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Human sperm is a male gamete which fertilises the ovum (female gamete) to produce a zygote. A human baby contains 46 (44 + 2) chromosomes. 23 chromosomes from the mother and 23 from the father come together to form the baby. Amongst the 23 chromosomes from the father (sperm), 22 are autosomes while the remaining last one is a sex chromosome (X or Y).
Autosomes are those chromosomes which carry the human DNA but do not have a role in determining the sex of the zygote. They exist in 22 pairs and are numbered according to their varied shapes and sizes. For instance, as shown in the figure above, chromosome 1 is the largest of them all and the size keeps decreasing till it ends up with a really small 22nd pair of chromosomes.
With the exception of sex-related traits, autosomes control the inheritance of other traits. For example, whether a person will be blue-eyed or brown-eyed, whether they will be intelligent or not, and whether they will have curly or straight hair are all determined by autosomes.
Autosomes | Allosomes |
---|---|
Exist in 22 pairs | Exist in single pairs (XX or XY) |
Common to both males and females | Different in males and females |
Labelled with numbers from 1 to 22 | Labelled with alphabets |
All 22 pairs of autosomes are homologous. | Female chromosomes are homologous (XX), but male chromosomes (XY) are not. |
Do not determine the sex of the zygote. | Determine the sex of the zygote. |
Each pair contains 2 chromosomes of the same height. | In males, the Y chromosome is shorter than X. |
Position of the centromere is the same in all autosomes. | Position of the centromere may vary. |
A human has 44 autosomes. | A human has 2 sex chromosomes. |
A fully-developed sperm is divided into four parts- head, neck, middle piece, and tail, encapsulated in a layer of plasma membrane. The head of the sperm contains the nucleus along with the acrosome. The acrosome is a cap-like structure at the tip of the sperm which contains enzymes to dissolve the ovum wall and facilitate fertilisation.
The middle part of the sperm is called the middle piece which contains mitochondria. It provides energy for the sperm to swim through the female vagina. Connecting the head and the middle piece is the neck which has a centriole contained in it. This centriole facilitates the cleavage of the cells in a zygote after fertilisation. The sperm also contains an elongated tail which helps it to swim through the vagina up to the fallopian tube. The tail forms a major portion of a sperm’s body.
A human sperm cell contains 23 chromosomes. Out of these, only 22 are autosomes. These autosomes contain the usual human DNA with an exception of the sex-determining DNA. They possess the quality to influence basic traits of a human being like eye colour, hair type, face shape, intelligence, and so on.
Autosomal traits can be divided into two categories- dominant and recessive. The dominant traits are those which occur due to the presence of the dominant gene on the autosomes. These determine which traits will occur more commonly in the human population than others. On the other hand, recessive autosomal traits are those that only show up when they are present in a pair in a person. These are usually mutated genes which deviated from the normal at some point in time. The presence of these dominant or recessive genes governs if the human being will suffer from an autosomal genetic disorder or not.
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