science - DNA, mitosis, meiosis, inheritance, genes and chromosomes, cell cycles, evolution etc (term 3) Flashcards
if diagram is needed or if any questions relate to the cell cycle, please use diagrams written in notebook for help and remember to always do practise questions for the cycles or pedigrees!
what is DNA/deoxyribose nucleic acid?
a molecule that carries genetic information for the development, functioning, growth and reproduction of all organisms.
where is DNA found?
it is found inside of the nucleus of cells
what are the building blocks of DNA?
nucleotides
what parts is the sub-unit made up of?
phosphate( phosphate group), sugar (deoxyribose sugar) and a base (nitrogenous base)
how do the nitrogenous bases in DNA pair up?
adenine (A) pairs up with Thymine (T) and Cytosine (C) pairs up with Guanine (G)
describe the shape of DNA?
DNA has a double helix shape, resembling a twisted ladder. The two strands coil around each other, with the sugar-phosphate backbone forming the sides and paired nitrogenous bases as the steps
what are chromosomes made up of?
Each chromosome is made by DNA that is tightly coiled around proteins called histones.
what is a gene?
a section of DNA on a chromosomes that codes for specific trait
what is chromatin
a material that makes up a chromosome that consists of protein and DNA
how many pairs of chromosomes do humans have?
23 pairs - 46 chromosomes
what is the structure of a chromosome?
it starts off as a single strand (chromatid) and then its replicated into two strands called sister chromatids. Within these sisters, there is a centromere and a specific gene on each end.
what are homologous chromosomes?
chromosomes containing the same type of genetic information
what happens when a cell is ready to divide?
DNA forms into chromosomes in the nucleus, while at other times it remains in a less condensed form called chromatin.
what is a karyotype?
the general appearance of the complete set of chromosomes in the cells of species
what is the cell cycle?
a series of events that a cell goes through to grow and replicate its DNA and divide.
what are the two types of cells in the human body?
sex: sperm and ovum
somatic: all your body cells, except your sex cells (germ cells)
what is mitosis?
how a somatic cell divides and it is usually used for growth, repair and replacement of cells
what phase happens before mitosis occurs?
interphase: the cells grow and the DNA replicates (chromatin, nuclear membrane, centriole)
What are the phases of mitosis?
PMAT - prophase, metaphase, anaphase, and telophase (cytokinesis)
what happens in prophase?
chromosomes become more visible, nuclear membrane breaks down and mitotic spindle form from the centrioles
what happens in metaphase?
chromosomes line up in the middle of the cell and the spindle attaches to the centromere of the chromosomes.
what happens in anaphase?
sister chromatids are pulled to opposite sides of the cells.
what happens in telophase?
nuclear membrane forms around chromosomes and the cytoplasm splits the cell into two identical daughter cell, followed by cytokinesis
what is the final product of mitosis?
two identical daughter cells
what do spindle fibres do?
control the movement and separation of chromosomes during division
mitosis + meiosis table?
mitosis: occurs in body/somatic cells, has one division, it creates more body cells, it has 46 chromosomes in daughter cells, it makes two cells, and its function is to repair, grow and replace old cells.
meiosis: occurs in testes and ovaries (gonads), has two divisions, it creates sperm and ovum (gametes), it has 23 chromosomes in daughter cells, it makes four cells and its function is to produce sex cells for reproduction
what is meiosis?
a special process of nuclear division which results in the production of sperm and ova.
what does meiosis involve?
involves two rounds of division and results in four daughter cells (each daughter cell contains only half the original number of chromosomes - haploid)
what are the two stages?
meiosis 1: homologous chromosomes separate, creating two daughter nuclei.
meiosis 2: two daughter nuclei divide and sister chromatids are separated, creating four gametes.
what is a haploid cell? (n)
- contains 1 set of chromosomes
- found in gametes (23)
gametes: sperm and egg cells
what is a diploid cell? (2n)
- contains two sets of chromosomes
- found in somatic cells (46)
somatic: skin, lung cells, etc
what happens before meiosis occurs?
interphase: DNA replicates
what occurs in meiosis 1 (PMAT1)
prophase 1, metaphase 1, anaphase 1, and telophase 1 (cytokinesis)
what occurs in meiosis 2 (PMAT2)
prophase 2, metaphase 2, anaphase 2, and telophase 2 (cytokinesis)
describe meiosis 1:
prophase 1: homologous chromosomes pair up, nucleus membrane goes away and chromosomes condense and crossing over occurs.
