1. Gene Linkage and Mapping & Human Genetics and Pedigrees
Sections

3. Drosophila Melanogaster
- Fruit Flies
- Used in numerous genetic experiments
- Easy to breed
- Quick turn around for new generations
- Simple genetic make-up
Only 4 chromosomes!!!

4. Mendel’s Experiments What types of organisms did he use?
What was he trying to determine?
Conclusions?
Organisms inherit traits from their parents
Law of segregation
Law of independent assortment

5. Dihybrid crosses! Oh no!

6. Punnett and Bateson Got different results for their dihybrid crosses
not the normal 9:3:3:1
Suggested some genes are “linked” together somehow

7. Thomas Hunt Morgan Used fruit flies in his experiments
Also got different results than 9:3:3:1
Noticed some traits were generally inherited together
He called these “linked”

8. Alfred Sturtevant Was a student of Morgan’s
Hypothesized cross-over frequency took place more with genes that were closer together
The closer the genes are to each other, the more likely they are to be linked

9. Sturtevant’s Experiments
Tracked 3 linked traits in fruit flies
Body color, eye color, and wing size

10. Sturtevant’s Experiments
He kept track of how many times the traits DID NOT appear together
Percentage they did not appear together = frequency of cross-overs
Was able to formulate linkage maps from his results

11. What is a linkage map?
The mapping of the general location of a gene or genes on the actual chromosome

12. Sex-linked disorders These suck for us, gentlemen
Females can only be carriers for such disorders
Usually have a normal gene that masks the effects
Males do not, since we only have the “Y” chromosome
Have no choice but to express the disorder

13. The passing on of hemophilia

15. Tracing autosomal genes
Done with the use of a pedigree chart
Organisms that express dominant traits have to be…?
Organisms that express recessive traits have to be…?
Organisms that express dominant traits can have a child that expresses dominant traits if the parents are…?

17. Tracing sex-linked genes
Have to keep gender in mind at all times!!!
Colorblindness
Normal vision genotypes
XMXm (female carrier)
XMXM (female non-carrier)
XMY (male non-carrier)
Colorblind vision Genotypes
XmXm (female affected)
XmY (male affected)

19. Are you colorblind?

20. What is this called?
What is it showing?