B13
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Meiosis
1) cell grows and DNA replicates 2) First division is when each chromosome pulled to each end 3) cytoplasm and cell membrane divide to form two new cells, each with one set of chromosomes 4) Second division so copy of each chromosome pulled to each end of the cell 5)cytoplasm and cell membrane divide again forming 4 genetically DIFFERENT gametes Half the no. of chromosomes from parent cell
ASEXUAL(mitosis) • aphids • Mexican hap-plants • bacteria • cells of the body
ADVANTAGES: Faster Less energy needed One parent needed DISADVANTAGES: No genetic variety No evolution through natural selection More likely to die in changes to environment
SEXUAL(meiosis) • human gametes = sperm and egg • plant gametes = pollen and egg 🧚🏻♀️Opposite of mitosis card so just memorise one of them🧚🏻♀️
ADVANTAGES: Genetic variety May survive when changes to environment DISADVANTAGES: Need to find partner Slower Fewer offspring
Meiosis & Mitosis comparison
Meiosis: Mitosis: 4 genetically different 2 identical cells Cells divide twice One division Gametes with half no. Same no. of chromosomes Of chromosomes Sexual Asexual
DNA
• polymer made up of two strands forming a double helix - contained in structures called chromosomes found in the nucleus(2)
Human Genome: Memorise spec reference
• search for genes linked to different types of diseases • understanding and treatment of inherited disorders • tracing human migration patterns from the past
Nucleotide= Base Enzyme= Protein
A — T C — G Sequence of three—amino acid—protein
DNA Transcription Translation Protein (6 marks)
• template is produced from the DNA in a nucleus • template leaves the nucleus and binds to surface of the ribosome • a carrier molecule with an amino acid attached which is complementary to the template attaches • different carrier molecules keep bringing specific amino acids adding to the growing chain • protein chain detaches and folds into correct shape
Explain how mutation could cause an enzyme to not work (4 marks) Diagram usually given
1) incorrect base sequence 2) incorrect amino acid sequence 3) incorrect protein made 4) active site changed 5) enzyme no longer fits the substrate
Chromosomes
Human Body = 23 pairs 22 = control characteristics 1 = determines sex Female= XX Male= XY
Genetic Screening Cystic fibrosis
ADVANTAGES: Greater chance of having child without cystic fibrosis Cystic fibrosis not passed onto future generations Child with CF difficult/expensive to bring up DISADVANTAGES: Operation dangers Cruel to embryos Cost of procedure Possible damage to embryos