B6 specification

• Describe features of sexual and asexual reproduction

  • sexual reproduction involves fusion of male & female gametes, leading to genetic variation in offspring
  • asexual reproduction requires 1 parent & makes genetically identical clones
• Describe what happens during meiosis

  1. before cell divides, it duplicates genetic info, forming 2 armed chromosomes which arrange into pairs
  2. 1st division: chromosome line up at centre & pulled apart so new cell has 1 of each pair
  3. 2nd division: chromosomes line up in centre & arms are pulled apart
  4. 4 gametes with single sets of chromosomes which are all different due to it being shuffles up
• describe what happens during meiosis & compare to mitosis

  • meiosis:
  • occurs in gamete formation
  • produces 4 different haploid cells
  • involves 2 divisions
  • leads to genetic variation
  • mitosis:
  • produces two identical diploid cells
  • responsible for growth, repair & asexual reproduction
  • involves 1 cell division
• describe what happens at fertilisation

  • fusion of sperm & egg, creating a diploid zygote
  • restores full chromosome number
  • leads to genetic variation in offspring due to randomly inherited traits
• describe structure of DNA & its role in storing genetic info inside cell

  • DNA is a double helix & polymer
  • DNA wraps around proteins to form chromosomes, carrying genetic information in genes
  • encodes instructions for protein synthesis
• what are genes & what they do

  • genes: small section of DNA
  • code for specific amino acid which makes protein
• Explain the term 'genome' and the importance of the human genome

  • genome: entire set of genetic material in an organism
  • The Human Genome Project has...
  • helped identify genes responsible for genetic disorders
  • led to develop effective medical treatments
  • improved understanding of human evolution
• describe how characteristics are controlled by one or more genes, including examples

  • some characteristics are controlled by a single gene
  • different forms of a gene = allele
  • alleles present, or genotype, develop characteristics that can be expressed as a phenotype
  • dominant always expressed
  • recessive only expressed if there's 2 copies
  • most characteristics are a result of multiple genes interacting, rather than a single gene
• Explain important genetic terms

  • Gamete – reproductive cell
  • Chromosome – DNA-packed structure found in nucleus
  • Gene – segment of DNA coding for a protein
  • Allele – different forms of a gene
  • Genotype – genetic makeup (e.g., BB, Bb)
  • Phenotype – observable traits (e.g., brown eyes)
  • Dominant – expressed even with one copy (B)
  • Recessive – only expressed with two copies (b)
  • Homozygous – same allele (BB or bb)
  • Heterozygous – different alleles (Bb)
• Describe cystic fibrosis as an inherited disorder

  • caused by a recessive allele
  • effects cell membranes & causes sticky mucus in airways & pancreas
• Describe polydactyly as an inherited disorder

  • dominant allele
  • extra finger or toe
  • 50% chance if 1 parent has
• Evaluate social, economic & ethical issues concerning embryo screening

  • for
  • help people from suffering
  • costs government & tax payers money to treat disorders
  • laws in place to stop it from going too far
  • against
  • implies people with disorders are undesirable
  • might create designer babies
  • screening is expensive
• describe how chromosomes are arranged in human body cells, including function of sex chromosomes

  • Humans have 23 pairs of chromosomes
  • Sex chromosomes determine biological sex:
  • XX = female, XY = male.
  • other chromosomes control various traits.
• describe what variation is & how it can be caused within a population

  • Variation: Differences in phenotypes between individuals
  • Causes
  • Genetic variation (different alleles from parents)
  • Environmental factors
  • Combination of both
• describe mutations and explain their influence on phenotype and changes in a species

  • Mutation: changes to gene, creating genetic variant
  • can contribute to evolution if beneficial mutations are inherited over generations & can become common through natural selection
• explain the theory of evolution by natural selection

  • Proposed by Charles Darwin
  • Key principle:
  • advantageous traits survive competition & reproduce
  • over time, favorable traits become more common in populations & species changes- evolves!
• describe how new species can be formed

  • speciation: phenotype changes so much because of natural selection it becomes a new species
  • happens when population become reproductively isolated- offspring isn't fertile
• extinction

  happens when...

