Cell Division & Inheritance

• Genes are found inside DNA which is found inside chromasomes which are found in the nucleus
• Nucleus > Chromasome > DNA > Gene
• DNA contains instructions to make amino acids which create proteins which fold to make a particular shape
• The proteins control which characteristics someone has
• DNA is read in the nucleus and the proteins are made in the cytoplasm at the ribosomes

Mitosis:

• Cells divide by mitosis so organisms can grow and replace damaged cells and tissues
• One cell becomes two, so all the cells are identical
• Happens in asexual reproduction 
• First the chromasomes are copied, then the cell divides

• When a fertilised egg begins to divide, the first cells are unspecialised
• In animals, cells become specialised early on, but plant cells usually remain undifferentiated

Stem Cells:

• Undifferentiated cells
• Useful in medical research as they can develop into different types of cells, eg. brain cells, liver cells etc.
• Doctors get stem cells from embryos, umbilical cords, bone marrow etc.
• Can be used to treat previously incurable conditions, such as damaged organs and birth defects
• However, new cells could be rejected by the body
• Using cells from embryos results in ethical issues

Meiosis:

• Gametes are produced in the ovaries and testicles
• The new cells only contain half the number of chromasomes and the combination of genes is different
• Gametes fuse together so the fused cell haas the correct number of chromasomes

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Gregor Mendel:

• First person to continuously repeat an experiment and write down the results
• He would choose flowers to be the parents and use a paintbrush to pollinate them
• He was the first person to suggest seperatley inherited factors (genes)
• However, no one believed him because he wasn't a scientist and because he had no way of explaining or providing evidence as genetics hadn't been explained yet

• Males are XY
• Females are **
• Females only have X chromasomes, so the sperm is the gamete which controls whether the resulting child will be male or female

Allele: Alternative forms of a gene- tall/ short, blue/ green/ brown eyes

Genotype: Alleles in a cell- RR or Rr

Phenotype: The characteristic- tongue roller, blue eyes

Dominant: Allele for the characteristic which is always shown if the allele is present

Recessive: Allele for the characteristic only shown if no dominant

Homozygous: 2 of the same allele- RR, rr

Heterozygous: Different alleles- Rr

• Jeffereys used the variability of DNA to develop genetic fingerprinting
• Certain parts of the DNA are variable amongst the population, but some are similar among related people
• He used this to make genetic fingerprinting which can be used to show if a sample of DNA comes from the same person, related person, or a complete stranger

• Forensics uses g.f. to find suspects
• Maternity/ Paternity tests use g.f. to see if a man or woman and a child are related

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Mutations:

• When an organism develops a new characteristic that no other member of the species has had before
• Mutations may be caused a chemical change or when the DNA isnt copied properly
• They can be helpful because the can give the organism a survival advantage so the mutated organisms live on to become better at surviving
• The mutated gene controls which enzymes are created which controls which characteristic is formed as the sequence of amino acids is changed

Polydactyly:

• When someone has an extra finger/thumb
• Caused by a dominant allele, so can be passed down even if only one parent has it

Cystic Fibrosis:

• Thick, sticky mucus cannot be coughed up, leading to difficulties breathing and frequent lung infections
• Cannot digest food properly as enzymes cannot pass into the gut, causing a shorter life span
• Can be found using a sweat test as they have 2-5 the amount of salt in their sweat
• No cure, but can be treated with physiotherapy, inhalors, antibiotics, gene therapy ( testing)
• Recessive allele
• A carrier of CF (has one CF allele but shown no signs) has a possibility of producing a child with CF with another carrier

Hungtington's Disease: Controlled by dominant allele

Embryo Screening:

• Parents can warned whether or not to have the child
• Can select healthy embryos to keep
• Could harm embryo/ cause miscarriage
• Expensive
• Unethical as all babies should have the right to life

Stem Cells:

• Can find cures or treatments to previously untreatable diseases
• Generally uses embryos which would have been destroyed anyway
• Not stable
• Unethical as all babies have the right to life
• Expensive to develop- money could be spent elsewhere