Define heredity . Explain the mechanism of heredity.
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Meaning of Heredity:
The offspring’s of any particulars species resembles its parents in a general way. The young of cats are always kittens and never puppies. With respect to details, however, there is a lot variation. No kittens are exactly alike. Some may be black, others white, and still others may have a mottled fur.
In some instances the young may resemble one of their parents or they may have characteristics similar to those of their grand-parents rather than their own parents. This passage of characters from one generation to another is called inheritance or heredity. It is resemblance based upon descent.
Heredity may be defined as the occurrence in the living organisms of qualities that are derived from their ancestors. Heredity includes not only physical but also physiological qualities. These qualities may be either expressed or they may be latent in the offspring.
Differences among members of any particular species are spoken of as variations. These may be fluctuating or phenotypic variations which depend upon environmental factors or these may be germinal or genotypic variations which are not influenced by the environment.
The phenotypic variations are not heritable, whereas the genotypic variations are handed down to the progeny from one generation to another. The science of Genetics seeks to account for the resemblance or difference between the young and its ancestors. It is concerned with the heritable or genotypic variations of an individual and with laws governing the process of inheritance.
Mechanism of Heredity:
Since higher organisms reproduce sexually and since the sperm and the egg are the only materials which pass from the parents to the offspring, the mechanism of heredity must be located in the gametes. Since only the head of the sperm enters the egg and since the head is the nucleus of the sperm it is reasonable to state that the nucleus of the male gamete is the bearer of paternal characters.
The egg contains not only a nucleus but also some amount of cytoplasm. So the matter is not clear in this case, but it may be assumed that the maternal and paternal characteristics are handed on to the new individual in the same way.
It has been proved by experiments that:
(1) Mature eggs caused to develop by parthenogenesis produce individuals with only maternal characteristics;
(2) An egg which is first deprived of its nucleus and then fertilized by a sperm produces an individual with only paternal characters. The results of these two experiments confirm the view that the transmission of hereditary characters depends upon the nucleus.
Modern geneticists have observed certain ultra-microscopic particles called genes which are arranged in a linear series upon the chromosomes of the gametes. The genes are composed of special kinds of nucleoproteins whose chemical and physical properties are obscure.
They appear as beads or cross bands upon certain chromosomes. A gene is regarded as a factor for a single heritable character. It is the unit of inheritance that is transmitted from the parents to the offspring, and is responsible for a particular character, such as colour of the eye or texture of the hair.
A gene always acts by interaction with other genes, the cytoplasm, and the environment. Recently Miller has been able to produce gene mutation in the fruitfly Drosophila by exposing them to the bombarding action of the X-rays.
Normally gene mutations occur during meiosis by random sorting of chromosomes —any single gamete receiving either one or the other of each homologous pair. Thus gene mutations are the real cause of heritable variations. Phenotypic variations are not inherited.
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The offspring’s of any particulars species resembles its parents in a general way. The young of cats are always kittens and never puppies. With respect to details, however, there is a lot variation. No kittens are exactly alike. Some may be black, others white, and still others may have a mottled fur.
In some instances the young may resemble one of their parents or they may have characteristics similar to those of their grand-parents rather than their own parents. This passage of characters from one generation to another is called inheritance or heredity. It is resemblance based upon descent.
Heredity may be defined as the occurrence in the living organisms of qualities that are derived from their ancestors. Heredity includes not only physical but also physiological qualities. These qualities may be either expressed or they may be latent in the offspring.
Differences among members of any particular species are spoken of as variations. These may be fluctuating or phenotypic variations which depend upon environmental factors or these may be germinal or genotypic variations which are not influenced by the environment.
The phenotypic variations are not heritable, whereas the genotypic variations are handed down to the progeny from one generation to another. The science of Genetics seeks to account for the resemblance or difference between the young and its ancestors. It is concerned with the heritable or genotypic variations of an individual and with laws governing the process of inheritance.
Mechanism of Heredity:
Since higher organisms reproduce sexually and since the sperm and the egg are the only materials which pass from the parents to the offspring, the mechanism of heredity must be located in the gametes. Since only the head of the sperm enters the egg and since the head is the nucleus of the sperm it is reasonable to state that the nucleus of the male gamete is the bearer of paternal characters.
The egg contains not only a nucleus but also some amount of cytoplasm. So the matter is not clear in this case, but it may be assumed that the maternal and paternal characteristics are handed on to the new individual in the same way.
It has been proved by experiments that:
(1) Mature eggs caused to develop by parthenogenesis produce individuals with only maternal characteristics;
(2) An egg which is first deprived of its nucleus and then fertilized by a sperm produces an individual with only paternal characters. The results of these two experiments confirm the view that the transmission of hereditary characters depends upon the nucleus.
Modern geneticists have observed certain ultra-microscopic particles called genes which are arranged in a linear series upon the chromosomes of the gametes. The genes are composed of special kinds of nucleoproteins whose chemical and physical properties are obscure.
They appear as beads or cross bands upon certain chromosomes. A gene is regarded as a factor for a single heritable character. It is the unit of inheritance that is transmitted from the parents to the offspring, and is responsible for a particular character, such as colour of the eye or texture of the hair.
A gene always acts by interaction with other genes, the cytoplasm, and the environment. Recently Miller has been able to produce gene mutation in the fruitfly Drosophila by exposing them to the bombarding action of the X-rays.
Normally gene mutations occur during meiosis by random sorting of chromosomes —any single gamete receiving either one or the other of each homologous pair. Thus gene mutations are the real cause of heritable variations. Phenotypic variations are not inherited.
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Transfer of characteristics from parents to offspring is called heredity.
It is due to heredity that puppies are similar to dogs,squabs are similar to peigons and infants are similar to human.
Though there are many similarities between parents and their offsprings there are some differences too.These similarities and differences are all the effects of heredity.
The structure in the nucleus of cells that carries the hereditary characteristics is called the chromosome.Genes which contain the information about hereditary characteristics in coded form are located on chromosomes.
Imformation necessary for protein synthesis in the cell is stored in DNA.
segments of DNA molecule are called genes.
Genes control the structure and function of the cells of the body.Also they transmit the hereditary characteristics from the parents to offspring.Hence genes are said to be the functional units off heredity.
It is due to heredity that puppies are similar to dogs,squabs are similar to peigons and infants are similar to human.
Though there are many similarities between parents and their offsprings there are some differences too.These similarities and differences are all the effects of heredity.
The structure in the nucleus of cells that carries the hereditary characteristics is called the chromosome.Genes which contain the information about hereditary characteristics in coded form are located on chromosomes.
Imformation necessary for protein synthesis in the cell is stored in DNA.
segments of DNA molecule are called genes.
Genes control the structure and function of the cells of the body.Also they transmit the hereditary characteristics from the parents to offspring.Hence genes are said to be the functional units off heredity.
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