Section outline

  • General

    Collapse all Expand all

  • 普内特广场

    What will you learn
    ::你会学到什么

    • What are Punnett squares
      ::什么是Punnett 广场
    • How the genotype and phenotype of offspring are predicted using Punnett squares
      ::如何使用Punnett 方形预测后代的基因型和苯型
    • How Punnett squares help in determining missing genotypes
      ::Punnett 方形如何帮助确定失踪的基因型
    • Punnet squares for two characteristics
      ::两个特性的 Punnet 方形

    Close-up of an eye surrounded by freckles, emphasizing skin pigmentation variation.

    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 possible genotypes and phenotypes is often aided by a .
    ::是的! 雀斑是某些人皮肤下面的色质斑块, 暴露在太阳之下。 雀斑是一种遗传性特征, 其原因是存在一种主要基因。 预测可能的基因型和人型往往由一种egg 来辅助。

    Punnett Squares
    ::普内特广场

    A Punnett square is a chart that allows you to easily determine the expected percentage of different genotypes in the offspring of two parents. An example of a Punnett square for is shown below. In this example, both parents are heterozygous for flower color ( Pp ). The gametes produced by the female parent are at the top of the chart, and the gametes produced by the male parent are along the side. The different possible combinations of in their offspring are determined by filling in the of the Punnett square with the correct letters (alleles). 
    ::Punnett 方块是一个图表,您可以轻松地确定双亲后代中不同基因型的预期百分比。 下面是Punnett 方块的示例。 在此示例中,双亲都是花色异体体。 母父母产生的色子位于图表的顶端, 父父父子所生成的色子在图的侧面。 他们的后代可能的不同组合通过用正确字母填入 Punnett 方块( alleles) 来决定。

     

    Predicting Offspring Genotypes
    ::热星型

    In the cross shown above , you can see that one out of four offspring (25 percent) has the genotype PP , one out of four (25 percent) has the genotype pp , and two out of four (50 percent) have the genotype Pp . These percentages of genotypes are what you would expect in any cross between two heterozygous parents. Of course, when just four offspring are produced, the actual percentages of genotypes may vary by chance from the expected percentages. 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.
    ::在上面的十字架上,可以看到,四分之一的后代(25%)有基因型PP,四分之一的后代(25%)有基因型P,四分之二的后代(50%)有基因型Pp。这些基因型的百分比是两个血型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比不同。然而,如果你考虑到数百个这样的交叉和数千个后代,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 percentages of phenotypes in the offspring of this cross from their genotypes. P  is dominant to p , so offspring with either the PP  or Pp  genotype will have the purple-flower phenotype. Only offspring with the pp  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 percentages that got in his first .
    ::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比。 P 位居第一位, 具有 PP 或 Pp 位居第一位的后代将拥有紫花型。 只有具有 pp 位位居第一位的后代将拥有白花型。 因此, 在这个十字架上, 四个后代中有三个( 75%) 拥有紫花, 四分之一( 25%) 拥有白花。 这些比例与他的第一个相同 。

    Determining Missing Genotypes
    ::确定缺少的基因类型

    A Punnett square can also be used to determine a missing genotype based on the other genotypes involved in a cross. Suppose you have a parent plant with purple flowers and a parent plant with white flowers. Because the p  allele is recessive , you know that the white-flowered parent must have the genotype pp . The purple-flowered parent, on the other hand, could have either the PP  or the Pp genotype. The Punnett square below shows this cross. The question marks (?) in the chart could be either P  or p alleles.
    ::Punnett 方块也可以用来根据十字架上涉及的其他基因型确定缺失的基因型。 假设您有一个带有紫花的母植物和带有白花的母植物。 因为蛋白质是休眠的, 您知道白花父母必须具有基因型 。 另一方面, 紫花父母可以拥有 PP 或 Pp 基因型 。 下面的 Punnett 方块可以显示这个十字块 。 图表中的问题标记 (?) 可以是 P ,也可以是 P 。

    Can you fill in the missing alleles based on the given phenotypes of the flowers?
    ::您能否根据花朵给定的花型, 填充缺失的花名?

