Inheritance, Variation and Evolution Flashcards
DNA (Deoxyribonucleic Acid)
The genetic material in the nucleus of a cell or in plasmids
Chromosomes
- Long threads of DNA, which are made up of many genes
- 23 pairs of chromosomes in every cell (46 individual chromosomes)
Why is the 23rd pair of chromosomes in every cell important?
- They are known as the sex chromosomes
- There is an X and a Y chromosome
Gene
A small section of DNA that codes for a protein
Genome
Entire set of genetic material in an organism
The Human Genome
The complete set of all the different combinations of genes in humans, made by scientists
Why is the human genome useful?
- Allows scientists to identify genes that are linked to genetic diseases
- Can be used to trace migration of people’s ancestors
Inherited Disease
Genes that have been passed down from parents that cause disease
Allele
A different version of a gene that controls a characteristic
Homozygous
A genotype where the 2 alleles of a characteristic are identical
Heterozygous
A genotype where the 2 alleles of a characteristic are different
Dominant Allele
An allele that is expressed when it is present
Recessive Allele
An allele that is masked when paired with a dominant allele but expressed when paired with itself
Genotype
The collection of alleles that determine characteristics
Phenotype
Characteristics that are displayed as a result of your genotype
Why is it possible to have different genotypes but the same phenotype?
A heterozygous organism and a homozygous dominant organism can both have the same phenotype as they both express dominant allele characteristics
Nucleotide
A monomer of DNA made up of a phosphate group, a base and a sugar
What are the 4 different bases found in a nucleotide?
- A (adenine)
- C (cytosine)
- G (guanine)
- T (thymine)
Complementary Base Pairing
- Only complementary bases can pair when joining the double helix
- A only pairs with T
- C only pairs with G
Genetic Code
A sequence of bases on a strand of DNA
Triplet Code
Every 3 bases on a strand of DNA that code for 1 amino acid
How to triplets help make a protein?
- Our cells read the long chain of bases as triplet codes and makes the corresponding amino acid for each code
- The amino acid are combined into a chain in the same order as the triplet codes
- The chain folds up to form a protein
Main uses of proteins
- Enzymes
- Hormones
- Structural Proteins
Protein Synthesis
The process in which cells make proteins
How does protein synthesis work?
- Gene is copied in the nucleus so it’s small enough to leave it. This copy is mRNA
- mRNA to the ribosome
- An amino acid chain is made in the ribosome using mRNA
- The chain detaches from the ribosome and folds to form a protein
- The ribosomes require energy to make proteins
Polypeptide
A chain of amino acids
Mutation
A change in the DNA base sequence
What increases risk of mutation?
- Carcinogens
- Certain types of radiation
How do mutations work?
- If their was a change in the triplet code in a gene this changes what amino acid is being coded for
- This would change the overall polypeptide
- This changes the protein that is formed
- The protein would have a different shape/function
Non-Coding DNA
- DNA that isn’t part of a gene so it doesn’t form any proteins
- Responsible for gene expression
Gene Expression
Whether a present gene is turned on or off and can or can’t produce a certain protein
Types of Mutation
- Substitution
- Insertion
- Deletion
Substitution
One of the bases is substitutes for another random base
Insertion
An extra base is inserted into the sequence
Why is insertion worse than substitution?
