6-Inheritance, variation, evolution

• DNA

  • stands for deoxyribonucleic acid and is the chemical all of our genetic material is made of
  • is a polymer so is made up lots of similar units stuck together
  • has two strands that make a double helix
  • made up of 46 chromosomes
• chromosomes

  • there are 23 pairs - 46 chromosomes in a DNA strand
  • the 23rd pair are the sex chromosomes which are either xx for female or xy for male
• 1. genome
  2. chromosome
  3. DNA
  4. gene

  
• genes

  • are a small section of DNA that codes for a protein/ is a small segment of a chromosome
  • it is a code for a sequence of amino acids that form a protein and determines what type of cell it will be
  • there are 20 types of amino acids
• genome

  • the entire set of genetic material in an organism
  • as we know the complete human genome, genes that cause or increase the risk of inherited diseases can be identified
  • we can trace the migrations of our ancestors
• characteristics we inherit are determined by genes either by themselves or when they interact with other genes
• alleles are different versions/types of the same gene
• alleles

  • humans have one allele from each parent
  • homozygous - if they are the same
  • heterozygous - if they are different
  • dominant - always expressed when present
  • recessive - only expressed when there are 2
• • genotype is the collection of alleles that we have
  • phenotype is the observable characteristics you get from the genotype
• sexual and asexual reproduction

  • animals - sexual
  • plants - sexual and asexual
  • bacteria - asexual
  • fungi - asexual
• sexual reproduction

  • fertilisation - fusion of male and female gametes
  • genetically different offspring - combined DNA from two different parents
  • genetic variation - mixing of genetic material
  • achieved through meiosis
• gametes

  • they are haploids - have half the genetic material of a normal cell (23 chromosomes)
  • when two gametes fuse the resulting cell will have 46 chromosomes so will be a diploid
  • animals - sperm and egg
  • plants - pollen and egg
• asexual reproduction

  • only one parent is required
  • no genetic variation - no mixing of genetic material
  • genetically identical offspring
  • achieved through mitosis for eukaryotes
  • achieved through binary fission for prokaryotes
• meiosis

  1. replicate DNA
  2. chromosomes line up at the centre of the cell (randomly)
  3. chromosomes are pulled apart to each side of the cell
  4. cell splits
  5. the chromosomes in the newly formed cells line up at the centre
  6. chromosomes' arms are pulled to each side of the cell
  7. cell splits
  8. four genetically unique cells are the result (gametes)
• genetic diagrams

  • allow us to see the different combinations of alleles from 2 parents
  • use the 2 parents' genotype to find the genotype combinations and then the phenotypes
  • can be displayed through Punnett square

  A) dd

  
• family trees/pedigrees

  • homozygous recessive - ff
  • homozygous dominant - FF
  • heterozygous - Ff

  
• inherited disorders - polydactyly

  • when someone is born with extra fingers or toes
  • caused by a dominant allele
• inherited disorders - cystic fibrosis

  • affects the cell membranes and causes thick, sticky mucus build up in the lungs or digestive system
  • caused by a recessive allele
• inherited disorders - IVF

  • cells from an embryo can be taken for embryo screening to check the genes and see if it carries any genetic disorders
  • parents can decide if they want to discard it and use another embryo
  • pros - reduce suffering (less people have health problems), save money (costly to treat genetic disorders)
  • cons - implies people with genetic disorders are undesirable, people may start screening for other traits (designer babies)
• differences in the characteristics of individuals within a population is called variation
• characteristics are determined by the genes that individuals inherit and the environment that individuals are exposed to
• mutation

  • is a change in the DNA code
  • most don't have an effect on proteins so don't change the individual's phenotype
  • if the proteins are changed it usually results in bad characteristics though sometimes they can be beneficial
• natural selection

  • 'survival of the fittest' and evolution theory developed by Charles Darwin
  • evolution is the process by which the inherited characteristics of a population change over time due to natural selection - can lead to formation of a new species
  • his theory has been proven - antibiotic resistance, fossil records
  • beneficial mutations can contribute to an individual's chance of survival and are more likely to reproduce
• selective breeding