  1. environment changes quickly
  2. new predator
  3. new disease
  4. can't compete with another species for food
  5. catastrophic event
• Describe what selective breeding is

  • artificial selection of mates by humans for useful traits
• Explain the process of selective breeding

  1. choose ones with desired characteristics
  2. breed
  3. select best offspring & breed them
  4. repeat until trait gets stronger & all offspring will have trait
• • gene pool: number of different alleles in a population
• risks of selective breeding

  1. reduces gene pool and leads to inbreeding which causes defects
  2. lack of variation means they're susceptible to new diseases
• describe what genetic engineering

  • transferring genes responsible for a desirable characteristic into another organism
• process of genetic engineering

  1. useful gene is isolated from organism with enzymes & inserted into vector
  2. vector is usually a virus or bacterial plasmid
  3. when vector is introduced to target organism, useful gene is inserted into its target cells
  4. usually transferred during the early stages of an organism's development
• examples of genetic engineering

  1. bacteria modified to produce insulin to treat diabetes
  2. Genetically Modified (GM) crops
• explain some benefits, risks and concerns related to genetic engineering

  • + pros
  • increase crop yield
  • can provide nutrients in places where people are lacking
  • already being grown, often without problems
  • - cons
  • reduced farmland biodiversity, affecting wild flowers & insects
  • not everyone is sure they're safe & might not understand effects on human health
  • concern transplanted genes may get out into the natural environment
• Describe some sources of evidence for evolution

  1. replacement by minerals
  2. casts & impressions
  3. preservation

  • all examples of fossils
• describe what fossils are

  • fossils: remains of organisms from thousands of years ago, found in rocks
• what can we learn form fossils

  • evidence that organisms lived ages ago
  • how much organisms have changed over time
• how are fossils formed

  • gradual replacements by minerals
  • bones dont decay & are replaced by minerals & sediment around it turns into a rock
  • casts & impressions
  • impressions can be made into soft material which hardens
  • preservation where there's no decay
  • in amber, there's no oxygen so decay microbes don't survive
  • glaciers too cold for microbes
  • peat bogs too acidic
• explain why there are few traces of the early life forms

  • many early life forms were soft bodied so decayed completely
  • fossils formed millions of years ago could have been destroyed by geological activity
•  consequences of lack of traces for early life forms in terms of our understanding of how life began

  • we dont really know how life began regardless of the multiple hypotheses
• Describe how antibiotic-resistant strains of bacteria can arise and spread (inc MRSA)

  • bacteria can have mutations which can lead to antiobiotic-resistant strains as gene becomes more popular
  • bacteria reproduce rapidly
• MRSAs

  • superbugs are resistant to most antibiotics which are becoming more common
  • MRSAs are a common superbug in hospitals & are fatal if it enters bloodstreams
• describe how the emergence of antibiotic-resistant bacteria can be reduced & controlled, to incl limitations of antibiotic development

  1. don't use antibiotics for diseases that aren't bacterial or non-serious conditions
  2. take full course to ensure all bacteria is destroyed so none are left to mutate

  • farmers use antibiotics to prevent animals from becoming ill & grow faster which can make resistant strains & spread to humans
  • rate of development of new antibiotics is slow & expensive
• Describe how organisms are named and classified in the Linnaean system

  • made in 1700s by linnaeus
  • groups living things according to characteristics & structure
• stinky - species

  ghalib - genus

  farts - family

  out - order

  concentrated - class

  poopy - phylum

  kittens - kingdoms
• Explain how scientific advances have led to the proposal of new models of classification, inc three-domain system

  • 1990, woese proposed 3 domain system
  • based off RNA sequences

  1. archaea: primitive bacteria like extremophiles
  2. bacteria: true bacteria, lots of biochemical differences between archaea
  3. eukoryota: broad range of organisms with nucleus & other organelles
• Explain how scientific advances have led to the proposal of new models of classification, inc three-domain system

  BINOMIAL NAMING SYSTEM

  • genus species
  • worldwide system
  • 1st part genus, 2nd part species
• describe & interpret evolutionary trees

  • shows how different species are related
  • shows common ancestors
  • more closely related, more characteristics they're like to share