Download Ch. 10.4: Meiosis & Mendel`s Principles

Ch. 10.4: Meiosis & Mendel’s
Principles
Objectives:
1. Summarize the
chromosome theory of
inheritance.
2. Explain how genetic
linkage provides
exceptions to
Mendel’s principle of
independent
assortment.
Vocabulary
Chromosome theory of
inheritance
Gene locus
Genetic linkage
Chromosome Theory of Inheritance

Genes are located on
chromosomes.

Behavior of
chromosomes during
meiosis & fertilization
accounts for inheritance
patterns.

Chromosomes segregate
and independently
assort during meiosis.
Meiosis I: Homologous chromosomes
separate.
Gametes will either get paternal allele or maternal allele due to
independent assortment of chromosomes.
Which allele is
present in
gamete is
random …
depends on how
chromosomes
line up during
metaphase.
INDEPENDENT ASSORTMENT: Genes on DIFFERENT
chromosomes.



Genes located on
separate chromosomes
sort independently
during Meiosis.
Agrees w/ Mendel’s
discoveries.
Color and texture of
peas are not
linked…they are not
inherited together.
If genes on diff. Chromosomes did NOT sort independently, then yellow smooth and
green wrinkled parents could not produce yellow winkled or green smooth offspring.
Genes on Same Chromosome tend
to be LINKED.
They are not sorted independently.
Exception to Mendel’s rules.
Gene Loci
Loci = location of gene (allele)
on chromosome.
Chromosome from mother
Chromosome from father
Gene Loci & Genetic Recombination:

Crossing over during
Prophase I:
 Makes new combinations
of traits (alleles) in
offspring.
 Shuffles Alleles
 Makes combinations not
found in parents.
But… some traits (genes/alleles) are more likely to be reshuffled
than others.
Genetic Linkage



Tendency for alleles on
same chromosome to be
inherited together.
Closer genes are on
chromosome = Less likely
to exchanged during crossover.
Greater distance b/w alleles
= more likely to be
recombined.
Genetic Linkage
Linked Genes: Close
together on
chromosome. Travel
together during
crossing over.
A and B (and a and b) are close together
C (and c) is far from A and B.