Biology Topic 6 - Inheritance, Variation And Evolution Flashcards
What is sexual reproduction?
-type of reproduction
-involves production of gametes by mitosis
-a gamete from each parent fuses to form a zygote
-genetic information from each gamete is mixed
What are gametes?
-Sex cells
-haploid(half the number of chromosomes)
What is meiosis?
-form of cell division involved in formation of gametes in reproductive organs
-chromosomes number is halved
-involves two divisions
What must occur prior to meiosis?
Interphase-copies of genetic information are made during this process
What happens during the first stage of meiosis?
-chromosome pairs line up along the cell equator
-the pair of chromosomes are separated and move to opposite poles of the cell
-chromosome number is halved
What happens during the second stage of meiosis?
-chromosomes line up along cell equator
-chromatids are separated and move to opposite poles of the cell
-four unique haploid gametes are produced
Why is meiosis important for sexual reproduction?
-it increases genetic variation
-it ensures that the zygote formed at fertilisation is diploid
What is the advantage of sexual reproduction?
-Creates genetic variation in offspring, increasing probability of a species adapting to and surviving environmental changes
-natural selection can be made quicker in selective breeding to increase food production
Describe the disadvantages of sexual reproduction?
-two parents are required. This makes reproduction difficult in endangered populations or in species which exhibit solitary lifestyles
-more time and energy is required so fewer offspring are produced
What is asexual reproduction?
-type of reproduction
-involves mitosis only
-produces genetically identical offspring known as daughter cells
Describe the advantages asexual reproduction
?
-only one parent is required
-lots of offspring can be produced in short period of time
-requires less energy and time as do not need a mate
What is the disadvantage of asexual reproduction?
No genetic variation reducing the probability of a species being able to adapt to environmental change
What is DNA?
-a double stranded polymer of nucleotides, wound to form a double helix
-the genetic material of the cell found in its nucleus
Define genome?
Entire genetic material of an organism
What is a chromosome?
A long, coiled molecules of DNA that carries genetic information in the form of genes
How many chromosomes do human body cells have?
46 chromosomes (23 pairs)
Define gene?
A small section of DNA that codes for a specific sequence of amino acids which undergo polymerisation to form a protein
Explain how a gene codes for a protein?
- a sequence of three bases in a gene forms a triplet
-each triplet codes for an amino acids
-order of amino acids determines the structure and function of protein formed
What is protein synthesis?
Formation of a protein from a gene
What are the two stages of protein synthesis?
1-transcription
2-translation
What does transcription involve?
The formation of mRNA from a DNA template
Outline transcription
1-DNA double helix unwinds
2-RNA polymerase binds to a specific base sequence of non-coding DNA in front of a gene and moves along the DNA strand
3-RNA polymerase joins free RNA nucleotides ton complementary bases on the coding DNA strand
4-mRNA formation complete. mRNA detaches and leaves the nucleus
What does translation involve?
A ribosome joins amino acids in a specific order dictated by mRNA to form a protein
What is mutation?
A random change in the base sequence of DNA which results mostly in no change to the protein coded for, or genetic variations of the protein
Mutations occur continuously
What is non-coding DNA?
DNA which does not code for a protein but instead controls gene expression
Describe the effect of a gene mutation in non-coding DNA
Gene expression may be altered, affecting protein production and the resulting phenotype
What are alleles?
Different versions of the same gene
What is a dominant allele?
A version of a gene where only one copy is needed for it to be expressed
What is a recessive allele?
A version of a gene where two copies are needed for it to be expressed
What is meant when an organism is homozygous?
When an organism has two copies of the same allele
What is meant when an organism is heterozygous?
When an organism has two different versions of the same gene
What is the genotype?
The genes present for a trait
What is the phenotype?
The visible characteristics
What is three problem with single gene crosses?
Most characteristics are controlled by multiple alleles rather than just one
What is an inherited disorder?
A disorder caused by the inheritance of certain alleles
How are embryos screened for inherited disorders?
During IVF, one cell is removed and tested for disorder-causing alleles
What is gene therapy?
The insertion of a normal allele into the cells of a person with an inherited disorder to functionally replace the faulty allele
What are sex chromosomes?
A pair of chromosomes that determine sex:
-males=X + Y
-females = two X chromosomes
What is a sex-linked characteristic?
A characteristic that is coded for by an allele found on a sex chromosome
What is variation?
Differences in the characteristics of individuals in a population is called variation
What are the two causes of variation within a species?
-genetics
-environment
-a mixture of both
What is genetic variation?
-variation in the genotypes of organisms of the same species due to the prescience of different alleles
-creates differences in phenotypes
What creates genetic variation in a species?
