b6 Flashcards
what is sexual reproduction?
a type of reproduction that involves the production of gametes by meiosis
a gamete from each parent fuses to form a zygote
genetic information from each gamete is mixed so the resulting zygote is unique
what are gametes?
sex cells, they are haploids
what is a haploid?
a cell with half the number of chromosomes
what are the gametes in humans?
males: sperm cells
females: eggs cells
what are the gametes in plants?
pollen and egg cells
what is meiosis?
cell division that is involved in the formation of gametes in reproductive organs
amount of chromosomes are halved
involves 2 divisions
why is meiosis important for sexual reproduction?
increases genetic variation
ensures that the zygote formed at the fertilisation is a diploid
what is asexual reproduction?
a type of reproduction that only involves mitosis
produces genetically identical offspring known as daughter cells
what does asexual reproduction lead to?
genetically identical offspring (clones)
what are the advantages of sexual reproduction?
genetic variation in offspring
increased probability in surviving environmental changes
resistant to disease
increase rate of natural selection due to selective breeding
what are the disadvantages of sexual reproduction
requires more time and energy
difficult for isolated organisms
what are the advantages of asexual reproduction?
use less energy
is quicker
only needs 1 parent
what is the disadvantage of asexual reproduction?
no genetic variation
susceptible to disease
what organisms reproduce using both asexual and sexual reproduction?
malarial parasites
fungi (mushrooms)
strawberry plants/daffodils
where do malarial protists reproduce asexually?
in human host because it is quicker
where do malarial protists reproduce sexually?
in the mosquito
when do fungi reproduce asexually/sexually?
asexual reproduction by spores
sexual reproduction to give variation
when do plants like strawberries and daffodils reproduce asexually?
when there is less minerals available they produce runners that turn into new plants
when do strawberries/daffodils reproduce sexually?
when circumstances are usual, they produce seeds through sexual reproduction
what happens during the first stage of meiosis?
chromosome pair line up along the cell equator
the pair of chromosomes are separated and move to opposite poles of the cell
number of chromosomes halved
what happens in the second stage of meiosis?
chromosomes line up along the cell equator
chromosomes are separated and move to opposite poles of the cell
four unique haploid gametes are produced
how is variation formed during meiosis?
the chromosomes are randomly split into the gametes: independent assortment
what happens at fertilisation?
gametes join and restore the normal number of chromosomes, the new cell divides by mitosis, the embryo develops and cells differentiate
what is DNA?
a double stranded polymer of nucleotide and form a double helix
where is dna contained?
in structures called chromosomes
what is a chromosome?
a long coiled molecule of dna that carries genetic information in the form of genes
what is a gene?
a small section if dna that codes for a specific sequence of amino acids which make a specific protein
what is a genome?
the entire genetic material of an organism
what are the monomers of dna?
nucleotides
what are nucleotides made up of?
pentose sugar
phosphate group
one of four bases: A,T,C,G
how many bases is needed for an amino acid?
a sequence of three bases is the code for a particular amino acid
how does the order of the bases coordinate with the production of proteins?
the order of bases controls the order in which amino acids are assembled to produce a particular protein
what is protein synthesis?
the formation of a protein from a gene
what are the two stages of protein synthesis?
transcription
translocation
what does transcription involve?
formation of mRNA from a DNA template
what does translation involve?
a ribosome joins amino acids in specific order dictated by mRNA to form a protein
what are the stages of protein synthesis?
- dna unwinds so the bases are now exposed
- gene is copied into mRNA
- mRNA diffuses out of the nucleus into the cytoplasm
- mRNA passes through ribosome
- ribosome assembles amino acids into a particular order to make a protein molecule
what happens when the protein chain is complete?
they fold to form a unique shape
why do proteins have a unique shape?
so they are able to do their job as enzymes, hormones or forming structures in the body
what are enzymes and hormones specific to?
enzymes: active site
hormones: receptors
which bases are complementary to each other?
C is always linked to G
T is always linked to A
what is mutation?
a random change in the base sequence of DNA
what is the effect of a gene mutation in coding DNA?
most do not alter the function and if so they only alter it slightly
few mutations code for an altered protein with a different shape
what happens to an enzyme if the shape of a protein changes?
enzyme may no longer fit the substrate binding site
what are the types of mutations in protein synthesis?
insertion
deletion
substitution
what is insertion?
an extra base is inserted in a gene
what is deletion?
one base in the gene is removed
what is substition?
one base is swapped with another one
how can the way genes are expressed be changed?
non coding parts of DNA can switch genes on and off so variations in these areas of DNA can affect how genes are expressed
what is non coding DNA?
