways (multiple traits).
Ex. Sickle-cell anemia has many symptoms
•
Epistasis: One gene affects the expression of a gene at a
different locus. (2 genes - one trait: nonadditive)
Ex. One gene in Labrador determines whether the dog deposits a
lot of melanin or a small amount of melanin, Another gene
determines whether the melanin will be deposited at all. If the
second gene is recessive, the Labrador has no melanin
independent of the first gene.
•
Polygenic inheritance: The additive effect of two or more genes
on a trait.
Ex. Several genes are involved in skin color with an additive
effect on the amount of pigment.
Nature vs. Nurture
• Are we a product of our genetics or our
environment?
• Phenotype is not rigid and has a general
“range” due to our genetics.
• Bell curve
Pedigree
• Pedigree: A family tree for a particular trait
used to indicate family history.
• Carriers: Individuals that are
heterozygous for a particular negative trait.
The individual doesn’t have the trait, but
they carry one bad gene that could be
potentially passed onto offspring.
Pedigree
Barr Bodies
• One of each X chromosome is inactivated.
• The inactivated X is called a Barr Body.
• Calico cats are produced by inactivating
different X chromosomes in different
regions of the cat
More terms
• Linked genes: Genes on the same
chromosome, thus they are inherited
together.
• Sex-linked genes- Genes found on the sex
chromosomes.
• Recombinants- Organisms resulting in the
sharing of DNA from two different
organisms. (sexual reproduction)
Mitochondrial DNA: All from mom in
her egg