It could transmit information to the next generation. It reproduced itself faithfully. Plant the mango, get a mango. Not a Banana, Bees give bees and birds give birds. And even more than that, notes the things giving the same species, but within a species you can see the strong resemblances. If we take human beings particular types Of noses or the height Of the individual will be difference, It would transmit in a family. So people knew somehow there was something very important about the information that was transmitted, which brings familial resemblance. So for thousands of years, people wondered bout familial resemblance.
Folks being folks would make up explanations for it. Information was combined from both parents and blended in offspring, known as Heredity. “Heredity is the transmission of characteristics from parent to offspring”. We have puzzled our heredity since before works were written down. It is important to know that for 200 or more years, people were just completely confused about this concepts. The road to Mendel: Early ideas of heredity Our understanding of heredity starts with a series of European farmers, who were trying to improve varieties of agricultural plants for economic and trade repose.
They carried out matting called =crosses’ between individual plants and selecting the desirable offspring of the each cross. Little progress in solving the puzzle was made, however, until Gregory Mendel conducted some simple but significant experiments in his monastery garden a century ago. What emerged from this obscure garden was the key to understand the heredity. Gregory Johann Mendel cultivating his plants in the garden, which was located in Born, Czechoslovakia. Mendel studied how differences between varieties of peas were inherited when the varieties were crossed with one another.
Mender’s Experiments: The history of modern genetics dates back to the middle of the nineteenth century, when Gregory Johann Mendel (1822-1884). An Austrian Monk, performed quantitative studies of inheritance. He carried out his breeding or crossing experiments on the garden pea and published his results in the journal ‘Transactions of the Natural History society of Bruin’ Mendel presented completely new theory of inheritance in this journal. Though it was a well-documented work, it did not attract wide attention until after his death. His work was rediscovered in 1 900, simultaneously by Hugo De Varies in
Holland, Carl Corners in Germany and Erich Teacher’s in Austria. All three readily gave to Mendel the credit that was due to him. Mendel is often referred to as Father of Genetics, because of his contribution to an understanding of some of the basic principles of heredity. His experiments still serve as an excellent examples for the simpler hereditary patterns. These principles collectively form “Madeline genetics” Mendel picked peas for good reasons. Peas didn’t take up that much space in the monastery garden. And peas have other features where the fertilizing organs re enclosed in a kind of closed keel.
They self-fertilize, usually. And there’s no risk that pollen from some other plant is going to get in there. You can open it up and put pollen in. But it’s an ideal plant for doing genetics because we don’t randomly get much cross-pollination. He’s got pod color, pea color, the shape, whether they’re inflated pea pods or constricted pea pods. He’s got whether the flowers are purple or white, whether the flowers are at the top or along the middle there, the stem length. These are seven traits that he studies intensely in his peas. And he shows that hey all transmit completely faithfully when you just self-breed the particular strain.
Mendel presented completely new theory of inheritance and followed certain criteria for his breeding experiments: 1 . Selection of distinctive characters (tall X dwarf, round X wrinkled, green X yellow etc. ) 2. Selection of true breeding varieties ( that would show the same characters in the same way in the offspring in succeeding generations) 3. Controlled fertilization Monophonic cross In monophonic cross Mendel selected one character for his experiment (single pair of contrasting character), he made crosses between purple and white flower plants. The plant with which, Mendel started his experiments known as parental generation.
All the offspring obtained by purple flower plant and white flower parental cross over resulting in purple flower. The offspring were called hybrids and considered as Fl first filial generation. Then Fl plants were allowed for self- fertilization. The plants produced by self-fertilization of Fl generation are taken as belongings of IF that is second filial generation. The F-2 generation included both purple and white flower plants, there were no plants of intermediate color or blended in any of the generation. -2 generation is important because the reappearance of white flower, which was disappear in Fl .
The ratio Of the purple and white flower plant in IF generation was Purple X white flower Fl generation (purple) Self-fertilization purple (3) white(l ) Principal of dominance is only one of the two contrasting character will appear or expressed. In monophonic cross Fl generation showed only one type of plants that is purple flowers and named as dominant and other one is called as recessive. Purple was dominant in Fl generation. But Mendel does one more thing, He counted. He didn’t just observe qualitatively. He just dint stop, he did it again. He actually did it for seven different traits.
