Free Biology NEET Video Lectures for Principles Of Inheritance And Variation

00:00:51 Today I am here to present the topic principles of inheritance and variation the fifth chapter in 12th biology. Before going into the details of this chapter, we have to clear the points. Why to study genetics? What is genetics? And why the two children of the same family differ each other and why the identical twins are resembling each other. You might have seen in your family also the children are differing from their parents in some of the fundamental characters and similarly children are resembling with

00:02:01 their parents also in most of their characters. Why this happens? You may be amazing. You might have think about it many times. So here in this chapter we will learn why it happens. So heredity you might have heard this term resemblance of progenies with their parents in most of the characters. For example, if the mother is having curly hair, the daughter is also having curly hair in some cases. Father is having white complexion and the son is also having the same white complexion. So like this in most of the

00:03:07 characters the progenies are resembling with their parents. So resemblance of a parents resemblance of a progenies with the parents in most of the characters that we will call it as heredity and similarly some of the progenies differ from their parents and that phenomenon we will call it as variation. Now when we study about these two aspects heredity and variation then it forms the branch genetics. So genetics is a branch of biology that deals with heredity and variation. The term genetics that was coined by

00:04:09 William Badson in 1906 and the father of genetics Gregor Johan Mendel. As I told you in the introduction, what is a heredity? The tendency of the progenies to resemble with their parents in most of the characters. And if the progenies differ from their parents then that phenomenon that is known as variation. Now before going to the details I would like to present a life sketch of Mendel. He was born in 1822 in a present family in Moravia in Austria. He became a monk in the Augustinian monastery at Brun in Austria

00:05:25 in 1843. Later he was ordained as a priest in 1847. And he became a teacher also. He conducted hybridization experiments on pea plants at his monastery garden from 1856 to 1865. He published his findings in the year 1866 in the annual proceeding of natural history society of Brun. His laws from the form the basis of science for genetics. So he is known as the father of genetics. He attended courses in physics, maths and science in Vienna University. He conducted hybridization experiments or breeding experiments in

00:06:36 garden P at his monastery garden from 1856 to 1865. But his work remain hidden for a long period of time. Why it happens? Why his work remain unnoticed for a longer period of time? His work was ahead of his time. His work was published in a journal that has a limited circulation at that time. He himself was not sure about his findings. He followed mathematical approach in working out the biological problems. But it was very strange at that time. All the biologists were busy with the Darwin's theory of evolution.

00:07:43 So his work remained hidden for a long period of time. But later in 1900 his work was rediscovered by a group of three scientists. Hugo Dies of Netherland, Carl Corins of Germany, Eric Von Shermark of Austria rediscovered the valuable Mendel's work in 1900. You can see here the pictures called Corin, Hugo Dies, Eric Von Shermark, the three scientists who rediscovered Mendel's work. Mendel selected the experimental material that is garden P. Its scientific name is pyome sativ. Why he selected pea plant as his experimental

00:09:05 material even though there are so many flowering plants with fragrance beautiful colors huge sized flowers. But why he selected this particular plant garden P for his hybridization experiment? You all know it is a herbaceious plant, very small plant with a very short life cycle. Within a one year it will produce its flowers and it will perishes. So it is easy for us to conduct hybridization experiments and we will get the results very quickly. The second reason is availability of a large number of

00:09:57 varieties. Innumerable number of varieties of pea plants are available. So any scientist can use any of these varieties for his experiment. then this plant will produce a large number of seeds. The availability of a large number of seeds is at another reason for selecting PL plant as experimental material. So if a plant is having only one seed sometimes it will not germinate. So in that particular case the result of the hybridization experiment was not obtained. So here there is no chance for this flop of the hybridization program

00:10:49 because large number of seeds and thereby larger number of progenies will be produced. Presence of a large number of contrasting characters. Now here I would like to mention what is a contrasting character. Different expressions of the same character that is called as contrasting character. For example, if we are considering the character flower color, then purple as well as white the two extremes they are the contrasting characters. Then the this particular uh flower that possess it is a bisexual

00:11:40 flower which have self-pollination. Pollen grains of the same flower will fall in the stigma of the same flower. Self-pollination. It is bisexual in the sense that it has both male as well as female sex organ in the same flower. Now when you see this flower it's corola is a pegium one that is papillionous corola. Now I'll show you the diagram of a papillion corola. It is simply known as butterfly like corola. There is one standard petal of large size. Then there are two wing petals and there are two

