B5 - genes, inheritance and selection Flashcards
what is the genome?
the entire genetic material of an organism
what is an allele?
- a version of a gene (also known as a variant)
- different forms of one gene
what is asexual reproduction?
a form of reproduction that only involves a single parent and creates genetically identical identical offspring
what is a chromosome?
a long, coiled molecule of DNA that carries genetic information in the form of genes
what is DNA?
- deoxyribonucleic acid
- a polymer that is made of two strands twisted around each other forming a double helix; it contains all the genetic information
what does diploid mean?
when a cell has a full set of chromosomes
what does dominant mean?
an allele that is always expressed when present; represented by a capital letter
what is an enzyme?
biological catalysts that increase the rate of chemical reactions
what is a gamete?
sex cell
what does haploid mean?
when a cell has half the number of chromosomes
what is mRNA?
- messenger RNA
- an RNA subtype that carries genetic information from the nucleus to the ribosomes during protein synthesis
what is the nucleus?
an organelle found in most eukaryotic cells that contain the cell’s genetic material and controls the activities of the cell
what is a Punnett square?
a grid used to determine potential outcomes of a genetic cross
what does recessive mean?
an allele that is only expressed if two
what is a seedbank?
a place where seeds are preserved in order to preserve genetic diversity
what is sexual reproduction?
- reproduction that involves the fusion of male and female gametes; this method of reproduction produces genetic variation
- where genetic information from two organisms (a father and a mother) is combined to produce offspring which are genetically different to either parent
what is single gene inheritance?
inheritance of characteristics that are controlled by a single gene
what is transcription?
the unzipping of the DNA molecule around the gene, copying it to mRNA in the nucleus
what is translation?
translating the mRNA sequence to an amino acid sequence during protein synthesis
what is meiosis?
a form of cell division that produces gametes; they are not genetically identical and contain half the number of chromosomes
what is the genetic material stored in?
the nucleus
what is genetic material arranged into?
chromosomes
what is each chromosome?
one very long molecule of DNA that’s coiled up
what is a gene?
a short length of a chromosome
what do genes determine the production of?
proteins
what does genes controlling the production of proteins control the development of?
different characteristics e.g. dimples, and how an organism functions
what are different versions of genes called?
alleles
what are differences between organisms of the same species called?
variation
what is the genotype?
- all of the genes and alleles that an organism has
- the genetic make up of an organism
what is the phenotype?
- the characteristics that an organism displays
- the physical characteristics of an organism; it is due to interactions between the genotype and the environment
besides the genotype, what else can affect an organism’s phenotype?
interactions with its environment
what is most variation in phenotype determined by?
a mixture of genetic and environmental factors
what causes variation within a species?
- genetic variation
- environmental variation
what are the two types of variation?
continuous and discontinuous
what is continuous variation?
- when the individuals in a population vary within a range, there are no distinct categories e.g. humans can be any height within a range, not just tall or short
- variation that can take any value between two extremes e.g. height or weight
what do characteristics that are influenced by more than one gene or that are influenced by both genetic and environmental factors usually show?
continuous variation
what is discontinuous variation?
- when there are two or more distinct categories, each individual falls into only one of these categories (there are no intermediates) e.g. humans can only be blood group A, B, AB or O
- variation that can only take discrete values e.g. eye colour
what are characteristics that are only influenced by one gene and that aren’t influenced by the environment likely to show?
discontinuous variation
what type of graph is used to display continuous variation?
a histogram
- often bars are removed and just the line showing the trend drawn
what type of graph is used to show discontinuous variation?
a bar chart
what are mutations?
- changes to the genome
- a random change in DNA which increases variation; they may have a neutral, beneficial or damaging effect on the phenotype
what are causes of mutations?
- viruses
- ionising radiation
- chemicals
- UV light
how can viruses cause mutations?
- viruses take over a cell and inject their own nucleic acid into the cell, this allows it to reproduce and hijack the cell
- some of these viruses can cause cancer e.g. HPV - human papilloma virus
- some forms of this virus interact with our DNA at a region that codes for a protein called p53
- if this gene is altered, it can cause many forms of cancer e.g. cervical cancer
how can ionising radiation cause mutations?