DNA which does not code for a protein but instead controls gene expression
what are alleles?
different version 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 by homozygous?
an organism that has two copies of the same allele: both dominant or both recessive
what is meant by heterozygous?
an organism that has two different alleles: one dominant and one recessive
what is a genotype?
the gene present for a trait
what is a phenotype?
visible characteristic
what is an inherited disorder?
a disorder caused by the inheritance of certain alleles
what are the 2 examples of inherited disorders?
polydactyly and cystic fibrosis
what is polydactyly?
having an extra finger or thumb, it is caused by a dominant allele
what is cystic fibrosis?
when too much mucus is produced in lungs or pancreas: mucus in lungs blocks airway snd stop oxygen entering blood
caused by a recessive allele
how are embryos screened for inherited disorders?
a cell is removed and tested for disorder causing allele, if no allele the embryo is implanted inti the uterus
what are ethical issues of embryo screening?
beliefs in society that being disabled is seen as less human
destruction of embryos
designer babies: parents convenience
what are the economic issues with embryo screening?
costs of hospital treatment and medication
what are sex chromosomes?
a pair of chromosomes that determine sex
what is the pair of sex chromosomes in both male and female?
males have X and Y chromosomes
females have 2 X chromosomes
what is the chance that the child will be male?
50%
how is the y chromosome different to the x chromosome?
y chromosome is shorter and contains less genes than x chromosomes do
what is a karotype?
shows all chromosomes in an organism
what is the definition of variation?
difference between different/same species
what causes variation within a species?
genetics
environment
both
what are the genetic differences within a species?
eye colour
hair colour
ear lobes
ability to roll your tongue
what are the environmental differences within a species?
piercings
tattoos
hair dye
accents
what are the differences within a species that are both genetic and environmental?
height
weight
what is genetic variation?
variation in the genotypes of organisms of the same species due to the presence of different alleles
what creates genetic variation in a species?
spontaneous mutations
sexual reproduction
how does most mutation affect an organisms phenotype?
neutral mutation has no effect on phenotype as it doesnt change the sequence of amino acids
what does some mutation cause?
minor changes in an organisms phenotype e.g. eye colour
what happens very rarely with mutations?
it can completely change the sequence of amino acids and can result in a non functional protein so may have severe changes to phenotype
what is evolution?
a change in the inherited characteristics of a population over time
why does evolution occur?
due to natural selection which may result in the formation of a new species
what is the theory of natural selection?
all species of living things have evolved from the simple life forms that first developed more than three billion years ago
how does natural selection occur?
variation in population due to mutation
one allele provides an advantage to an organism
organism is likely to survive and reproduce
able to pass on the allele to it offspring
this will lead to a change in population over time
how do you know when two populations of one species become different?
they have a big difference in phenotype so cannot interbreed to produce fertile offspring
what is selective breeding?
any population has variation
a group of organisms with a selected characteristic are bred together
select offspring with desired trait and breed together
repeated for multiple generations
what are the examples of characteristics selected for selective breeding?
disease resistance in crops
higher milk/meat production in animals
gentle nature in domestic dogs
large/unusual flowers
what are the main advantages of selective breeding?
make profits
change in characteristic of a population
what are the disadvantages of selective breeding?
inbreeding
genetic disease
less variation
long process
smaller gene pool
what is genetic engineering?
a process that involves modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic
what are examples of genetic engineering?
plants have been genetically engineered to be resistant to disease/to produce bigger fruits
bacteria cells have been genetically engineered to produce useful substances such as human insulin to treat diabetes
what is the process of genetic engineering?
- restriction enzyme cut DNA
- gene is placed into a plasmid
- plasmid is inserted into embryo of another organism
or - plasmid is inserted inti bacteria and the bacteria divides
what are the advantages of genetic engineering?
used in medical treatment
create crops that are more resistant to disease
crops are bigger/grow quicker
what are the disadvantages of genetic engineering?
long term affect not known
genes transfer across the environment: environmental impacts e.g. reduction in biodiversity
expensive products (GM crops)
what are the names for crops that have undergone genetic engineering?
genetically modified crops
what do genetically modified crops involve?
resistant to insect attack or to herbicides
how can plants be cloned?
taking plants cuttings
tissue culture
what is tissue culture?
using small groups if cells from a part of a plant to grow identical new plants
why is tissue culture important?
important for preserving rare plant species or commercially in nurseries
what is cuttings?
an older but simple method used by gardeners to produce identical new plants from a parent plant
what is the method of plant cuttings?
a branch is cut off from the parent plants
lower leaves of the branch are removed and the stem is planted
plant hormones are used to encourage new root development
plant is covered to keep warm and moist
new roots and plants is formed
what is embryo cell cloning?
