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BIOL 205
Ian D Chin- Sang

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 • examples: • 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 or Ab/aB 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 meiotic products? 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: ← hypothesis Working with independent assortment Predicting Progeny ratios. Geneticists can work in two di
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