00:12:49 keals. So this particular type of corona that is easy for doing the hybridization experiments. So here you can see the standard petal large one and outer petal and on either side there are two wing petals which are kept inside to this standard petal and there are two uh ke petals and inside this ke petal they present the sex organs that is and as well as gynium. So it is easy for the scientist to do hybridization experiments here. It is easy to open the petals and do the cross-pollination then we can close it also. So that is

00:13:36 advantage of having this particular papillonious type of corola here. Here you can see the pea flower garden pea flower purple as well as white. As I mentioned earlier these two are the contrasting character for the color of the flower. The single trait color of the flower with the two different extreme expressions that is one purple and the other is white. And here you have you can see the round shaped seeds. Now we can familiarize some of the important terms in this one. First it is very important about to

00:14:32 know what is a gene. As we all know that gene is the unit of heredity. It is the unit of inheritance of characters from parents to offspring. It is the unit of transmission of a character from parents to offspring which is a part of the DNA that is present in the chromosomes seen in the nucleus of a cell and each and every character of an organism is controlled by a pair of genes. Now the next important thing is alals or at another name is alilomorphs. The alternative forms of the same gene controlling the same trait or the

00:15:28 same character which is seen in the same locus of a homologous chromosome that is known as alals or alilomorphs. For example, when we consider the character tall, when we consider the character height of the stem, there also dwarfness. So capital T and small T are the two alles controlling the same character length of the stem or even height of the plant which are seen in the same locus of the homologous chromosome. Now coming to the phenotype. Phenotype refers to the external character of an organism for a particular trait or it is

00:16:37 the external appearance or it is the expression of a gene gene product. It is controlled by the genes as well as the external environment. Now coming to the genotype, it refers to the genetic makeup or even the genetic constitution of an individual for a particular trait. By seeing a particular individual, we can say only the phenotype, not the genotype. We can never say that if a tall man is walking through the road. We can't say that capital T capital T is working or we can't say that capital T small T is

00:17:27 working. We can say only tall man is working. So we can say only the phenotype not the genotype. Now coming to homozygous. An individual that bears two similar alles at a given locus for a particular character. For example, capital R capital R gene that controls the phenotype red color of the flower. Now regarding heterosygus an individual bios two different alles for a particular character and seen at the given locus. For example, if an individual is hetereroygous tall then it will be represented as capital T

00:18:22 small T. And for red flower color if the plant is hetererozygous then we will write it as capital R small R. Now regarding pure line or pure breeding or true breeding an individual that produces same type of phenotype same type of characters in all the progenies in all the generations. then it is pure breeding or true breeding or pure line and such individuals will be always homozygous. So later in this chapter there will come so many problems genetics problems there it will be given only as pure line or pure breeding. So

00:19:23 here the concept must be clear a pure line plant or an individual that will be always homozygous and it will breeds the true it will produce the same phenotype for all the generations in all the progenies. Now how can we convert a plant or an individual into a pure breeding one? We can do continuous inbreeding in the case of animals and in plants we can do continuous self-pollination. So by continuous self-pollination or by continuous inbreeding we can convert an individual into a pure breeding one or a pure line

00:20:13 or a true breeding one or into a homozygous one. Now how a character can be symbolized? Symbolization of characters. The first letter of the character dominant character that is taken. We will consider the do the first letter of the dominant character. For example, the character is tall. Tall begins with the T. So we will be uh take the first letter T and it is written as capital letter for dominant character and the same letter T if we are writing in small letters it will form the recessive character.

