Topic 6 - Inheritance, Variation + Evolution Flashcards
What does sexual reproduction involve?
The fusion of male and female gametes
What are the gametes called in animals?
Sperm and egg cells
What are the gametes called in flowering plants?
Pollen and egg cells
What happens in sexual reproduction?
There is a mixing of genetic information which leads to a variety of offspring
How are gametes fused?
Meiosis
What does asexual reproduction involve?
Only one parent and no fusion of gametes
What happens in a sexual reproduction?
There is no mixing of genetic information so it leads to genetically identical offspring (clones)
What is the process of asexual reproduction called?
Mitosis
How do cells in reproductive organs divide?
Meiosis to form gametes
What happens when a cell divides to form a gamete?
- Copies of the genetic information are made
- the cell divides twice to form four gametes, each with a single set of chromosomes
- all gametes are genetically different from each other
What is fertilisation?
When gametes join to restore normal number chromosomes
How does the new cell formed in fertilisation divide?
Mitosis
What happens when the fertilised cell divides by mitosis?
The number of cells increases and as the embryo develops cells differentiate
What are the advantages of sexual reproduction?
- Produces variation in offspring
- if environment changes they have a survival advantage by natural selection
- natural selection can be sped up by humans in selective breeding to increase production
What are the advantages of asexual reproduction?
- Only one parent needed
- more time and energy-efficient as only one parent
- faster
- many identical offspring
Which organisms reproduce by both methods depending on the circumstances?
- Malarial parasite
- fungi
- plants
How do malarial parasite reproduce in different circumstances?
Asexually in human host but sexually in the mosquito
How do you fungal reproduce in different circumstances?
Asexually by sports but also reproduce sexually to give variation
How do some plants reproduce by both methods depending on the circumstances?
Produce seeds sexually but also reproduce asexually by runners such as strawberries, or bulb division such as daffodils
What is DNA?
A polymer made up of two strands forming a double helix contained in structures called chromosomes in the genetic material in the nucleus
What is a gene?
A small section of DNA on a chromosome that codes for a particular sequence of amino acid to make a specific protein
What is the genome of an organism?
The entire genetic material of that organism
How much do we know about human genome?
The whole human genome has now been studied and will have great importance medicine in the future
How does understanding the human genome help disease?
It allows scientists to identify genes in the genome that are linked to different types of diseases
How does knowing the link between genes and disease help?
Could help us to understand it better and help us to develop effective treatments for them
How can the human genome help geographic studies?
They can trace the migration of certain populations by investigating the differences in their genomes to work out when new populations split off and what route they took
Describe DNA
A polymer made from four different nucleotides each consisting of a common sugar and phosphate group with one of four different bases attached to the sugar
What are the four bases of DNA?
A, C, G and T
What does a sequence of three bases make in DNA?
The code for a particular amino acid
What does the order of bases in DNA control?
The order in which amino acid‘s are assembled to produce a particular protein
What is the DNA polymer made up of?
Repeating nucleotide units
What is protein synthesis?
Process in which cells make new proteins
Describe protein synthesis
Ribosomes use a copy of the code in the DNA using a messenger RNA to transfer the code out of the nucleus to the ribosomes where the correct amino acid‘s are brought to the ribosome in the correct order by carrier molecules
What happens when the protein chain is complete?
It folds up to form a unique shape enabling the proteins do their job as enzymes, hormones or forming structures in the body such as collagen
What is complimentary base pairing?
A Pairs up with T and C Pairs up with G
What are mutations?
Change to the genetic code
When do mutations occur?
Continuously
What happens when a mutation happens?
Most do not alter the protein or only alter it slightly so that its appearance or function is not changed
What happens if a mutation codes for altered protein?
It will change shape and an enzyme may no longer fit the substrate binding site or a structural protein may lose its strength
Do all parts of DNA code for proteins?
No
What do non-coding parts of DNA do?
They can switch genes on and off so variations in these areas of DNA may affect how genes are expressed
What is a gamete?
