Phenotypes The observable characteristics of an organism are its phenotype Phenotypic variation is the difference in phenotypes between organisms of the same species In some cases, phenotypic varia...
Epigenetics An organism’s internal or external environment can influence gene expression patterns The levels of regulatory proteins or transcription factors can be affected in response to environme...
Cell Differentiation Stem cells become specialised through differential gene expression This means that only certain genes in the DNA of the stem cell are activated and get expressed Every nucleus ...
Stem Cells in Medicine As stem cells have the ability to differentiate into other specialised cell types, they are very valuable in medical research and treatments as they have the potential to rep...
Stem Cells A stem cell is a cell that can divide (by mitosis) an unlimited number of times Each new cell (produced when a stem cell divides) has the potential to remain a stem cell or to develop in...
Meiosis: Source of Genetic Variation Meiosis gives rise to cells that are genetically different from each other and is the type of cell division used to produce gametes (sex cells) During meiosis, ...
Locations of Genes on a Chromosome Every chromosome consists of a long DNA molecule that contains several hundred or even thousands of different genes coding for different proteins A length of DNA ...
Fertilisation in Mammals During sexual intercourse, semen is ejaculated high up into the vagina of the female, near the cervix The sperm cells then follow a chemical trail released by the egg cell ...
Mammalian Gametes Gametes Gametes are the sex cells of an organism For example, the sperm and egg (ovum) cells in humans Gametes fuse during fertilisation to form a zygote Fertilisation is the fusi...