- x-rays, alpha rays, beta radiation
- always background radiation but increased doses can penetrate body and cause cancers
- huge energy in radiation can break bonds between DNA strands and cause changes to bases
how can chemicals cause mutations?
- loads of chemicals we use daily have been found to be carcinogens e.g. tobacco, nitric oxide, mustard gas, asbestos, alcohol, arsenic
- these can be free radicals; a chemical that can oxidise other chemicals e.g. DNA
how can UV light cause mutations?
- electromagnetic radiation
- less energy than ionising radiation so usually only causes skin cancers
what are the effects of mutations?
- silent mutation: often has no affect on the gene, even if DNA bases have mutated it may not affect order of mine acids or effected part not important to function of protein being produced
- alleles: a change in DNA can create a different version of a gene
- cancer: mutations can cause cancer; when cells grow and divide uncontrollably
why do mutations mean for the sequence of DNA bases in the gene?
it changes
what can mutations produce?
a genetic variant
what can gene mutations sometimes lead to?
as the sequence of DNA bases in a gene codes for the sequence of amino acids that make up a protein, gene mutations sometimes lead to changes in the protein that it codes for
what is the case with most mutations?
they have no affect on an organism’s phenotype
does all DNA code for proteins?
less than 2%!
what can variants affect?
coding and non-coding DNA
coding DNA…
- genes which provide the instructions required to synthesise proteins
- only a small proportion of the genes in the genome may be expressed at any time
- genes must be activated if they are to be expressed
non-coding DNA…
- does not code for proteins
- influences protein synthesis by interacting with coding regions of DNA
- can cause activation/deactivation of genes in the coding DNA
how can mutations in coding DNA affect the proteins coded for by the gene?
it can affect the protein’s structure and the way that it functions
how can mutations in non-coding DNA affect genes?
it can affect how genes are expressed
- they can stop the transcription of mRNA so the protein coded for by that gene is not produced at all
what does sexual reproduction produce?
genetically different cells
what do the mother and father produce in sexual reproduction?
gametes; in animals these are sperm and egg cells
what do gametes contain?
gametes only contain half the number of chromosomes of normal cells
what is the name given to only containing half the number of chromosomes of normal cells?
haploid
what is it called when have the complete number of chromosomes?
diploid
what happens at fertilisation?
a male gamete fuses with a female gamete to produce a fertilised egg; the fertilised egg ends up with the full set of chromosomes so is diploid
what does the fertilised egg then undergo?
cell division by mitosis
what does the fertilised egg develop into as it undergoes cell division?
an embryo
where does the embryo inherit it’s characteristics from?
both parents as it’s received a mixture of chromosomes from it’s mum and dad
what is cell division?
when a cell reproduces to make more cells, the DNA has to make an exact copy of itself
what do cells need to divide for?
- growth and repair
- asexual reproduction
- sexual reproduction
how might a dog breeder use the technique of sexual reproduction to create a new variety of dog?
- selecting 2 parents
- desirable characteristics
- breeding together
how might a plant breeder us the technique of asexual reproduction to produce daffodil bulbs?
- select a successful daffodil plant
- split the bulb
what is meant by a clone?
- new organism that is genetically identical to it’s parent
what are some advantages of asexual reproduction?
- fast
- cheap
- no need to find 2 parents
- known end result
what are some disadvantages of asexual reproduction?
- all susceptible to the same disease
- no new varieties produced
what are some advantages of sexual reproduction?
- greater genetic variation
- resistance to disease
- new varieties produced
what are some disadvantages of sexual reproduction?
- expensive
- slow process
- unknown outcome
- not always a lot of offspring
- mates required
what are the phases of mitosis?
- interphase
- prophase
- metaphase
- anaphase
- telophase
- cytokinesis
what happens during interphase?
each chromosome replicates so it contains two identical chromatids
what happens during prophase?
chromosomes become visible by shortening and thickening
what happens during metaphase?
the chromosomes align up along the centre of the parent cell
what happens during anaphase?
the two chromatids in each chromosome are pulled apart to the opposite poles of the cell
what happens during telophase?
there are now two nuclei
what happens during cytokinesis?
the cell splits in two to produce two daughter cells, each containing the same chromosomes
what are gametes produced by?
meiosis
how is meiosis different to mitosis?
it doesn’t produce identical cells
what are the main features of meiosis?
