Genetics / Inheritance and Variation Flashcards
What is a mutation?
A mutation is a change in the sequence of bases in DNA - this interrupts protein synthesis
Types of mutations
Types of mutations: subsitution, deletions or insertions of one or more nucleotides within a gene
What is a point mtuation?
A point mutation is when only one nucleotide is affected
Effect of a substitution mutation
A subsitution mutation of a nucleotide changes the codon on which it occurs - diff amino acid - diff primary structure - may be no effect due to degenerate nature
Effect of an insertion or deletion of a nucleotide
Insertion or deletion of a nucleotide leads to a frameshift mutation - reading frame of bases changed
Effects of different mutations
Effects of different mutations:
-No effect
-Damaging ie non-functional protein synthesis
-Beneficial
What are mutagens?
Mutagens increase the rate of mutation - it is a chemical, physical or biological agent which causes mutations
Causes of mutations
Causes of mutations:
-Mutagens
-Rare spontaneous loss of a base
-Free radicals which are oxiding agents affecting nucleotide structures and therefore base pairing
Examples of mutagens
Examples of mutagens:
-Physical - x rays - break DNA strands
-Chemical - deaminating agents - altering bases
-Biological - virus - insertion of DNA into a genome
Changes in chromosome structure due to chromosome mutations
Changes in chromosome structure due to chromosome mutations:
-Deletion - section of chromosome broke off and lost
-Duplication - section duplicated
-Translocation - sections broken off and joins other non-homologous chromosome
-Inversion - section broken off reversed then joined back onto chromosome
What are housekeeping genes?
Housekeeping genes are genes that code for enzymes necessary for metabolic reactions
What are tissue-specific genes?
Tissue-specific genes code for protein-based hormones required by certain cells at certain times for a short-lived response
Why is gene regulation needed?
Gne regulation is required for cells to specialise and work in a coordinated way
Levels of which genes operate which determine how they are regulated:
Levels of which genes operate which determine how they are regulated:
-Transcriptional (genes turned of/off)
-Post-transcriptional (mRNA modified to regulate transcription and types of protein produced)
-Translational (stopped or started)
-Post-translational (proteins modified after syntheses to change functions)
What are chromatins?
Chromatins is the complex formed when histones are wound around DNA
What is an operon?
An operon is a group of genes that are under the control of the same regulatory mechanism and are expressed at the same time
Why are operons effecient?
Operons are efficient way of saving recourses as when certain gene products are not needed, genes involved can be switched off
What is used when glucose is in short supply as a respiratory substrate for bacteria?
When glucose is in short supply, lactose is used as a respiratory substrate for bacteria
Structural genes involved in the lac operon
Lac operon - group of three genes - lacZ lacY lacA - structural genes that code for enzymes and are transcribed onto mRNA
Regulatory genes - lacoperon
Regulatory gene is located near the operon and codes for a repressor protein which prevents transcription of structural genes in the absence of lactose
What are repressor proteins in the lacoperon?
Repressor proteins prevents the transcription of the structural genes in the absence of lactose
-Constantly produced and binds to operator
Effect of repressor protein binding to an operator (lacoperon)
When the repressor protein binds to the operator, RNA polymerase is prevented from binding to DNA and beginning transcription - down regulation
What is a promotor in gene regulation? (lacoperon)
The section of DNA that is the binding site for RNA polymerase is called the promoter
What happens when lactose is present - lacoperon?
Lactose present -> binds to repressor protein -> changes shape and can’t bind to operator - so RNA polymerase binds to promoter and three structural genes are transcribed and enzymes are synthesies
How can bindings of RNA polymerase for transcription be increased?
Binding of cAMP receptor protein (CRP) speeds up transcription of genes - possible when CRP bound to cAMP (secondary messenger)
What happens in the lacoperon when glucose is present?
When glucose present -> levels of cAMP decreased -> reduces transcription of genes responsible for metabolism of lactose
Product of gene transcription
Product of gene transcription = pre-mRNA -> modified forming mature mRNA -> binds to ribosome for protein synthesis
Role of caps on mRNA
Cap = modified nucletode added to ends - helps stabilise mRNA and delay degradation in cytoplasm - also aids binding to ribosomes
Pre and post transcriptional control
Pre and post transcriptional control:
-Adding caps
-Splicing (removing introns and exons joining together)
How can RNA/mRNA be edited?
