Quantitative Traits

Quantitative TraitsDistribution of Corn Ear Lengths

0

10

20

30

40

50

0 10 20 30

Length of Corn Ears (inches)

Fra

cti

on

of

Po

pu

lati

on

P

F1

F2

Mendelian Explanation of a Quantitative Trait

Dihybrid Cross: (H1 h1 H2 h2) x (H1 h1 H2 h2)

H1 H2 H1 h2 h1 H2 h1 h2

H1 H2 H1 H1 H2 H2 H1 H1 H2 h2 H1 h1 H2 H2 H1 h1 H2 h2

H1 h2 H1 H1 H2 h2 H1 H1 h2 h2 H1 h1 H2 h2 H1 h1 h2 h2

h1 H2 H1 h1 H2 H2 H1 h1 H2 h2 h1 h1 H2 H2 h1 h1 H2 h2

h1 h2 H1 h1 H2 h2 H1 h1 h2 h2 h1 h1 H2 h2 h1 h1 h2 h2

Very small : Small : Medium : Large : Very Large 1 4 6 4 1

Study Question 3

How many discrete lengths would you predict to be possible if there were four identical Height genes?

ComplementationMultiple Infection

Multiplicityof Infection

Phage/Hosts

ComplementationFailure to Complement

Complementation

Study Question 4

•5 mutants of phage T2

•Mutants forms tiny plaques

•Complementation tests - coinfect E. coli with pairs

•How many genes are required for the wildtype phenotype?

Study Question 5-7Cross female #34 extra hairy x male #43 (Curly hair)

Possible genotypes of parents?Genotypes of F1 progeny?

#34: EE x #43: CC EC

One gene hypothesis

#34: EE ++ x #43: ++ CC E+ C+

Two gene hypothesis

#34: XEXE++ x #43: X+Y CC

Two gene hypothesis/one X-linkedX+XE C+XE Y C+

Recombination

Nicked strand invades other chromosomeOne strand nickedHomologous chromosomes pairOther strands breakRecombination complete

Recombination

No change (sequences are identical except for sites of mutation)

Recombination

Two novel DNA’s, different from parents

Complementation vs Recombination

Complementation Recombination

acts through protein acts through DNA

temporary permanent

efficient rare

useful to define genes useful to map genes