hey guys it's medicosis perfect status where medicine makes perfect sense let's continue our biology playlist in last videos we talked about the musculoskeletal system today we'll start a new sub Series in biology genetics let's go please watch these videos in order ever wonder why people are different it has to do with genes recall that the cell is the building unit of the living organism group of cells will make a tissue group of tissues will make organ a group of organs will make a system and a group of systems will perform your body functions who is the brain of the cell the nucleus because it contains your DNA deoxyribonucleic acid which is made of three things sugar backbone phosphate and nitrogenous bases what's the function of this lovely DNA it encodes for proteins such as your enzymes which carry lots of body functions basically open and you biochemistry textbook what do you see lots of enzymes all of them M are coded by DNA especially a piece of DNA known as the gene also recall that this DNA is arranged in 46 chromosomes inside your nucleus sugar backbone which is deoxyribose sugar nitrogenous bases could be any one of these and phosphate pause and review here's your DNA double helix inside your cell it will wrap around histones in order to get tight and packed into chromosomes you have 46 of these in each somatic cell if you want to make a copy of your own DNA this is called replication if you want to convert DNA to RNA this is transcription take that RNA to proteins this is translation and of course your enzymes are proteins please look at this picture one more time here is the big picture in genetics let's go your nucleus has DNA packed into 46 chromosomes like this this is one chromosome which is made of two chromatids a piece of the DNA I.E a piece of that chromosome contains what a gene like this and you got two copies two forms two alleles one from Mommy one from Daddy who's your daddy the location of that Gene on the chromosome is called Locus now suppose that we have a tall individual that tall individual could be uppercase t uppercase t or uppercase t lowercase T what is that medicosis because the capital T dominates over the small T put differently the Big T is dominant but the small T is recessive that's why Big T Big T this is tall Big T's multi also tall how about small teeth multi that will be a short individual let's look at this person capital T capital T exactly the same homologous homozygous and tall but let's look at this person oh small T small T homozygous but short look at this person oh one big one small hetero different zygous and he is tall next penetrance versus expressivity penetrance what are you trying to say well look at these individuals all right I have six individuals all of them have a certain alley let's call it a so here's a you have a you got an A you also get an A A A all of them are A's however half of them are blue in color the other half are not so when I ask you what percentage of the population Express the phenotypes are either physical appearance the answer is 50 this fifty percent is called penetrance which means the allele a was able to penetrate into half of the population the next question is different suppose that all of these individuals have a certain genotype let's call it P P but look at at them some of them are not purple at all some of them are mildly purple others are a darker purple others are in even darker purple what's that expressivity in this case variable expressivity because some of them have no purple some of them have mild purple moderate purple or severe purple this could be a disease such as a condition known as neurofibromatosis well you will see patients with no symptoms patients with mild symptoms of the disease others with moderate symptoms and others with severe symptoms expressivity so let's recap your body is made of systems each system has organs each organ has tissues each tissue has cells each cell has a nucleus nucleus has 46 chromosomes each chromosome has two chromatids which are chromatin a piece is called the gene you got a copy from Mommy a copy from Daddy these alternative copies are alleles the locus is the location of the gene on the freaking chromosome white said James FPS of the DNA a sequence of the DNA which determines your characteristics genetically speak H Gene may have Alternative forms known as alleles look at the AL with the AO the allele is the alternative a l with a l usually each gene has two alleles one from Mommy one from Daddy do we have exceptions yes we do have exceptions such as the system for blood grouping it has three alleles IA IB and I O A dominates over o b dominates over o but between A and B is co-dominance what's the genotype your genetic makeup something that I cannot see how about phenotype something that is observable it's a manifestation of the genotype example your genotype could be capital a capital A or capital a capital O either way your phenotype will be blood group a here's the system in a nutshell we have two antigens A and B isn't o an antigen no o means zero then we have four blood types a b a b or o o is zero because this person lacks the a antigen and lacks the B antigen as well we have three alleles IA IB and I O A dominates over o b dominates over o o is always recessive between A and B there is co-dominance and you end up with six possibilities why six because you have two chromosomes with three alleles so if my genotype is o o my phenotype will be just oh because o is recessive so U will be o how about a a you'll be a how about O A or a o a dominates over o you'll become a phenotypically speaking baby you are b b o b dominates over the O and U are B how about a b you will remain a b have both antigens now please pause and review we'll continue in the next video If you like this video you will also enjoy my renal physiology course on my website meticosisperfectness.com I also have a brand new surgery high yields course thank you for 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