metaphase 1: homologous chromosomes line up in the middle of the cell
anaphase 1: homologous chromosomes sperate and move to opposite sides of the cell
telophase 1: nuclear membrane reforms, followed by cytokinesis
describe meiosis 2:
prophase 2: chromosomes condense, nuclear membrane dissolves
metaphase 2: chromosomes line up in the middle
anaphase 2: sister chromatids separate
telophase 2: nuclear membrane forms, followed by cytokinesis which produces four non-identical daughter cells with 23 chromosomes
what is a person’s characteristic caused by?
inherited: a set of genes they inherit from their parents
acquired: the environment in which they develop into
what is a phenotype and a genotype?
phenotype: the observable characteristics of an organism
genotype: the set of genes an organism has
what is an Allele?
each different version of each gene
what is a homozygous chromosome and a heterozygous chromosome?
homozygous: when the allele for the characteristic is the same (BB or bb)
heterozygous: if the alleles for the characteristic are different (Bb)
what is a dominant and recessive allele?
dominant alleles and recessive alleles are always expressed in the cells phenotype but dominant alleles are represented by an uppercase letter and recessive alleles are represented by a lowercase letter
what is a useful way of organising inheritance charts in families?
pedigrees
what are some key things to know when looking at a pedigree?
- a square represents a male and a circle represents a female
- whether they are shaded or not shows if the individuals are affected by the trait or disease.
- identical twins have, for example two squares making a triangle while non-identical twins have a circle and a square in a triangle.
- if an individual is deceased, they get crossed out.
- draw in age order (oldest to youngest)
what is biodiversity?
the number and variety of genes and species in an ecosystem
what is species diversity?
the number of different species in an ecosystem
what is genetic diveristy?
the range of variation in the genes within a species
what is evolution?
the change in the characteristics of a species over a long period of time.
what is the idea behind evolution?
that every species originated from a common ancestor
what was Lamarck’s hypothesis?
- suggested that organisms adapt to their environment during their life time and claims that if adaption was beneficial then it would be passed onto offspring. (idea of passing traits was correct but only genetic traits)
what was Darwin’s theory?
- suggested idea of ‘survival of the fittest” or Natural Selection
- noticed that organisms were well suited to their environments as well as the well adapted organisms survive and pass on characteristics.
- organisms that aren’t well adapted will die and not pass on their characteristic.
how did Darwin come up with his theory?
He went on a voyage on the H.M.S Beagle for five years, and during those five years the voyage visited Galapagos Islands. Darwin noticed that although the different islands had similar creatures and plants, many seemed to have adapted to suit their local environments. Finches (a type of bird), for example, had different beaks on each island, suited to eating the particular seeds or insects found there
definition of species
a group of organisms that can successfully reproduce to form fertile offspring
what are the two ways in which variation is carried through generations?
genetic variation: mutations within genes that are passed through generations
environmental variation: acquired characteristics which are settled for in response to the environment.
what are mutations?
random and sudden change to the DNA of an individual; they can be beneficial, lethal or have no affect
what can a change in the genetic code in DNA lead to?
a change in the production of the protein that is coded for and produced by that section of DNA
why are beneficial mutations essential for evolution to occur?
they increase an organisms chance of surviving or reproducing so they’re likely to become common over time as well as lead to new versions of protein that help organisms adapt to change.
what is the genetic diversity within an individual?
mutations: changes in genetic material sexual reproduction (gamete combinations): random joining of sperm and ova at fertilisation
crossing over: exchanging parts of chromosome
independent assortment: random assortment of chromosomes; from homologous pairs into gametes
what is a gene pool?
consists of all the copies of all genes in that population
what is an allele frequency?
refers to how common an allele is in a population
what is genetic diversity in a population?
gene flow: immigration, emigration
random genetic drift: change occurs by chance
natural selection: some variations provide people with increase chance of survival - pass onto offspring, increasing favourable variation over time.
explain a gene flow:
if new individuals immigrate or emigrate of a region, they can increase or decrease the diversity in the local population by introducing alleles or removing them. Some mutations will be helpful while some may cause weakness
explain genetic drift:
mechanism of evolution in which allele frequencies of a population change over generations due to chance events. (stronger in small pops)
- may have major effects when a population is sharply reduced by size by a natural disaster (bottleneck effect) or when a small group splits off from main population to found a colony (founder effect)
what is bottleneck effect?
it’s an example of genetic drift that happens when the size of a population is severely reduced by natural disasters.
what is founder effect?
one that occurs when a small group of individuals break off from a large population to found a colony.
