Sex-Linked Inheritance: Concepts and Case Studies | 伴性遗传的概念与实例分析

📚 Sex-Linked Inheritance: Concepts and Case Studies | 伴性遗传的概念与实例分析

Sex-linked inheritance refers to the pattern of inheritance of genes located on sex chromosomes (X and Y in humans). Because these chromosomes determine an individual’s sex and carry many genes unrelated to sex determination, the transmission of these genes follows distinct patterns that differ between males and females.

伴性遗传是指位于性染色体（人类中为X和Y染色体）上的基因所表现出的遗传模式。由于这些染色体决定个体的性别，并且携带许多与性别决定无关的基因，因此这些基因的传递遵循着在男性和女性之间有所不同的独特规律。

1. Sex Chromosomes and Sex Determination | 性染色体与性别决定

In humans, females have two X chromosomes (46,XX), while males have one X and one Y chromosome (46,XY). The mother always passes an X chromosome to her offspring, while the father passes either an X (producing a daughter) or a Y (producing a son).

在人类中，女性有两条X染色体（46,XX），而男性有一条X和一条Y染色体（46,XY）。母亲总是将一条X染色体传给后代，而父亲则传递一条X（生育女儿）或一条Y（生育儿子）。

The Y chromosome is small and contains few genes, most of which are involved in male sex determination and spermatogenesis. The X chromosome is much larger and contains thousands of genes, most of which are not directly related to sex.

Y染色体较小，所含基因很少，其中大多数参与男性性别决定和精子发生。X染色体大得多，包含数千个基因，其中大多数与性别并无直接关系。

2. Key Concepts of Sex-Linked Inheritance | 伴性遗传的关键概念

A gene is said to be sex-linked when it is located on a sex chromosome. Genes on the X chromosome are called X-linked; genes on the Y chromosome are called Y-linked. Because males have only one X chromosome, they are hemizygous for X-linked genes.

当基因位于性染色体上时，该基因就被称为伴性遗传基因。位于X染色体上的基因称为X连锁基因；位于Y染色体上的基因称为Y连锁基因。由于男性只有一条X染色体，因此对于X连锁基因而言，男性是半合子。

For X-linked traits, males inherit their X chromosome from their mother, so they cannot pass X-linked alleles to their sons. A father passes his X chromosome only to his daughters. This criss-cross pattern of inheritance is a hallmark of X-linked traits.

对于X连锁性状，男性从母亲那里获得X染色体，因此他们不能将X连锁等位基因传递给儿子。父亲只将他的X染色体传给女儿。这种交叉遗传模式是X连锁性状的典型特征。

3. Modes of Sex-Linked Inheritance | 伴性遗传的类型

Sex-linked traits can be classified based on whether the allele is on the X or Y chromosome, and whether it is dominant or recessive. The main categories are:

伴性性状可根据等位基因位于X还是Y染色体，以及是显性还是隐性来分类。主要类型包括：

X-linked recessive | X连锁隐性遗传
X-linked dominant | X连锁显性遗传
Y-linked (holandric) inheritance | Y连锁遗传（限雄遗传）

X-linked recessive traits are expressed in all males who carry the mutant allele, because males have no second X chromosome to mask the effect. Females must inherit two mutant alleles to express the trait, so affected females are rare.

X连锁隐性性状在所有携带突变等位基因的男性中都会表达，因为男性没有第二条X染色体来掩盖其效应。女性必须遗传两个突变等位基因才会表现出该性状，因此患病女性非常罕见。

4. Classic Example 1: Red-Green Colour Blindness | 经典实例一：红绿色盲

Red-green colour blindness is an X-linked recessive condition caused by mutations in the OPN1LW or OPN1MW genes located on the X chromosome. These genes encode photopigments in cone cells of the retina. Affected individuals have difficulty distinguishing red and green colours.

红绿色盲是一种X连锁隐性遗传病，由位于X染色体上的OPN1LW或OPN1MW基因突变引起。这些基因编码视网膜视锥细胞中的光色素。患病者难以区分红色和绿色。

Since the allele is recessive and X-linked, the pattern of inheritance shows: affected males are more common than affected females; an affected male cannot pass the allele to his sons, but all his daughters are carriers; carrier females can pass the allele to half of their sons, who will be affected, and to half of their daughters, who will be carriers.

