Download Meiosis and Sex

Meiosis and Sex-linked traits
Ch. 10.4-10.5
Objectives
1. Explain chromosome theory of inheritance
2. Understand genetic linkage
3. 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
• Genetic Linkage:
– 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!