lecture 10: from gene to phenotype i fexam 1: review fchapter 6 fquestions & concepts fgenes...
Post on 21-Dec-2015
215 views
TRANSCRIPT
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
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?
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)
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
GENE INTERACTION
genes never do anything by themselves levels of interaction between alleles of
1. the same gene
2. different genes
GENE INTERACTION
3 ways to study these interactions
1. genetic analysis (ch 6)
2. functional genomics (ch 12)
3. proteomics (ch 12)
GENES & GENE PRODUCTS
1st clue from human “inborn metabolism error” PKU (phenylketonuria) autosomal recessive
phenylalanine tyrosine
phenylpyruvic acid (toxic)
GENES & GENE PRODUCTS
“1 gene - 1 enzyme” hypothesis Beadle & Tatum (1940s, Nobel Prize) Neurospora crassa (haploid fungus) mutants (by irradiation) & analysis
GENES & GENE PRODUCTS
supports growth of all genotypes
GENES & GENE PRODUCTS
GENES & GENE PRODUCTS
GENES & GENE PRODUCTS
3 arginine auxotrophs (arginine metabolism mutants) mapped to different loci... different genes growth on medium supplemented with different
related compounds
GENES & GENE PRODUCTS
chemical structure biochemical pathway (B & T)
precursor ornithine citrulline arginine
enzyme X enzyme Y enzyme Z
GENES & GENE PRODUCTS
results arginine metabolism biochemical pathway
arg-1+ arg-2+ arg-3+
precursor ornithine citrulline arginine
enzyme X enzyme Y enzyme Z
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
GENES & GENE PRODUCTS
GENES & GENE PRODUCTS
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
DOMINANT & RECESSIVE ALLELES
mutation recessive + allele haplosufficient mutation dominant + allele haploinsufficient
P
F1
F2
red x white
red x red
¾ red + ¼ white3 : 1
dominant & recessive alleles...
DOMINANT & RECESSIVE ALLELES
P
F1
F2
red x white
pink x pink
¼ red + ½ pink + ¼ white1 : 2 : 1
incomplete dominance (= semidominance)...
INCOMPLETELY DOMINANT ALLELES
phenotypes are quantitatively different
are pink flowers more red or more white?
INCOMPLETELY DOMINANT ALLELES
why is this not blending?
ABO blood type i recessive to both dominant alleles (IA & IB > i)
GENOTYPE PHENOTYPE ANTIGENS ANTIBODIES RECEIVE FROM DONATE TO IAIA
IAi A A anti-B A & O A & AB
IBIB
IBi B B anti-A B & O B & AB
IAIB AB AB none all AB ii O none anti-A & -B O all
CODOMINANT ALLELES
IAIB is AB, qualitatively different from A or B
ABO blood type 6 possible genotypes & 4 possible phenotypes
GENOTYPE PHENOTYPE ANTIGENS ANTIBODIES RECEIVE FROM DONATE TO IAIA
IAi A A anti-B A & O A & AB
IBIB
IBi B B anti-A B & O B & AB
IAIB AB AB none all AB ii O none anti-A & -B O all
MULTIPLE ALLELES
influences variation of trait in populations
CONDITIONAL ALLELES influenced by environment, e.g.:
temperature (hot or cold) desiccation nutrient requirement chemicals infection
P
F1
F2
shi+ x shits
shi+/shits x shi+/shits
all active @ 25º
1
e.g.: temperature sensitive shibire (paralyzed) mutant
CONDITIONAL ALLELES
shits wild type @ 25º = permissive temperature
P
F1
F2
shi+ x shits
shi+/shits x shi+/shits
¾ active + ¼ paralyzed @ 29º
3 : 1
e.g.: temperature sensitive shibire (paralyzed) mutant
CONDITIONAL ALLELES
shits paralyzed @ 29º = restrictive temperature
LETHAL ALLELES homozygotes lethal (can be dominant or recessive)
e.g., yellow (AY) allele in mice
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
AY/AY AY/A
AY/A A/A
P
F1
don’t see these
2/3 AY/A yellow + 1/3 A/A black
Cy–/Cy– Cy–/Cy+
Cy–/Cy+ Cy+/Cy+
P
F1
Cy– Cy–
Cy+ Cy+
¾ alive + ¼ dead
3 : 1
e.g.: Curly (Cy) mutations in Drosophila
LETHAL ALLELES
—— x ——
2/3 curly + 1/3 wild type
STERILE ALLELES homozygotes sterile (can be dominant or recessive)
e.g., fruitless (fru) allele in Drosophila
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 fruitlessfru/fru fruitless x fru+/fru+ wild type
do not mate, no progeny
P
F1
F2
P
F1
mbmB– mbmB–
mbmB+ mbmB+
¾ alive + ¼ sterile
3 : 1
e.g.: mushroom body miniature B (mbmB) mutations
STERILE ALLELES
mbmB+
mbmB–
———— x ————
homozygous mbmB– live but give no offspring