1. Genetic Linkage
Chapter 11, Section 5

2. The Chromosome Theory of Inheritance
It is the chromosomes that segregate and assort independently during gamete formation
On a pair of homologous chromosomes, alleles of a gene reside at the same location called a gene locus

3. Meiosis: Gamete Formation
An organism is either homozygous or heterozygous for each gene
The alleles carried on different chromosomes assort independently into gametes

4. Genetic Linkage and Crossing Over
Genes that are carried on the same chromosome are often inherited together  genetic linkage
Crossing over can separate linked genes
In general, alleles with loci close together will stay together; Alleles farther apart are more likely to be separated by crossing over

5. Sex-Linked Genes
Discovered by American Geneticist Thomas Hunt Morgan in the early 1900s studying fruit flies
Normally, fruit flies have red eyes, but Morgan discovered that some mutant flies had white eyes (most of which were males)

6. Sex-Linked Inheritance Patterns
About 2,000 genes have been mapped to the X chromosome, and only about a dozen have been mapped to the Y chromosome
Females must inherit two copies of a sex-linked recessive allele to express it; males only need ONE COPY of the allele to express it
Ex: XrXr = white-eyed female
XrY = white-eyed male

7. Morgan’s Experiment
Morgan’s F1 Generation

8. Sex-Linked Disorders Colorblindness (effects 1 in 100 males)
Red-green colorblindness
Orange-blue colorblindness
Hemophilia (effects 1 in 5,000 male births and 1 in 20,000 female births)
A complication in which blood does not clot normally