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International Baccalaureate · IB Diploma · Biology · SL Тема 30 3:54 Английское озвучивание · Английский + китайские субтитры (встроенные)
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Two parents can carry a recessive allele 等位基因 without expressing the associated phenotype.
双亲可以携带隐性等位基因而不表现出相应的表型。
Their children do not have to match the parents phenotypically.
他们的子女在表型上不必与父母一致。
An allele is a variant of a gene.
等位基因是基因的一种变体。
A genotype lists alleles; a phenotype is the expressed characteristic, influenced by genotype and sometimes environment.
基因型列出等位基因；表型是表达出的特征，受基因型和有时环境的影响。
Dominant and recessive describe the relationship between alleles, not how common they are.
显性和隐性描述的是等位基因之间的关系，而非其常见程度。
Allele: A variant of a gene.
等位基因：基因的变体。
Genotype: The alleles an organism carries.
基因型：生物体携带的等位基因。
In a simple monohybrid cross Aa times Aa, gametes carry A or a.
在简单的单基因杂交Aa乘以Aa中，配子携带A或a。
Combining independent gametes gives AA, Aa, Aa, and aa.
组合独立的配子可得AA、Aa、Aa和aa。
The predicted probabilities describe many possible fertilizations, not a fixed order of children.
预测的概率描述的是许多可能的受精情况，而非固定的后代顺序。
In the lab: Write parental genotypes and gametes before making the grid.
在实验室中，绘制棋盘格之前先写出亲本基因型和配子。
State the inheritance model and phenotype key.
说明遗传模型和表型对照表。
Use a pedigree to check consistency with a model; do not infer certainty from a small family alone.
使用系谱图检验与模型的符合性。 不要仅凭一个小型家族就推断出确定性结论。
Known: Aa cross Aa with complete dominance.
已知：Aa 与 Aa 杂交，完全显性。
Probability of aa is one quarter, which is twenty-five percent.
aa 的概率为 1/4，即 25%。
Probability of the dominant phenotype is three quarters, which is seventy-five percent.
显性表型的概率为 3/4，即 75%。
If four children are born, there is no guarantee that exactly one has the recessive phenotype.
如果生了四个孩子，不能保证恰好有一个具有隐性表型。
Your turn: In Aa × aa, what percentage of offspring are predicted to be aa?
轮到你了。 在Aa乘以aa中，预测有多少百分比的后代是aa？
Pause the video and work it out.
请暂停视频，自己算一算。
Check: the square gives Aa, Aa, aa and aa, so 50 percent are aa.
核对：棋盘格为 Aa、Aa、aa、aa，所以 50% 是 aa。
A dominant allele can be rare.
显性等位基因也可能很罕见。
Mutation is a source of new variation. Selection changes the relative success of existing variants, rather than directing mutations toward a goal.
突变是新变异的来源；自然选择改变现有变体的相对成功率，而不是引导突变朝向特定目标进行。
Not true: A dominant allele must be the most common allele in a population.
不正确。 显性等位基因必须是种群中最常见的等位基因。
Dominant describes how an allele is expressed in a heterozygote, not how common it is.
显性描述的是等位基因在杂合子中的表达方式，而非其常见程度。
A dominant allele can be rare in a population and a recessive allele can be common; frequency depends on inheritance and selection, not dominance.
显性等位基因在种群中可能很罕见，而隐性等位基因也可能很常见。 频率取决于遗传和选择，而非显隐性。
An allele is a variant of a gene.
等位基因是基因的变体。
In a simple monohybrid cross Aa times Aa, gametes carry A or a.
在简单的单因子杂交Aa乘Aa中，配子携带A或a。
Watch for: A dominant allele can be rare.
请注意：显性等位基因可能很罕见。
In Aa times Aa, 16 offspring are produced.
在Aa乘以Aa中，产生16个后代。
The expected number of aa is 4.
aa的预期数量是4。
That is a probability, not a guarantee.
这是一种概率，而非保证。
Dominant does not mean most common.
显性并不意味着最常见。
The result is an expected count of 4.
结果是预期计数为4。
One parent gives A or a; the other can give only a.
一个亲本给出A或a，另一个只能给出a。
So each offspring has a one-in-two chance of Aa and a one-in-two chance of aa.
因此每个后代有二分之一的概率是Aa，二分之一的概率是aa。
For Aa crossed with aa under complete dominance, find the probability that two independently conceived offspring both have the recessive phenotype.
在完全显性条件下，Aa 与 aa 杂交，求两个独立受孕的后代都表现隐性表型的概率。
Does a family of two have to match the ratio?
一个有两个孩子的家庭必须符合这个比例吗？
One half squared is one quarter.
二分之一的平方是四分之一。
Mendelian probabilities describe repeated independent outcomes; a family need not contain one child of each phenotype.
孟德尔概率描述的是多次独立结果；一个家庭不一定每种表型各有一个孩子。
State complete dominance and independence.
要说明完全显性和相互独立这两个前提。
Pause and check yourself. Explain each point on screen in your own words, then change one number in the last example and say which assumption must still hold.
暂停一下，自我检查：用自己的话解释屏幕上的每个要点，再改动最后一个例子中的一个数字，说明哪个假设仍然必须成立。