Sex determination

The mother’s egg normally contributes an X chromosome in every fertilisation. The father produces two types of sperm in roughly equal numbers: X-bearing and Y-bearing. An X sperm joined with the egg forms XX, while a Y sperm forms XY. Thus the chromosome contributed by the father’s sperm determines the usual chromosomal sex combination; option B is correct. This does not imply choice or control by either parent.

In the standard human model, the egg contributes an X chromosome. If the fertilising sperm also carries X, the zygote receives X from each parent, giving the combination XX. This combination is typically associated with a female child, so option A is correct. A Y-bearing sperm would produce XY, which is why options B and D do not fit the stated condition.

The egg always contributes an X chromosome, whereas a sperm may contribute either X or Y. When a Y-bearing sperm fuses with the X-bearing egg, the zygote has the chromosome combination XY. In the usual human sex-determination system, XY develops as a male child. Therefore, option B is correct. Option A would result from XX; options C and D do not describe this fertilisation outcome.

In the usual human XX–XY system, the mother’s egg carries an X chromosome, whereas the father’s sperm carries either X or Y. Fertilisation by an X-bearing sperm produces XX, generally female; fertilisation by a Y-bearing sperm produces XY, generally male. Thus the paternal sex chromosome determines the chromosomal sex of the child. Option A is correct; food, blood group, and birthplace do not determine it.

The mother’s egg normally contributes an X chromosome. If the father’s sperm also contributes an X chromosome, the zygote receives X + X, giving the chromosomal combination XX. In the standard human XX–XY system, XX generally develops as a female, so option A is correct. An XY combination is usually male; the other choices do not follow from the stated chromosome combination.

The governing concept is chromosomal sex determination in humans. Human females generally have XX sex chromosomes and produce ova carrying only X. Human males generally have XY chromosomes and produce sperm carrying either X or Y. Fertilisation by an X-bearing sperm gives XX, while fertilisation by a Y-bearing sperm gives XY. Thus the sex-chromosome combination determines sex; food, blood group and height do not.

The governing concept is the XX–XY system of human sex determination. A mother’s egg normally contributes an X chromosome, whereas the father produces two kinds of sperm: X-bearing and Y-bearing. X sperm plus X egg gives XX, while Y sperm plus X egg gives XY. Thus the sperm determines which sex-chromosome combination forms, making option A correct. The mother contributes an essential chromosome too, so the distractors incorrectly deny her role or the existence of chromosomes.

The governing concept is chromosomal sex determination in humans. The egg contributes one X chromosome, and the stated sperm also contributes one X chromosome. Adding the two contributions gives X + X = XX. In the standard school-level XX–XY system, XX is the usual female chromosomal combination. XY would require a Y-bearing sperm, YY cannot result because the egg supplies X, and OO is not a human sex-chromosome combination. Therefore A is correct.

The governing concept is the XX–XY mechanism of human sex determination. The egg contributes X, while the sperm specified in the question contributes Y. Their union therefore gives X + Y = XY. In the standard school classification, XY is the usual male chromosomal combination. XX would result from an X-bearing sperm, YY cannot form because the egg does not carry Y, and XO represents a different chromosomal condition rather than the stated fusion. Hence option B is correct.

The governing concept is the human XX–XY sex-determination system. Every normal egg contributes an X chromosome. A sperm carrying X produces XX after fertilisation, whereas a sperm carrying Y produces XY. Since the type of sperm is not controlled by the mother, blaming her for a girl child has no scientific basis. Option A correctly describes the chromosome contributions; B and C deny essential parental roles, and D confuses nutrition with inherited chromosomal determination.

For the usual human chromosomal system, the mother contributes an X chromosome in her egg, while the father contributes either X or Y in his sperm. Combining the given chromosomes gives X + Y = XY. The XY chromosomal combination is conventionally associated with a male child, so option A is correct. An XX combination would be associated with a female child; options C and D do not follow from the stated chromosome pair.

In the usual human XX–XY system, every egg produced by the mother carries an X chromosome. A father produces two types of sperm: some carry X and some carry Y. Fertilisation by an X-bearing sperm gives XX, while fertilisation by a Y-bearing sperm gives XY. Thus the sperm determines whether the zygote is XX or XY, making option A correct. This does not mean that the father controls the outcome consciously.

The egg contributes X and the sperm contributes Y. Combining these chromosomes gives XY: X + Y = XY. In the standard human chromosomal model taught at this level, XX is associated with a female child and XY with a male child. Therefore option B is correct. Option A would result from X + X, while options C and D ignore the definite chromosome combination produced at fertilisation.

The mother’s egg contributes one X chromosome, and in this case the father’s sperm also contributes X. Their union produces the combination XX: X + X = XX. In the standard human chromosomal model, XX corresponds to a female child, so option A is correct. A Y chromosome is absent in this combination, so it cannot be YY or XY, and fertilisation can still produce a zygote.

In the usual human chromosomal system, the mother is XX, so every ovum carries an X chromosome. The father is XY, so sperm may carry either X or Y. Fertilisation by an X-bearing sperm produces XX, while fertilisation by a Y-bearing sperm produces XY. Therefore option A is correct. The mother contributes a chromosome, and the other options incorrectly deny chromosomal determination or the father’s two sperm types.

The usual human XX-XY mechanism shows why blaming the mother is scientifically unjustified. Every normal ovum contributes an X chromosome. A sperm contributes either X or Y; XX generally develops as female and XY generally as male. Thus the father’s sperm determines which sex-chromosome combination forms, although fertilisation is a contribution from both parents. Option A is correct; B, C and D contradict this mechanism.

In the standard human system, the ovum always contributes one X chromosome because the mother is XX. A female chromosomal combination is XX, so the fertilising sperm must also contribute X: X from the ovum plus X from the sperm gives XX. A Y-bearing sperm would produce XY, while a sperm without a chromosome or both sperm together does not describe normal fertilisation. Therefore option A is correct.

The human ovum normally contributes X, while a Y-bearing sperm contributes Y. Their fusion gives X + Y = XY, the usual male sex-chromosome combination. An X-bearing sperm would instead give X + X = XX, generally female. Only one sperm normally fuses with one ovum, so both combinations do not form together, and fertilisation does produce a definite chromosomal combination. Therefore option A is correct.

The governing concept is the XX–XY mechanism of human sex determination. A mother’s egg normally contributes an X chromosome, whereas a father produces sperm carrying either X or Y. Fertilisation with an X-bearing sperm gives XX, while fertilisation with a Y-bearing sperm gives XY. Thus the sperm determines which combination forms. Option A is correct; B, C, and D incorrectly describe the chromosomes contributed by the mother or father.

Human eggs normally carry an X chromosome, whereas sperm may carry either X or Y. Fertilisation by an X-bearing sperm usually produces an XX zygote, and fertilisation by a Y-bearing sperm usually produces an XY zygote. Thus the sperm’s sex chromosome determines the chromosomal combination, although biological development is more complex than a simple label. A is correct; the other factors do not determine chromosomal sex.