由于该等位基因是隐性且位于X染色体上，其遗传模式表现为：患病男性多于患病女性；患病男性不会将等位基因传给儿子，但所有女儿均为携带者；携带者女性可将等位基因传给一半的儿子，使其患病，也可传给一半的女儿，使其成为携带者。

Xᴺ = normal allele, Xⁿ = colour-blind allele; Male genotype: XⁿY; Female carrier: XᴺXⁿ

5. Classic Example 2: Haemophilia | 经典实例二：血友病

Haemophilia is an X-linked recessive bleeding disorder. Haemophilia A results from a deficiency of clotting factor VIII, while haemophilia B results from factor IX deficiency. Both genes are located on the X chromosome. Because blood clotting is impaired, affected individuals may bleed excessively after injury.

血友病是一种X连锁隐性出血性疾病。A型血友病由凝血因子VIII缺乏引起，B型血友病由凝血因子IX缺乏引起。这两个基因均位于X染色体上。由于凝血功能受损，患病者受伤后可能出血过多。

A famous example is the royal family of Queen Victoria. She was a carrier, and her descendants spread the allele into several European royal families. Many affected males were born, demonstrating the typical X-linked recessive inheritance pattern.

一个著名的例子是维多利亚女王的王室家族。她是携带者，她的后代将该等位基因传播到多个欧洲王室家族，诞生了许多患病男性，展现了典型的X连锁隐性遗传模式。

6. Classic Example 3: White-eye Mutation in Drosophila | 经典实例三：果蝇白眼突变

Thomas Hunt Morgan’s experiments with Drosophila melanogaster provided early evidence for sex-linked inheritance. He discovered a white-eyed male mutant and crossed it with a red-eyed female. All offspring in the F1 generation had red eyes, indicating red is dominant. In the F2 generation, all females were red-eyed, but half of the males were white-eyed.

托马斯·亨特·摩尔根利用黑腹果蝇进行的实验为伴性遗传提供了早期证据。他发现了一只白眼雄蝇突变体，并将其与红眼雌蝇杂交。F1代所有后代均为红眼，说明红眼为显性。在F2代中，所有雌蝇均为红眼，但一半雄蝇为白眼。

This result was surprising because the expected Mendelian ratio of 3:1 was observed only among males. Morgan concluded that the white-eye allele is located on the X chromosome and has no homologous allele on the Y chromosome. This confirmed the chromosomal theory of inheritance.

这一结果令人惊讶，因为预期的孟德尔3:1比例只在雄性中出现。摩尔根得出结论：白眼等位基因位于X染色体上，且在Y染色体上没有同源等位基因。这证实了染色体遗传学说。

7. X-Linked Dominant Inheritance | X连锁显性遗传

In X-linked dominant inheritance, a single mutant allele on the X chromosome is sufficient to produce the phenotype in both males and females. However, affected males are usually more severely affected, and if the condition is lethal, affected males may die before birth.

在X连锁显性遗传中，X染色体上的单个突变等位基因就足以在男性和女性中都产生该表型。然而，患病男性通常症状更严重，如果该疾病是致死的，患病男性可能出生前即死亡。

An example is vitamin D-resistant rickets (hypophosphatemic rickets). Affected males transmit the trait to all their daughters but to none of their sons. Affected heterozygous females transmit the trait to half of their children, regardless of sex, because the allele behaves as a dominant allele.

一个例子是抗维生素D佝偻病（低磷血症性佝偻病）。患病男性会将该性状传给她所有的女儿，但不传给任何儿子。患病杂合女性会将性状传给一半的子女，无论性别，因为该等位基因表现为显性。

8. Y-Linked Inheritance | Y连锁遗传

Y-linked (holandric) inheritance involves genes located on the Y chromosome. Since only males have a Y chromosome, Y-linked traits are passed from father to all sons and never appear in females. There are very few known Y-linked traits in humans.

Y连锁（限雄）遗传涉及位于Y染色体上的基因。由于只有男性拥有Y染色体，因此Y连锁性状由父亲传给所有儿子，且从不出现在女性中。人类已知的Y连锁性状非常少。

An example is hairy ears (hypertrichosis pinnae auris), where affected males have excessive hair on the outer ear. This trait is transmitted directly from father to son. Because the Y chromosome does not recombine with the X chromosome in the pseudoautosomal regions, the Y-linked allele remains intact across generations.

一个例子是耳多毛症（耳廓多毛症），患病男性外耳上有过多毛发。该性状直接由父亲传给儿子。由于Y染色体在拟常染色体区以外不与X染色体重组，Y连锁等位基因在世代间保持完整。

9. Genetic Analysis with Punnett Squares | 利用庞纳特方格进行遗传分析

To predict the probability of offspring inheriting an X-linked trait, a Punnett square can be used. Consider a carrier female (XᴺXⁿ) married to a normal male (XᴺY). The Punnett square below shows the possible offspring genotypes.

