1. DNA Replication video:

3. Drosophila are easily bred and produce a large number of offspring
have 4 pairs of chromosomes
species of choice by Thomas Hunt Morgan
hit them with X-rays trying to find mutants
after 2 years of searching he finally found a mutant fly – one with white eyes

4. XX XY X X X Y XX XX XY XY XX XY X X X Y XX XX XY XY
interbred the white eyed fly and the red eyed fly
F1 generation – all red eyed
F2 generation – typical 3:1 ratio of red to white eyed flies
but…..no females had white eyes – and half the males had red eyes and half had white eyes
so Morgan hypothesized that the gene for eye colour was on the X chromosome X X X Y XX XX XY XY

5. X-linked diseases Carrier female: XX Affected Male: XY XX XY X X X Y
X-inactivation XX XX XY XY
e.g. hemophilia
Duchenne Muscular Dystrophy

6. Genes located on the same chromosome – the genes tend to be inherited
Linked genes:
Genes located on the same
chromosome – the genes
tend to be inherited
together
linked genes
go through if independent assortment happened
then see what really did happen

8. frequency of recombination is 50% (independent assortment)
Note: if two genes
are on different
chromosomes – the
frequency of recombination
is 50% (independent
assortment)
crossing over changes the frequency of recombination
frequency depends on the distance between linked genes

9. Down Syndrome What happens if there are problems during meiosis?
trisomy: a gamete is produced with an extra chromosome 21
Robertsonian translocation -

10. Philadelphia chromosome - CML