- An insertion means all bases are shifted along by one
- This alters all triplet codes in the gene
- The amino acid chain would be completely different
Deletion
One of the bases is removed from the sequence
Sexual Reproduction
- Relies of fusion of male and female gametes (fertilisation)
- Offspring have a mix of both parents’ genes
- Offspring are genetically different from parents
- This introduces variation through generations
Gametes
- Sperm and egg in animals
- Pollen and egg in plants
- Contain only half the genetic material of normal cells
- Made through meiosis
Asexual Reproduction
- Only one parent
- No gametes needed
- Offspring are genetically identical so no variation
- Achieved by mitosis in eukaryotes (animals, plants, fungi)
- Achieved by binary fission in prokaryotes (bacteria)
Asexual Reproduction Advantages
- Only needs one parent
- Process is fast so a single organism can easily colonise a new area
Asexual Reproduction Disadvantages
- All offspring are clones so no genetic variation (more likely to wipe a population with disease)
- Less chance of adapting to new conditions, e.g. change in climate
Sexual Reproduction Advantages
- Lots of genetic variation within a population (less likely to be wiped by disease)
- Population can adapt to changing conditions (through evolution)
Sexual Reproduction Disadvantages
- Requires 2 parents
- Can take a while to find a mate
- Resources are used to impress a mate but it doesn’t aid their survival
Haploid
A cell that contains 1 set of chromosomes
Diploid
A cell that contains 2 sets of chromosomes
Meiosis
- DNA of both chromosomes are replicated (chromosomes form an X shape)
- Chromosomes line up in pairs along the centre of the cell
- Chromosome pairs are pulled apart and cell splits in 2
- Second division - chromosome Xs are pulled apart
- Makes 4 genetically unique cells called gametes
Genetic Diagrams
Show all the different combinations of alleles from 2 parents
Cystic Fibrosis
- Recessive inherited disorder
- Lungs and digestive system become clogged with mucus
Polydactyly
- Dominant inherited disorder
- Born with extra fingers and toes
Inherited Disorder
Group of conditions passed on in alleles that is inherited from a person’s parent’s
Embryo Screening
- Embryo cells are taken and screened for genetic disorders
- Parents and doctors can choose to keep the embryo or discard it and choose a different one
Pros of embryo screening
- Reduces overall suffering (fewer people with genetic disorders)
- Saves money
Cons of Embryo screening
- Implies that people with genetic disorders are undesireable and increases prejudice
- People could start screening for other traits (e.g. eye colour, gender)
Mendel’s Pea Plants
- Took a green and a yellow pea plant and bred them
- All the offspring were yellow
- Bred the offspring
- 3/4 were yellow, 1/4 were green
- Conclusion was that ‘hereditary units’ were passed down generations
- Tried this with different traits (height, flower colour) and came to the same conclusion
History of Genetics after Mendel
- Chromosomes were discovered and observed in the late 1800’s
- Similarities between chromosomes and hereditary units in early 1900’s
- Structure of DNA determined in 1953
- Entire human genome written in 2003
Variation
Differences between individuals
Mutation (genetic variation definition)
A change in the DNA code so the protein it codes for is different
Natural Selection
The process where a species changes over time to respond to changes in the environment, or competition between organisms to survive
Process of Natural Selection
- Beneficial mutation occurs in a individual make them more likely to survive and reproduce
- Gene of beneficial mutation is passed on to offspring
- Beneficial gene spreads through the population until the species has ‘evolved’
Theory of Evolution
- All species of living things evolved from simple life forms that developed around three billion years ago
- Inheritance of certain characteristics in a population over multiple generations could lead to a change in the species
Speciation
- The phenotypes of 2 different populations of a species become so different they can’t interbreed to produce fertile offspring
- A new species is formed
Selective Breeding
A process where humans
individuals of a population for particular genetic characteristics
Process of Selective Breeding
- Individuals with desired characteristics with a population are selected and bred
- Offspring with desired characteristic are bred together
- Process is repeated until the offspring express desired characteristic
Drawbacks of Selected Breeding
- Reduces the gene pool of the population
- Inbreeding meaning offspring are prone to diseases/inherited defects
- Less variation so agriculture suffers (population can be wiped by disease)
Gene Pool
All the genes and alleles found in a population
Genetic Engineering
A process where an organism’s genome is modified by introducing a gene from another organism to give a desired characteristic.
