B1- YOU AND YOUR GENES
GENES, CHROMOSOMES AND DNA:
NUCLEUS-> CHROMOSOMEà DNAà GENE
§ Most cells in the body have it and it contains genetic material
§ The genetic material in the nucleus is organised into chromosomes.
§ The human body cells have 23 pairs and the sex cell 23 individuals.
§ Every chromosome has one long strand of DNA.
§ This gives the chromosome shape
§ Short length of a chromosome.
§ They can come in different versions of the same genes which are called Alleles.
§ They control the development of characteristics e.g. eye colour etc. And the way an organism functions.
§ Each gene is a code for making a protein
§ Different versions of proteins means we end up with different characteristics
§ Structural proteins- skin hair blood etc. Collagen is a structural protein found in bones etc
§ Functional proteins- digestion and break down molecules. Amylase breaks down starch
Genotype & Phenotypes-
§ All of the genes it has
§ Characteristics the organism displays are called phenotypes
§ Come characteristics are controlled only by genes.
§ Other characteristics are caused by environment
§ Some characteristics can be controlled by both e.g. weight
VARIATION AND GENES
§ One chromosome comes from every parent
§ We have 23 pairs and 46 chromosomes
§ When the sperm fertilises the egg during reproduction, the fertilised egg cell will get 23 pairs of chromosomes
§ 2 chromosomes in a pair are found in the same place and carry the same gene
§ Children will get some alleles from both parents
§ They will never be identical unless they are twins or clones
§ Every child will have a new combination of alleles
§ When people produce sperm or egg cells, their chromosomes separated go into different cells
§ Millions of different chromosome combinations
§ Brothers and sisters will look a bit alike but not entirely
INHERITENCE AND GENETIC DIAGRAMS
§ Combinations of alleles determines the phenotype and only one allele is shown
§ HOMOZYGOUS- two alleles the same for the particular gene
HETEROZYGOUS- two different alleles for the particular gene
§ DOMINANT- the more powerful allele which would always be shown against one recessive allele
RECESSIVE- The weaker allele that will only show when with another recessive alleles e.g. cystic fibrosis
§ This diagram shows what happens when both parents are carriers of cystic fibrosis. The child has a 25% chance of becoming a sufferer and a 50% chance of becoming a carrier. However, there is only a 25% chance of being normal. By knowing how inheritance works, you can create family trees to interpret if the offspring will have a disease etc.