He got this 3 to 1 ratio. Alleles do not blend in heterozygous. When gametes are formed in heterozygous diploid individuals, the alleles segregate from one another. Each gametes has an equal probability of possessing either member of an allele pair. Observation and interpretation of the monophonic cross CLC The hybrid offspring always resembled one of the parents, did not have an intermediate flower color. L] The first filial generation Fl plants all had purple flowers. Mendel referred to the trait expressed in the Fl plants as dominant and to the alternative trait, which was not expressed in the Fl as recessive. The plants obtained from self-pollination of Fl generation exhibited the recessive trait (second filial IF generation). L] Mendel counted the numbers of each type among the IF progeny, Amongst the 929 total IF individuals 705 had purple flower and 224 had white flowers. 0 14th of the IF individuals exhibited the dominant trait and 14th displayed the recessive trait. The ratio of dominant directories among the IF plants was always 3:1 D The study of IF plants in later generation he found that the one quarter that were recessive were always true breeding.
Where 13rd of the dominant IF were true breeding. The genotype ratio 1 is the really distinguished with true-breeding dominant, not determining and one quarter true-breeding. D For each pair of traits that Mendel examined, one alternative was not expressed in the Fl hybrids although it reappeared in the F-2 0 In the pairs of alternative traits one trait must have been latent in the Fl generation. O He concluded that the traits segregate among the progeny Of particular cross, and some plants express one trait some exhibit other.
Law of segregation/Law of purity of gametes: It states that whenever a pair of factors for character brought together in a hybrid, they segregate during the formation of gametes. Hence each gamete is pure with reference to this character. (Mendel was not having any idea of chromosomes or genes. However he used the term *air of factor’ or unit factors for the word we use =gene’) In monophonic cross Fl was having both the unit factors purple and white flower, but purple color factor was dominant over dwarf factor. Dwarf being recessive factor could not express.
To explain this according to Mender’s scheme the parental plant of pure breed with identical factors are denoted as UP for purple flower and up for dwarf. The hybrid obtained in first generation was (Up) having both the factors. The zygote produced by parental generation can have only (Up) hence the offspring obtained were of only Purple, because on p (purple factor) can express itself = p’ does not produce any effect as is dominant over Mendel proposed a simple model of terminologies containing simple assumptions and making clear predictions. . Parents do not transmit their physiological traits Or form directly to their offspring. Rather, they transmit distinct information about the traits, Mendel called factors. 2. In diploid organisms, with respect to each trait or parent, contains two factors, which may or may not be the same. If the factors are different the individual is said to be heterozygous for that characteristic. If they are the same the individual is homozygous. 3. The alternative forms of a factor, leading to alternative character traits are called alleles. 4.
The two alleles, one contributed by the male and one by the female gamete. Alleles do not blend with one another or altered in any other way. When the individual matures, produces its own gametes, these gametes include equal proportions Of the elements that the individual received from its two parents. 5. In heterozygous individuals one allele achieves expression which is dominant the other allele is present but unexpressed is recessive. 6. The physical appearance of an individual is its phenotype and the alleles that an individual contains as its genotype.
Test cross and Back cross: A cross involving the Fl individuals with either of the two parents is called jack cross. A back cross between the Fl hybrid and dominant parental type will produces only dominant individuals the cross between Fl and recessive parental type both the phenotypes appear in the progeny The cross between Fl and recessive parent is called test cross (Pix up). All the test crosses are back cross but all the back crosses are not a test cross. Only the cross with the recessive parental type is test cross.
Test cross helps to test whether the individual is homozygous or heterozygous. Test cross produces 2 types of offspring 50% of them would show the dominant and other 0%would show the recessive. Debris cross Mendel derived the law of segregation from experiments in which he followed only a single character, such as flower color. He did his second experiment following two characters at the same time seed color and seed shape debris cross. Mendel crossed a pea plant producing Round yellow seeds with one producing green and wrinkled seeds of pure breed variety.
In Fl generation plants obtained producing only round yellow seeds F-1 were allowed for self-pollination to get IF generation. In IF generation, 4 different types of plants were produced that is a) Round allow b) Round green c) wrinkled yellow d) wrinkled green. Phenotype ratio of 4 types of plants were 9:3:3:1 Round, Yellow X Wrinkled, Green Round, Yellow (Fl generation) Round Yellow(9), Round Green(3), Wrinkled Yellow(3), Wrinkled Green(l) Law of independent assortment: The factors for two or more pairs of contrasting characters are distributed independently of one another at the time of gamete formation.
Egg: The individual factors for rounded and wrinkled nature of the seeds and their yellow and green appeared in different combinations. Parental plants contain identical factors for each character. Round(R), wrinkled(r),Yellow(Y), green(g), then the parents plants contain RAY and ray. Thus parent Of homozygous for both the factors Assessment of debris cross IF generation by Punned square At the time of the formation of gametes, each parent produces gametes of only one type RAY and ray ( according to the law of segregation).