Example of Genetic Engineering
- Genetically engineered bacteria to produce insulin to treat type 1 diabetes
- GM crops that produce more nutrients, are resistant to disease or are bigger and better quality
- E.g. Golden rice produces lots of beta carotene (vitamin A) which stops blindness
Gene Therapy
- Used to treat inherited disorders
- A person is given the healthy version of a gene
- Difficult to get it to work as the faulty gene is found in all the cells of the body
- Solution is to transfer the gene at an early stage of development (egg/embryo stage)
Pros of GM crops
- Makes crops with desirable characteristics
- Makes more food for less money which is beneficial for developing countries
- Makes sure plants have particular nutrients
Cons of GM crops
- Don’t know the impacts of GM crops on health
- GM crops could reach the wild and outcompete local plants which changes the whole ecosystem
Process of Genetic Engineering
- Desired gene is isolated using enzymes and is inserted into a vector (usually a bacterial plasmid or a virus)
- Vector inserts the gene into the required cells in the organism’s early development
- This is so that they develop with the desired characteristic
Cloning by Transplanting a Cell Nucleus
- Take an egg from a donor female and enucleate it (remove its nucleus)
- Take an adult body cell from the organism being cloned and enucleate it
- Put the nucleus of the body cell into the enucleated egg cell
- Stimulate the with an electric shock so it acts like a zygote and divides by mitosis to form an embryo
- Implant the embryo into a surrogate mother so it develops and is eventually born
Cloning Transgenic Animals
- Scientists place human genes into DNA of other organisms
- Once an organism has DNA from another species, the organism is transgenic
- Scientists will clone the transgenic organisms they’ve already made
- E.g. Cows, sheep and goats are genetically engineered to produce human proteins
Cloning by Embryo Transplants
- Pick male and female organisms with desirable traits
- Take their sex cells and fertilise the egg cell to produce a zygote
- Let the zygote develop into an embryo
- Separate the embryo into smaller embryos
- Place embryos into surrogate mother so they develop into identical clones
Advantages of Cloning vs Selective Breeding
- Quicker
- Genetically identical/No variation
- No mating needed
Cloning plants with cuttings
- Choose plant you want to clone
- Cut off a small part (ideally shoot or branch)
- Place the cutting in soil with nutrients and hormones
- The cutting will grow into a clone of the original plant
Advantages of cloning by cuttings
- Quicker
- Cheaper
Micropropagation (Using plant tissues)
- Find a plant with desirable characteristics
- Take small pieces of plant tissues from the stem and sterilise them
- Place the plant in agar containing growth hormones and let them grow calluses
- Transfer calluses into soil with nutrients so they grow into plantlets
- Transfer plantlets to pots so they grow into adult clones
How are plant tissues removed and transferred to the agar?
- Cut the plant with a scalpel
- Transfer with tweezers
- Sterilise with sterilising equipment
Fossils
Preserved remains or traces of a dead organism
Gradual Replacement of Minerals
- Body parts decayed slowly
- As they decayed, they were replaced with minerals and form rock structures in the same shape as the original structures
Casts and Impressions
- Casts are formed when an organism is buried in soft material (clay)
- As the clay hardens it leaves a gap the same shape and size of the organism
- Impressions are when organisms leave marks in the ground (footprints)
Preservations
- No decay occurs due to lack of oxygen and moisture
- Organisms get stuck in amber or pit tar and remain intact
Why are there gaps in the fossil record?
- Many early life forms were soft bodied so would have decayed quickly
- Some fossils may have bee destroyed
Extinction
Occurs when there are no remaining individuals of a species alive
Reasons for Extinction
- Environment changes quickly (temperature)
- Arrival of new predators
- Human hunting
- Disease
- New species outcompetes
- Catastrophic event
Species
A group of genetically similar organisms that can interbreed and produce fertile offspring.
Process of speciation
- Isolation separates 2 populations of the same species
- The environment is different on either side of the barrier
- Both populations experience different selection pressures so different traits become favourable for the 2 populations
- Natural selection occurs and after many generations the populations are so different from each other they can’t interbreed anymore
- Speciation has occurred
How does Antibiotic Resistance occur?
- Mutations of bacterial pathogens produce new strains
- Some strains are resistant to antibiotics and aren’t killed
-They survive and replicate so the population of the resistant strain rises - The resistant strain spreads as people aren’t
immune to it and there isn’t an effective treatment.
Why is Antibiotic resistance a problem?
- Doctors give out antibiotics where they won’t help
- Farmers put antibiotics in the food of healthy animals
Linnean System
- Grouped species based on characteristics and bone structure
- Kingdom, Phylum, Class, Order, Family, Genus, Species
- Binomial Naming System:
- Species named after their Genus and Species
- Genus is in capital letter only and name is written in italics
3 Domain System - Carl Woese
- 3 Domains that go above kingdoms
- Archaea (primitive bacteria living in extreme environments)
- Bacteria (true bacteria)
- Eukaryota (all eukaryotes)
Pneumonic to Remember classification
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