in this video i will teach you how to read a karyotype so what are we looking at when we see this image this is a person's entire genome a full set of their dna which contains all of their genes that influence their traits as you can see the genome is split into 46 individual molecules of dna called chromosomes these chromosomes come in pairs so we can see that there are 23 pairs of chromosomes and all together 46 total chromosomes a karyotype which is what we are looking at here is a picture of all the chromosomes in a person's genome when a scientist analyzes a person's karyotype they are looking at the number and relative appearance of all the chromosomes in their cell's nucleus each person has two of each type of chromosome one donated in the egg from their mother and one donated in the sperm from their father so we can see we have two chromosome number ones and two chromosome number twos and so on and so forth while these two chromosomes came from different parents they contain the same kinds of genes in the same locations the chromosomes in a pair like this are said to be homologous chromosomes homo meaning same because they contain the same genes in the same locus in fact a specific gene will generally be located in the same locus on a specific type of chromosome across an entire species for example the call 11a1 gene which holds the code for the protein collagen is always going to be found in the same locus on chromosome 1 right around here in any human chromosome number 1. these homologous pairs could have different versions of a gene between them but they both have the gene in the same location now as you can see in this image there are chromosomes that are numbered 1 through 22. these are called autosomal chromosomes or autosomes these chromosomes contain genes that are not directly responsible for determining the sex of the organism these other two chromosomes are the sex chromosomes human males have an x and a y chromosome while human females have two x chromosomes so here you can see we have a female karyotype because we see two x chromosomes where the sex chromosomes are located and here we have a male karyotype because you see one x chromosome and one y chromosome you will notice that the y chromosome is significantly smaller than the x chromosome so when scientists look at a karyotype they are looking for specific things first they look to make sure there are 46 total chromosomes occasionally due to mistakes in the production of eggs and sperm a person will end up with too many or too few chromosomes causing diseases that lead to issues in development and potentially death for example monozomi is a condition in which you only have one chromosome where you should have a homologous pair in this karyotype a person is affected with turner syndrome which results from having only a single x chromosome instead of two chromosomes we can see the second sex chromosome is missing this person will suffer from a series of physical abnormalities as well as infertility and challenges with mental development trisomy is a condition in which you have three homologous chromosomes instead of two this is a karyotype of a person suffering from trisomy 21 which you may know as down's syndrome you can see this person has three copies of chromosome 21. this extra copy will cause delays in both mental and physical development and it will cause a shortened lifespan in addition to looking at the number of chromosomes on a karyotype doctors will look for the shape of these chromosomes this will tell them if there have been any pieces of dna lost or gained which could result in a disease chromosomes that are shorter than usual or longer than usual would tip the scientists off that something has gone awry in the gamete development so these are just a few conditions you can diagnose while karyotyping if you're interested in learning more about how monosomian trisomy occur you can see my video on non-disjunction