genetics chapter 4 Flashcards
what is an exon?
base sequence coding for a sequence of amino acids/primary structure
what are the three components of nucleotides?
a penrose sugar, a phosphate group, an organic base
describe the structure of DNA
made up of a depxyribose sugar, phosphate group, and one of the four organic bases (A,T,C,G)
hydrogen boned keep the bases together
describe the role of RNA
transfers genetic information for DNA to ribosomes for protein synthesis
which bases are purine and which are pyramidine
purine (double ring) = adenine, guanine
pyrimidine (single ring) = cytosine, thymine, uracil
how is DNA diffrent in eukaryotic cells to prokaryotic cells?
eukaryotic cells = found in nucleus, long and linear. associated with histone protiens to form chromosomes.
prokaryotic cells = short and circular. not associated with protiens
what is the gentic code?
the order of bases on DNA, consits of codons (triplets of code that code for a sequence of amino acids).
identify features of gentic code?
non-overlapping = each triplet is only read once
degenerate = more than one triplet codes for the same amino acid.
universal = same bases and sequneces used by all species.
what is a gene?
a seqencue of bases on a DNA molecule that codes for a specific seqence of amino acids to make a polypeptide.
what is a locus?
a fixed position on a DNA molecule occupied by a gene.
what is an allele?
diffrent versions of the same gene, found at the same locus on a chromosome.
what are exons and introns
exons = rigons of DNA that code for amino acid sequences. separated by one or more introns
introns = reigons of DNA that do not code for anything.
where are introns found?
between exons within genes
what is the genome?
the complete set of genetic information contained in the cells of an organism
what is the proteome?
the complete set of protiems that can be produced by a cell
describe the strcture of messenger RNA
a long, single strand. its base sequence is complemetary to the DNA it was ranscribed from.
advantages of using mRNA rather than DNA for translation.
shorter and contains uracil = breaks down quickly so no excess polypeptide forms.
single- stranded and linear = ribosome moves along strand and tRNA being to exposed bases.
contains no introns.
describe the structure of transfer RNA
a single strand of around 80 nucleotides that have been folded over. on one end is an anti-codon, and the opposite end is and amino acid binding site.
what is produced by transcription?
mRNA
where does transcription take place?
in the nucleus
outline the process of transcription
- DNA uncoiled into two strands with exposed bases. one used as a template
-free nucleotides line up next to their complimantary bases, and are joined together by RNA polymerase.
what happens to mRNA after transcription?
in eukaryotic cells, pre-mRNA must be spliced to remove introns, leaving only the coding regions. then it moves out of the nucleus and attaches to a ribosome.
what is produced by translation?
protiens
where does translation take place
in the cytoplasm (on ribosomes)
outline the process of translation
- the anti-codon of tRNA attaches to complemantary bases on the mRNA
-amino acids bonded to tRNA form peptide bonds, continuing to form a polypeptide chain untill a stop condon is reached - this process requires ATP
what is a mutation?
an alteration to the DNA base seqence often arise spontaneosly during DNA replication
why might a mutation not lead to change in tho amino acid sequence?
- genetic code is degenerate so mutation may end up coding for same amino acid as the original triplet
- mutation may occur in intron
what is a substitution mutation?
when a nucleotide in the DNA sequence is replaced by another. this is more likely to be a quiet mutation, meaning no change occurs in the amino acid sequence.
what is a deletion mutation?
when a nucleotide in the DNA sequence is lost. this is more likely to be harmful and significant, as it leads to a frame shift which means the entire amino acid sequence will be different
what is a mutagenic agent?
factors that increase the rate of gene mutation.
what is a polyploidy chromosome mutation?
where an individual has three or more sets of chromosomes instead of two.
what is chromosome non-disjunction?
when chromsomes failto separate correctly in meiosis, resulting in gametes with one more or less chromosome than normal.
what is meiosis?
a form of cell division that produces four genetically diffrent haploid cells, known as gametes
how does meiosis differ from mitosis?
- meiosis produces four genetically diffrent cells with half the number of chromsomes as the parent cells
- mitosis produces two genetically identical cells with the same number of chromosomes as the parent cells.
what happens during meiosis 1?
- homologous chromsomes pair to form bivalents.
- crossing over (exchange of sections of genetic materials) occurs ar chiasmata.
- cells divides into two. homologous chromosomes separate randomly. each cell contains either maternal or paternal copy.
what happens during meiosis 2?
- independent segregation od sister chromatids
- eah cells divides again, producing 4 haploid cells.
in which two ways does meiosis produce genetic varition?
- crossing over during meiosis 1
- independent assortment of homologous chromosomes and sister chromatids
results in new combinations of alleles.
define population
all the organisms of a particular species that live in the same place
define genetic diversity
the total number of diffrent alleles in a population
what advantage does a high genetic diversity provide
ability to adapt to change in enviorment, allows natural selection to occur
explain how natural selection results in developemtn of new characteristics.
- random mutations result in new alleles
- some alleles provide an advantage, making an individual more likely to survive and reproduce.
