Reaching the Age of Adolescence

Reproductive Phase of Life and Sex Determination

Sex Determination: As we grow up, we notice various changes in our body. Why do they happen? Well, most of it is attributed to adolescence. Not only you, but each one of us face these changes. It is absolutely normal! As we all know, adolescence is a transition period in life between childhood and adulthood.  Let’s go through a reproductive system, menstrual cycle and sex determination in details.

As a part of growth mechanism, the body undergoes a lot of changes physically as well as psychologically. Puberty commences the sexual maturity in adolescents. Hormones play a major role during this period. However, the reproductive phase in boys and girls are different.

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Reproductive System: Menstrual Cycle

Adolescence marks the onset of reproductive phase in boys and girls. The development of secondary sexual characteristics is the beginning of this. Once the gonads begin to produce gametes (sperm in male and ovum in female), they are capable of reproducing. However, the production of gametes in males and females takes place in different ways.

Reproductive phase in both females and males begin at puberty. In males, reproductive phase lasts until death but in females, it ends by the age of 50 years. Menstrual cycle/ menstruation mark the commencement of puberty in girls. In a girl, reproductive phase emerges from the age of 10 to 15 when she attains the puberty. When puberty arrives eggs in ovaries starts to mature.

One of the ovaries releases the matured ovum in every 28 to 30 days. This is called ovulation. The uterus becomes thicker and prepares itself for implantation. If the egg fuses with the sperm it becomes fertilized. The fertilized egg (egg fused with sperm) leads to pregnancy.

Contrary to this, unfertilized egg leads to shedding of uterus walls and causes bleeding in women. Menstruation is the bleeding phase. Menarche is the first menstrual flow. By the age of 50 years, menstrual cycle stops forever and is marked as menopause. The time interval from one menstrual cycle to another can vary from 28 to 30 days.

reproductive system

The sex hormones along with few other hormones are responsible for this phase in women. The variation in these hormones may change the ovulation day. The irregularity in menstrual cycle is also attributed to hormonal imbalances. However, what is interesting to know is how the sex of a child is determined!

Sex Determination

In the nucleus of every cell in the human body, we have chromosomes. All the human beings have 23 pairs of chromosomes in the nuclei of their normal body cells.Out of these 23 pairs of chromosomes, one pair of chromosomes is called sex chromosome. The two chromosomes that determine the sex of an offspring or baby are called sex chromosomes.The two sex chromosomes are named X chromosomes and Y chromosomes.

The gametes are special cells called reproductive cells.The gametes contain only 23 single chromosomes and hence, they have only one of the two sex chromosomes that exist in the normal body cells. In females, all the gametes or all the egg cells contain X chromosomes.

In males, half of gametes or sperms have X chromosomes and half of gametes or sperm have Y chromosomes. The baby developed from XX chromosome of sex chromosome in the zygote is a girl. And, the baby developed from XY combination of sex chromosomes in zygote will be a boy.

Solved Example

Question: Write a note on the sex determination of a baby.

Answer: The sex of a baby to be born is decided at the moment the egg cell of woman gets fertilized by the sperm of man and pregnancy occurs. The instructions for determining the sex of baby are present in the sex chromosomes which are in the nucleus of the fertilized egg called zygote.

  • If a sperm carrying X chromosome fertilizes an egg cell which carries X chromosomes, then the zygote formed will have XX combination of sex chromosomes due to which the child born will be a girl.
  • If a sperm carrying Y chromosomes fertilizes an egg cell which carries X chromosomes, then the zygote formed will have XY combination of sex chromosomes due to which the child born will be a boy.

The sex of unborn child depends on whether the zygote formed at the time of fertilization has XX combination of sex chromosomes or XY combination of sex chromosomes. It is the sperm of man that determines the sex of the child. This is because half of the sperms have X chromosomes and other half have Y chromosomes. The egg cells or ova of woman cannot decide the sex of the child because all the egg cells contain the same sex chromosomes, X chromosomes.

  • If the father contributes X sex chromosomes at fertilization through its sperm, the baby born will be a girl.
  • If the father contributes Y sex chromosomes at fertilization through its sperm, the baby born will be a boy.

Father is responsible for the sex of the baby which is born.

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