    Note that two of the four offspring in the above cross have white flowers. Now you know that the offspring in the second row must have the pp  genotype. One of their p  alleles obviously comes from the white-flowered ( pp ) parent, because that’s the only allele this parent has. The other p  allele must come from the purple-flowered parent. Therefore, the parent with purple flowers must have the genotype Pp .
    ::请注意, 上述十字架上的四个后代中有两个有白色花朵。 现在你知道第二行的后代必须拥有 pp gennutype。 他们的蛋白质之一显然来自白花(pp) 父母, 因为这是他父母唯一拥有的。 另一个蛋白质必须来自紫花父母。 因此, 有紫花的家长必须拥有基因型 Pp 。

     

     

    Punnett Square for Two Characteristics
    ::两个特点的普内特广场

    When you consider more than one characteristic at a time, using a Punnett square is more complicated. This is because many more combinations of alleles are possible. For example, with two genes each having two alleles, an individual has four alleles, and these four alleles can occur in 16 different combinations.
    ::当每次考虑一个以上的特性时,使用Punnett方形比较复杂。这是因为可以使用更多的异变组合。例如,如果两种基因各有两个异变,个人就有四个异变,而这四种异变可以以16种不同组合发生。

    In the Punnett square for two characteristics (shown below), G represents the dominant allele for green pod color, and g represents the recessive allele for yellow pod color. F represents the dominant allele for full pod form, and f represents the recessive allele for constricted pod form. In this cross, known as a dihybrid cross , both parents are heterozygous for pod color ( Gg ) and pod form ( Ff ). Test your understanding by answering the questions based on the given cross with the help of the Punnett square.
    ::在Punnett广场上,两种特性(如下表所示),G代表绿缓冲色的主要异差,G代表黄色缓冲色的主要异差。F代表全缓冲形的主要异差,F代表收缩缓冲形的主要异差。在这个十字架上,双亲都称为三合二十字架,双双为异丁二色异丁二醇(Gg)和缓冲色(Ff)。在Punnett广场的帮助下,根据给定的十字架回答问题,检验你的理解。

     

     

    DID YOU KNOW?
     Although Punnett squares are pretty accurate, they cannot predict the genotypes and phenotypes of offspring for traits controlled by many genes, like hair color, skin color, or height in humans.
     

     

     

    Summary
    ::摘要

    • A Punnett square is a chart that allows you to determine the expected percentages of different genotypes in the offspring of two parents.
      ::Punnett广场是一张图表,可以确定父母双方后代中不同基因型的预期百分比。
    • A Punnett square allows the prediction of the percentages of phenotypes in the offspring of a cross from known genotypes.
      ::Punnett广场可以预测已知基因型十字的后代中苯型的百分比。
    • A Punnett square can be used to determine a missing genotype based on the other genotypes involved in a cross.
      ::根据交叉体涉及的其他基因型,可使用Punnett广场确定缺失的基因型。

    Review
    ::回顾

    1. What is a Punnett square? How is it used?
    ::1. 什么是Punnett广场?如何使用?

    2. Draw a Punnett square of an Ss x 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 x ss十字的Punnett方形。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。

      A A
    ? A? Aa
    ? Aa A?

    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?

    5. What are the genotypes of gametes of a AaBb self-pollination?
    ::5. AABB自污染的基因类型是什么?

    6. Mendel carried out a dihybrid cross to examine the inheritance of the characteristics for seed color and seed shape. The dominant allele for yellow seed color is Y , and the recessive allele for green color is y . The dominant allele for round seeds is R , and the recessive allele for a wrinkled shape is r . The two plants that were crossed were F1 dihybrids RrYy . Identify the ratios of traits that Mendel observed in the F2 generation. Create a Punnett square to help you answer the question.
    ::6. 门德尔用两合金十字架检查种子颜色和种子形状特征的继承情况,黄种种子颜色的主要代号是Y,绿色颜色的主要代号是y。圆种的代号是R,皱纹形状的主要代号是r。横穿的两株植物是F1二合金。确定门德尔在F2代中观察到的特征的比例。创建普内特广场帮助您回答问题。