Why does zygote have 46 chromosomes

Sperm can have either an X chromosome or a Y chromosome. If a sperm with an X chromosome fertilizes the egg, the new cell will have two X chromosomes. One came from the father's sperm and one came from the mother's egg.

Since the sex chromosome that is made is XX, the cell will grow into a girl baby. If a sperm with a Y chromosome fertilizes the egg, the new cell will have an X and a Y chromosome. The X came from the mother's egg and the Y came from the father's sperm. Since the sex chromosome that is made is XY, the cell will grow into a boy baby. Figure How the sex of a baby is set.

One sex chromosome comes from each parent. Follow the arrows to see the possible match-ups. If a gene is faulty, there will be a problem with the part of the body it directs.

This is called a genetic defect. There is a gene that tells certain cells in the body how to make clotting factor. There are also genes that tell how to make von Willebrand factor VWF and how to make each part of a platelet. If there are problems with any of those genes, the factor or platelets that are made may not work right. There may not be enough factor made.

The person will have a bleeding disorder. What type the person has depends on which gene has the defect. A sex-linked gene is any gene that is found on the sex chromosome labeled X. The instructions that these genes give are called sex-linked traits. If a defective gene is on the X chromosome, it is called a sex-linked disorder. It will occur almost exclusively in men. Hemophilia and color blindness are both sex-linked disorders.

The genes that cause them are on the X chromosome. The 22 pairs of chromosomes that are not the sex chromosomes are called autosomes. If a disorder is carried by a gene on one of these autosomes, it is called an autosomal disorder.

Since it is on the autosome and not the sex chromosomes, it can occur in both males and females. When the 23 chromosomes from the father's sperm and the 23 from the mother's egg meet, they pair up.

The genes on the chromosomes pair up, too. The paired genes, one from each parent, carry the plans for the same part of the body. For instance, the gene for hair color from the father pairs up with the gene for hair color from the mother. Sometimes one of the genes in the pair is stronger and blocks the instructions from the other gene. The stronger gene that takes control is said to be dominant. The gene whose instructions are blocked is called recessive.

A recessive gene will have a chance to send its instructions to the cells only if it is paired with another recessive gene. The X chromosome is significantly longer than the Y chromosome and contains hundreds more genes. Because the additional genes in the X chromosome have no counterpart in the Y chromosome, the X genes are dominant. This means that almost any gene on the X, even if it is recessive in the female, will be expressed in males.

These are referred to as X-linked genes. Genes found only on the Y chromosome are referred to as Y-linked genes, and expressed only in males. Genes on either sex chromosome can be called sex-linked genes. There are approximately 1, X-linked genes, though most of them are not for female anatomical characteristics. In fact, many are linked to disorders such as hemophilia, Duchenne muscular dystrophy, fragile-X syndrome and several others. They are responsible for red-green color blindness, considered the most common genetic disorder and found most often in males.

The non-sex feature X-linked genes are also responsible for male pattern baldness. In contrast to the large X chromosome, the Y chromosome contains only 26 genes. Sixteen of these genes are responsible for cell maintenance. Nine are involved in sperm production, and if some are missing or defective, low sperm counts or infertility may occur.

One gene, called the SRY gene, is responsible for male sexual traits. The SRY gene triggers the activation and regulation of another gene, found on a non-sex chromosome, called the Sox9.

The Sox9 triggers the development of non-sexed gonads into testes instead of ovaries. Abnormalities in the sex chromosome combination can result in a variety of gender-specific conditions that are rarely lethal.

Female abnormalities result in Turner syndrome or Trisomy X, according to the U. National Library of Medicine. Turner syndrome occurs when females have only one X chromosome instead of two.

Symptoms include failure of the sex organs to normally mature, which may lead to infertility, small breasts and no menstruation; short stature; a wide, shield-shaped chest; and a wide, webbed neck. Trisomy X syndrome is caused by three X chromosomes instead of two.

Symptoms include tall stature, speech delays, premature ovarian failure or ovarian abnormalities, and weak muscle tone — although many girls and women exhibit no symptoms. Males can be affected by Klinefelter syndrome. Symptoms include breast development, abnormal proportions such as large hips, tall height, infertility, and small testicles. Live Science.