Mutations And Cell Division Flashcards
Describe what a mutation is.
A mutation is any change to the sequence of bases. Mutations are important when they occur in genes, because changing the sequence of bases in a gene can change what it codes for.
Define the term mutagen.
A mutagen is a physical or chemical agent which causes mutations in DNA.
List two examples of mutagens.
There are lots of different mutagens! Some common examples you might have come across include: Physical mutagens: UV radiation in sunlight, gamma radiation, x-rays.
Chemical mutagens: Ethidium bromide, lead, mercury and other heavy metals.
Define cell division.
Cell division (i.e. mitosis) is the process whereby one cell splits into two (divides). The cell first makes a copy of its
DNA. It then grows larger, before splitting in half. This produces a new cell, so that there are now two. Each new cell gets its own set of DNA and organelles. The resulting cells are called daughter cells.
List four reasons why a cell might need to divide in a living organism
ur reasons why a cell might need to divide in a living organism:
a. Repair: When you get an injury, such as a cut, some cells are killed. Living cells on either side of the wound divide to produce new cells, replacing those which were destroyed.
b. Replacement: Cells don’t live forever. Most cells in your body will only live for a short period of time before they become less able to do their jobs effectively. These cells will die and will be replaced by new cells. For example, your skin cells are continually dying and being replaced by a layer of new, fresh skin cells underneath.
c. Growth - in order to grow larger, a multicellular organism needs to produce more cells. You have more cells in your body now than you did when you were a baby.
d. Reproduction - organisms reproduce by producing new cells - either by producing gametes, for sexual reproduction, or by producing identical copies of their cells in asexual reproduction.
What is mitosis?
Mitosis is a type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus. The process of mitosis is essential to life: it provides new cells for growth and replaces old and dying cells.
What is meiosis?
Meiosis begins like mitosis. First, the DNA replicates, which causes each chromosome to be duplicated. At first, the identical chromosome copies are joined together at their centromere, the centre part of the chromosome. After duplication, the pairs of chromosomes line up in the centre of the cell. How the different pairs of chromosomes line up with respect to the other pairs is random. The spindle fibres will pull the copies of the homologous pairs apart before the cell divides. The spindle fibres pull apart the duplicated pairs of homologous chromosomes and the parent cell divides into two daughter cells. Each of these daughter cells is going to divide again. This creates four daughter cells, each with just one copy of each chromosome. These daughter cells have half the number of chromosomes of the parent cell, and are genetically different. These daughter cells are the sex cells, or gametes.
Meiosis produces gametes, which have half the number of chromosomes as the mother cell and
are not genetically identical.
What is crossing over in meiosis?
Before the spindle fibres pull the chromosomes apart, crossing over, also known as recombination, can occur. Crossing over happens while the duplicated homologous chromosomes are lined up in the centre of the cell. The two innermost chromosomes can swap bits of DNA - this is the “crossing over”. This creates genetic variation, because now there are different combinations of alleles on the chromosomes. This can lead to different combinations of traits in the phenotype.
What is independent assortment in meiosis?
Independent assortment is the process where the chromosomes move randomly to separate poles during meiosis. A gamete will end up with 23 chromosomes after meiosis, but independent assortment means that each gamete will have 1 of many different combinations of chromosomes.
Compare and contrast mitosis and meiosis. Think about what kind of cells they occur in, the number of fighter cells produced and how many chromosomes they have, whether ‘crossing over’ is involved and the purpose for each type of cell division.
Mitosis is the type of cell division used to produce new body cells. These new body cells have the same number of chromosomes as the original cell and are genetically identical to it.
Mitosis occurs in body cells, such as the skin and muscle. In contrast, meiosis only occurs in specific types of cells in the reproductive organs, such as the testes and ovaries in mammals, or in the flower for flowering plants.
Define a zygote.
A zygote is a special type of cell formed when two gametes, such as a sperm and an egg, fuse together. The zygote is the very first living cell of the offspring.
Compare and contrast asexual and sexual reproduction. Think about the number of individuals required, the kind of cell division involved and how genetic variation is affected.
Asexual reproduction only involves a single organism. The organism produces offspring using mitosis. Each daughter cell produced in this way will go onto become its own organism. Each will be genetically identical to the parent (clones of the parents). No genetic variation is produced. Sexual reproduction involves two organisms of the same species. Each organism produces gametes using meiosis. The gametes are sex cells with half the number of chromosomes found in the body cells of the parent. The gametes are not genetically identical to each other or to the parent. During sexual reproduction, two gametes fuse. This is called fertilisation and results in a zygote, which is a single cell with a full set of chromosomes, the same number as in the body cells of the parents. Half of its chromosomes have come from its mother; half from its father. The zygote is the first cell of the offspring. Since it is produced from gametes which are not genetically identical to either parent, the offspring is also genetically different to the parents, so sexual reproduction creates genetic variation.
Explain the relationship between gametes and zygotes.
Eachgametehashalfthenumberofchromosomesofabodycellforthespecies.Whenthegametes fuse, the zygote produced has the normal number of chromosomes for a body cell.
Explain the relationship between homologous chromosomes and fertilisation in sexual reproduction.
In many multicellular organisms like humans, chromosomes come in homologous pairs. In any given homologous pair, one chromosome came from the mother and one from the father.