00:21:09 So this is one system of symbolization where we are using the first letter of the dominant character and it is written in capital then it will form dominant character and if it is written in small letter then it will form the recessive character. There is yet another method of representation also where we can select the recessive character. Then the first letter of that recessive character is selected. It can be written as capital for dominant character and if it is written as small letter then it will form the recessive

00:21:58 character. Here you can see the condition. We will take the character contrasting character dwarf. This is the recessive character. It begins with the letter D. That first letter we are considering and we are using capital D for representing the dominant character tall. And we are using small letter D for representing the dwarf that is the recessive character. So there are two system of symbolization of a particular character. Now before going to this monohybrid across what are the characters studied

00:22:52 by Mendle that we have to learn. Mendle studied a seven pairs of contrasting characters. First one length of the stem or even height of the stem. Here the contrasting characters are tall and dwarf. Second character is color of the flower. Here are the contrasting character is purple and white. Now coming to the third one position of the flower. It is axial and terminal color of the board. There comes green. and yellow. Then shape of the pod. There comes inflated and constricted. Color of the seed,

00:25:28 yellow and green shape of the seat. Here comes round and ringled. So here you can see the seven pairs of contrasting characters studied by Mendel. Mendel considered only one character at a time and studied the inheritance of a particular character fully at a time. So the different seven pairs of contrasting characters that each and every child should learn and try to identify which one is dominant and which one is recessive. It is very very important in this context for doing the genetics problems. So the first

00:26:43 character here is length of this term. The different expressions you can see here one is tall and the other is dwarf. That means same character or the trait is expressed in two different alternative forms. There is one tall and the other is dwarf. Contrasting characters. Here the first one tall is dominant and dwarf is recessive. Second character study by Mendel is color of the flower. The different expressions are purple and white. The two extreme contrasting characters expressions phenotype. Here purple is dominant over

00:27:46 white. In some context it in some of the genetics problems you can see red versus white. Then red is dominant over white. Now coming to the position of the flower axial and terminal. Now what is axial? You know the angle between leaf and stem that is called axle. And if the flower is seen in the axle then that flower is known as axial flower. And if it is seen at the tip of this term then it is terminal flower. Correlate this one as or memorize this one. Which one is dominant and which one is recessive? You can use

00:28:40 the correlation in your alphabet. A comes first. So A is dominant. That means axial is dominant here. And the other character you know that is terminal. Now after the flower there comes the fruits that means sp here we will say a spot color of the pot you know the prominent color in plants that is green and here also the thing is again you can apply G comes first then why so G is dominant that means green is dominant and LO is recessive. Now in the port the next character is its form or shape shape of

00:29:33 the port. Inflated and constricted. Inflated means external appearance. You can't see any position of the seed. But you will be have you will have the doubt whether it has seed or not. It will be just like thin and flat. And in constricted port you can see it clearly an external appearance of the seed can be felt outside itself. Constrictions are there. And when we consider this one capital I as well as C I is longer one. So you can again correlate it as the dominant character. inflated one is

00:30:22 dominant. Now coming to seed. Seeds are seen inside the pond. So next character we will say the seed that means color color of the seed just a reverse of the color of the pod. You can see here. So first you memorize color of the pod then only comes the seed. So just reverse of this case you can apply here that is the memorization in this aspect. So color of the seed the dominant character will be yellow and recessive character will be green. Now coming to the shape of the seed or form of the seed. Form of the

00:31:08 seed is round and the other one is wringled with the wringles. Here there is no wrinkle at all. It is smooth surface round and prominent one. The round and wringled. Here also you can see which letter comes first. R will come first in your alpha in your uh alphabets. So here round is dominant over wringled. So in this way you have it to memorize all these seven pairs of contrasting characters. It is highly essential to learn the genetics and its problems properly. So no need to bart it by correlated study. You can memorize all

00:31:54 these things. Just step by step you have it to move analyze a plant. First you can see the height of the stem, length of the stem with the tall and dwarf, color of the flower, purple and white. Then coming to the second character of the flower that is position axial terminal. Then color of the pod green and yellow. Shape of the pod or form of the pod inflated constricted. Color of the seed just the reverse of color of the pod that is yellow and green. Then form of the seed or even shape of the seed round and

00:32:48 wringled. Now we will move to the next aspect. The basic of this one genetics monohybrid cross mono means single a cross involving two parents and these two parents are differing in one pair of contrasting characters. So a cross involving two parents differing in one pair of contrasting characters that is called as monohybrid cru. For example, we are using the character here length of the stem or height of the plant where the contrasting characters are tall and dwarf. If we are using the character

00:33:48 color of the flower then the contrasting characters are purple and white. So these two examples we can make so many examples out of these seven pairs of contrasting characters. So this example where we are using only one pair of contrasting character. Two parents are involved and they are differing in only one pair of contrasting character. So it is an example of monohybrid cruise. No mental detailed hybridization experiment. First selection of pure breeding parents. As I have already told you pure