A mature haploid male or female sex cell which is able to unite with another of the opposite sex in sexual reproduction to form a zygote
What is a chromosome?
A thread like structure of nucleic acid and protein found in the nucleus carrying genetic information in the form of genes
What is a gene?
A distinct sequence of nucleotides forming part of a chromosome
What is an allele?
Alternative forms of a gene that arise by mutation and are found at the same place on a chromosome
What is a dominant allele?
It always shows even if the individual has one copy of the allele
What is a recessive allele is?
Only shows if the individual has two copies of the recessive allele
What does homozygous mean?
When an individual has two of the same allele
What does heterozygous mean?
When the individual has one each of two different alleles
What is a genotype?
Demonstrate the alleles present for particular characteristic
What is a phenotype?
The physical appearance resulting from the inherited information
Give examples of characteristics controlled by a single gene
- Fur colour in mice
- red – green colour blindness
How did the present alleles operate?
At a molecular level to develop characteristics that can be expressed as a phenotype
What are most characteristics a result of?
Multiple genes interacting rather than a single gene
What are inherited disorders caused by?
The inheritance of certain alleles
Describe polydactyly
Having extra fingers or toes is caused by a dominant allele
Describe cystic fibrosis
A disorder of cell membranes caused by a recessive allele
Give reasons against embryonic screening
- Implies that people with genetic problems are undesirable
- it may come to a point where everyone wants to screen the embryo so they can pick the most desirable one
- expensive
Give reasons for embryonic screening
- help to stop people suffering
- treating disorders costs a lot of money
- there are laws to stop it from going too far
How many pairs of chromosomes ordinary human body cells contain?
23 pairs
What are the chromosomes for female?
XX
What are the chromosomes for a male?
XY
What is variation?
Differences in the characteristics of individuals in a population
What is variation caused by?
- Differences in inherited genes (genetic causes)
- different conditions in which they have developed (environmental causes)
- differences in a combination of genes and the environment
How varied are a population of species generally?
Extensive genetic variation
What causes variation?
Mutations
What is a mutation?
Changes to the sequence of bases in DNA
What does variation cause?
- Most have no effect on the phenotype
- some influence it
- very few determine the phenotype (create a new one)
What happens if a phenotype created from a mutation is suited to environmental change?
It can lead to a relatively rapid change in the species
What is evolution?
A change in the inherited characteristics of a population over time through process of natural selection which may result in the formation of a new species
What does the theory of evolution by natural selection state?
All species of living things have evolved from simple life forms that first developed more than 3 billion years ago
What happens if two populations of one species becomes so different in phenotype?
They can no longer interbreed to produce fertile offspring so they have formed two new species
What is selective breeding?
The process by which humans breed plants and animals for particular genetic characteristics
How long have humans been doing selective breeding?
For thousands of years since they first bred food crops from wild plants and domesticated animals
What does selective breeding involve?
Choosing parents with the desired characteristic from a mixed population and breeding them to form offspring with the desired characteristics
What happens in selective breeding once the offspring have been made?
From the offspring those with the desired characteristics are bred together, this continues over many generations until all the offspring show the desired characteristic
What are the commonly chosen characteristics for selective breeding?
- Disease resistant plants
- animals which produce more milk or meat
- domesticated and gentle dogs
- large or unusual flowers
What is the negative side of selective breeding?
It can lead to inbreeding
What is inbreeding?
Where some breeds are particularly prone to disease or inherited effects
How does inbreeding occur?
Reduction of the gene pool
What does reduction of the gene pool lead to?
Less chance of any resistant alleles being present in the population
What is genetic engineering?
Modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic
How have plant crops been genetically engineered?
To be resistant to diseases or to produce bigger better fruits
How have bacterial cells been genetically engineered?
To produce useful substances such as human insulin to treat diabetes
What happens in genetic engineering?
Genes from the chromosomes of humans and other organisms can be ‘cut out‘ and transferred to cells of other organisms
What are genetically modified crops?
