inheritance, variation, and evolution Flashcards
what is sexual reproduction
a type of reproduction
involves the production of gametes by meiosis
a gamete from each parent fuses the form a zygote
genetic information from each gamete is mixed so the resulting zygote is unique
what are gametes
sex cells, sperm cells and egg cells in animals, pollen and egg cells in flowering plants
haploid - half the no. of chromosomes
what is meiosis
form of cell division involved in the formation of gametes in reproductive organs
chromosome number is halved
involves two division
what must occur to 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 cells
chromosome number is halved
what happens during the 2nd stage of meiosis
chromosome line up along the cell equator
the chromatids are separated and move to opposite poles of the cell
four unique haploid gametes are produced
why is meisosis important for sexual reproduction
increases genetic variation
ensures that the zygote formed at fertilisation is diploid
describe fertilisation and its resulting outcome
gametes join together to restore the normal number pf chromosomes and the new cell then divides by mitosis
as the embryo develops, cells differentiate
what is the advantage of sexual reproduction
creates a genetic variation in offspring increasing the probability of a species adapting to and surviving
environmental changes
natural selection can be speeded up by humans in selective breeding to increase food production
disadvantages of sexual reproduction
to parent are required. this makes reproduction difficult in endangered populations or in species which exhibit solitary lifestyle
more time and energy is required so offspring are produced in fewer no.
what is asexual reproduction
type of reproduction
involves mitosis only
produces genetically identical offspring, also known as daughter cells
advantage of asexual reproduction
only one parent is required
lots of offpring can be produced at one time, enabling rapid colonisation of an area and reducing competition from other species
requires less energy and time as they do not need a mate
disadvantage of asexual reproduction
no genetic variation reducing probability of a species being able to adapt to environmental changes
describe the cicrumstances in which fungi reproduce sexually and asexually
asexual reproduction by spores
sexual reproduction to give variation
describe the circumstances in which plants reproduce sexually and asexually
sexual reproduction to produce seeds
asexual reproduction by runners or bulb division
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
the entire genetic material of an organism
why is understanding the human genome important
important for developing medicine in the future
- searching for genes linking to different diseases
- understanding and treating inherited disorders
- tracing human migration patterns from the past
what is a chromosome
a long, coiled molecule of DNA that carries genetic information in the form of genes
how many chromosomes do human body cells have
46 chromosomes
how many chromosomes do human gametes have
23 chromosomes
define gene
a small section of DNA that codes for a specific sequence of amino acids which undergo polymerisation to form a protein
what are the monomers of DNA
nucleotides
what are DNA nucleotides made up off
- common sugar
- phosphate group
- one of 4 bases: A,T,C,G
name the full Ames of the 4 bases found in nucleotides
adenine
thymine
cytosine
guanine
describe how nucleotides interact to form a molecule of DNA
sugar and phosphate molecules join to form a sugar-phosphate backbone in each DNA strand
base connected to each sugar
complementary base pairs joined by weak hydrogen bonds
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 acid
the order of amino acids determines the structure and function of protein being formed
why is the folding of amino acids important in proteins such as enzymes
the folding of amino acids determines the shape of the active site which must be highly specific to the shape of its substrate
what is protein synthesis
the formation of a protein from a gene
what are the 2 stages of protein synthesis
transcription
translation
what does transcription involve
the formation of mRNA from a DNA template
explain transcription
- DNA double helix unwinds
- RNA polymerase binds to a specific base sequence of non-coding DNA in front of a gene and moves along the DNA stand
- RNA polymerase joins free RNA nucleotides to complementary bases on the coding of DNA strand
- 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
explain translation
- mRNA attaches to a ribosome
- ribosome reads the mRNA bases in triplets. each triplet codes for one amino acid which is brought to the ribosome by a tRNA molecule
- a polypeptide chain is formed form the sequence of amino acids which join together
what is mutation
a random change in the base sequence of DNA which results in mostly no change to the protein coded for, or genetic variants of the protein
mutations occur continuously
describe the effect of a gene mutation in coding DNA
if a mutation changes the amino acid sequence, protein structure and function may change
if a mutation does not change amino acid sequence, there is no effect on protein structure or function
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 resulting phenotype
what new 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 2 copies are needed for it to be expressed
what is meant an organism is homozygous
when a organism has 2 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 a genotype
the genes present for a trait
what is the phenotype
the visible characteristic