00:34:38 breeding means true breeding or pure line. That plant is homozygous in genotype and it will produce only the same phenotype for all the generations. It breeds true in its phenotype. So we can consider a true breeding plant or a pure line plant for the hybridization program. Suppose it is not available we can convert it into a pure breeding plant by continuous self-pollination and pure breeding plants will be always homozygous that is yet another concept that we have to memorize and they will pass the

00:35:28 character as such to the progenies to the offsprings. Second step hybridization of the selected parents. Mendel selected in the original cross the tall plant is taken as male parent and dwarf plant is taken as female parent. Before doing the hybridization experiment, we have to cover the flowers in order to avoid contamination with foreign pollen grains. Then collect the pollen grains from the tall male plant and dusted on the stigma of the dwarf female plant. That means we are doing hybridization or even cross

00:36:33 pollination. After doing the crosspollination also we have to bag the flower the crosspollinated flour in order to avoid contamination with foreign pollen grains. Now after maturity collect the seeds and sewn sewing the seeds. After that the hybrid plants are obtained. Menel analyzed the plant in the first generation and it was found that all the plants all the plants of the first generation were tall in phenotype. Now here it is written as F1 generation. One means first and F stands for filial. The first filial

00:37:31 generation. Now what is the meaning of the word filial? Fil refers to offsprings progenies. So the first hybrid progenies are produced by the crossing of P generation. P generation means parental generation. The symbol F1 that is the first filial generation F1 the term was coined by Badson and Santos in the year 1902. In the third step, Mendel conducted self-pollination in the F1 hybrid plants and in order to produce the F_sub_2 generation. F_sub_2 here means second filial generation. That means the

00:38:31 generation in which the second hybrid progenies are produced by the selfing of F1 progenies. Mendel observed in the F2 generation three tall that means 75%age of the F2 progenies were tall in phenotype and 25%age of the F2 progenies are dwarf in phenotype again he conducted self-pollination among the F2 progenies and produced the F3 generation. The third generation, third filial generation. In the F3 generation, the result obtained was amazing. One third of the tall progenies produced only tall

00:39:46 progenies and 2x3 tall progenies of the F2 generation produced both the tall and dwarf progenies in the ratio 3 is to 1 again 1 by4 that means out of the whole progenies of the F2 generation 25%age they are dwarf and they produced only dwarf progenies in the F3 generation. So listen once again I am repeating the observation of F2 monohybrid. See the results of the F2 generation. You can see here three tall and one dwarf progeny selfing of the F2 progenies to produce the F3 generation. And here in the F3

00:40:58 generation 1x3 tall plants produced the tall plants only and the 2x3 tall plants produced both the tall and dwarf in the ratio 3 is to1. 1x4 of the F2 progenies that is the dwarf progeny produced only dwarf as I have shown to you in this punet square and after that we are coming to the conclusion the phenotypic ratio is 3 is to 1 as we got three tall and one dwarf in F2 generation. Genotypic ratio is 1 is to2 is to1 that is one homozygous 2 hetererozygous and one homozygous and recessive. Again one capital T, capital

00:42:13 T individual. Two individuals are having capital T and small T. One individual is having small T small T. So the genotypic ratio is 1 is to 2 is to 1. Now it is the time for you to answer the questions, the review questions. First question for you, how can we convert a bisexual flower into a female flower? Yes, your answer is here. We can convert a bisexual flower into a female flower by removing the anthers before dehyence. You know dehyence that is splitting up of the anther at the time of maturity to

00:43:15 release the pollen grains. So removal of hers before dehyence from a bisexual flower that is called as emasculation and it is done to convert a bisexual flower into a female flower and its role is to prevent selfpollination. Now here is your second question. We have given different set of characters. Here you have to identify which among the following is dominant and recessive. Here the characters are excel flour, wringled seeds, red flower, constricted part, yellow seed and green part. You have to

00:44:15 identify which among these is dominant character and which are the recessive characters. Yes, your answer. Axial flower, red flower, yellow seed, green pod are dominant. Wringled seed, constricted pod are recessive. Now it is the time for you to ponder about it or think it over. Is there any need for emasculation in a pea plant that is considered as male parent? If not, why it is so? Thank you. [Music]