10 pts b.a. plzzzz help!!!?

In snapdragons the inheritance of a lower color of size of leaves are examples of incomplete dominance. When red-flowered plants are crossed with white ones, all the flowers are pink. Similarly, when plants with broad leaves are crossed with plants of narrow leaves, the offspring have intermediate leaves. Cross a homozygous red-flowered, broad-leaved plant with a homozygous white-flowered narrow leaved plant. What kind of offspring are produced in the F1 generation? Now cross two of these plants and find the phenotype ration of the offspring. Explain the relationship of the 9:3:3:1 ration to the one you obtained.





Plz help..this is due monday and im a freshman in H bio and my teacher hates me and i seriously asked for help multiple times but my teach acts like i'm not even there

10 pts b.a. plzzzz help!!!?
OK, first a couple of definitions: for a simple allele (let's call it "A"), the dominant trait is "A" and the recessive is "a"; this is always the convention. Homozygous would be "AA" or "aa" and heterozygous is "Aa" or "aA". Let's say that the "A" allele is "tall" and "a" is "short". In true dominance, both "AA" and "Aa" will be a tall person; in incomplete dominance, "Aa" will be someone of medium height.





Now, on to the problem. A homozygous red, broad plant is RR-BB, and the white, narrow homozygous plant is rr-bb. So when you cross these, the first (F1) generation all have to be Rr-Bb (or rR-bB, but the convention is to always write the capital letter first). So with incomplete dominance, all the F1's will be pink-flowered with medium-width leaves.





Now these are crossed. What can you get? For the flower color you can get RR, Rr and rr, right? But in what ratio? It would be 1:2:1 since you have one RR, two Rr's and one rr (if you don't know how to get this, Google "Punnett Square"). The easiest way to add in the leaf width is to write down all the possible combinations (RRBB, RRBb, RRbb, RrBB, RrBb, Rrbb, rrBB, rrBb and rrbb). Now start going through the F2 generation--you already know that you have one RR, two Rr's and one rr. Start with the RR--it can have one BB, two Bb's and one bb. Put a little tick mark beside the nine combinations as you generate them. Now do the same with Rr--but don't forget that you have **two** of them, so you'll have to put two tick marks each time you get the genotype. Now the rr's. When you get all this done, look at the nine genotypes. If you did it right, for the nine genotypes I wrote above you should get the ratio


1:2:1:2:4:2:1:2:1. Due to incomplete dominance, the phenotype ratio will be the same! If you had true dominance, however, then the RR and Rr genotypes would be the same, as would the BB and Bb. In this case you would group RRBB,RRBb,RrBB and RrBb together. You would also group the rrBB and rrBb together, and group the Rrbb and RRbb together. If you do this, the ratio collapses to 9:3:3:1.





Hope this helps!

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