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.

 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. INDEPENDENT ASSORTMENT: Genes on DIFFERENT chromosomes. 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.

 Tendency for alleles on same chromosome to be inherited together.  Closer genes are on chromosome = Less likely to exchanged during cross- over.  Greater distance b/w alleles = more likely to be recombined. Genetic Linkage

Linked Genes: Close together on chromosome. Travel together during crossing over. Genetic Linkage A and B (and a and b) are close together C (and c) is far from A and B.