They have had their genes modified
Give an example of a GM crop?
Ones that are resistant to insect attack or herbicides
What can GM crops generally show?
Increased yields
What are the concerns about GM crops for wildlife?
The affects on populations of wild flowers and insects
What are the concerns about GM crops for humans?
The effects of eating GM crops on human health have not been fully explored
What is gene therapy?
Modern medical research is exploring the possibility of genetic modification to overcome some inherited disorders
Describe the process of genetic engineering to get the required gene
Enzymes are used to isolate the required gene which is then inserted into a vector which is usually a bacterial plasmid or virus
Describe the process of genetic engineering to insert the gene
The vector is used to insert the gene into the required cells
Describe the process of genetic engineering for the development of the gene
The genes are transferred to the cells of animals, plants or microorganisms at an early stage in their development so they develop the desired characteristics
What is tissue culture?
Using small groups of cells to form part of a plant to grow identical new plants
Why is tissue culture important?
It is important for preserving rare plant species or commercially in nurseries
What are cuttings?
Simple method used by gardeners to produce many identical new plants from a parent plant
What are embryo transplants?
Splitting apart cells from a developing animal embryo before they become specialised, then transplanting the identical embryos into host mothers to grow the cloned animals
Describe stage one adult cell cloning?
The nucleus is removed from the unfertilised egg cell
Describe stage two of adult cell cloning?
The nucleus from an adult body cell (such as a skin cell) is inserted into the egg cell
Describe stage three of adult cell cloning
Electric shock stimulates the egg to divide to form an embryo
Describe stage four of adult cell cloning
These embryo cells contain the same genetic information as the adult skin cells
Describe stage five of adult cell cloning
When the embryo has developed into a ball of cells, it is inserted into the womb of an adult female to continue its development
Who was Gregor Mendel?
An Austrian monk who noted how characteristics in plants were passed on from one of generation to the next
What were the three conclusions that Mendel reached from his genetic experiments with pea plants?
- Characteristics implants are determined by hereditary units
- hereditary units are passed on to offspring unchanged and can be dominant or recessive
What is the history of understanding the gene pool in The late 1800s?
scientists became familiar with chromosomes and how they behaved during cell division
What is the history of understanding the gene pool in the early 20th century?
There were similarities in the way that chromosomes and hereditary units acted
It was proposed that the units were found on chromosomes which we now know as genes
What is the history of understanding the gene pool in 1953?
The structure of the DNA was determined allowing scientists to find out exactly how genes worked
Who proposed the theory of evolution by natural selection?
Charles Darwin
How did Charles Darwin prove the theory of Evolution by natural selection?
A result of observations from his trip and years of experimentation linked to developing knowledge of geology and fossils
What was Darwin’s conclusion about individual organisms?
Individual organisms within a particular species show a wide range of variation for characteristic
What was Darwin’s conclusion about individuals in an environment?
Individuals with characteristics most suited to the environment and more likely to survive to breed successfully
What was Darwin’s conclusion about survival of the fittest?
The characteristics that have unable these individuals to survive are then passed on to the next generation
Where did Darwin put his evidence for his findings?
In 1859 he published his ideas in his book ‘On the origin of species‘
At first why was there controversy surrounding Darwin’s revolutionary new ideas?
- It went against religious beliefs
- he couldn’t fully explain it as there was not enough evidence
What were Lamarck’s theories about evolution?
Based mainly on the idea of the changes that occur in an organisms life time can be inherited
Give an example to prove Lamarck’s theory?
Because a giraffe needed to reach the leaves on the top of the trees its neck grew longer, The offspring of this giraffe would then be born with a longer neck
What did Wallace propose about evolution?
The theory of evolution by natural selection and published joint writings with Darwin in 1858 prompting Darwin to publish his own the following year
What is Wallace best known for?
- He worked worldwide getting evidence for evolutionary theory
- Warning colouration in animals
- Theory of speciation
What has led to our current understanding of the theory of speciation?
