hello guys welcome to my lecture in this lecture today i'm going to talk to you about basics of genetics for beginners let me first begin by the definition of genetics genetics is a branch of biology that is concerned with the study of genes genetic variation and heredity in organisms so what is genetics basically as the name suggests it is the study of the genes and the genetic variation and heredity in organisms or individual. Okay, so this is the definition of genetics. Now let me introduce you to another term which is called trait.
So what is a trait? A trait is a physical characteristics or attributes. So this trait can be the height of the person, color of the eye, color of the skin or color of the hair etc.
If you have a look at this picture here, the picture of a beautiful girl. she has a black hair and brown skin. these are her traits and she is short. this is also her trait. so what is a trait?
a trait is nothing but simple physical characteristics or attributes of an organism or an individual. that is a trait. so for this girl here, her black hair, brown skin and short height. these are some of the examples of her traits. head injury or genetic information is found in the DNA.
The definition of the DNA I'll discuss later. I want you to have a look at this picture here. This picture here shows the schematic representation of the cell.
What is a cell? A cell is the smallest structural and functional unit of the organism. In the center of the cell we have something called the nucleus and in the nucleus chromosome is present okay so chromosome is present in the nucleus of the cell so i'm now i'm gonna talk to you about what is chromosome and what is dna so the dna is the double helical structure like shown here in the picture which is very very long so this dna is quite super quiet around some proteins and it's it's and it's very very very condensed and when it's a quile and superquile around some proteins and condensed it comes in the form of chromosome okay so what is a chromosome chromosome is a dna which has wrapped around some specific proteins quile and superquile and condensed to become the chromosome okay so why why there is a need for the dna to to become condensed because dna is long and double helicon long structure like this and it cannot fit in this small nucleus.
Nucleus is very very small. When the DNA is long like this, it cannot fit in this nucleus. Therefore, it has to wrap around some specific proteins and become super quality structure and condensed.
Only in the form of chromosome, then only it can fit in the nucleus. The purpose of the chromosome is because the DNA cannot fit as such therefore it has to Quile and superquile around some specific proteins to to form a condensed structure the chromosome like here So that it can fit in the nucleus. So this is the definition of chromosome and the DNA Okay, so now now you know about the DNA and chromosome So what is a gene so is shown by the box here a gene is a segment a segment of the DNA which code for specific proteins which in turn express some specific traits. That is called a gene.
Not all parts of the DNA is coding. Some parts of the DNA is coding and making proteins and expressing some specific traits while the remaining part of the DNA is non-coding. So like I said the box on the DNA strand above is a special section. why it's a special section because it codes for some protein which in turn express specific trait okay that is a dn that is a gene so genes code for a specific protein that code for specific traits we human beings have two genes for every traits two genes for every trip or all genes comes in pair why it is so because we human beings have 23 pairs of chromosome so one from father one from the male gamete and the other from mother or the female gamete so So basically we have in each pair we have homologous chromosome.
So what are these homologous chromosomes? Homologous chromosomes are the chromosomes which are similar in size and the structure and they they carry Similar genes which code for similar proteins which in turn express Similar traits. Okay, so these are homologous genes. So for example in this chromosome here Let's say that this is the gene that codes for the protein which express height and this also is the gene that codes for the protein which express height in this chromosome, this gene of this chromosome and this gene of this chromosome both of these, they actually code for the specific trait height ok, so therefore this gene is called an allele and this one is also called an allele in a pair Okay, so basically what is an allele? An allele is one gene in a pair in a homologous chromosome So one gene in a pair that is called allele which code for the specific trait For example here I have said that this one and this one both of these they code for the protein which in turn expresses specific trait Let's say that is height.
So therefore this is called an allele So what is an allele? An allele is one gene in a pair So that is called an allele. Okay, so I repeat this is a very very important concept So what is an allele? We have a homologous chromosome like I have shown here and this This gene and this gene both of these they code for the proteins which in turn express similar traits Let's say that they are responsible for the height So therefore this one is called an allele or and also this one is called allele So one gene in a pair that is called allele.
So these two chromosomes are homologous chromosomes. Okay, so what is an allele? An allele is one gene in a pair.
One gene in a pair. So good. So now I want you to think like this.
Okay, in the nucleus we have the chromosomes. What is chromosome? Chromosome is DNA plus some specific proteins supercondensate, right?
So and then comes the DNA. Okay, because DNA and in the DNA there's some segment of the DNA or some specific segment or the part or the section of the DNA is the gene. And the gene actually, one gene in a pair that is called an allele.
So I want you to think like the concept of chromosome DNA, gene and allele in the boxes shown here like this. Just think like that. The big box is chromosome and smaller than that one is DNA, smaller than that one is gene and the smallest one is an allele.
Okay, just think like this. So more definition. What is a locus?
I explained I already explained what is a gene. A gene is a specific segment of a DNA So now I will explain what is a locus. A locus is a location of a gene on a chromosome Let's say that this is a chromosome.
