Do you know? There are 10000 genetic disorders caused by mutations in single genes. Individually, this disorders are rare. But, as a whole, they affect 1% of the total population. Dear students, assalamualaikum I'm doctor Md Imran Waheed Welcome to my channel 'Anatomy with Imran' Today we will talk about single gene disorders. By watching this video You will be able to understand different types of genetic disorders mechanism of inheritance of these disorders and at the end you will be able to i
dentify the type of disorder by looking at the pedigree. There are different types of genetic disorders For example disorders due to single gene inheritance Due to defects in the multiple genes enhanced by environmental factors Chromosomal abnormalities I mean structural and numerical abnormalities of chromosome and mutation and defect in the mitochondrial DNA. So, genetic disorders actually consist of all these things. But, today we will only discuss about single gene disorders. Let's first und
erstand what is single gene disorder You can see a chromosomal picture of a somatic cell. There are 22 pairs of autosome and 1 pair of sex chromosome. The sex chromosomes can either be XX or XY Now, lt's focus on a single chromosome for example, if we focus on chromosome 7 We can see that there 900-1000 genes in this particular chromosome. We know that some genes are dominant and some are recessive by character. The arrow indicates a gene known as CFTR. It is a recessive gene. Mutation in this g
ene is responsible for a clinical disorder known as cystic fibrosis. I think, now you can understand what is meant by single gene disorder. Again, single gene disorders comprise a spectrum of certain genetic disorders. We have autosomes and sex chromosomes. Again, we have genes of dominant and recessive characters. Considering these, single gene disorders can be classified into these four categories Autosomal dominant autosomal recessive X-linked dominant X-linked recessive We will discuss one b
y one. At first, we will understand the mechanism of inheritance then, we will see some examples. Please look at the picture. The arrow indicates mutation of a dominant gene. The sons and daughters who will inherit the single copy of that mutated gene will be affected. Since the copy is dominant it will express. In this pattern of inheritance both males and females are equally affected. Usually, 50% offsprings have the probability of being affected. Again, both parents nay be normal and the offs
pring can get a new mutation So, this is another way of having autosomal dominant disorder. Now we will see some examples. Huntington's disease is a neurodenerative disorder mostly affecting the basal ganglia Marfan syndrome is a connective tissue disorder Usually the patients have Tall stature, and long arms and fingers. Now, lets come to our next category. In this picture, you can see both parents have got the mutation The mutated gene is recessive by character. So, the parents themselves are
healthy Now, what is the probability of their offsprings of being affected? The offspring, who will receive both copy of the mutated gene will only have the disorder. Usually, 25% offspring are affected. Now, the offsprings who will inherit a single copy will be the carriers. The carriers will be healthy They will have no symptoms But, the they will pass the defected gene to the next generation. Cystic fibrosis is an good example of such autosomal recessive disorder. Here, the mucus becomes thic
k and sticky obstructing the airway. Another example is sickle cell anemia In this case, Sickle shaped RBC are produced They less capacity of carrying oxygen. Please note, cansanguinous marriage leads to such disorder in the next generation. Now, come to our next category X-linked dominant inheritance In this picture, you can see Father has got the mutation In dominant gene of X chromosome. Now, what is probability of being affected among his offsprings? Here, we need to consider 2 things Number
one Dominant gene will always express. Another is sons do not receive X chromosome from father Only daugther receives X chromosome from father. So, sons will not be affected and all the daughters will be affected. Let's consider another scenario. Here, mother has got the mutation. Now, what will happen? Sons and daughters both receive X chromosome from mother. Sons and daughters who will inherit the mutated gene will be affected. One example of this type of disorder is fragile X syndrome. The c
hild usually has developmental delay and learning disability. Let's discuss our last category X-linked recessive inheritance. It is very obvious that the mutation will be in the X- chromosome and the gene will be recessive. Isn't it? Now, what will happen to the offsprings? We already know thats ons do not receive any X chromosome from father. So, they will be healthy Again, daughters inherit two copies of X chromosome One from father and one from mother. So, the daughters inheriting the defect
ed gene from father will be the carriers. What if the mother carries the mutated gene Here, we need to consider two things. Son onle has one X chromosome which he only receives from mother. So, the son will be affected And the duaghter receives two copy of X chromosome If she receives one mutated copy from her mother she will be carrier. So, here son is the affected person. And duaghter is the carrier. Duchenne muscular dystrophy is an exampe of X-liked recessive disorder. The patient has progre
ssive muscular weakness. Another example is color blindness. Here, the patient usually cannot differentiate between red and green. Let's find out the disorder from the pedigree analysis Let's introduce ourselveswith some of the symbols that will be required to analyze the pedigree. Left one having the plus sign is the female and the right one is the male. Female is also indicated by circle and male by square. Now, central dot or central coloration indicates the unaffected carrier. And the total
change of color indicates that the person is affected. So, unaffected no color change and affected change of color. Please observe the pedigree first Then, you have to identify the type of disorder. At first, you have to consider is it dominant disorder? or recessive disorder? Dominant gene will always express. Here, we can see that There are some carrier state So, this not not dominant This is recessive disorder Again, is it autosomal or sex liked disorder? In autosomal disorder male and female
are equally affected Here, from the parents female is affected and from the grandchildren male is affected. Again, in X-linked recessive disorder, Females are the carrier, and males are not the carrier In this edigree, we can see males as carrier. So, this is definitely a pedigree of autosomal recessive disorder. Let's looks at our second pedigree. Let's first consider Is it a dominant disorder or recessive disorder? We can observe in all generations, there are affected individuals. So, it is i
ndicating a dominant disorder. Again, male and female both are affected in different generations. There is no such incidence only daughters are affected inheriting from father or only sons are affected inheriting from mother. Theerefore, we can say that it is a pedigree of autosomal dominant disorder. Now, look at our third pedigree. Is it dominant or recessive? You can see there are carrier state and in all generations individuals are not affected. Due to skip of generation we can say that this
is a recessive disorder. Please notice, females are the carrier and males are the affected. Let's consider from the first generation From father, by inheriting the defective gene the daughter has become carrier. And she has passed the defected gene to her sons and they have become affected in third generation. So, this is definitely X-linked recessive disorder. This one is for you. Please try to identify the type of disorder and let me know in the comment section. I think you have got a general
idea about the types of disorder and how to idenfy it from the pedigree analysis. You can also make punnete square and identify the percentage of the affected individuals. But, I have shown you the simpliest approach. If you like this video share it with your friends, and please subscribe the channel to stay in touch.
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