1. LECTURE 10: FROM GENE TO PHENOTYPE I
exam 1: review
chapter 6
questions & concepts
genes & gene products
allele interactions
gene & protein interactions
chi-square applications

2. CHAPTER 6: QUESTIONS how do genes influence the organism?
what are gene products?
... & what are they doing?
do alleles determine a specific phenotype?
how do genes interact?
can we dissect gene interactions using mutations?

3. CHAPTER 6: CONCEPTS
if 2 haploid genomes (i.e., the gametes of diploids) each with 1 recessive mutation are combined
 mutant phenotype?... the mutations are allelic (they identify alleles of the same gene) or
 wild type phenotype?... the mutations are not allelic (they identify alleles of different genes)

4. CHAPTER 6: CONCEPTS dominance can be complete or incomplete
some mutations can cause lethality or sterility
expression of some mutations can be dependent on environment  conditional mutations
most traits are determined by sets of genes that interact with the environment
modified monohybrid ratios reveal allele interactions
modified dihybrid ratios reveal gene interactions

5. GENE INTERACTION genes never do anything by themselves
levels of interaction between alleles of
1. the same gene
2. different genes

6. GENE INTERACTION 3 ways to study these interactions
1. genetic analysis (ch 6)
2. functional genomics (ch 12)
3. proteomics (ch 12)

7. GENES & GENE PRODUCTS 1st clue from human “inborn metabolism error”
PKU (phenylketonuria)
autosomal recessive
phenylalanine  tyrosine 
phenylpyruvic acid (toxic)

8. GENES & GENE PRODUCTS “1 gene - 1 enzyme” hypothesis
Beadle & Tatum (1940s, Nobel Prize)
Neurospora crassa (haploid fungus)
mutants (by irradiation) & analysis

9. supports growth of all genotypes
GENES & GENE PRODUCTS
supports growth of all genotypes

10. GENES & GENE PRODUCTS

11. GENES & GENE PRODUCTS

12. GENES & GENE PRODUCTS
3 arginine auxotrophs (arginine metabolism mutants)
mapped to different loci... different genes
growth on medium supplemented with different related compounds

13. GENES & GENE PRODUCTS chemical structure  biochemical pathway (B & T)
enzyme X enzyme Y enzyme Z
  
precursor  ornithine  citrulline  arginine

14. GENES & GENE PRODUCTS
results  arginine metabolism biochemical pathway
arg arg arg-3+
  
enzyme X enzyme Y enzyme Z
  
precursor  ornithine  citrulline  arginine

15. DNA  mRNA  polypeptide
GENES & GENE PRODUCTS
results  “1 gene - 1 enzyme” hypothesis
more accurately “1 gene - 1 polypeptide”
most genes encode physical structure of proteins
DNA  mRNA  polypeptide
some genes encode functional RNA only, e.g.
tRNA
rRNA

16. GENES & GENE PRODUCTS

17. GENES & GENE PRODUCTS

18. ALLELE INTERACTION interactions between alleles of one gene
1. dominance / recessiveness
2. semi-dominance = incomplete dominance
3. co-dominance (e.g.: IA & IB of ABO system)
4. multiple alleles (e.g.: IA, IB & i of ABO system)
5. conditional (e.g.: temperature sensitive)
6. lethality
7. sterility

19. DOMINANT & RECESSIVE ALLELES
mutation recessive  + allele haplosufficient
mutation dominant  + allele haploinsufficient

20. DOMINANT & RECESSIVE ALLELESP F1 F2
red x white 
red x red
¾ red + ¼ white :

21. INCOMPLETELY DOMINANT ALLELES
incomplete dominance (= semidominance)... P F1 F2
red x white 
pink x pink
¼ red + ½ pink + ¼ white
: :
phenotypes are quantitatively different

22. INCOMPLETELY DOMINANT ALLELES
are pink flowers more red or more white?
why is this not blending?

23. CODOMINANT ALLELES ABO blood type
i recessive to both dominant alleles (IA & IB > i)
IAIB is AB, qualitatively different from A or B

24. MULTIPLE ALLELES ABO blood type
6 possible genotypes & 4 possible phenotypes
influences variation of trait in populations

25. CONDITIONAL ALLELES influenced by environment, e.g.:
temperature (hot or cold)
desiccation
nutrient requirement
chemicals
infection

26. shi+/shits x shi+/shits
CONDITIONAL ALLELES
e.g.: temperature sensitive shibire (paralyzed) mutant P F1 F2
shi+ x shits 
shi+/shits x shi+/shits
all 25º 1
shits wild  25º = permissive temperature

27. CONDITIONAL ALLELES
e.g.: temperature sensitive shibire (paralyzed) mutant P F1 F2
shi+ x shits 
shi+/shits x shi+/shits
¾ active + ¼ 29º :
shits  29º = restrictive temperature

28. LETHAL ALLELES homozygotes lethal (can be dominant or recessive)
e.g., yellow (AY) allele in mice

29. ¼ AY/AY lethal + ½ AY/A yellow + ¼ A/A black
LETHAL ALLELES
homozygotes lethal (can be dominant or recessive)
e.g., yellow (AY) dominant allele in mice
AY/A  x AY/A  
¼ AY/AY lethal + ½ AY/A yellow + ¼ A/A black P F1
don’t see these
AY/AY
AY/A
A/A
2/3 AY/A yellow + 1/3 A/A black

30. LETHAL ALLELES e.g.: Curly (Cy) mutations in Drosophila Cy– Cy–
¾ alive + ¼ dead :
—— x —— P F1
2/3 curly + 1/3 wild type
Cy–/Cy–
Cy–/Cy+
Cy+/Cy+

31. STERILE ALLELES homozygotes sterile (can be dominant or recessive)
e.g., fruitless (fru) allele in Drosophila

32. STERILE ALLELES homozygotes sterile (can be dominant or recessive)
e.g., fruitless (fru) allele in Drosophila
fru+/fru  x fru+/fru  
¾ wild type + ¼ fruitless
fru/fru fruitless  x fru+/fru+ wild type 
 do not mate, no progeny P F1 F2

33. STERILE ALLELES e.g.: mushroom body miniature B (mbmB) mutations
mbmB– mbmB–
mbmB mbmB+ 
¾ alive + ¼ sterile :
mbmB+
mbmB–
———— x ———— P F1
homozygous mbmB– live but give no offspring