- the cell divides twice, forming 4 gametes
- the gametes are genetically different from each other
- results in variation
where is the only place that meiosis occurs in humans?
the reproductive organs (ovaries and testes)
explain division 1 of meiosis
- before cell starts to divide, it duplicates its DNA (so there’s enough for each new cell), one arm of each X-shaped chromosome is an exact copy of the other arm
- in the first division in meiosis (there are two divisions) the chromosomes line up in pairs in the centre of the cell; one chromosome in each pair came from the organism’s mother and one came from the father
- the pairs are pulled apart, so each new cell only has one copy of each chromosome; some of the fathers chromosomes and some of the mother’s chromosomes go into each new cell
- each new cell will have a mixture of the mother’s and father’s chromosomes; mixing up the genes like this is important as it creates genetic variation in offspring
explain division 2 of meiosis
- in the second division the chromosomes line up again in the centre of the cell; similarly to mitosis, the arms of each chromosome are pulled apart
- you get 4 haploid gametes, each only has a single set of chromosomes; the gametes are all genetically different
what are key points to remember about meiosis?
- it occurs in two divisions (I and II) that superficially resemble mitosis
- meiosis produces 4 haploid cells that are genetically different
what does heterozygous mean?
when an individual has two non-identical alleles of a gene e.g. Bb
what does homozygous mean?
when an individual has two identical alleles of a gene e.g. bb
what is crossing over?
- during prophase and metaphase of meiosis I, homologous pairs of chromosomes pair up closely
- chromatids twist around each other; the point where they join are called chiasma
- fragments of non-sister chromatids swap over and so genes are exchanged
what are random combinations?
- 4 daughter cells have completely different combinations of chromosomes
- this is because of random assortment of chromosomes each time the cells divide (there is no ‘decision’ made as to where the chromosomes line up and which way they are pulled)
when and what did Gregor Mendel do?
- 1860s
- experiments to find out how different characteristics are passed on from parents to their offspring = father of genetics
what were Mendel’s main conclusions?
- characteristics in plants were determined by inherited factors (now called genes)
- inherited factors are passed on from both parents, one unit from each
- characteristics can ‘jump’ a generation because some factors are stronger (dominant) that others (recessive)
when and what did Friedrich Miescher do?
- 1869
- discovered material in the nucleus that he termed ‘nuclein’
- he lysed white blood cells from pus
- showed nuclein made of H O N and P and there was unique ratio of phosphorus to nitrogen
when and what did Phoebus Levine and Frederick Griffiths do?
- 1920s
- found that DNA consists of long chain of repeating chemical units
- units made of phosphate group, sugar and a base
- bases: A,G,C,T
when and what did Oswald Avery do?
- 1944
- proves that DNA codes for characteristics
- discovered bacteria have ability to transfer DNA between them
when and what did Erwin Chargaff do?
- 1950
- the proportion of bases in DNA of different species varied but in any DNA: no. of A=T and no. of G=C
when and what did Rosalind Franklin and Maurice Wilkins do?
- 1952
- Franklin took high-resolution photos of DNA fibres using x-rays
- deduced basic dimensions of DNA strands, and that phosphates on outside of probably helical structure
when was the DNA double-helix structure confirmed?
- 1953
- first double helix model of DNA
- described two helices held together by complimentary base pairs
- Nobel Prize in 1962
when and what did Sir Alec John Jeffreys do?
- 1984
- DNA fingerprinting and profiling
- except for identical twins, everyone’s DNA is unique
- uses of DNA fingerprinting: paternity testing, forensic science etc
when and what was the Human Genome Project?
- completed in 2003
- HGP was international
- goal: determining sequence of base pairs in human DNA
- goal: identifying and mapping all genes of human genome from physical and functional standpoint
- took 20 years to sequence the 24000 genes in human body
when and what was CRISPR?
- 2007
- gene transfer has been developed
- present day; research into genetic diseases etc
when and what did Jennifer Doudna and Emanuel Charpentier do?
