The Chromosomal Basis The Chromosomal Basis of Inheritance of Inheritance

Marie ČernáMarie Černá

Thomas Hunt MorganThomas Hunt Morgan 19101910ss - 20s- 20s

Morgan’s experimentsMorgan’s experiments

fruit fly: Drosophila melanogaster

– prolific breeders (100s of offspring / 2 weeks) – 4 pairs of chromosomes (8, XY; 8, XX)

Morgan’s lawsMorgan’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 mapsGenetic 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 determinationSex 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

LiteratureLiterature

Biology, eighth edition,

Campbell, Reece

Unit three: Genetics

Chapter 15:

The Chromosomal Basis of Inheritance

Pages 286 - 296