-spontaneous mutations
-sexual reproduction
What is a mutation?
A random change to the base sequence in DNA which results in genetic variants
They occur continuously
What is the consequence of a new phenotype caused by a mutation being suited to an environmental change?
There will be a rapid change in the species
What is evolution?
-A gradual change in the inherited traits within a population over time
-occurs due to natural selection which may result in the formation of a new species
How do two populations become different species?
When their phenotypes become different to the extent that they can no longer interbreed to produce fertile offspring
What is selective breeding?
The process by which humans artificially select organisms with desirable characteristics and breed to produce offspring with similar phenotypes
What is the main advantage of selective breeding?
Creates organisms with desirable features
Other than in agriculture, where else is selective breeding useful?
-in medical research
-in sports e.g. horse racing
What is genetic engineering?
-the modification of the genome of an organism by the insertion of a desired gene from another organism
-enables the formation of an organism with beneficial characteristics
What is a use for genetically modified bacteria cells?
To produce human insulin to treat diabetes mellitus
What is the name for crops that have their genes modified?
Genetically modified crops
How is genetic engineering used to protect crops against insects?
-the gene for toxin production in Bt can be isolated and inserted into the DNA of crops
-Bt crops now secrete the toxin which kills any insect larvae that feed on it
What is a vector?
A structure that delivers the desired gene into the recipient cell
How can plants be cloned?
-taking plant cuttings
-tissue culture
What is tissue culture?
Using small groups of cells from part of a plant to grow identical new plants
What must be ensured when preparing tissue cultures?
Ensure aseptic conditions to prevent contamination by microorganisms
What does the growth medium contain?
Nutrients and growth hormones
Describe the plant cuttings method of plant cloning
Older but simpler method than tissue culture
Gardeners use this method to produce many identical new plants from a parent plant
What does embryo transplanting involve?
-pre-specialised cells from a developing animal embryo are split apart
-the resulting separate but identical embryos are transplanted into host mothers
Outline the theory of evolution by natural selection?
-individuals of a species show a wide range of variation for a characteristic
-those with the characteristic most suited to the environment will survive breed most successfully
-the desirable characteristic that has enabled the individuals to survive are passed onto their offspring
Why was Darwin’s theory of evolution not accepted initially?
-most people believed in creationism
-insufficient evidence to prove the theory
-the mechanism of variation and inheritance was not known at the time
What was jean-baptistery lamarck’s theory of inheritance?
That changes during the lifetime of an organism can be inherited
What is speciation?
The formation of a new species, when two populations become so varied that they cannot interbreed to produce fertile offspring
What is the definition of a species?
A group of organisms with similar characteristics which are able to interbreed to produce fertile offspring
Why is genetic variation so important in speciation?
Genetic variation produces phenotypic variation, some of which are better suited to the environment and are selected
How did Mendel study inheritance?
Through carry breeding experiments on plant animals analysing the ratio of characteristics in offspring
Why was Mendel’s work not recognised until after his death?
-he could not explain the mechanism of inheritance, as chromosomes were only discovered after his death
State two kinds of evidence used to show evolution
-fossils
-casting
How are fossils formed?
-parts of organisms that have not decayed due to conditions needed for decay being absent
-parts of organisms that have been replaced by minerals as they decayed
-traces of organisms are preserved, covered in sediment and becoming rock
Why are there few traces of early life-forms left behind?
They are mostly soft-bodied
How do fossils act as evidence for evolution?
Scientists can identify the ages of the fossils and use them to show how organisms change over time
What do branches in evolutionary trees indicate?
Where speciation has occurred
What is extinctions?
Where there are no individuals of a species still alive
State the factors that may lead to extinction?
-new disease
-predation
-competition
-changes to the environment
-catastrophic events
State the factors that may lead to extinction?
-new disease
-predation
-competition
-changes to the environment
-catastrophic events
What enables bacteria to evolve quickly?
Fast rate of reproduction
Why are resistant strains of bacteria dangerous?
People have no immunity to them and there is no effective treatment
Why is it difficult to keep up with emerging resistance strains?
Developing antibiotics have a high cost and take a long time to develop
What features are living creatures traditionally classified by?
By their structure and characteristics
Why were new classification models proposed?
-developments in microscopy allowed better examination of internal structures
-improvement in understanding of biochemical processes
Which organisms belong in the domain archaea?
Bacteria, usually living in extreme environments
Which organisms belong in the domain bacteria?
Bacteria
How are evolutionary trees created?
By examining the DNA of different species and analysing how similar the sequences are
