The Green Revolution in agriculture (1960-2000)
- doubling of population also occurred
- to keep up with demand food production also had to keep up w/ demand
What made the green revolution possible?
• identifying mutations in plants that would increase yield or nutritional value
• sd1: an allele for a recessive trait that results in short stature. Makes plants more resistant to
toppling over in wind and rain, also increase seed yield.
• why? Increase seed yield b/c putting less resources in growing taller
• bph2: an allele for a recessive trait that confers resistance to brown plant hoppers (insect)
• Can we make the double sd1;bph2 mutant?
◦ Yes we can: if on different chromosomes can be easy
◦ but if on same chromosome → more challenging
Mendel’s Law of Independent Assortment
A/a ; B/b GeneAand gene B are on different chromosomes
AB/ab GeneAand gene B are on the same chromosome
A/a · B/b Unknown position for geneAand gene B
heterozygote for a single gene:A/a = monohybrid
double heterozygote such as A/a; B/b = dihybrid.
Round and wrinkled phenotypes
* progenydoesn't look
like parents at all • let’s just look at seed shape:
◦ round: (315 +108)= 423
◦ wrinkled: (101 +32)= 133 3:1 round:wrinkled
• Let’s just look at seed color:
◦ yellow: (315 +101)= 416 3:1 yellow:green
◦ green: (108 +32)= 140
• so the two 3:1 ratios are hidden in the 9:3:3:1
• Note he did this with combinations of all seven
traits and always got the 9:3:3:1
To visualize the random combination of these two ratios we can use a branch diagram
What could the combination of the two 3:1 ratios mean biologically?
• Mendel's Second Law: Different gene pairs assort independently in gamete formation*.
• For two heterozygous gene pairs A/a and B/b, the b allele is just as likely to end up in a gamete
with an a allele as with an Aallele, and likewise for the B allele.
* We now know that this only applies to genes on different chromosomes
We have explained the 9:3:3:1 phenotypic ratio as two randomly combined 3:1 phenotypic ratios.
But can we also arrive at the 9:3:3:1 ratio from a consideration of the frequency of gametes, the actual
How do we calculate the frequency of meiotic products from the F1 dihybrid R/r;Y/y Punnett square illustrating the genotypes underlying a 9 : 3 : 3 : 1 ratio
Mendel went on to test his principle of independent assortment:
Working with independent assortment
Predicting Progeny ratios.
Geneticists can work in two di