1. Meiosis and Sex-linked traitsCh

2. Objectives Explain chromosome theory of inheritance
Understand genetic linkage
Explain sex-linked genes and why more common in males

3. Chromosome Theory of Inheritance
Mendel’s findings were not widely accepted at first
During the 1900’s, parallels discovered between genes and chromosomes
This is referred to as the chromosome theory of inheritance:
Chromosome Theory of Inheritance:
Genes located on chromosomes
accounts for inheritance patterns

4. Chromosome Theory of Inheritance
Remember, diploid individuals have 2 sets of homologous chromosomes
One from mom, one from dad
Gene locus:
Alleles of a gene reside at same location

5. Genetic Linkage and Crossing Over
Tendency for alleles on one chromosome to be inherited together
Closer the genes, the greater the genetic linkage
Farther apart, greater chance of separation

7. Sex Linked Genes What two sex chromosomes make up a male? Female?
Male = XY, Female = XX
Which chromosome is physically larger?
The X. It can hold a lot more genetic info
Sex linked gene:
Any gene on a sex chromosome

8. Sex-linked Disorders Many sex-linked disorders are recessive alleles
Let’s say that white eyes in fruit fly is an example
Disorders always carried on X chromosome (Y doesn’t have any room, too small)
What does all this mean?

9. Sex-linked Disorders
If disease is recessive and always carried on X chromosome, then females (XX), will most likely have dominant form of allele on other chromosome --> don’t get disorder.
If males (XY) have allele for disorder on their X chromosome, they will get disorder because Y chromosome doesn’t carry alleles.

10. Rare!