1. Ch. 10 Genes/Chromosomes Chromosome Theory of Heredity
Genes located on chromosomes (Sutton)
Genes can be linked (Morgan)
Genes can cross over (Morgan/Sturtevant)
Autosomes/Sex chromosomes (Stevens)
Sex Linked genes (Morgan)
Mutations
Chromosomal mutations – genes
Mutation in genes – nucleotides
Gene Expression
Incomplete dominance
Codominance
Polygenic inheritance

2. THOMAS MORGAN

3. Morgan’s DISCOVERY of LINKED GENES
Characteristics of linked genes
WHEN GENES ARE CLOSE TOGETHER ON A CHROMOSOME THEY TEND TO BE INHERITED TOGETHER
LINKED GENES tend to not SEPARATE from one another during Crossing Over Prophase I
During Cross Over in Prophase, they tend to stay together instead of separating and switching

4. How Morgan Discovered Linked Genes
USED DROSOPHILA Genus name
common name Fruit flies WHY?
They Mature in 2 weeks
They Produce large numbers of offspring
They only have 4 pair of chromosomes
One pair are the Sex CHROMOSOMES

5. The Experiment for Linked Genes Part I
Thomas crossed PURE BRED fruit flies for two traits
Homozygous Dominant GRAY BODIES & NORMAL WING SIZE (GGWW) with Homozygous Recessive flies that had BLACK BODIES & SMALL WINGS (ggww)
GG WW X gg ww
WHAT Genotype DID HE EXPECT IN THE OFFSPRING?
GgWw
WHICH IS WHAT HAPPENED
Okay Big deal!
What do you think he did next?

6. MORGAN’S Experiment Part II
GgWw x ggww GW gw Gw gW
He then crossed an F-1 of the GgWw hybrid offspring w/a recessive ggww
What would you expect?
Fill out this punnett-
he did not get as expected…
¼ GRAY NORMAL
¼ GRAY SHORT
¼ BLACK NORMAL
¼ BLACK SHORT
INSTEAD, he got…

7. Experiment’s Results for Part II
gg ww alleles
Gg Ww alleles
Expected
Actual Results
2300 total offspring

8. MORGAN’S RESULTS http://nortonbooks
41.5% GRAY body/Normal wings
41.5% BLACK body/small wings
8.5% GRAY body/Small wings
8.5% BLACK body/Normal wings
MORGAN’s Conclusion
The genes for wing size and body color were so commonly inherited as only two combinations either gray body/normal wing or black body/small wing that they had to be …
on the same chromosome!
This indicated that the genes for body color and wing size were…
LINKED onto one chromosome.

9. Crossing Over Explains the other 8
Crossing Over Explains the other 8.5% combinations of either Black Body/Normal Wing or Gray body/Small Wing
Chromosome combinations for gametes
Homologous chromosomes

10. This means that even though genes can be linked,
They can sometimes separate from one another during
Crossing Over in Meiosis

11. Cross-over Used to Map Genes
Short Arm
Bands Represent Genes
Long Arm

12. GENE MAP
If you know the frequency of how often genes cross over, you can use the percentage to estimate how far apart the genes are from on another on a chromosome
This is called a Gene Map
So if two genes have an 8% frequency of crossing then are they far apart or close on a chromosome? B c A

13. NETTIE STEVENS Discovered Sex Chromosomes
She worked with MEALWORMS
DISCOVERED they had 20 chromosomes.
MALES had 19 regular size & 1 small one. The Females all the same size chromosomes
SHE SAID “THE 19 that were the same are AUTOSOMES (body chromosomes), & the other set were SEX CHROMOSOMES”
FRUIT FLIES same for male/females
Males have XY
Females have XX

14. GENES ON SEX CHROMOSOMES http://www. mhhe
A gene located on a A SEX CHROMOSOME is called a SEX-LINKED GENE
MORGAN DISCOVERED the 1ST SEX-LINKED gene in fruit flies
He crossed a PUREBRED Dominant RED-EYED FEMALE W+W+ with a PUREBRED recessive WHITE-EYED WW MALE
Let’s take a look at the 1st cross.

15. Morgan’s 1st Sex Linked Cross
All offspring had red eyes

16. MORGAN’S 2nd CROSS
HE crossed from the F-1 generation a heterozygous FEMALE, W+W RED-EYED with a RED-EYED W+ MALE (note only 1 allele!
Let’s do the cross
HE got a 3:1 RATIO of Red eye to White eye, but only MALES had WHITE EYES! Why?
Since no FEMALES had WHITE EYES Morgan hypothesized that EYE COLOR must be a SEX-LINKED gene
IT must be on the X CHROMOSOME
The Y chromosome does not carry a gene for EYE COLOR
• The RECESSIVE TRAIT White eyes, is inherited more often in males that receive the r allele on their one and only X CHROMOSOME

17. MORGAN’S EXPERIMENTAL CROSS
White eyed male
Red eyed female
All females had red eyes
All males had red eyes
3:1 ratio red eyes to white eyes
Only males had white eyes

18. Mutations
Gene mutations – chemical change that affects the DNA molecule of a specific gene during DNA replication
Chromosomal mutation – change in the number or the structure of chromosomes during meiosis

19. Mutations http://learn. genetics. utah
Point mutation -single nucleotide is misplaced
A substitution may not be fatal, since there is redundancy in the amino acid codons
BUT it can code for the wrong amino acid which creates an incorrect or nonfunctional protein
Frame shift mutation - the deletion/insertion of a single nucleotide causes a frame shift which often results in a nonfunctional protein

20. Chromosomal mutations

21. http://en. wikipedia. org/wiki/Chromosomal_translocation http://www
DUPLICATION, INVERSION, DELETION, TRANSLOCATION

22. Nondisjunction http://www. mhhe
Failure to separate chromosomes evenly during meiosis
Chromosomal mutations involving whole or complete pairs of chromosomes
3n-triploidy
4n-tetraploidy
Having more then one set of chromosomes-polyploidy
Fatal in humans, beneficial in plants

24. http://www. pbs. org/wgbh/nova/genome/program
13:08 time ONE WRONG LETTER

25. JOSEPH KOLREUTER 1760-Crossed white rr x red RR carnations
He got…Rr which were pink!
Phenotype was in between the parents
He crossed the Rr hybrid F-1 and got red, white and pink combos
This shows that R is incompletely dominant over the r gene
r does not code for a protein but R can not compensate for this so an intermediate hybrid is created

26. INCOMPLETE DOMINANCE
A PHENOTYPE
THAT IS INTER-
MEDIATE OF
EITHER GENE

27. CODOMINANCE Two genes are expressed equally
ONE gene is not DOMINANT over the other gene
Two dominant genes
Are expressed
How does this happen?

28. POLYGENIC INHERITANCE
OF SEVERAL
GENES TO
EXPRESS A
SINGLE TRAIT
LIKE SKIN COLOR

29. Concept map scientists in this chapter