splitting apart cells from a developing animal embryo before they become specialised, then transplanting the identical embryos into host mothers
how is the embryo made for embryo cell cloning?
sperm is removed from a selected organism with a particular characteristic and used to fertile an egg cell and produce an embryo
what is the result of embryo cell cloning?
offspring are identical to each other not identical go parents
what is adult cell cloning?
producing a clone identical to one of parents
how is adult cell cloning performed?
the nucleus is removed from an unfertilised egg cell
nucleus from an adult cell inserted into the egg cell
an electric shock stimulates the egg cell to divide by mitosis and form an embryo
embryo is inserted inti the womb of an adult female to continue its development
what is the theory of evolution by natural selection?
individuals of a species short a wide range of variation for a characteristic
those were the characteristic more similar to the environment will survive and breed most successfully
The characteristics that has enabled these individuals to survive or then pass on to the next generation
who came up with the theory of evolution?
Charles Darwin and he published his ideas in “on the origin of species”
why was the theory of evolution only gradually accepted?
The theory challenge is the idea that God made animals and plants
there was insufficient evidence at the time
The mechanism of inheritance and variation was not known until 50 years after the theory was published
what did Lamarck suggest?
traits that the parents had due to the environment were passed on to the offspring, but he had no knowledge of genes or the concept of genetic inheritance
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 and produce fertile offspring
what is the process of speciation through geographic isolation?
populations are geographically isolated
populations are living in different environments
genetic variation in each population better adapted organisms will survive and reproduce
they will pass on genes and alleles to offspring
Who was the scientist that wrote on paper about natural selection before Darwin?
Alfred Wallace
what will happen to the two populations that are geographically Isolated?
The population will no longer be able to interbreed and they will now be a different species to one another
what did Gregory Mendel do in the discovery of genetics?
He carried out breeding experiments on plant and analysed the ratio of characteristics in offspring
what did Mendel call the things that offspring were inheriting?
heredirity units
why was Mendel’s work night accepted by other scientists?
it was not a scientist
there was no evidence of gene or DNA
What discovery proved Mendel’s theories correct?
The discovery of chromosomes in the 20th century
chromosomes contain ions which Mendel would’ve called heredirity units
what evidence is used to show evolution?
fossils
antibiotic resistance in bacteria
how are fossils formed?
from parts of organisms that have not decayed because one or more of the conditions needed to decay absent
When parts of the organism are replaced by minerals as they dedicate
preserved traces of organisms such as footprints
how are organisms preserved?
they are trapped in tar or amber and there isn’t oxygen presents for decomposers
which part of organism’s decay?
The soft parts
What are bones replaced by?
minerals
why are early life forms hard to track by fossils?
they were soft bodies meaning that they left a few traces behind and what was left behind was destroyed by geological activity
how do fossils act as evidence for evolution?
Scientist can identify the ages of fossils and use them to show how organisms change overtime
what do branches and evolutionary trees indicate?
Where speciation has occurred
what is extinction?
Where there are no individuals of species still alive
what factors lead to extinction?
New disease/pathogens
New predators
Competition
Changes to the environment
Natural disasters e.g. ice age
what are the different types of fossils?
Skeleton
Shells
Footprints
Faeces
What enables bacteria to evolve quickly?
they reproduce and divide at a fast rate
what is the process of antibiotic resistance bacteria evolving?
mutations occur in bacteria producing genetic variation
certain strains are resistant to antibiotics and are not killed when antibiotic is applied
resistance strain survive reproduce
overtime the population of resistance strains increase
why are resistant strains of bacteria dangerous?
people have no immunity to them, and there is no effective treatment
what is an example of an antibiotic resistant bacteria?
MRSA
What can be done to reduce the rate of development of antibiotic resistant bacteria?
doctors refrain from inappropriately prescribing antibiotics
patients should complete the prescribed course of antibiotics so all bacteria is killed
restrict agricultural uses of antibiotics
why is it difficult to keep up with emerging resistance strains?
The development of new antibiotics is costly and slow
what are the causes of organisms determined by carl linnaeus?
Kingdom
phylum
class
order
family
genus
species
what features are organisms traditionally classified by?
structure and characteristics
what is the binomial system of naming organisms?
genus followed by species name
why were new classification models proposed?
Development in microscopy allowed better examination of internal structures
improvement in understanding of biochemical processes
what are the three domains?
archaea
eukarya
bacteria
what organisms belong in the archaea domain?
bacteria (primitive bacteria usually living in extreme environments)
what organisms belong in the bacteria domain?
true bacteria
what organisms belong in the eukarya domain?
plants
animals
fungi
protists
what are evolutionary trees?
a method used by scientists to show how they believe organisms are related
how are evolutionary trees created?
by examining the DNA of different species and analysing how similar the sequences are
