M1 L3: Mendelian Genetics Flashcards
What did Mendel learn and who did he learn it from?
1) “particulate” physics from Doppler
2) plant hybridization from Unger
3) probability theory from Ettinghausen
What type of traits did Mendel study? What are the 5 reasons these lucky?
Dichotomous traits, two outcomes with no intermediates. Lucky for 5 reasons
1) environment didn’t affect the traits
2) each trait was determined by one gene
3) each gene had two alleles
4) no effect of sex because peas are monecious (make m/f gametes)
5) traits display complete dominance
What are the two advantages of using peas?
Can self fertilize (one plant can provide eggs and pollen)
Can control crosses (artificial cross fertilization by controlling which plant donates each gamete)
What hypothesis did Mendel’s experiments test? Why was he able to test it?
Blending inheritance, his experiments had 5 key features
1) controlled crosses, always knew identity of parents
2) used pure-breeding strains of peas
3) used dichotomous traits, no ambiguous intermediates
4) quantified his results statistically and could predict outcomes
5) performed replicate, reciprocal crosses, and test crosses
What is a parental cross? What did it reveal? How? What question did it lead to?
Cross two parents that are each true breeding for a different trait
Revealed principle of dominance and rejected blending inheritance.
Dominance bc all offspring looked exactly like one parent. That is the dominant phenotype. Rejected blending bc offspring didn’t look like a mix of the parents
Is dominance intrinsic to the trait, or is it determined by the sex of the parent?
What is a reciprocal parental cross? What did it reveal? How? What question did it lead to?
Used the same true-breeding plants from before but switched which one donated the egg and pollen
Revealed that dominance is intrinsic to the trait and both parents contribute genetic material. It doesn’t matter if the purple flower donates egg or pollen, offspring are always purple
Is the recessive allele destroyed or overridden?
What’s a monohybrid cross? What did it reveal? How? What question did it lead to?
All offspring from the parental cross are F1 heterozygotes. Monohybrid crosses two of them.
Revealed alleles exist in pairs bc 3:1 phenotype ratio. Plants crossed must have a dominant and recessive allele for recessive phenotype to come back.
Revealed law of segregation (offspring w/ recessive phenotype only got recessive allele from each parent, even though parents were hets)
What is the genetic makeup of the purple flowers in the F2 cross?
What does the 3:1 phenotypic ratio from the monohybrid cross reflect? What would it mean if the 3:1 ratio was disrupted?
Dom and rec gametes are produced in equal freq AND gametes unite at random
Deviation from 3:1 phenotype ratio would suggest gametes NOT made in equal ratio
What are the F3 self crosses? What did they reveal? How? What did it further support?
Self fertilize all of the F2s
Revealed 1/3 of F2s with dom phenotype were homo, 2/3 of F2s with dom phenotype were hets. PROVEN BC 1/3 produced all dom phenotype offspring, 2/3 produced 3:1 phenotype offspring
3:1 ratio again supports alleles existing in pairs and gametes uniting at random
How did Mendel figure out the genotype of plants with the dom phenotype? What else did the results support?
Test crosses, cross a dom phenotype unknown genotype with a rec phenotype (automatically known genotype)
Expect 1:0 all dom offspring if dom parent is homo dom (all offspring hets), expect 1:1 offspring if dom parent is het (offspring het or homo rec)
Results support alleles exist in pairs, random gamete union
How did Mendel explain the results of parental and monohybrid crosses?
Each trait determined by 2 particles of heredity (alleles), which are unchanged when passed between generations
One particle from each parent (egg/sperm)
Heredity is particulate, not blending, bc recessive traits can skip a generation
Monohybrid cross gives 3:1 phenotypic ratio and 1:2:1 genotypic ratio, both prove SEGREGATION, gametes formed in EQUAL RATIOS, gametes unite at RANDOM
What are Mendel’s first 3 postulates
1) Unit factors exist in pairs
2) one trait is always dom, one always rec
3) segregation, the 2 alleles separate in gamete production
What’s a dihybrid cross? What does it reveal? How?
Cross 2 plants that are true-breeding for 2 dif traits, F1 all double hets
Cross F1 double hets, get 9:3:3:1 phenotypic ratio
Revealed independent assortment. Gamete receiving dom/rec allele for one gene does not influence getting alleles for other genes BECAUSE 3:1 ratio maintained for indiv traits
How did Mendel solidify his finding of independent assortment?
Dihybrid test cross. Cross double het with double rec, got 1:1:1:1 phenotypes (showed gametes still formed in equal ratios, unaffected by alleles for other genes)
What are the 4 rules of Mendelian transmission
1) product rule: probability of 2 independent events @ the same time = product of their individual probabilities
2) sum rule: probability of 1 of many mutually exclusive events = sum of their independent probabilities
3) conditional probability: conditioning on one outcome, what’s the probability of another outcome
4) binomial probability: predict the probability of each combo of outcomes (for event with 2 possible outcomes done many times) p=dom, q=rec