  • select the animals with the best characteristics and breed them together, select the offspring with the best characteristics and breed them together, repeat this throughout other generations
  • cons - reduces population's gene pool (alleles) and can lead to inbreeding making offspring prone to disease or inherited defects, less variation
• genetic engineering

  • taking a gene responsible for the desirable characteristic from one organism and transfer it to another organism for it to develop the same trait - modifying it's genome
  • organisms of different species can modify organisms from other species
• examples of genetic engineering

  • sheep - drugs in their milk
  • bacteria - produce insulin
  • crops - increasing size and quality, resistant to diseases and herbicides
• genetic engineering - gene therapy

  • treating inherited disorders
  • give a person the healthy version of a gene
  • very difficult as the new gene would have to be transferred to every cell in the body, can be fixed by transferring it at an early stage of development
• genetic engineering - crops

  • pros - desirable characteristics (produce more, resistant to disease) so more food for less money
  • cons - unknown how genetically modified plants can affect our health, can make their way into the wild and compete with ecosystems and change them
• genetic engineering - transferring genes

  • find gene and cut that section of DNA out to isolate it using enzymes
  • insert the gene into a vector e.g. virus, bacterial plasmid
  • introduce the vector to the organism so it can start producing the protein
• two techniques to clone plants

  • cuttings
  • micropropagation (tissue culture)
• cloning plants - cuttings

  • can be used to easily and cheaply clone a desirable plant

  1. cut off a small part of a plant (growing shoot or branch)
  2. place the cutting in soil along with nutrients and hormones
  3. the cutting will grow into a clone of the original plant
• cloning plants - micropropagation - tissue cultures

  • cell structures to produce many clones and is more expensive

  1. cut off a small pieces of plant tissue - explants - from the tips of the stems
  2. sterilise the explants to remove any microorganisms
  3. place the explants in agar with growth hormones and nutrients until they grow into calluses
  4. transfer the calluses into soil to grow into plantlets
  5. transfer plantlets into their own pots to grow into clones
• fossils

  • fossils are the remains or impression of an organism from millions of years ago found in rocks
  • they are used as evidence for evolution as we can see how organisms changed
• ways in which fossils are formed

  • hard parts such as shells or bones undergo gradual replacement by minerals as they decay really slowly
  • animals can leave casts or impressions like footprints as they get covered in layers of sediment that become rock
  • preservation of dead animals and plants in peat bogs, amber, tar pits, ice as there is not enough oxygen for decay
• fossil record

  • it is not complete
  • some organisms are soft bodied so do not fossilise well as they decay very quickly
  • fossils formed long ago could've been destroyed due to natural disasters
• extinction

  • when no individuals of that species remain

  could happen if:

  • an environment changes too quickly
  • a new predator arrives
  • a new disease that wipes them out
  • a species they competed with outcompetes them
  • catastrophic event
• antibiotic resistance

  1. person has bacterial infection and takes course of antibiotics
  2. as bacteria multiply, some get mutations that make them resistant to the antibiotics
  3. the antibiotics kill all the bacteria except the resistant ones
  4. the resistant strains of bacteria grow and multiply as they are not competing with the others
  5. antibiotic resistant strain infects others
• bacteria that are resistant to lots of different types of antibiotics are known as superbugs such as MRSA

  • these are relatively common
  • they usually affect hospitals and end in fatalities
• reasons for antibiotic resistance

  • doctors prescribe antibiotics when they are not necessary - mild bacterial infection, viral disease
  • many people don't take their full course of antibiotics so not all bacteria are killed
  • huge amounts are given to farm animals so they grow faster
• classification

  • 1770's - Carl Linnaeus came up with the Linnean system to group species together according to their characteristics and bone structure
  • Kingdom, Phylum, Class , Order, Family, Genus, Species
  • Linnaeus also proposed the binomial naming system - just genus and species name
  • every country can use it