Anonymous asked in 科學生物學 · 2 decades ago


因為我問過教授了, 聽了他的解釋還是霧霧的...

教科書上的敘述及問題又不太了解, 尤其是back cross...


因為我對這方面的中英文轉換不太行, 所以大部分都是英文的...

1. When green seed producing avocado's were crossed with yellow seed producing avocado's the result were--1/2green:1/yellow

When yellow seed producers were crossed the result were all yellow seeds. Draw the two crosses. Is yellow dominant or recessive? What would be the result if the green seed producers used in the first part of the question were crossed with each other?

2. A cross was made between 2 short-tailed cats. The resulting litter containded 6 short-tailed kittens, 2 long-tailed kittens and 3 kittens without tails. Explain.

2 Answers

  • Anonymous
    2 decades ago
    Favorite Answer

    1. try with yellow being the domiant first:1st cross has to be: Yy(yellow)) x yy(green)YyyYyyyresult: half yellow half green2nd cross is between the two yellow: Yy x Yynow, it's obvious, knowing monohybrid crosses yield a phenotypic ratio of 3:1, that this cross cannot yield 100% yellowtherefore, yellow must be recessive (green is dominant)and you can prove it by:1st cross: Gg (green) x gg (yellow)GggGgggresult: half green half yellow(i took the long way to explain this.. of course you can do this with a whole less paper work)2nd cross: gg x ggggggresult: ALL YELLOW ^^What would be the result if the green seed producers used in the first part of the question were crossed with each other?well, the cross would be Gg x Ggand knowing your monohybrid cross phenotypic ratio of 3:1your result will be 3 green : 1 yellow2. this could be the case of incomplete dominance, where the homozygous dominant (AA) yielded "long tail" and homozygous recessive (aa) yielded "no tail"and the heterozygous (Aa) is an blend of the two, giving a "short tail" traitthe numbers somewhat match a typical Aa x Aa cross genotypic ratio of 1AA:2Aa:1aahope this helps!

    2005-12-06 11:34:37 補充:

    Chi Squre test... i don't remember how to do it.. all i remember is the number crunching...^^|||

    but i mean, these questions are fairly elementary and straightforward... just really don't see the point of involving all the possibilities

    if you want to add on anything pls go ahead~ ^^

  • 2 decades ago

    (TO 拓子)For second part, you should use Chi square test to see whether your hypothesis matches with the Mendels theory. I guess you almost reach the goal, so I am not going to solve it. You may complete it ASAP...GO..GO..

    2005-12-06 11:01:26 補充:

    There are some special ratio for the crosses. Audience should ponder why they are to be resulted. For example, 1:4:6:4:1, 9:3:3:1, 9:3:4, 9:7, 15:1, 13:3 and so forth.

    2005-12-06 11:02:28 補充:

    These ratios should also be confirmed via Chi Square Test when you have data. Father Mendel found his theory without knowing Gene and Hardy-Weinberg principle. I should say that he had a special gift from God without doubt

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