In the past lessons we started talking about human genetics we analyzed its limitations and we said that it must be studied in specific ways such as with the analysis of family trees well another typical study method of human genetics consists in the identification of chromosomes through the karyotype And this is exactly what we will talk about now [Music] the karyotype is the complete chromosomal set of an individual the term derives from the Greek cariuan which means nucleus and cupos which means model figure and we can then roughly translate the term as image of the nucleus image of the chromosomes present inside the nucleus The karyotype shows the number, shape and size of the individual 's chromosomes and the analysis of this image is used to verify the presence of supernumerary or missing chromosomes but also the presence of any large structural defects supernumerary or missing chromosomes that is anomalies in the number of chromosomes we had already mentioned it in lesson 44 talking about the main anomalies affecting the sex chromosomes but let's try to understand each other better and go a little deeper into human chromosomes are visible only in dividing cells And then to obtain a karyotype an image of the chromosomes present in the nucleus these are blocked during mitotic division Let's say they are frozen in metaphase or in late mitotic prophase once the image is obtained the chromosomes can be identified based on their length the position of the centromere and the damage that is obtained by coloring them with specific dyes now the chromosomes of the human being are numbered from the pair of homologous chromosomes number 1 to the pair of homologous chromosomes number 22 however we know that the human being has 23 pairs of chromosomes the 23rd pair of chromosomes is given by the sex chromosomes a normal male with 22 pairs of non-sex chromosomes or autosomes an X chromosome and a Y chromosome sex chromosomes only partially homologous a normal female with 22 pairs of non-sex chromosomes or autosomes and two chromosomes mix the sex chromosomes in the image you see that for each pair of homologous chromosomes I have colored a chromosome Of Pink and a chromosome Of blue this is because each of us for each pair of chromosomes inherits one of the two homologous chromosomes from the father and one of the two homologous chromosomes from the mother But let's get to the alterations in the number of chromosomes we distinguish two categories Polyploidy and neoplasia to understand polyploidy common condition in plants marara in animals we must first take a step back the somatic cells of human beings have a diploid chromosome set that is two N means as just outlined that each chromosome is present in two copies of homologues polyploidy is the condition in which each chromosome is present in more than two copies of homologues bananas for example are triploid that is each chromosome is present in three copies rare in animals in humans polyploidy affecting all somatic cells is lethal and is sometimes found in aborted embryos and spontaneously and prematurely the concept of aneuploidy instead is simpler it is still an anomaly in number of chromosomes but this time due to the additional presence or absence of a single chromosome trisomic karyotypes indicated as two n+1 present only one extra chromosome monosomic karyotypes indicated as two n-1 lack one member of a pair of homologous chromosomes lack only one chromosome the most known example of Trisomy in humans is of the autosomal type we are talking about Trisomy of chromosome 21 or Trisomy 21 this aneuploidy present in the majority of individuals with Down Syndrome is one of the most common chromosomal anomalies in humans individuals with Trisomy 21 have 47 chromosomes instead of 46 because they have an extra chromosome 21 in excess that is they have three copies instead of two of chromosome 21 the most known example of monosomy in humans is of the sexual type autosomal monosomies are extremely rare Turner Syndrome individuals with this syndrome not having the y chromosome develop as women but have a y chromosome X minus this condition is indicated as x0 where zero refers to the absence of the second sex chromosome aneuploidies are generally due to mediotic divisions or more rarely abnormal mitotic divisions divisions in which the chromosomes do not separate this phenomenon of abnormal division is called non-disjunction it can affect both autosomes and sex chromosomes and can occur with different effects in meiosis 1 or 2 or in mitosis the meiotic non-disjunction that occurred in the father in the mother of a future individual means that an abnormal gamete resulting from a meiotic non-disjunction unites with a normal gamete produced by the other parent in which the non-disjunction did not occur thus forming a zygote in possession of an abnormal number of chromosomes normal number of chromosomes that will then be present in all the cells of the future individual that will develop from this abnormal zygote mitotic non-disjunction instead occurs in successive development phases it follows that not all cells of the individual but only a part of them present anomalies in the number of chromosomes given this first difference let's now focus on periodic non-disjunction What happens if for example this phenomenon occurs in the pair of sex chromosomes of a man there are two cases non-disjunction in the first meiotic division and non- disjunction in the second meiotic division case 1 normally in the anaphase of the first meiotic division the two homologous chromosomes separate and in the case of the pair of sex chromosomes present in a man the X chromosome separates from the Y chromosome if the non-disjunction occurs in the first meiotic division Then the man in whom this phenomenon occurs produces two spermatozoa containing both an X chromosome and a Y chromosome each and two spermatozoa lacking both sex chromosomes the spermatozoa containing both the X chromosome and the Y chromosome fertilizing normal human cells that contain only one X chromosome produce xxxy zygotes these zygotes develop into male individuals because is the Y chromosome present with Kleinfelter's syndrome individuals with this syndrome finally have a male appearance but have poorly developed testicles sperm cells that lack sex chromosomes fertilizing normal egg cells produce x0 zygotes these zygotes develop into female individuals Why does the Y chromosome feel with Turner's syndrome individuals with this syndrome have a female appearance but have various and poorly developed testicles case 2 normally in the phase of the second meiotic division the two sister chromatids of each chromosome separate the pair of sex chromosomes of a male is XY therefore if the non- disjunction occurs in the second meiotic division it may happen that the two sister chromatids of the X chromosome do not separate case 2A or the two sister chromatids of the Y chromosome case 2B the non- disjunction in the second meiotic division in a male may be due to the chromosome meaning of the Y chromosome in the case of non- disjunction in the second meiotic division of the X chromosome case 2A the male in whom this phenomenon occurs produces A sperm containing two chromosomes A sperm devoid of sex chromosomes and two sperm containing one Y chromosome each The latter two sperm containing only one Y chromosome each are normal and by fertilizing normal egg cells produce normal male children The sperm devoid of sex chromosomes again fertilizes a normal egg cell and produces a female with Turner Syndrome x0 The sperm with two chromosomes Finally fertilizing a normal egg cell produces a female called triple X xxx Females who despite the three chromosomes are generally normal and fertile In the case of non-disjunction in the second meiotic division of the Y chromosome Case 2B the male in whom this phenomenon occurs produces A sperm containing two Y chromosomes A sperm devoid of sex chromosomes and two sperm containing one X chromosome each In parallel with what was said for Case 2A The latter two sperm containing only one X chromosome each are normal and fertilizing normal egg cells produce normal female children the sperm without sex chromosomes fertilizing a normal male cell produces a female with Turner Syndrome x0 the sperm with two Y chromosomes fertilizing a normal egg cell produces a male called XY karyotype we are talking about karyotype and not XY disidromy because the individuals are fertile males and many of them do not show any noteworthy symptoms All clear you see how everything is connected about connections and it has been connected with me with biology for all new and future content like the video if I have been helpful and if you have not done so yet subscribe to the channel to support my educational project with this simple click Hello and good wishes to all