- if its isolated from original population, then they may not represent the full genetic diversity of the original population.
that is because the alleles in founding population may be present at different frequencies than in original or just may be missing all together.
why is variation important?
codes for an individuals phenotype which may better suit that organisms environment than others (increased chance of survival) - passing advantageous gene to offspring.
what are the four things that humans have done to impact genetic diversity?
artificial selection, artificial insemination, IVF, cloning
how does artificial selection occur?
when humans breed organisms that have desirable traits, increasing the likelihood of that trait being passed onto next generation however, it reduces biodiversity
how can artificial selection be done through?
in-breeding: within families, increase the likelihood of the common trait)
cross-breeding: combining two desirable traits
or unintentionally through hunting or through antibiotics/insecticides.
what is an adaption?
when a genetic variation increases the chance of survival in that ecosystem
what are the three types of adaption?
structural (change to body), behavioural ( change to behaviour), physiological (change to body function)
what is natural selection?
process of introducing a new selective pressure on a population. The selective pressure is a factor which influences survival e.g disease, predators, limited food
what did Darwin conclude from his observations?
favourable variations would tend to be presented and unfavourable ones would be destroyed
what is the process when natural selection occurs?
- those with variations that allow them to survive to reproductive age can mate and have offspring.
- the offspring will receive the allele that give the favourable variation
- over many generations, the favourable allele will be present in majority of individuals, while unfavourable alleles will be present in a much smaller percentage
what does Charles Darwins Theory survival of the fittest state?
- there is a variation of inherited characteristics in a species.
- in a struggle to survive those members with favourable traits will have a greater chance of surviving (great chance of passing on their inherited traits)
- overtime, the species will posses traits that are better suited to their environment
what is speciation?
the formation of new species - over many generations two, populations become sufficiently different that they can no longer interbred. (if this occurs the two will be regarded as different)
what are the types of evolution?
phyletic, divergent, convergent, co-evolution
what is phyletic evolution?
when one population progressively changes over time to become a new species
what is divergent evolution?
when one population splits into two
(EVOLUTION OF HOMOLOGOUS STRUCTURES - organ, bones, beaks that have a similar feature but different function)
what is convergent evolution?
different species develop similar traits because they live in similar environments. (EVOLUTION OF ANALOGOUS STRUCTURES - same structure but different function)
what is co-evolution?
different species that evolve alongside one another - flowering plants and their pollinators
what are the steps to speciation?
- variation of characteristics is present in population
- the breeding population becomes isolated
- different characteristics arise through random genetic drift, mutations, and environmental pressures
- environment changes and because of selection, some characteristics are favoured over others. Those best suited will survive.
- survivors produce and pass on favourable genes and features to offspring
- the frequency at which genes for the characteristic appears increases.
- the isolated population is now quite different and producing new species
what are fossiles?
preserved remains or traces of a once-living organism.
how do fossils form?
- sediment: animal buried by sediment shortly after it dies, the bones are protected from rotting by the layer of sediment.
- layers: sediment layers accumulate above the animals remains and minerals such as silica (silicon and oxygen) slowly replace the calcium phosphate in bones.
- movement: movements of tectonic plates lifts up the sediments and pushes the fossil closer to the surface
- erosion: form the rain, river, and wind they wear away remaining rock layer. Eventually erosion or digging will expose preserved remains.
what are the types of fossiles?
petrified: minerals dissolved in water underground have replaced all or part of an organism
moulds: hard parts of an organism, the hard part dissolves over time, leaving behind a hole in the shape of the organism
casts: a mold is filled in with dissolved minerals that harden in the shape of the shell/organism
carbon films: thin layer of carbon left when all other organic parts have broken down, leaving an image.
trace fossils: footprints, scratch marks or nests preserved in layers of sediment
preserved remains: entire organism trapped in amber, tar or ice.
what are vestigial structures?
a structure that during the course of evolution has been reduced in size or lost its function (in humans wisdom teeth, tailbone, appendix)
what is comparative embryology?
embryos of different vertebrate species that have homologous strcutures.
what is biogeography?
the study of the distribution of species and ecosystems in a geographic space and through geological time.
what is a phylogenetic tree?
a branching diagram representing evolutionary relationships and a series of common ancestors
explain protein sequences:
an organisms DNA determines the protein that it makes, many organisms need similar proteins but the arrangement of amino acids make it vary.
explain comparative studies of DNA
- all living things use the same DNA code, when speciation first occurred, the two new species would have very similar DNA however the longer they’ve been separated, the greater the difference in DNA (lots of inactive or junk DNA that don’t code for anything)