为了预测后代患X连锁性状的概率，可以使用庞纳特方格。考虑一位携带者女性（XᴺXⁿ）与正常男性（XᴺY）婚配。下面的方格展示了可能的后代基因型。

	Xᴺ (mother)	Xⁿ (mother)
Xᴺ (father)	XᴺXᴺ (normal female)	XᴺXⁿ (carrier female)
Y (father)	XᴺY (normal male)	XⁿY (affected male)

The results show that there is a 25% chance of an affected male (XⁿY), a 25% chance of a carrier female (XᴺXⁿ), a 25% chance of a normal female, and a 25% chance of a normal male. Importantly, no daughters are affected, but half of the daughters are carriers.

结果显示，有25%的概率为患病男性（XⁿY），25%的概率为携带者女性（XᴺXⁿ），25%为正常女性，25%为正常男性。重要的是，没有女儿患病，但一半女儿为携带者。

10. Pedigree Analysis of Sex-Linked Traits | 伴性性状的系谱分析

Pedigree charts are often used in exam questions to identify the mode of inheritance. To determine whether a trait is X-linked recessive, look for these features: affected males usually outnumber affected females; the trait can skip generations through carrier females; affected males often have unaffected parents, but the mother is a carrier; an affected male never passes the trait to his sons, but all his daughters become carriers.

系谱图常用于考试题目中以判断遗传方式。要确定一个性状是否为X连锁隐性，可寻找以下特征：患病男性通常多于患病女性；该性状可通过携带者女性隔代遗传；患病男性的父母通常正常，但母亲为携带者；患病男性不会将性状传给儿子，但所有女儿均成为携带者。

For X-linked dominant traits, affected males pass the trait to all daughters and no sons; affected females pass the trait to half of both sons and daughters. These distinct patterns allow geneticists to classify the inheritance mode from a pedigree.

对于X连锁显性性状，患病男性将性状传给所有女儿，而不传给儿子；患病女性将性状传给一半儿子和一半女儿。这些不同模式使遗传学家能够从系谱中分类遗传方式。

11. Key Takeaways for A-Level Biology | A-Level生物重点总结

In CIE A-Level Biology, you should be able to explain the difference between autosomal and sex-linked inheritance, draw and interpret Punnett squares for X-linked crosses, and analyse pedigree diagrams to deduce genotypes.

在CIE A-Level生物考试中，你应该能够解释常染色体遗传与伴性遗传之间的区别，绘制并解释X连锁杂交的庞纳特方格，并分析系谱图以推断基因型。

Males are hemizygous for X-linked genes, so they express all X-linked alleles.

男性对于X连锁基因是半合子，因此会表达所有X连锁等位基因。
A father transmits his Y chromosome to all sons, so Y-linked traits show father-to-son transmission.

父亲将Y染色体传给所有儿子，因此Y连锁性状呈现父子传递模式。
X-linked recessive traits appear more frequently in males and can skip generations via carrier females.

X连锁隐性性状在男性中更常见，并可通过携带者女性隔代遗传。
X-linked dominant traits affect both sexes, but affected males transmit to all daughters only.

X连锁显性性状影响两性，但患病男性只会传给所有女儿。

12. Conclusion | 结论

Sex-linked inheritance provides a clear illustration of how chromosomal location of genes affects their transmission patterns. The examples of red-green colour blindness, haemophilia, Drosophila white eye, vitamin D-resistant rickets, and hairy ears demonstrate the different modes of X-linked recessive, X-linked dominant, and Y-linked inheritance.

伴性遗传清晰地展示了基因的染色体位置如何影响其传递模式。红绿色盲、血友病、果蝇白眼、抗维生素D佝偻病和耳多毛症等实例分别展示了X连锁隐性、X连锁显性和Y连锁遗传的不同方式。

Understanding these concepts enables students to solve genetic cross problems and pedigree questions with confidence. For exam success, always identify whether a trait is dominant or recessive, whether it is autosomal or sex-linked, and then apply the appropriate rules to predict offspring outcomes.

理解这些概念能够使学生自信地解决遗传杂交问题和系谱题目。要在考试中取得好成绩，请务必判断性状是显性还是隐性，是常染色体还是伴性遗传，然后运用相应规则预测子代结果。

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Sex-Linked Inheritance: Concepts and Case Studies | 伴性遗传的概念与实例分析