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  • Punnett 广场 - 高级

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    Can the appearance of freckles be predicted?
    ::雀斑的外观能预测出来吗?

    Yes! Freckles are pigmented patches that appear under the skin of some people, upon exposure to the sun. Having freckles is an inherited trait resulting from the presence of a dominant gene for that trait. Predicting the possibility of a genetic cross is often aided by a .
    ::是的! 雀斑是某些人皮肤下的色质斑块, 暴露在太阳之下。 雀斑是一种遗传性特征, 其遗传性因存在一种主要基因而产生。 预测遗传交叉的可能性往往会得到一个egg 的帮助 。

    Predicting Genotypes with Punnett Squares
    ::使用 Punnett 广场预测 Geno 类型

    developed the law of segregation by following only a single characteristic, such as pod color, in his . Biologists use a diagram called a Punnett square , to help predict the probable inheritance of in different crosses. The Punnett square is named after its developer, British geneticist Reginald C. Punnett.
    ::生物学家使用一个称为Punnett广场的图表来帮助预测不同十字架上可能继承的财产。 Punnett广场是以其开发者英国遗传学家Reginald C. Punnett命名的。

    In a monohybrid cross , such as the one in the Figure  , the Punnett square shows every possible combination when combining one maternal (mother) allele with one paternal (father) allele. In this example, both organisms are heterozygous for flower color Bb (purple). Both plants produce gametes that contain both the B and b alleles. The of any single offspring showing the dominant trait is 3:1, or 75%. To develop a Punnett square, possible combinations of alleles in a gamete are placed on the top and left side of a square. For a monohybrid cross ( Table ), individual alleles are used, whereas for a dihybrid cross ( Table  ), pairs of alleles are used. A Punnett square for a monohybrid cross is divided into four squares, whereas a Punnett square for a dihybrid cross is divided into 16 squares. How many boxes would a Punnett square need if three traits were examined? The squares are filled in with the possible combinations of alleles formed when gametes combine, such as in a zygote .
    ::Punnett 广场在将一位母亲(母亲)和一位父亲(父亲)结合成一位父亲(父亲)时展示了各种可能的组合。在此示例中,两种生物都是花色Bb(棕色)的异体体。两种植物都产生含有B和b等色的调子。任何显示主要特性的子系为3:1或75%。为了开发一个Punnett方形,在将一位女方形中的异灵可能组合放在一个方形的顶部和左侧。对于一个单体的十字(表),使用个别的异体,而对于一异体的十字(表),则使用一对异体。单体十字的Punnett方形分为四个方形,而一异体十字的Punnett方形则分为16个方形。如果检查了三个特性,那么Punnett方形的方形会有多少个框需要?当游戏组合时,方形会以所有电子组合的形式填满。

    lesson content
    This Punnett square shows a cross between two heterozygotes, Bb. Do you know where each letter (allele) in all four cells comes from? Two pea plants, both heterozygous for flower color, are crossed. The offspring will show the dominant purple coloration in a 3:1 ratio. Or, about 75% of the offspring will be purple.
      A a
    A AA Aa
    a Aa aa
      AB Ab aB ab
    AB AABB AABb AaBB AaBb
    Ab AABb AAbb AaBb Aabb
    aB AaBB AaBb aaBB aaBb
    ab AaBb Aabb aaBb aabb

    Predicting Offspring Genotypes
    ::热星型

    In the cross shown in Figure , you can see that one out of four offspring (25 percent) has the genotype BB , one out of four (25 percent) has the genotype bb , and two out of four (50 percent) have the genotype Bb . These percents of genotypes are what you would expect in any cross between two heterozygous parents. Of course, when just four offspring are produced, the actual percents of genotypes may vary by chance from the expected percents. However, if you considered hundreds of such crosses and thousands of offspring, you would get very close to the expected results—just like tossing a coin.
    ::在图中显示的十字架上,可以看到四分之一的后代(25%)有基因型BB,四分之一(25%)有基因型Bb,四分之一(25%)有基因型Bb,四分之二(50%)有基因型Bb。基因型的这些百分比是两个异体动物父母之间的任何交叉中你所期望的。当然,只要产生四个后代,基因型的实际百分比可能与预期的百分数不同。然而,如果你考虑到成百上千个这样的交叉数和数千个后代,你会非常接近预期的结果 — — 就像抛硬币一样。

    Predicting Offspring Phenotypes
    ::预测外源类型 预测外源类型

    You can predict the percents of phenotypes in the offspring of this cross from their genotypes. B is dominant to b , so offspring with either the BB or Bb genotype will have the purple-flower phenotype. Only offspring with the bb genotype will have the white-flower phenotype. Therefore, in this cross, you would expect three out of four (75 percent) of the offspring to have purple flowers and one out of four (25 percent) to have white flowers. These are the same percents that Mendel obtained in his first . The Punnett square is visual representation of .
    ::您可以从他们的基因型中预测这个十字架的后代中苯型的百分率。 B 占主要值的b, 因此B或Bb基因型的后代将具有紫花型。 只有bb基因型的后代将具有白花型。 因此, 在这个十字架上, 您可以期望四个后代中有三个( 75%) 有紫花, 四分之一( 25%) 有白花。 这些是Mendel第一次获得的百分率。 Punnett 广场是可见的 。

    Summary
    ::摘要

    • A Punnett square shows all the possible genotypes that can result from a given cross. It is also used to predict possible phenotypes in offspring.
      ::Punnett 方块显示所有可能由给定十字体生成的基因类型。 该方块还用于预测后代中可能的苯型。

    Review
    ::回顾

    1. What is a Punnett square? How is a Punnett square useful?
    ::1. 什么是Punnett广场?Punnett广场如何有用?

    2. Draw a Punnett square of an Ss × ss cross. The S allele codes for long stems in pea plants and the s allele codes for short stems. If S is dominant to s , what percentage of the offspring would you expect to have each phenotype?
    ::2. 绘制 Ss × ss 十字的Punnett 方块。豆子植物长茎的Salle代码和短茎短茎的Sele代码。如果S占优势,你期望每个苯型的后代占多大比例?

    3. What letter should replace the question marks (?) in this Punnett square? Explain how you know.
    ::3. 在此Punnett广场上,应该用什么字母取代问题标记(?)?解释你怎么知道。

    4. How do the Punnett squares for a monohybrid cross and a dihybrid cross differ?
    ::4. 单环和双环十字的Punnett方形如何不同?