Topic 6 - Inheritance, Variation and Evolution Flashcards
Describe sexual reproduction
- fusion of gametes
- requires 2 parents (egg and sperm cell)
- offspring contain a mixture of their parents’ genes (unique individuals made)
Describe asexual reproduction
- no fusion of gametes
- only one parent required
- offspring are identical to parents (clones)
Pros and cons of sexual reproduction
+ allows genetic variation
+ allows selective breeding
- slow
- needs to find a mate
Pros and cons of asexual reproduction
+ less energy
+ fast
- faulty genetic material may be passed on
- bad if environment changes
What are some organisms that use both types of reproduction?
- parasite that causes malaria - sexual in mosquito and asexual in human
- fungi spores
- plant seeds
Describe the process of meiosis
- chromosomes copy themselves (giving double the amount)
- the copied chromosomes arrange themselves as pairs
- the pairs line up in the centre of the cell
- the pairs are pulled apart by protein fibres (some of the fathers and mothers chromosomes go into each cell)
- the chromosomes line up again and are pulled apart
- the chromosomes now separate, giving 4 cells with half the amount of original chromosomes
Describe meiosis in 3 words
copy divide divide
Where does meiosis occur?
gametes (sex cells)
What does meiosis produce?
4 different haploid cells
Define the genome
All of the genetic material in an organism
Why is understanding the human genome really important for science and medicine?
- allows scientists to link genes to different types of diseases
- knowing which genes are linked to inherited diseases helps scientists understand them better and develop treatments
- scientists can use DNA sequencing to trace human migration patterns from the past
Define a gene
A short section of a chromosome.
What is DNA made of?
DNA is a polymer made of two strands in a double helix structure.
What are some issues with people knowing your genome?
- can be sold to 3rd parties
- who does the DNA belong to?
- can lead to being targeted by drug companies
What are positives of knowing peoples genomes?
- can identify criminals
- can discover family
What are nucleotides made up of?
- a sugar
- a phosphate
- one base
How many bases is DNA made up of?
4
How many bases code for 1 amino acid?
3
What does a gene code for?
a particular sequence of amino acids to make a protein
Which bases pair with which?
A - T
C - G
What do the non-coding parts of DNA do?
they switch genes on and off - they control whether or not a gene is expressed
How does DNA cause a protein to be synthesised? (6 marks)
- DNA is the code for making proteins
- the code consists of base pairs (A-T and C-G)
- DNA is too big to leave the nucleus so it makes a single strand copy of itself (mRNA)
- the messenger RNA goes into the ribosomes and is translated (the bases are read)
- 3 bases code for one amino acid
- the tRNA brings amino acids to the ribosomes and the the correct order
- amino acids join up to make proteins
Define a mutation
a change in the DNA code - they occur continously
Describe the 3 types of mutations
- insertions - new base is inserted in the DNA base sequence where it shouldn’t be
- deletions - a random base is deleted from the sequence
- substitutions - a random base in the DNA base sequence is changed
Which are the least and most damaging types of mutations?
- insertion and deletion are the most damaging - they change the code for every amino acid after the mutation point
- substitution only affects 1 amino acid
Explain how a change in the base pair sequence of DNA can lead to a non-functioning enzyme. (6 marks)
- mutations change the sequence of base pairs
- if the sequence changes, the amino acids will change so the protein will have a different shape
- enzymes are proteins
- if the shape changes, the substrate won’t fit in the active site and it can’t bind
Define homozygous
two alleles are the same
Define heterozygous
one of each allele
Describe how to answer a punnett square question
- write the parents alleles genotype
- draw a punnett square
- write the outcomes (probability in %)
Define a dominant allele
only one copy is needed to have feature (stronger)
Define a recessive allele
both copies are needed to have feature
Define an allele
different versions of the same gene
Define a genotype
the pair of alleles someone has
Define a phenotype
the feature someone has
Describe polydactyly
- extra digits (fingers or toes)
- caused by a dominant allele
Describe cystic fibrosis
- causes a build up of mucus
- caused by a recessive allele
What is selective breeding?
when humans breed plants and animals for desired characteristics
What are some examples of desired characteristics?
- animals that produce more meat or milk
- crops with disease resistance
- dogs with a gentle nature
- plants with big/unique flowers
Describe the process of selective breeding
- select the animals which have the characteristics you’re after
- breed them
- select the best of the offspring and breed them together
- continue this process over several generations
What are drawbacks of selective breeding?
- reduces the gene pool (the number of different alleles) in a population - leads to inbreeding
- more chance of inheriting harmful genetic defects
- a new disease would be more dangerous because of the lack of variation - less chance of any resistant alleles being present
What is the theory of evolution?
all of today’s species have evolved from simple life forms that first started to develop over three billion years ago
Define evolution
organisms changing over time through natural selection to best adapt to their environment
Describe natural selection
- in any population, there is variation
- mutations may cause increased variations
- organisms compete for resources
- some organisms are better adapted
- these organisms will survive and breed, passing on genes for beneficial phenotypes to their offspring
What are the 7 words you need to describe natural selection?
- variation
- mutation
- adaption
- survive
- breed
- genes
- offspring
Why wasn’t Darwin believed?