Wallace did much pioneering work and more evidence overtime
What is isolation?
Populations of species are separated
What causes isolation?
A physical barrier that geographically isolate some individuals from the main population
Why do populations develop different characteristics as a cause of a barrier?
Conditions on either side of the barrier will be slightly different so different characteristics will be more common in each population because natural selection operates differently
What is stage one of speciation?
A physical barrier separates the two populations of the same species
What is stage two of speciation?
The population adapts to its new environment and shows genetic variation because they have a wide range of alleles
What is stage three of speciation?
Individuals with characteristics that make them better adapted to their environment have a better chance of survival and are more likely to breed successfully
What is stage four of speciation?
The alleles that control the beneficial characteristics are more likely to be passed on to the next generation so the populations adapt to the new environment
What is stage five speciation?
The two populations become so wildly different that they won’t be able to breed with one another and therefor have become separate species
Give examples of evidence for Darwin‘s theory?
- Fossil record
- knowledge of resistant bacteria
What are fossils?
The remains of organisms from millions of years ago which are found in rocks
What are the three ways a fossil can be formed?
- Gradual replacement by minerals
- from casts and impressions
- from preservation in places where no decay happens
How can a fossil be formed by gradual replacement by minerals?
Elements of an animal which don’t decay are eventually replaced by minerals forming rock like substances that are shaped like the original element
The surrounding sediments also trying to rock that the fossils stays distinct
How can fossils be made from casts and impressions?
When an organism is buried in a softer material like clay it later hardens around it and the organism decays, leaving a cast of itself
How can a fossil be made from preservation in places where no decay happens?
- In Amber and tar pits there is no oxygen or moisture so decay microbes can’t survive
- in glaciers it’s too cold for the decay microbes to work
- Pete Boggs are too acidic for decay microbes
Why can scientists not be certain about how life began on Earth?
- Many early life forms were softbodied so they left no traces behind
- Many traces have been destroyed by geological activity
What can we learn from fossils?
How much or how little different organisms have changed as life developed on Earth
When does extinction occur?
When are no remaining individuals of the species still alive
What factors cause extinction?
- The environment changes too quickly
- A new predator kills them all
- New disease kills them all
- they can’t compete with another species food
- A catastrophic event happens that kills them all
Why can bacteria evolve rapidly?
They reproduce at a faster rate
How are new strains of bacteria made?
Mutations of bacterial pathogens
Why are some strains of bacteria not killed by antibiotic?
They might be resistant to antibiotics
What happens when antibiotic resistant strains of bacteria survive?
They reproduce so the population of resistant strain increases, it will then spread because people are not immune to it and there is no effective treatment
Give an example of a resistant strains of bacteria?
MRSA
What can be done to reduce the rate of development of antibiotic resistant strains of bacteria?
- Don’t over prescribed antibiotics
- complete the course of antibiotics so none survive to mutate
- The agricultural use of antibiotics should be restricted
What are the problems with the development of new antibiotics?
It is costly and slow so on likely to keep up with the emergence of new resistant strains
How are living things traditionally classified?
Into groups depending on their structure and characteristics in a system developed by Carl Linnaeus
How did Linnaeus classify living things?
Kingdom, phylum, class, order, family, genius and species
How are organisms named?
By the binomial system for genius and species
What happened to classification due to improvements in microscopes?
Evidence of internal structures became more developed and the understanding of biochemical processes progressed
What did the new evidence due to improvements in microscopes lead to?
New models of classification were proposed
What happened due to evidence available from chemical analysis?
There is now a 3 domain system developed by Carl Woese
How are organisms divided in the three domain system?
- archaea (primitive bacteria usually living in extreme environments)
- bacteria (true bacteria)
- eukaryota (includes protists, fungi, plants and animals)
What are evolutionary trees?
A method used by scientists to show how they believe organisms are related
How do evolutionary trees work?
They use current classification data for living organisms and fossil data for extinct organisms