how are dominant alleles represent in a Punnett square
the are represented using uppercase letter
how are recessive alleles represented in a Punnett square
they use the lowercase version of the same letter as the dominant allele
what is the problem with a single gene crosses
most characteristics are controlled by multiple alleles rathe than just one
what is an inherited disorder
a disorder cause by the inheritance of certain alleles
give 2 examples of inherited disorders
- polydactyly - caused by a dominant allele
- cystic fibrosis - causes by recessive allele
how are embryos screened for inherited disorders
during IVF: one cell is removed and tested for disorder causing alleles. if the cell doesn’t have any indicator alleles then the originating embryo is implanted into the uterus
what are ethical issues concerning embryo screening
- I could lead to beliefs in society that being disabled or having a disorder is less human or associated with inferiority
- the destruction of embryos with inherited disorders is seen by some as murder as these would go on to become human beings
- it could be viewed as part as the concept of designer babies as it may be for the parents convince
what are economical issues concerning embryo screening
- costs of hospital treatment and medication will need to be considered if it known that a child will have an inherited disorder and finical support explored if necessary
what are social issues concerning embryo screening
- social care for children with inherited disorders may need to be considered if parents are unable to provide care
- if an embryo is found to have an inherited disorder and is terminated, this can prevent a child and its parents from potential suffering in the future do to the disorder
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 ethical issues concerning gene therapy
- some people believe that it is going against god or “playing god”
- the introduced genes could enter sex cells and be passed onto future generations
what are sex chromosomes
a pair of chromosomes that determine sex
- males have an x and Y chromosome
- females have 2 X chromosomes
why does the inheritance of a Y chromosome mean that an embryo develops into a male
testes development in an embryo is stimulated by a gene present on the Y chromosome
what is a sex-linked characteristic
a characteristic that is coded for by an alley found on a sex chromosome
what are the majority of genes found on the X chromosome rather than the Y chromosome
the X chromosome is bigger than the Y chromosome so more genes are carried on it
what is variation
differences in the characteristics of individuals in a population is called variation
what are the 2 causes of variation within a species
genetics
environment
a mixture of both the above
what is genetic variation
- variations in the genotypes of organisms of the same species due to the presence of different alleles
- creates differences in phenotypes
what creates genetic variation in a species
spontaneous mutations
sexual reproduction
what is mutation
a random change to the base sequence in DNA which results in genetic variants
they occur continuously
3 types of gene mutation
insertion
deletion
substitution
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 2 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 them to produce offspring with similar phenotypes
give examples of characteristics selected for in selective breeding
disease resistance in crops
higher milk or meat production in animals
gentle nature in domestic dogs
large flowers
advantage of selective breeding
- crops produce higher yield of grain
- cows produce a greater supply of milk
- plants produce larger fruit
- domesticated animals
other than agriculture, where else is selective breeding useful
in medical research
sports (horse riding)
disadvantage of selective breeding
- reduction in the gene pool
- inbreeding results in genetic disorders
- development of other physical problems
- potential to unknowingly select harmful recessive alleles
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
examples of uses for genetically modified plants
disease resistance
produce larger fruits
what is the use for genetically modified bacteria cells
to produce human insulin to treat diabetes mellitus
benefits of genetic engineering
- increased crop yields for growing population
- useful in medicine
- GM crops produce scarce resources
risks of genetic engineering
- long term effects of consumption of GM crops unknown
- negative environmental impacts
- late-onset health problems
- genetically modified seeds are expensive
what is the name for crops that have had their genes modified
genetically modified crops
how is genetically 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 have now secreted the toxin which kills any insect that feed on it
what are the benifits of Bt crops
- increased crop yields
- lessens the need for artificial insecticides
- Bt toxins is specific to certain insect larvae so it is not harmful to other organisms that ingest it
what are the risks of Bt crops
- long term effects of consumption
- insect larvae may become resistance
- killing insect larvae reduces biodiversity
describe the process of genetic engineering
- DNA is cut at specific base sequences by restriction enzymes to create sticky ends
- vector DNA cut using the same restriction enzymes to create complementary sticky ends
- legase enzymes join the sticky ends of the DNA and vector DNA forming recombination DNA
- recombination DNA mixed with and taken up by target cells
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
describe how plants are grown using tissue culture
