Inheritance, Variation and Evolution Flashcards
1
Q
DNA (Deoxyribonucleic Acid)
A
The genetic material in the nucleus of a cell or in plasmids
2
Q
Chromosomes
A
- Long threads of DNA, which are made up of many genes
- 23 pairs of chromosomes in every cell (46 individual chromosomes)
3
Q
Why is the 23rd pair of chromosomes in every cell important?
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- They are known as the sex chromosomes
- There is an X and a Y chromosome
4
Q
Gene
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A small section of DNA that codes for a protein
5
Q
Genome
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Entire set of genetic material in an organism
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Q
The Human Genome
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The complete set of all the different combinations of genes in humans, made by scientists
7
Q
Why is the human genome useful?
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- Allows scientists to identify genes that are linked to genetic diseases
- Can be used to trace migration of people’s ancestors
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Q
Inherited Disease
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Genes that have been passed down from parents that cause disease
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Q
Allele
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A different version of a gene that controls a characteristic
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Homozygous
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A genotype where the 2 alleles of a characteristic are identical
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Heterozygous
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A genotype where the 2 alleles of a characteristic are different
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Dominant Allele
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An allele that is expressed when it is present
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Recessive Allele
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An allele that is masked when paired with a dominant allele but expressed when paired with itself
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Genotype
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The collection of alleles that determine characteristics
15
Q
Phenotype
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Characteristics that are displayed as a result of your genotype
16
Q
Why is it possible to have different genotypes but the same phenotype?
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A heterozygous organism and a homozygous dominant organism can both have the same phenotype as they both express dominant allele characteristics
17
Q
Nucleotide
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A monomer of DNA made up of a phosphate group, a base and a sugar
18
Q
What are the 4 different bases found in a nucleotide?
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- A (adenine)
- C (cytosine)
- G (guanine)
- T (thymine)
19
Q
Complementary Base Pairing
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- Only complementary bases can pair when joining the double helix
- A only pairs with T
- C only pairs with G
20
Q
Genetic Code
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A sequence of bases on a strand of DNA
21
Q
Triplet Code
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Every 3 bases on a strand of DNA that code for 1 amino acid
22
Q
How to triplets help make a protein?
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- 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
23
Q
Main uses of proteins
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- Enzymes
- Hormones
- Structural Proteins
24
Q
Protein Synthesis
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The process in which cells make proteins
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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
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Polypeptide
A chain of amino acids
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Mutation
A change in the DNA base sequence
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What increases risk of mutation?
- Carcinogens
- Certain types of radiation
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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
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Non-Coding DNA
- DNA that isn't part of a gene so it doesn't form any proteins
- Responsible for gene expression
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Gene Expression
Whether a present gene is turned on or off and can or can't produce a certain protein
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Types of Mutation
- Substitution
- Insertion
- Deletion
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Substitution
One of the bases is substitutes for another random base
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Insertion
An extra base is inserted into the sequence
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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
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Deletion
One of the bases is removed from the sequence
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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
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Gametes
- Sperm and egg in animals
- Pollen and egg in plants
- Contain only half the genetic material of normal cells
- Made through meiosis
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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)
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Asexual Reproduction Advantages
- Only needs one parent
- Process is fast so a single organism can easily colonise a new area
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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
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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)
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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
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Haploid
A cell that contains 1 set of chromosomes
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Diploid
A cell that contains 2 sets of chromosomes
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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
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Genetic Diagrams
Show all the different combinations of alleles from 2 parents
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Cystic Fibrosis
- Recessive inherited disorder
- Lungs and digestive system become clogged with mucus
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Polydactyly
- Dominant inherited disorder
- Born with extra fingers and toes
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Inherited Disorder
Group of conditions passed on in alleles that is inherited from a person's parent's
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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
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Pros of embryo screening
- Reduces overall suffering (fewer people with genetic disorders)
- Saves money
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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)
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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
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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
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Variation
Differences between individuals
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Mutation (genetic variation definition)
A change in the DNA code so the protein it codes for is different
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Natural Selection
The process where a species changes over time to respond to changes in the environment, or competition between organisms to survive
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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'
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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
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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
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Selective Breeding
A process where humans
individuals of a population for particular genetic characteristics
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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
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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)
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Gene Pool
All the genes and alleles found in a population
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Genetic Engineering
A process where an organism's genome is modified by introducing a gene from another organism to give a desired characteristic.
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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
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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)
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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
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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
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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
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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
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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
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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
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Advantages of Cloning vs Selective Breeding
- Quicker
- Genetically identical/No variation
- No mating needed
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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
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Advantages of cloning by cuttings
- Quicker
- Cheaper
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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
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How are plant tissues removed and transferred to the agar?
- Cut the plant with a scalpel
- Transfer with tweezers
- Sterilise with sterilising equipment
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Fossils
Preserved remains or traces of a dead organism
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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
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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)
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Preservations
- No decay occurs due to lack of oxygen and moisture
- Organisms get stuck in amber or pit tar and remain intact
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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
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Extinction
Occurs when there are no remaining individuals of a species alive
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Reasons for Extinction
- Environment changes quickly (temperature)
- Arrival of new predators
- Human hunting
- Disease
- New species outcompetes
- Catastrophic event
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Species
A group of genetically similar organisms that can interbreed and produce fertile offspring.
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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
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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.
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Why is Antibiotic resistance a problem?
- Doctors give out antibiotics where they won't help
- Farmers put antibiotics in the food of healthy animals
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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
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3 Domain System - Carl Woese
- 3 Domains that go above kingdoms
- Archaea (primitive bacteria living in extreme environments)
- Bacteria (true bacteria)
- Eukaryota (all eukaryotes)
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Pneumonic to Remember classification
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