The Fl offspring will all be of one variety only with Round and Yellow genotype will be Ray. It is called debris because it is a hybrid for two characters, it is heterozygous for both genes. Debris test cross: A debris test cross involves crossing of the Fl debris with a double excessive parental type. Ray (Fl) X ray (P) ray Ray Round Yellow Ray Green r ray Wrinkled Genotype and Phenotype ratio is : 1 : 1 Patterns of inheritance Mendel explained inheritance in terms of discrete _factors’ genes that are passed along from generation to generation according to the rules of probability.
Mender’s laws are valid for all sexually reproducing organisms, including garden peas and human beings. However Mender’s law stop short of explaining some patterns of genetic inheritance. For most sexually reproducing organisms, cases where Mender’s laws can strictly account for he patterns of inheritance are relatively rare and often the inheritance patterns are more complex. The offspring of Mender’s pea crosses always looked like one of the two parental varieties. This is _Complete dominance’ the dominant allele had the some phenotypes effect whether present in one or two copies.
Madeline inheritance and its physical basis in chromosomal behavior Gregory Mender’s -?hereditary factorial were purely an abstract concept when he proposed their existence in 1860. At that time, no cellular structures were known that could house these imaginary units. Even after chromosomes were iris observed, many biologists remained skeptical about Mender’s laws of segregation and independent assortment until there was sufficient evidence that these principles of heredity had a physical basis in chromosomal behavior. Today, we know that genes-?Mender’s -?factorial-?are located along chromosomes.
We can see the location of a particular gene by tagging chromosomes with a fluorescent dye that highlights that gene. Using improved techniques of microscopy, cytologists worked out the process of mitosis in 1875 and meiosis in the asses. Cell division The ability of organisms to produce more of their own kind is the one harmonistic of all living things. The continuity of life is based on the reproduction of cells or cell division. Cell division plays several important roles in life. The division of one prokaryotic cell reproduces an entire organism.
The same is true of a unicellular eukaryote. Cell division also enables multicultural eukaryote to develop from a single cell, like the fertilized egg that gave rise to the two-celled embryo and after it is fully grown organism, cell division continues to function In renewal and repair, replacing cells that die from normal wear and tear or accidents. The cell division process is an integral part of the cell cycle, the life of a cell from the time it is first formed from a dividing parent cell until its own division into two daughter cells.
Passing identical genetic material to cellular offspring is a crucial function of cell division. There are two types of cell division Mitosis and meiosis. Mitosis produces 2 diploid (an) daughter cells which are genetically identical to the parent cells. Meiosis produces 4 each haploid (n) containing half as many chromosomes as the parent cell; genetically different from the parent cell and from each other. All though chromosomes were discovered more than a century ago, the exact number of chromosomes that human possess was not established accurately until 1956.
After the development of appropriate techniques to determine accurate number, shape and form of chromosomes were studied. The number of chromosomes present in the various species were determine Human beings normally have 46 chromosomes in their somatic cells, Pious stadium a pea plant contains 14, Drosophila having 8 chromosomes. Conventionally, the 23 different kinds of human chromosomes are arranged into seven groups, each characterized by a different size, shape and appearance (A-G). Of 23 pairs, 22 are perfectly matched in both males and females and are called outcomes.
The remaining pair is called the sex chromosomes (X & Y). Two unlike members in males (XX); in females, it consists Of two similar members (XX). Us Mary of Key concepts Mender’s quantitative approach to the monophonic and debris experiments. Scientific approach to identify Mendel two laws of inheritance. Mender’s genetic vocals Degree of dominance. Mendel inheritance basis for Cell division Chromosomal inheritance In the early years of century it was not obvious that chromosomes were the icicles for the information of heredity.
The German scientist Carl Corners first suggested a central role for chromosomes in 1 900 in one of the papers announcing the rediscovery of Mender’s work. Soon after, observations that similar chromosomes paired with one another in the process of meiosis led directly to the chromosomal theory of inheritance. Cytology and genetics converged when biologists began to see parallels between the behavior of chromosomes and the behavior of Mender’s proposed hereditary’ factors during sexual life cycles.
Chromosomes present in pairs in diploid cells; homologous chromosomes separate and alleles segregate during the process of meiosis and fertilization restores the paired condition for chromosomes. These parallels noted independently by Walter S Sutton and Theodore Bovver in 1902. According to this theory, 1 . Reproduction involves the initial union of only two cells, egg and sperm. If Mender’s model is correct, then these two gametes must make equal hereditary contributions. Sperm, however, contain little cytoplasm. Therefore the hereditary material must reside within the nuclei of the gametes. . Chromosomes segregate during meiosis in a fashion similar to that exhibited by the alleles Mendel studied. 3. Gametes have a copy of one member of each pair of homologous chromosomes; diploid individuals have a copy of both members of the pair. Similarly, Mendel found that gametes have one allele of a gene and that diploid individuals have two. 4. During meiosis, each pair of homologous chromosomes orients on the metastases plate independently of any other pair. This independent assortment of chromosomes is a process similar to the independent assortment of alleles that Mendel studied. 5.