- select a plant that shows desired characteristics
- cut multiple small sample pieces from meristem tissue
- grow in a Petri dish containing growth medium
- transfer to compost for further growth
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
advantages of growing plants by tissue culture
- fast and simple process
- requires little space
- enables the growth of many plant clones with the same characteristics
- useful in the preservation of endangered plant species
disadvantages of growing plants by tissue culture
- reduction in the gene pool
- plant clones often have low survival rates
- could unknowingly increase the presence of harmful recessive alleles
describe the plant cutting 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
process of plant cuttings method of plant cloning
- a branch is cut off from the parent plant
- the lower leaves of the branch are removed and the stem is planted
- plant hormones are used to encourage new root development
- a plastic bag is used to cover the new plant to keep it warm and moist
- new roots and a new plants is formed after a few weeks
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
describe how adult cell cloning is performed
- nucleus is removed from an unfertilised egg cell
- the nucleus from an adult body cell, is inserted into the egg cell
- the electric shock stimulates the nucleated egg cell to divide and it forms an embryo
- the embryo cells contain the same genetic information as the adult body cell
- when the embryo is a ball of cells, it is inserted into the uterus of an adult female to continue developing
outline the theory of evolution by natural selection
individuals of a specific show a wide range of variation for a characteristic
those with the characteristics 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
what was Darwins theory of evolution not accepted initially
- most people believed in creationism
- insufficient evidence to prove the theory
- the mechanism of variation and the inheritance was not known at the time
what was jean-baptists lamarcks theory of inheritance
that changes during the lifetime of an organisms can be inherited
what is specification
the formation of a new species, when 2 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
outline the process of specification through geographic isolation
- two populations of the same species are separated geographically
- geographically isolating prevents interbreeding and mixing of genes between the populations
- due to different selective pressures, different mutations occur producing different phenotypes in each population
- over time, the 2 populations ma evolve so that they are not able to interbreed
why is genetic variation important in specification
genetic variation produces phenotypic variation, some of which are better suited to the environment and are selected for
how did Mendel study inheritance
through carry breeding experiments on plants and analysing the ratio of characteristics in offspring
why was mendels work not regnosised until after his death
he could not explain the mechanism of inheritance, as chromosomes were only discord after his death
it was not communication well to other scientists and was not published in a reputable specific journal
state 2 kinds of evidence used to show evolution
fossils
antibiotic resistance in bacteria
how are fossils formed
plants of organism 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 rocks
why are there few traces of early life forms left behind
mostly soft-dodied
how do fossils act as evidence for evolution
scientists can identity 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 occurs
what is extinction
where there are no individuals of a species still alive
state the factors that may lead to extinctions
- new disease
- predation
- competition
- changes to the environment
- catastrophic events
what enables bacteria to evolve quickly
the fast rate of their reproduction
outline the process of antibiotic resistance bacteria evolving
- mutations occur in bacteria producing genetic variation
- certain strains are resistance to antibiotics and are not killed when the antibiotic is applied
- resistance strains survive and reproduce
- over time, the population of the resistant strain increase
why are resistance strains of bacteria becoming dangerous
people no immunity to them and there is no effective treatment
state an example of a resistance strain of bacteria
MRSA
what can be done to reduce the rate of development of antibiotic resistance bacteria
- refrain from inappropriately prescribing antibiotics
- complete the prescribed course of antibiotics
- resist agricultural uses of antibiotics
why is it difficult to keep up with emerging resistant strains
developing antibiotics have a high cost and take a long time to develop
what are the classes of organism as determined by carl Linnaeus
kingdom
phylum
class
order
family
genus
species
which features are living creatures traditionally classified by
structure and characteristics
what is the binomial system of naming organisms
genus name followed by species name
why are new classification models proposed
developments in the microscopy allowed better examination of internal structures
improvement in understanding of biochemical processes
state the 3 domains
archaea
eukaryotic
Bacteria
which organisms belong in the domain archaea
bacteria
usually living in the extreme environments
which organisms belong in he domain bacteria
bacteria
which kingdoms belong in the domain eukarya
plants
animals
fungi
protists
how are evolutionary trees created
by examining the DNA of different species and analysing how similar the sequences are
