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The Chromosomal Basis
of Inheritance
Marie Černá
Thomas Hunt Morgan
1910s - 20s
Morgan’s experiments
fruit fly: Drosophila melanogaster
– prolific breeders (100s of offspring / 2 weeks)
– 4 pairs of chromosomes (8, XY; 8, XX)
Morgan’s laws
linked genes on the same chromosome
• are located linearly in the gene loci
• tend to be inherited together
Genetic recombination
• Independent assortment of
chromosomes (unlinked genes)
- 50% frequency
• crossing over (linked genes)
- the greater the distance between two genes,
the more points there are between them
where crossing over can occur
1 centimorgan = 1% recombination frequency
Genetic maps
• linkage map
- based on recombination frequencies
• cytological map
- based on stained bands of chromosomes
that can be seen in the microscope
• genetic map
- based on DNA nucleotide sequences
Sex determination
• in mammals (humans),
some insects (fruit flies)
• in some insects
(grasshoppers, crickets, roaches)
• in birds, some fishes,
some insects (butterflies, moths)
• in bees and ants
Literature
Biology, eighth edition,
Campbell, Reece
Unit three: Genetics
Chapter 15:
The Chromosomal Basis of Inheritance
Pages 286 - 296