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flower color in pea plants: purplephenotype (appearance) has genotype (actual alleles): PP or PpGenotype and Phenotype Because of the different effects of dominant and recessive alleles, an organisms traits do not always reveal its genetic composition Therefore, we distinguish between an organisms phenotype: physical appearance and its genotype: genetic makeup
TestcrossUse to determine genotypeof individual that has dominant phenotype. By crossing a homozygous recessive individual with the unknown, any recessive alleles will be revealed. Used as a tool for geneticists
Sperm 1/41/41/41/41/41/41/41/49/163/163/161/16YR YR yr yr Yr Yr yR yR YYRR YYRr YyRR YyRr YYRr YYrr YyRr Yyrr YyRR YyRr yyRR yyRr YyRr Yyrr yyRr yyrr dihybrid cross: following two traits Punnett square Cross: YyRr x YyRr gametes gametes Egg Yellow: 12 green: 4 Yellow to green ratio: 3:1 Round: 12 wrinkled: 4 Round to wrinkled ratio: 3:1 Reveals independent assortment as each trait maintains the expected ratio Overall phenotypic ratio 9:3:3:1 genotypic ratio 1:2:1:2:4:2:1:2:1 9 (yellow/round):3(yellow/wrinkled):3(green/round):1(green/wrinkled)
The Law of Independent Assortment seed color: yellow (dominant) green (recessive) seed shape: round (dominant) wrinkled (recessive) dihybrids •Crossing two, true-breeding parents differing in two traitsproduces dihybrids in the F1generation, heterozygous for both characters •A dihybridcross-a cross between F1dihybrids, can determine whether two characters are transmitted to offspring as a package or independently •Mendel identified his second law of inheritanceby following two traitsat the same time
If on different chromosomes, each pair of alleles segregates independently of other pairs of alleles during gamete formation –Genes located near* each other on the same chromosome tend to be inherited together (* too close for recombination to occur between them). The Law of Independent Assortment Meiosis Gametes with independent assortment of chromosomes Parental cell with 3 pairs of homologous chromosomes
Probability- a measure of how likely it is that an event will occur •When tossing a coin, the outcome of one toss has no impact on the outcome of the next toss •In the same way, the alleles of one gene segregate into gametes independently of another genes alleles- with no impact on the segregation of anothe
the probability that ≥2 independent events will occur together is the productof their individual probabilities The probability of flipping a coin and getting two “tails” in a row = the productof the individual probabilities.