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Chapters 1-2
Mendelian Genetics and
Nucleic Acid Structure
23 August, 2006
Overview
• Mendel refuted the blending hypothesis, proposing
particulate units of inheritance - genes.
• The idea of genetic inheritance gained support from the
behavior of chromosomes in meiosis and fertilization.
• Linkage analysis can give information about the relative
location of genes on chromosomes.
• The success of Mendelian genetics increased the importance
of characterizing the genetic material.
• Chromosomes are composed of DNA and protein - the DNA
is the genetic material.
• Nucleic acid structure gives important insight into genetic
function.
Review of Mendelian Inheritance
• Genes influence characters, and
may occur in a number of different
allelic forms.
•Each organism / cell has two
copies of each gene, and may be
homozygous or heterozygous.
•Gametes carry a single allele of
each gene. Alleles are distributed
randomly to gametes.
•Fertilization combines the alleles
present in the two participating
gametes.
Incomplete Dominance
Independent Assortment
Linkage and Recombination
• Linked genes are carried on the same chromosome.
• Homologous chromosomes exchange genetic material during synapsis.
This changes the combinations of alleles that are possible
• Recombination frequency is proportional to physical distance.
Genetic maps use crossover frequency to order groups of linked genes.
•Genes are carried on chromosomes, and are inherited
unchanged and undiluted.
•Mutations are rare events that change one allele to another.
•A genetic material that was inherited unchanged and
undiluted, but subject to rare mutation answered a major flaw
in evolutionary theory.
•The success of genetics intensified interest in the nature of the
genetic material.
•Chromosomes are composed of DNA and Protein. Most
biologists thought that Protein was the genetic material, while
DNA was structural.
DNA is the Genetic Material
•DNA but not protein can transform bacteria.
Viral Genes are nucleic acids
The structure of DNA elucidated its function.