- it went against religious theories
- DNA wasn’t discovered yet - so he couldn’t explain why traits were passed on
- there wasn’t much evidence
Who came up with the theory of evolution?
Charles Darwin
What was Jean-Baptiste Lamarck’s theory?
he argued that the organism will change over its lifetime - he thought that if a characteristic was used a lot by an organism, it would become more developed during its lifetime
Define genetic engineering
Genetic engineering means altering the genome of one organism by adding genes from another organism
Describe the process of genetic engineering
- a useful gene is cut from one organism’s genome using enzymes and is inserted into a vector (bacterial plasmid)
- the vector is introducted into the targetorganism and the useful gene is insterted into its cell
Describe some uses of genetic engineering
- bacteria have been genetically modified to produce human insulin (used to treat diabetes)
- GM crops have improved features - e.g bigger fruit, disease resistant
- sheep have been genetically engineered to produce substances in their milk that can treat human diseases
Pros of genetic engineering
- can protect plants from being eaten
- produces useful human substances e.g insulin
- engineer plants to increase yield
- can treat genetic diseases through gene therapy
Cons of genetic engineering
- leads to less variation - reduces biodiversity
- transplanted genes may transfer to wild plants
- long term effects aren’t known
- hard to control
Name the 4 types of cloning
- tissue culture
- cuttings
- cloning embryos
- adult cell cloning
Describe tissue culture (cloning)
a tissue sample is taken and combined with hormones to grow large amounts of clones of the parent plant
Give some pros and cons of tissue culture (cloning)
+ can produce thousands of offspring
+ helps scientists preserve rare plant species
- more expensive than taking cuttings
- requires equipment
Describe taking cuttings (cloning) and give some pros and cons
cut some leaves off the plant and replant them with rooting powder
+ cheap and easy
- not very reliable
Describe cloning embryos (for cows)
- give fertility hormones to a top-quality cow, collect her eggs and fertilise them to produce embryos
- divide each embryo into cells, and each cell will grow into an identical embryo
- transfer embryos to host mothers and identical calves will be born
Give some pros and cons of cloning embryos
+ can produce more calves
- skilled and expensive work
Describe the process of adult cell cloning
- nucleus is removed from an unfertilised egg cell
- nucleus is taken from an adult body cell
- the nucleus from the adult cell is inserted in the empty egg cell
- new egg cell gets an electric shock to stimulate it to start dividing
- inserted into surrogate mother
Give some pros and cons of adult cell cloning
+ we can make copies with desired characteristics
+ endangered species can be repopulated
- low success rate
- cloned animals have short life spans
- regarded as immoral
Define species
A group of similar organisms that can reproduce to give fertile offspring
Define speciation
the formation of new species - occurs when populations of the same species become so different that they can no longer breed to produce fertile offspring
What are the key terms for a speciation question?
SIGNS
Speciation:
Isolation
Genetic variation
Natural selection
Species
Describe speciation
- 2 groups of the same species become isolated
- the animals start adapting to their environment though natural selection
- natural selection works differently on the different populations
- after generations of adaptation and natural selection, the 2 populations are so different, they can no longer produce fertile offspring
- speciation has occured
Which scientist was a pioneer of the system of speciation?
Alfred Russel Wallace
What did Gregor Mendel do?
- he carried out breeding experiments on pea plants
- he found that the inheritance of each characteristic is determined by ‘units’ that are passed on to offspring
What 3 conclusions did Mendel reach?
- characteristics in plants are determined by “hereditary units”
- hereditary units are passed on to offspring unchanged from both parents - one unit from each parent
- hereditary units can be dominant or recessive
Define fossils
Fossils are the remains of organisms which existed thousands/millions of years ago
Describe the 4 types of fossils
- trace - not the actual organism, but the impression it left behind e.g footprints
- permineralisation - harder parts of the animal/plant are replaced by minerals as they decay and become part of the rock
- hard part preservation - when the hard parts of an animal can’t decay
- whole organism preservation - whole animal is preserved
Why is the fossil record incomplete?
- lots are destroyed by the movement of the Earth
- lots of organisms don’t fossillise
- not all fossils have been discovered
Define extinction
when all members of a species have died out and none remain
What are some causes of extinction?
- new predators
- new diseases
- new competitors
- catastrophic event
etc.
Define antibiotic resistance
when a bacteria that used to be killed by an antibiotic isn’t affected by it anymore
How do we prevent antibiotic resistance?
- good hygiene
- doctors should not prescribe antibiotics inappropriately
- patients should complete their course of antibiotics
- the agricultural use of antibiotics should be restricted
What 2 things did Carl Linnaeus create?
- binomial naming system
- system of classification
What are the 7 groups Linneaus organised living things into?
- kingdom
- phylum
- class
- order
- family
- genus
- species
Describe Linnaues’ binomial naming system
Organisms are given a two part Latin name
- first part is the genus
- second part is the species
How did Woese change the classification system?
introduced the 3 domain system - splits organisms into 3 large groups called domains:
- archaea - thought to be primitive bacteria, live in extreme places
- bacteria - true bacteria
- eukaryota - everything else, including plants, animals, fungi etc.
domains are the boradest level of classification