- 2020
- won Nobel prize for chemistry for developing method of genome editing using CRISPR-Cas9 genetic scissors
what is an allele?
a version of a gene (also known as a variant)
what is an active site?
the part of the enzyme which is specific to the substrate and has a complimentary shape to it
what is an antibiotic?
a type of medication that helps cure bacterial disease by killing infective bacteria inside the body
what is antibiotic resistance?
the ability of bacteria to become resistant to the treatment that is being used to kill it i.e. antibiotics; this provides evidence for evolution
what is artificial classification?
the classification of organisms based on observable characteristics
what is biodiversity?
the variety of different organisms living in an ecosystem
what is evolution?
a change in the inherited characteristics of a population over time, though the process of natural selection, which may result in the formation of new species
what is extinction?
when all the members of a species have died
what is the fossil record?
the remains or impressions of dead organisms found in rocks that are millions of years old; they provide evidence for evolution
what are molecular phylogenetics?
finding evolutionary relationships between organisms on the basis of their DNA; this method can only be used in fossils that have DNA present
what is natural classification?
the classification of organisms based on their evolutionary relationships
what is natural selection?
the process by which advantageous alleles are passed down to offspring over many generations, increasing allele frequency; these alleles give rise to phenotypes best suited to the environment
what is a seedbank?
a place where seeds are preserved in order to preserve genetic biodiversity
what did Lamar suggest new species came from?
he said they all came from the fountain of life; primitive worms developed from the fountain into everything
what were the four observations that Darwin made?
- all organisms produce more offspring than survive to adulthood
- yet populations remain more or less constant in number
- members of the same species show variation in characteristics; this could be due to sexual reproduction or because a mutation has occurred
- some characteristics are inherited and so are passed onto the next generation
from his observations, what did Darwin conclude?
- all organisms are involved in a struggle for survival
- some individuals are better adapted to their environment than others
why did some people disagree with Darwin’s theory of nature selection?
- the main idea was that god made everything
- some scientists believed there wasn’t enough evidence
what is speciation?
the process of adaption being repeated with every generation, leading to the development of new forms, including new species
why do we use classification?
- identify species
- predict characteristics
- find or show evolutionary links
list Linnaeus’s system of classification
KINGDOM
PHYLUM
CLASS
ORDER
FAMILY
GENUS
SPECIES
what is a species?
a group of organisms that are able to reproduce naturally to produce fertile offspring
what is a hybrid?
the result of breeding between two organisms from two different species; infertile
why is it important to us binomial nomenclature?
global understanding
information on natural classification?
- based on evolutionary relationships between organisms
- through DNA sequencing, scientists can link evolutionary relationships between organisms
- organisms categorised using info about common ancestors and common structural features
- modern tech allows use of amino acid sequencing in proteins to determine how close relationships are
information on artificial classification?
- based on observations
- earliest methods of classification used comparisons of observable/non-evolutionary features to group
e.g. give birth to live young/eggs
why do closely related animals look different?
closely related species may have different features if they live in different types of habitats
why do some animals look similar even though they are not closely related?
similarities and differences between species need to be explained in terms of both evolutionary and ecological relationships
what is evidence for evolution?
- the fossil record
- comparative anatomy
- molecular evidence
- rapid changes in modern species
- extinction
what are the stages of the fossil record?
- death
- decay of soft parts
- covered in sediment
- compaction
- bone replaced by mineral
- erosion and uplift of rock
why is the fossil record incomplete?
- soft tissue decays so doesn’t fossilise
- fossilisation rarely occurred
- some fossils have not yet been discovered
- there have only been 9 examples of Archeopteryx ever found
- there are no complete specimens of Tyrannosaurus Rex
what is comparative anatomy?
similarities in anatomy demonstrates how organisms have evolved from a common ancestor
what is molecular evidence?
DNA na proteins can help us construct phylogenies
what is rapid changes in modern species referring to?
bacteria developing resistance to antibiotics etc
what is some information on extinction?
- it is estimated that 99% of all species that have ever lived on earth are now extinct
- they failed to adapt to changes in their evolved environment but forms that evolved from them survived