Madeline genes have specific loci/positions along chromosomes and it is the chi Romeos that undergo segregation and independent assortment. The proof that the genes were located on chromosomes was provided by single small fly. Mooring’s experimental evidence In 1 910 the American geneticist Thomas Hunt Morgan, studying the fly Drosophila melanomas, detected a mutant fly, a male fly that differed strikingly from normal flies of the same species. In this fly, the eyes were white instead of the normal red. Morgan immediately set out to determine if this new trait would be inherited in a Madeline fashion.
He first crossed the mutant male to a normal female to see if either red or white eyes were dominant. All Fl progeny had red eyes and Morgan therefore concluded that De eye color was dominant over white. Following the experimental procedure that Mendel had established long ago, Then he crossed flies from the Fl generation with each other. Eye color did indeed segregate among the IF progeny as predicted by Mender’s theory with an imperfect 3:1 ratio. Something was strange about Mooring’s result, that was totally unpredicted by Mender’s experiments is all the white-eyed IF flies were males.
Perhaps it was not possible to be a white-eyed female fly; to test this idea, Morgan destroyed one of the red-eyed Fl female progeny back to the original white-eyed male, he obtained white-eyed and red eyed males and females. So a female could have white eyes. Why then were there no white- eyed females among the progeny of the original cross? To solution to this puzzle proved to involve sex. In Drosophila the sex of an individual is influenced by the number of copies of a particular chromosome, the X chromosome that an individual possesses.
An individual with two X chromosomes is a female. An individual with only one X chromosomes which pairs with a large, dissimilar partner called Y chromosome is a male. Thus female thus produces only X gametes, whereas he male produces both X and Y gametes. When fertilization involves an X sperm the result is an XX zygote, which develops into a female. When fertilization involves a Y sperm, the result XX zygote, which develops into a male. The solution to Mooring’s puzzle lies in the fact that in Drosophila white eye trait resides on the X chromosome and it is absent from the Y chromosome.
Now we know that the Y chromosome carries almost no functional genes. The trait that is determined by a factor on the X chromosome is said to be sex linked or X-Inked. Knowing that white-eye trait is recessive to the red-eye raid, we can now see that Mooring’s result was a natural consequence of the Madeline assortment of chromosomes. When Biologists studying pea plants and Drosophila established that patterns of heredity reflect the segregation of chromosomes in meiosis, their discovery opened the door to the study of human heredity.
X- Linked inheritance consists of two similar members (XX). Mooring’s discovery of a white eyed trait that correlated with the sex of flies was a key episode in the development of the chromosome theory of inheritance. Because, two members of the pair of sex chromosomes could be relate with the behavior of the two alleles of the gene. The gene located on either sex chromosome is called a sex linked gene those located on Hysterectomies are called Y-linked gene, there are very few Y linked genes. Whereas X chromosome contain approximately >OHIO genes, which are called X-Inked genes.
Mooring’s experiment is one of the most important in the history of genetics, because it presented the first clear evidence that Sutton was right and that the factors (gene) determining Madeline traits do indeed reside on the chromosomes. The segregation of the white-eye trait, evident in he eye color of the flies, has a one-to-one correspondence with the segregation of the X chromosome, evident from the sexes of the flies. The white-eye trait behaves exactly as if it were located on an X-chromosomes.
The gene that specifies eye color in Drosophila is carried through meiosis as part of an X chromosome. In other works, Madeline traits such as eye color in Drosophila assort independently because chromosomes do. Thus Mooring’s results led to the general acceptance of Cotton’s chromosomal theory of inheritance. Thus, a typically Madeline trait, white-eye, is associated with an unambiguously horsewoman trait, -?sex. Al This result provided the first firm experimental confirmation of the chromosomal theory of inheritance.
This association of a visible trait that exhibited Madeline segregation with the sex chromosome (sex linkage) was the first case in which a specific Madeline gene could be said to reside on a specific chromosome. It firmly established the fusion of the Madeline and chromosomal theories, marking the beginning of modern genetics. X – linked genes in humans follow the same pattern of inheritance that Morgan observed for the eye-color locus he studied in Drosophila. Fathers pass X-Inked alleles to all of their daughters but to none of their sons.