| what are chromosomes | -Structure containing single DNA molecule and associated proteins - they carry genes |
| what do chromosomes look like | Various shapes and sizes – appearance changes over life of organism
- when condensed they are depicted as long oval shapes
- when uncondensed they are just floating strings |
| what types of chromosomes do eukaryotic cells have | linear chromosomes |
| where are chromosomes found in eukaryotic cells | nucleus |
| what does each chromosome possess | Each chromosome has a set of genes – passed on to daughter cells in mitosis and germ cell in meiosis |
| what chromosomes do prokaryotes have | Prokaryotes have a single circular chromosome – may also contain small circular DNA called plasmids which can move between cells |
| what is histone proteins | histone proteins are the substance that DNA is wrapped around |
| what is a nucleosome | they are sections of DNA which is wrapped around histone proteins
nucleosomes are particles, so they give DNA the appearance of string beads |
| what is the main function of nucleosomes | serve to package DNA efficiently and protect it from enzymatic degradation |
| what happens to nucleosomes when chromosomes are condensed | when chromosomes are condensed nucleosomes fold producing supercoils |
| what is a centromere | Chromosomes have a constriction point called a centromere which divides the chromosome in to two sections called chromosome arms |
| what are chromosome arms | they are the two sides of a chromosome separated by a centromere |
| what are the names for the two types of chromosome arms | the shorter arm is the p arm and the longer the q arm – p arm is always on top |
| what are the names for the four positions centromeres can be in | metacentric, submetacentric, acrocentric and telocentric |
| where is the centromere if a chromosome is metacentric | centromere is in the centre - p and q are equal |
| where is the centromere if a chromosome is submetacentric | centromere closer to one side making q almost double the length of p |
| where is the centromere if the chromosome acrocentric | centromere is very close to one end |
| where is the centromere is the chromosome is telocentric | centromere is at the tip of the arm |
| how many genes does each DNA molecule have | Each DNA molecule has many genes |
| what is a locus | Each gene has a particular position called a locus on a specific chromosome |
| what is spacer DNA and what does it do | - Genes of each DNA molecule are separated by regions called spacer DNA
→ spacer DNA doesn’t code for a protein product
→ they space genes far enough apart that it enables enzymes and other molecules to interact with genes easily |
| what is a ploidy level | The number of sets of chromosomes in a cell |
| what is gametes ploidy level and how many sets of chromosomes do they have | Gametes have one set of chromosomes and are haploid (n) |
| what are somatic cells ploidy level and how many sets of chromosomes do they have | Somatic cells are diploid (2n) – two sets of chromosomes (1 from each parent)
-> Humans have a diploid number of 46 |
| what are homologous chromosomes | two chromosomes in a matching pair - have the same genes found in the same location
-> same genes but different DNA (different variations of each gene - one maternal and one paternal) |
| what is another name for homologous chromosome | homologues |
| what are sister chromatids | they are two chromosomes that are genetically identical and are created when DNA is duplicated |
| what are sex chromosomes | chromosomes involved in the determination of a person’s sex |
| what are allosomes | sex chromosomes |
| what is an autosome | chromosomes not involved in sex determination |
| what are mating types | some organisms (fungi and algae) don’t have allosomes and therefore don’t have sexes instead they have mating types |
| what are organisms called is they have two similar allosomes | individuals with two similar allosomes are of the homogametic sex |
| what are organisms called is they have two different allosomes | individuals with 2 different allosomes are of the heterogametic sex |
| what is haplodiploidy | in some species sex is determined by haplodiploidy – males develop from unfertilised eggs so are haploid and females are derived from fertilised eggs hence they are diploid (bees and wasps) |
| what are some environmental factors that can determine a species sex | some species sex is determined by environmental factors such as temperature (turtles and crocodiles), day length (some types of shrimp) or richness and availability of food resources (types of worms)
→ when sea turtles lay their eggs if the temperature is between 32 and 34 degrees there will only be females but if the temp is between 26 and 18 degrees, they will all be male |
| what is chromosome banding | Chromosome banding refers to alternating light and dark regions along the length of a chromosome, produced after staining with a dye. A band is defined as the part of a chromosome that is clearly distinguishable from its adjacent segments by appearing darker or lighter |
| what are banding types used for | banding types are specific and consistent in each species hence they can be used to distinguish between chromosomes and to identify changes in chromosome structure which may be associated with genetic abnormality |
| what is a karyotype | a karyotype is the image or picture of the full set of chromosomes from an organism’s cell – represented by chromosomes arranged in pairs according to length and centromere position |
| what are karyotypes used for | karyotypes allow scientists to compare chromosomes of related species and allows them to identify changes associated with genetic abnormalities such as changes in chromosome number or structure |
| what is the human karyotype | the human karyotype is made up of 22 pairs of autosomes and 1 set of allosomes
→ the autosomes are numbered 1-22 and are order largest to smallest
→ allosomes are usually shown after autosomes |
