<p>a defenition of a testcross:
a croos in order to find out if dominant phenotype inividual has heterozygous or homoz. alleals. To do that you cross it with hom. ressesive.
So A_ * aa is a test cross where _ means unknown</p>
<p>thanks? but you’re totally disregarding what I said.</p>
<p>no Aa connot be it
you do not know wether its Aa or AA, you want to find out, thats the point of a testcross</p>
<p>Exactly. Why would you do a test cross if you already knew the genetic makeup?</p>
<p>A test cross is a cross between a homozygous recessive to a unknown showing a dominant phenotype. In this way, if all the offsprings were shown with the dominant phenotype, that means the genetic makeup of the dominant parent was homozygous; while if the offspring are in a 3:1 ratio, the original dominant-chracterized parent was a heterozygous.</p>
<p>The may test…did it ask for an example of a test cross or something? I wouldn’t know. But if it said an example of, Aa x aa IS an example of a testcross.</p>
<p>No kidding, but considering the same question was on the May SAT and the answer choices didn’t have A_, the answer was AaXaa in may.</p>
<p>testcross is basicly crossing any of the dominant phenotype with ressesive phenotype
it could be
AaBbCc x aabbcc</p>
<p>NOPE! the answer is A_xaa because you don’t know the other gene…you’re doing the test cross to find if it’s homozygeous dominant or heterozygous dominant. I seriously doubt that the answer not that in may.</p>
<p>i doubt it too but for SAT the writers may have thought you are dubm and wouldnt know what the dash _ ment</p>
<p>lol, i just feel that how they think of us, that explains the casses where many answered fit, or none fit</p>
<p>Ugh, well then just tell me why the answer as AaXaa in may.</p>
<p>technically if there is no dash in the cross look for homozygous ressesive, every test cross has hom. ressesive and maybe they thought that that was exectly what you were looking for in the first place and gave you the answer</p>
<p>Um, are you sure it was exactly the same question?</p>
<p>The question was pretty direct… which of these is a test cross?</p>
<p>The only case where I can think that Aa x aa would be an answer would be if the question read:</p>
<p>The question was worded something like: An EXAMPLE of a test cross…</p>
<p>and AA x aa WASN’T an answer choice.</p>
<p>I also put the Pie Graph.</p>
<p>I thought (for that one question) that it was Nitrogen?
I don’t know, thats what I thought.</p>
<p>I missed the bony structure and the heart thing, and I left the uric acid thing and analogous to dog blank…</p>
<p>I thought it was (overally) pretty easy…
But that Nitrogen thing and the sex-linked is getting to me.</p>
<p>If you put the answer but erased it, they’ll still count the second answer, right? The mark wasn’t completely unseeable but it was pretty well erased so hopefully, the machine will grade it right and hopefully, its not ultra-sensitive.</p>
<p>I’m just scared I’ll get some points wrong because I changed my answer, ya know? <em>sigh</em></p>
<p>57all things do not breath through gills and lungs, some breath with simple diffusion</p>
<p>i think the answer was there must be moist membranes for respiration to take place</p>
<p>^ Yeah, thats the correct answer.</p>
<p>Is it Nitrogen or Phosphorus?</p>
<p>^Yep, you just have to think of some amphibians who breathe through their skins, and they always have to keep their integuments wet…</p>
<p>i put moist mem but why you need moiture to breeth?</p>
<p>It’s not necessarily “breathe” but respiration is a method of gas exchange, (O2 and CO2) and for gases to dissolve, they need a moist surface.</p>
<p>why do they need moist surface?</p>