章节大纲

  • A hand tossing a coin, illustrating the concept of probability in coin flips.

    What's the chance of the coin landing on heads?
    ::硬币落头的可能性有多大?

    There is always a 50-50 chance that a coin will land on heads. Half the time it will land on heads and half the time it will land on tails. What is the chance of it landing heads twice in a row? Or three times? These rules of probability also apply to genetics .
    ::硬币总有50-50个落到头顶的可能性。 硬币落到头部的一半时间, 落到尾部的一半时间。 它连续两次着陆头的几率是多少? 还是三次? 这些概率规则也适用于遗传学 。

    A parent only gives one factor for each trait to an offspring . If a parent has one dominant and one recessive factor for a trait, then, on average, half the time the dominant factor will be passed on, and half the time the recessive factor will be passed on. 
    ::父母一方只给后代每个特性一个系数。如果父母一方对某一特性有一个支配性系数和一个消停性系数,那么平均而言,主导性系数的半数时间将被传递,而消停性系数的半数时间将被传递。

    Probability and Punnett Squares
    ::概率和普内特广场

    A is a special tool derived from the laws of probability. It is used to predict the possible offspring from a cross, or mating between two parents.
    ::A是源于概率法则的一种特殊工具,用来预测来自十字架或双亲交配的可能后代。

    An example of a Punnett square ( Figure ) shows the results of a cross between two purple flowers that each have one dominant factor and one recessive factor ( Bb ).
    ::例如Punnett广场(图)显示两朵紫花之间交叉的结果,每朵紫花有一个支配因素和一个消退因素(Bb)。

    Punnett square illustrating genetic crosses between purple and white flower traits.

    The Punnett square of a cross between two purple flowers ( Bb ). A Punnett square can be used to calculate what percentage of offspring will have a certain trait.
    ::两朵紫花(Bb)之间的十字架的Punnett方块。Punnett方块可以用来计算后代中具有某种特性的百分比。

    To create a Punnett square, perform the following steps:
    ::要创建 Punnett 广场,请执行以下步骤:

    1. Take the factors from the first parent and place them at the top of the square ( B and b ).
      ::从第一父母的系数中取出系数,并将其置于方形的顶部(B和b)。
    2. Take the factors from the second parent and line them up on the left side of the square ( B and b ).
      ::从第二父母取因数,在方形左侧(B和b)排队。
    3. Pull the factors from the top into the boxes below.
      ::把因子从顶部拉到下方的盒子里
    4. Pull the factors from the side into the boxes next to them.
      ::把因素从侧面拉到旁边的箱子里

    The possible offspring are represented by the letters in the boxes, with one factor coming from each parent.
    ::可能的子女由盒子中的字母代表,每个父母有一个因素。

    Results:
    ::结果:

    • Top left box: BB , or purple flowers
      ::左上方框:BB或紫花
    • Top right box: Bb , or purple flowers
      ::右上方框:Bb或紫花
    • Lower left box: Bb , or purple flowers
      ::左下下框:Bb或紫花
    • Lower right box: bb , or white flowers
      ::右下下方框:bb或白花

    Only one of the plants out of the four, or 25% of the plants, has white flowers ( bb ). The other 75% have purple flowers ( BB , Bb ), because the purple factor ( B ) is the dominant factor. This shows that the color purple is the dominant trait in .
    ::4个植物中只有1个植物,即25%的植物有白花(bb),另外75%有紫花(BB,Bb),因为紫因子(B)是支配因素。这表明紫色是其中的主要特征。

    Now imagine you cross one of the white flowers ( bb ) with a purple flower that has both a dominant and recessive factor ( Bb ). The only possible gamete in the white flower is recessive ( b ), while the purple flower can have gametes with either dominant ( B ) or recessive ( b ).
    ::现在想象一下,你用紫色的花朵(bb)穿过白色的花朵(bb),紫色的花朵既具有支配因素,也具有消沉因素(Bb)。 白色花朵中唯一可能的调子是休眠(b),紫色的花朵可以具有支配因素(B)或休眠因素(b)的调子。

    Practice using a Punnett square with this cross (see Table ).
    ::使用 Punnett 方形使用此十字架练习(见表 )。

    b b
    B Bb Bb
    b bb bb

    Did you find that 50% of the offspring will be purple, and 50% of the offspring will be white?
    ::你有没有发现50%的后代是紫色的 50%的后代是白色的?

    Summary
    ::摘要

    • A Punnett square is a special tool used to predict the offspring from a cross, or mating between two parents.
      ::Punnett广场是一种特殊工具,用来从十字架或父母双方交配中预测后代。
    • In a Punnett square, the possible offspring are represented by the letters in the boxes, with one factor coming from each parent.
      ::在Punnett广场,可能的子女由盒子中的字母代表,每个父母有一个系数。

    Explore More
    ::探索更多

    Use the resources below to answer the questions that follow.
    ::利用以下资源回答以下问题。

    Explore More I
    ::探索更多

    • Gregor Mendel's Punnett Square at (5:03)
      ::Gregor Mendel的Punnett广场(5:03)
    1. What are Mendel's two rules of heredity?
      ::曼德尔的两种遗传规则是什么?
    2. If a pure bred black rabbit and a white rabbit mate, what will their potential offspring look like?
      ::如果纯种的黑兔子 和白兔子伴侣 他们的潜在后代会是什么样子?
    3. If two hybrid Ff rabbits mate, what will the offspring look like?
      ::如果两个混血兔子交配, 后代会是什么样子?

    Explore More II
    ::探索更多情况二

    • Punnett Square Calculator at
      ::Punnett 广场计算器
    1. If you cross an Aa individual with another Aa individual, what will the genotype ratio be in the next generation? What will be the phenotype ratio?
      ::如果你与另一个AA个人交叉,下一代的基因型比率是多少? 苯型比率是多少?
    2. If you cross an AABb individual with an Aabb individual, what will the genotype ratio be in the next generation? What will be the phenotype ratio?
      ::如果你与Aabb 个人通过AABB个人,下一代的基因型比率会是多少? 苯型比率会是多少?
    3. If you cross an AAbb individual with an aabb individual, what will the genotype ratio be in the next generation? What will be the phenotype ratio?
      ::如果你与Aabb 个人交叉,下一代的基因型比率会是多少? 苯型比率会是多少?

    Review
    ::回顾

    1. In peas, yellow seeds ( Y ) are dominant over green seeds ( y ). If a yy plant is crossed with a YY plant, what ratio of plants in the offspring would you predict?
      ::在豆类中,黄色种子(Y)比绿色种子是的占优势。 如果YY植物与YY植物交错,你预测后代的植物比例是多少?
    2. What ratio of plants in the offspring would you predict from a Yy x Yy cross?
      ::你从Yy x Yy十字路口 预测后代中的植物比例是多少?
    3. In guinea pigs, smooth coat ( S ) is dominant over rough coat ( s ). If an SS guinea pig is crossed with an ss guinea pig, what ratio of guinea pigs in the offspring would you predict?
      ::在麦地那猪中,光滑大衣(S)高于粗皮大衣(s ) 。 如果斯堪的纳维亚小猪与白鼠交叉,那么你预测这些后代中麦地那猪的比例是多少?
    4. What ratio of guinea pigs in the offspring would you predict from a Ss x ss cross?
      ::你从Ssxs十字架上可以预测 后代的豚鼠比率是多少?