Meiosis and Sex-linked traits Ch. 10.4-10.5

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

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

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

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

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

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?

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.

Rare!