IBDP Biology Chapter 3 Notes



These notes have specially been curated by expert teachers to simplify and enlighten concepts given in IB Biology HL. The notes are comprehensive in nature and are sufficient to study the chapter in depth and one need not look for other resources beyond the notes provided on our website which can be accessed for free. The notes for Cell Biology IBDP HL are available on our official website and can be downloaded for free. You are one click away from obtaining all that you need to score well in IB Biology HL.

The material made available on Tychr’s website is available for all IBDP subjects and is specially curated after an extensive amount of effort to ensure that the notes are in consonance with the IB curriculum and are an amalgamation from various textbooks prescribed by the IBO.Students often face a challenge understanding concepts, especially concepts that are new and tricky. These IB Biology Notes will help the student cover the chapter of Cell Biology entirely while explaining each and every concept in a detailed and easy way.

This unit on genetics begins with a brief explanation of what chromosomes, genes, and meiosis mean. Genetics is the study of genes, variation and heredity. We start the discussion with genes which are heritable factors influencing a specific character present on a locus( a particular position) on the chromosome. Different versions of genes are called alleles, which vary in a few bases only and are produced by mutations. Mutations are the sudden random changes in the genetic material which either confer an advantage or lead to disease. After this, we discuss the genome, the complete base sequence of organisms, and the human genome project, which sequenced this genome.

Then we examine chromosomes in humans (22 allosomes and 23rd sex chromosome which determines sex in humans: XX female XY male ) and how they determine the ploidy. Ploidy corresponds to the number of sets of chromosomes in a cell. Then we dive into meiosis, the particular type of cell division that halves the chromosomal content (2n to n; hence reductional division) seen in gametogenesis. Non-disjunction of chromosomes during meiosis leads to genetic disorders like down’s syndrome.

Finally, moving on to the last part of the chapter, we talk about Mendel’s concepts of inheritance and his experiments with pea plants and how recessive alleles express themselves only in homozygous conditions. We understand the terminology of F1 and F2 generations and extend this knowledge into the inheritance of disease, whether autosomal(sickle cell disease) or sex-linked (haemophilia), dominant or recessive. We end the discussion by talking about biotechnology, genetic transfer and cloning.