hi everyone welcome to IGCSE study buddy where you can revise biology topics from the Cambridge IGCSE syllabus if you are enjoying these videos so far please don't forget to hit the like button and subscribe to our Channel in this video you are going to learn part 1 of chapter 17 inheritance inheritance is the process by which genetic information is passed from parents to offspring this genetic information which is passed from parents to offspring is carried in the form of DNA DNA is located in the chromosomes of the cell so the nucleus of a cell contains structures called chromosomes chromosomes are made of DNA which contains genetic information in the form of genes a gene is a length of DNA that codes for a protein genes are sections of DNA that contain instructions for specific traits or characteristics such as eye color or height each gene comes in different versions called alleles these different versions of the same gene can lead to variations in the trait that the gene controls for example there are different alleles of the gene that determines blood type which can result in the a b a b or O blood types an allele is an alternative form of a gene let's learn about the inheritance of sex in humans normal human cells have 23 pairs of chromosomes that is 46 chromosomes these are known as diploid cells one of the pairs of chromosomes that is two chromosomes out of the 46 determines the sex or gender of an individual these chromosomes are therefore called the sex chromosomes the presence of X and Y chromosomes is what determines sex males have One X and one Y chromosome that is X Y while females have two X chromosomes XX so all female egg cells contain only an X chromosome whereas male sperm cells may contain an X or a y thus the gender of the baby depends on which sperm cell fertilizes the egg cell if a sperm carrying the father's X chromosome fertilizes the egg the fetus will be female if a sperm carrying his Y chromosome fertilizes the egg the fetus will be male six inheritance can be demonstrated through a Panet Square which is a genetic diagram where the X and Y chromosomes replace the usual alleles in the boxes we will come across more of this type of diagram later on when an egg cell from a female is fertilized it always has an X chromosome however a sperm cell from a male can have either an X or a y chromosome if the sperm cell that fertilizes the egg has an X chromosome the baby will be female but if it has a y chromosome the baby will be male DNA provides instructions for making proteins in cells these proteins perform various functions in the cell such as acting as enzymes that catalyze chemical reactions carrying molecules across the cell membranes and receiving signals from neurotransmitters the DNA controls cell function by controlling the production of proteins including enzymes membrane carriers and receptors for neurotransmitters the sequence of bases in a gene determines the sequence of amino acids used to make a specific protein the order of letters or bases in a gene provides instructions to ourselves on which order to assemble the amino acids to create a particular protein different sequences of amino acids give different shapes to protein molecules so proteins play an important role in cell function let's learn how a protein is made the sequence of bases in DNA is converted into a sequence of amino acids to form proteins the gene which codes for the protein is used to make an mRNA copy in the nucleus messenger RNA or mRNA is a copy of a gene so it's similar to a single strand of DNA the MRNA copies the DNA based sequences of the gene that codes for the protein this is called transcription the actual Gene coding for the protein remains in the nucleus mRNA molecules are made in the nucleus and moved to the cytoplasm the MRNA passes through the ribosomes the ribosomes uses the MRNA Strand and assembles amino acids into the protein molecules in the specific order based on the base sequences this is called translation the specific sequence of amino acids is determined by the sequence of bases in the MRNA this order of sequence is specific to each protein made most body cells in an organism contain the same genes but many genes in a particular cell are not expressed because the cell only makes the specific proteins it needs the genes for all proteins exist in every cell however not every type of protein is made in every cell depending on the sales function the cell only makes the proteins it needs the genes which are needed are switched on and the genes which are not needed are Switched Off when a gene is switched on it is expressed and the corresponding protein is produced when the protein is not needed the gene is Switched Off let's learn about haploid and diploid a haploid nucleus is a nucleus containing a single set of chromosomes which means it has one of each type of chromosome a deployed nucleus is a nucleus containing two sets of chromosomes which means it has a pair of each type of chromosome all humans have 23 different chromosomes in each cell so in a diploid cell there is a pair of each type of chromosome and in a human diploid cell there are 23 pairs of chromosomes that is a total of 46 chromosomes the gametes that is the egg and the sperm cells only have one copy of each chromosome meaning they have a total of 23 chromosomes in each cell nuclei with one set of unpaired chromosomes are known as haploid nuclei now let's learn about mitosis mitosis is nuclear division giving rise to genetically identical cells the details of the stages of mitosis are not required the role of mitosis in growth is that it helps organisms increase in size by producing new cells the role of mitosis in the repair of damaged tissues is that it promotes healing mitosis is important for the replacement of cells it continuously replaces old cells ensuring proper tissue and organ function and also mitosis is important in asexual reproduction it is involved in the production of genetically identical Offspring without fertilization the exact replication of chromosomes occurs before mitosis during mitosis the copies of chromosomes separate maintaining the chromosome number in each daughter cell so in our body cells there are two copies of each chromosome which makes them diploid before the cells divide the chromosomes make copies of themselves this ensures that when the cell splits into two each new cell still has two copies of each chromosome keeping them deployed stem cells are unspecialized cells that divide by mitosis to produce daughter cells that can become specialized for specific functions the zygote is an example of a stem cell it is a fertilized egg cell that has the ability to divide by mitosis and specialize into different cell types during early development next meiosis meiosis is a type of nuclear division also known as a reduction division in which the chromosome number is halved from diploid to haploid resulting in genetically different cells meiosis is involved in the production of gametes or six cells the details of the stages of meiosis are not required unlike mitosis where the number of chromosomes is doubled meiosis is a process where the number of chromosomes is halved so let's take a quick look at the differences between mitosis and meiosis in mitosis two daughter cells are produced whereas in meiosis four daughter cells are produced so daughter cells are deployed in mitosis and in meiosis daughter cells are haploid in mitosis genetically identical daughter cells are produced whereas in meiosis genetically different daughter cells are produced only one cell division occurs in mitosis but in meiosis two cell divisions occur so that concludes part 1 of chapter 17 inheritance hope this video helped you please share your thoughts and suggestions in the comment section thank you for watching and please don't forget to subscribe to IGCSE study buddy for more biology revision videos bye