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Heredity and Evolution

Sex-Linked Inheritance

How is it that parents and the offspring look similar? The progeny shares some traits or characteristics that are inherited from the parents, and this passes on again to the next generation. In a broader perspective, everything is related to genes, genetics, and heredity. In humans, this concept can be understood clearly through sex-linked inheritance.

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What is Sex-Linked Inheritance?

How does one determine whether an unborn baby is a male or a female? Did you know that the genes and the chromosomes play an important role in this determination? The sex of the individual is largely genetically determined.

A human being has 23 pairs of chromosomes. The 22 pairs of chromosomes are called autosomes and are the non-sex chromosomes. One pair of chromosomes is called the sex chromosomes. Every human individual, both male and female, has two sex chromosomes. Depending on the type of sex chromosomes present, the gender is determined. Females have XX, i.e. two X chromosomes while males have XY, i.e. one X chromosome and one Y chromosome.

Genes that are carried by the sex chromosomes are said to be sex-linked. They carry the genes that determine whether an individual is a male or female, along with other traits.

Sex Determination

Sex-Determination-( Source -Science of biogenetics)

Males have XY chromosome and Females have XX chromosomes. When a baby inherits the X chromosome from the father and the X chromosome from the mother, then the baby will be a female baby. When a baby inherits the Y chromosome from the father and the X chromosome from the mother, then the baby will be a male baby.

When you see the chromosomes, notice that it is the Y chromosome that determines the sex-linked inheritance of the baby. A mother i.e. a female has both XX chromosomes, whereas the father (male) has XY chromosomes. The Y chromosome of the male has a gene called SRY (“sex-determining region of Y”).

It is this gene that determines that a developing embryo will be a male. An embryo having XX chromosomes does not have SRY gene and hence develop into a female, while the embryo with XY chromosomes has the SRY gene and develops into a male.

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Sex-Linked Inheritance

Human Blood Groups and Their Inheritance

Did you know that your blood group is determined by the blood group of your parents? The inheritance of the blood groups is controlled by specific genes. In humans, there are different types of blood groups. The standard recognized form of classifying blood groups is the ABO blood grouping, given by Karl Landsteiner. According to this, there are four main blood groups, which are A, B, O and AB groups.

The following figure explains how blood groups are inherited from parents.

Determination Of Blood Groups( Source – Wikihow)

Solved Questions for You

Q.1: Explain why the father determines the sex-linked inheritance of the child?

Ans. The father (male) has XY chromosomes. The Y chromosome of the father has the SRY gene. (“Sex-determining region of Y”). This gene determines if an embryo will be a male or a female. An embryo having XX chromosomes does not have SRY gene and hence develop into a female, while the embryo with XY chromosomes has the SRY gene and develops into a male.

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