Okay, this is a chromosome. These two represents homologous chromosomes So the location of this gene for height This is called locus. Okay, so what is the locus for this red gene? This location here on this chromosome, that is the locus and the location for this green gene Which is the gene for seed shape.
So what is the locus? The locus is the location Location here on this chromosome. That is the locus.
So the locus is a specific location on a chromosome for a gene that Expresses of course some proteins which in turn express some traits. Okay, so that is the locus Locus is the name suggests a location of the gene on a chromosome. So I will now discuss some more terminologies here. Let's say that capital T represents dominant gene for the trait top and small t represents recessive gene for the trait short. Okay, so what is a heterozygous organism?
An individual or organism is said to be heterozygous for a given trait if one of the alleles is dominant while the other is recessive. For example capital T represents dominant allele and small t represents recessive allele. If an organism has capital T and small t together, that kind of organism is called heterozygous organism. Look at this picture here. This is a homologous chromosome pair.
If this is the capital T, this is an allele, this one is also an allele, but if this one is capital T representing for the tall and if this one is small, for the shot and this and if the organism has this this this this this one capital T and small t so this actually is called heterozygous organism or individual it's an it's for a given trait for the height they have tall and the shot mixed together okay so because capital T is the dominant allele so because the capital T is the dominant allele it will mask the expression of the protein coded by this allele. Okay, so if this one is the capital T, if this one is the small t, so this capital T will marks the expression of the protein by small t, hence the organism will be tall. So the result of this, the phenotype of this heterozygous organism will be tall because, why it will be tall is because we have here one allele as the dominant capital T. This capital T this dominant allele will mask the expression of the recessive allele Okay, the protein coded by the recessive allele which in turn actually expressed the height. Okay tall So we will get the tall organism here.
Why tall organism? Capital T will mask the expression of the small t Okay. So now another important concept is homozygous. So what is homozygous organism?
If an individual or organisms if in an individual or organisms for the given trace if both alleles are dominant that is called homozygous dominant for example if in this if in this case in this example if this one is also this one is capital t if this alleles is capital t dominant gene for the tallness and this one is also capital t this is this this capital t and this one is also capital t then we will have the organism that will have both capital t okay in its genetic makeup so then This kind of organism is called homozygous dominant because capital T represents dominant trait which is tall. So we will have the tall organism as the phenotype. Okay, so is a tall organism is the phenotype. Phenotype is the physical appearance.
Okay, physical appearance. So we'll have the tall organisms. So another homozygous, another type of homozygous organism is called homozygous recessive. So that is if an organism or individual for the given trace if both the alleles are recessive. That is called homozygous recessive For example if this is a small T and this one is a small T Now in this case this allele will express the trait the short because small T is The recessive gene and that course for this for the protein which will code for the short plant Okay, which will result in short plant.
So then we will have the short plant So if both the alleles are also recessive then like here small T and small T We will get the short plant that The results of this will be that the phenotype of the plant will be the short in homozygous Recessive the phenotype of the plant will be short why because both of the alleles are recessive and these recessive alleles are Expressing for the trait shortness. Okay, so we'll have the short plant here in heterozygous Heterozygous organism we got the tall plant because we had one Dominant allele and one dominant allele is enough to express the trait It's straight so we will get the tall plant because it will mask the expression of the recessive allele here in both the cases We have both dominant tall tall dominant allele So we will get the tall plant and here in this case or homozygous recessive case we have both recessive allele so the the end result will be we will get the Short plant in the phenotype of the plant will be short because both of these are recessive genes Expressing for the short trait. Okay So these are some definitions and now some more definitions. Genotype like I said earlier genetic makeup of an organism is called genotype. It actually tells what types of genes are found in the organism.
For example in heterozygous organism we have one dominant allele and one recessive allele. Okay so that is the genetic makeup of heterozygous organism. In homozygous organism there can be two types of homozygous organism. There will be two types.
One is homozygous dominant in homozygous dominant organism. We have we will have one dominant both the dominant alleles Okay, so we'll have both dominant alleles genetically and in homozygous recessive organisms. We will have both recessive alleles Genetically, okay So basically these different types of organisms the genotype is telling us what are the different types of gene genes found in the organisms the genetic makeup of the organism, so What is a phenotype? Like I said earlier, phenotype is the physical appearance of an organism or an individual in heterozygous organism capital T and a small t because here we have the dominant allele so it will mask the expression of recessive allele so we will have the tall plant okay it will have the tall plant so this is the phenotype tall plant in case of homozygous dominant where both alleles are dominant capital T and small t here also we will get the tall plant and this tall plant is the phenotype this homozygous dominant organism or dominant plant we can say plant because I'm giving here the example of plant in case of homozygous recessive in case of homozygous recessive plant we have both the recessive alleles small t small t representing for short so the phenotype of the plant will be the short will be short so phenotype is a physical appearance of an organism or an individual I hope this video was helpful I will come up with more videos on genetics thank you very much