- their offspring receive the new allele, and frequency continuous to increase over many generations.
what is directional selection?
occurs when environmental conditions change. individuals with phenotypes suited to the new conditions will survive and pass on their genes. over time the mean of the population will move towards these characteristics.
what is stabilising selection?
occurs when environmental conditions stay the same. individuals closest to the mean are favoured, and any new characteristics are selected against. results in low biodiversity.
define a niche
the role of a species within its environment. species sharing the same niche will compete with each other.
what are the three types of adaption?
anatomical (changes to body structure)
physiological (changes to bodily processes)
behavioural (changes to actions)
define species
a group of organisms that can interbreed to produce fertile offspring.
what are the advantages of courtship behaviour?
individuals can recognise sexually mature members of their own species of the opposite sex, synchronise mating, form a pair bond, and successfully breed.
define classification
the process of arranging organisms into groups.
name the eight groups in the classification hierarchy, from largest to smallest.
domain -> kingdom -> phylum -> class -> order -> family -> genus -> species
what system is used to give species a universal name?
binomial naming system
what are the two components to a binomial name?
generic name = the genus the organism belongs to. two closely relted species will share the same genus.
specific name = the species the organism belongs to.
how are binomial names handwritten?
the first letter of the generic name should be capitalised, with the rest in lowercase. the whole name should be underlined.
what is phylogenetic classification?
the process of arranging organsims into groups based on their evolutionary orgins and relationships.
how can we clarify evolutionary relationships between organsims/
analyse their molecular differences.
advances in immunology/genome
seqencing provide clear pictures of how related two organsims are.
explain hierarchical classification
- groups within groups
- no overlap between groups.
what is biodiversity?
a variety of living organsims. it can be measured in terms of species diversity and genetic diversity.
define community
all the diffrent species that live in one area and interact with each other.
how do you calculate index of diversity?
d=N(N-1)/En(n-1)
N = total number of organisms of all species
n= total number of organsims of each species.
similarities in eukaryptic and prokaryotic cells?
- made up of DNA nucleotides containing a deoxyribose, a phosphate group and a nitrogonous base
- nucleotides are joined together by a phosphodiester bond to make a polymer chain.
how is DNA in mitochonria and chloropasts structured?
- short
- circular
- not associated with histone proteins
what is a condon?
three bases on mRNA that code for a specific amino acid.
what is a start codon?
three bases at the start of every gene that initiate translation.
what is a stop codon?
the three bases at the end of genes that cause ribosomes to detach and therefore stop translation.
describe the process of transciption? (5 marker)
- the DNA helix unwinds to expose the bases to act as a template.
- only one chain of the DNA act as a template
- catalyzed by DNA helicase
- DNA helicase break the hydrogen bonds between bases.
- free mRNA nuceloties join with the complimentary DNA bases.
- RNA polymarse joins together the RNA nucleotides to create and now RNA polymer chain.
entire gene is copied .
describe the process of translation. (5 marker)
- mRNA will bing to a ribosome after leaving the nucleus.
- the ribosome will then attacht as the start codon
- tRNA with the complomentary anitcodon will then align with the start condon on mRNA. and is held together my the robosome
- the ribosome will move along one condon on the mRNA to allow the tRNA to attach to the next condon
- the two amino acids are then joined together by a peptide bond. this is catalysed by and enzyme and requires ATP
- this continous till it reaches the stop codon. then the ribosome detaches and translation ends.
what does base delition result in?
frame shift - changes all the codons, which is harmful as amino acids can be inccorectly coded for.
what is non- disjunction?
when a chomosome or chromatid doesnt equaly split during anaphase.
what two forms can non-disjuntion appear?
- polploidy = chanegs in whole set of chromosomes
- aneuploidy = changes in the number of indivudual chromsomes.
how does polypoidy occur?
the spondle fibres during interphase do not attacht on one side of the chromosomes. meaning the chromsomes arent properly pulled appart. this means 2 gamete contain no genetic material and 2 contain double the amount of genetic material. (diploid gamete)
what is indepent seggrigation
when homologous pairs of chromosmes line up on opposite eachother on the equator of the cell. the pairs are then separated.
what is crossing over?
when homologous pairs of chrosomes line up oppotise eachother t the equator in meosis 1. parts of the chromotids can become twisted around eachother. places tention on the chromotids and causes them to break and they swap. creates new combontation of alleles.
what is evolution ?
the change in allele frequency over many genrations of a population.
explain directional selection.
- occurs when there is a change in the environment
- when the advantagous allele is conding for a extreme trait (extreme change)
explain stablising selection
- whe the middle trait provides a selective advantage
- no change in the enviorment
- standatd deviation decreases
what is courtship behavior?
a sequence of actions which is unique to every species
- geneticly coded
- how animals can detect there own species to produce fertile offspring.
example of courtship behaviors
- dancing
- sounds
- releasing pherimones
- display of colourful feathers.
unique to the species.
two names in the binomial naming system
first name = genus
second name = species
what farming techinques can cause a decrease in biodiverstiy.
-descruction of hedgrows
- use of fertilizers
- use of pesticides
- selective breeding
- monocultures
-
how is biodiversity measured
using the index of diversity