RNA can be edited through addition, deletion or subsitution -> results in synthesis of different proteins
Mechanisms that regulate the process of protein synthesis
Mechanisms that regulate the process of protein synthesis:
-Degradation of mRNA
-Binding of inhibitory proteins
-Activation of initiation factors that aid binding of mRNA
Degradation of mRNA as a way to regulate protein synthesis
Degradation of mRNA as a way to regulate protein synthesis = more resistant the molecule -> longer itll last in cytoplasm -> greater quantity of protein synthesised
How RNA can be edited?
nucleotide sequence of some mRNA molecules can be changed through base addition, deletion or subsitution which results in syntheses of different proteins
What are protein kinases?
Protein kinases are enzymes that catalyse the addition of phosphate groups to proteins -> changes tertiary structure + function
-Enzyme activated by phosphorylation
-Regulators of cell activity’
-Also activated by cAMP
What does post-translation control protein modification include?
-Addition of non-protein groups ie lipids
-Modifying amino acids and formation of bonds
-Folding or shortening of proteins
-Modification by cAMP
What is morphogenesis?
Morphogenesis is the regulation of the pattern of anatomical development
What are homeobox genes?
Homeobox genes are a group of genes which all contain a homeobox
What is a homeobox in homeobox genes?
The homeobox in homeobox genes is a section of DNA180 base pairs long coding for a part of the protein 60 amino acids long that is highly conserved (the homeodomain)
-> The homeodain binds to DNA and switches other genes on/off
->Meaning homebox genes are regulatory genes
What are hox genes?
Hox genes are one group of homebox genes that are present in aimals and responsible for the correct positioning of body parts
What are diploblastic animals?
Diploblastic animals have two primary tissue layers
What are triploblastic animals?
Triploblastic animals have three primary tissue layers
Control of vertebrae
Vertebrae have developed from segments in the embryo called somites
Different symmetry seen in animals
Symmetry:
-Radial symmetry is seen in diploblastic animals - only top and bottom - eg jellyfish
-Bilateral symmetry - both left and right, head, tail
-Asymmetry - no lines of symmetry - ie sponges
Difference between mitosis and aptosis?
Mitosis results in cell division and therefore growth, wheras aptosis is programmed cell death - removing unwanted cells and tissues - also stimulates mitosis leading to tissue remodelling elsewhere
Factors affecting the expression of regulatory genes
Factors affecting the expression of regulatory genes:
Influenced by inernal and external environment - change in temp, light, hormones, psychological stress, drugs (eg thalidomide)
Stages of apotosis
Stages of aptosis:
-Internal or External signals
-Caspases break down key elements that maintain cell function
-DNAses destroy the DNA inside the nucleus
-The dead cells is ingested by a macrophage
Aptosis mechanism
Aptosis mechanism:
-Tightly controlled
-Signals internal or external
-Capsases break down key elements that maintain cell function
-DNAses destroy DNA inside nucleus
-Macrophage digests dead cell
What influences phenotypic variation?
Phenotypic variation is caused by a combination of both genes and the environment
What are the causes of genetic variation?
Causes of genetic variation include:
-Mutation
-Recombination
-Independant segregation
-Random fertilisation
What is recombination?
during meiosis, the genes on homologous chromosomes are reshuffled through a process called recombination – produces new combinations of genes
What is independant segregation?
Independant segregation is the segregation of chrmosomes into haploid cells, random seperation
What is meant by random fertilisation as a cause of genetic variation?
Random fertilisation - fusion of gametes, increases variation as pairs of chromosomes from two seperate individuals are combined
What is genetic linkage?
Linkase - when genes that are close to eachother on a chromosome are inhertied together as a single unit
What is meant by Mendel’s law?
Mendel’s law states that genes do not influence the sorting of alleles into gametes - not always the case as some allele combinations are inherited together (linkage)
What are autosomes?
Autosomes = all the chromosomes except sex chromosomes (X AND Y) - arranged in pairs (homologous chromosomes)
What is meant by autosomal linkage?
Autosomal linkage = genes close together on the same autosome are more likely to be transmitted to a gamete together
What are X-linked genes?
X-linked genes -> males only have one copy of an allele for X-linked genes 0> no allele for the same gene on the Y chromosome - known as hemizygosity
What does hemizygosity mean?
Hemizygosity - males only have one copy of an allele for X-linked genes - no role of dominance and recessiveness
What is haemophilia?
Haemophilia is an X-linked blood disorder
Reasons for chlorosis in plants
Chlorosis in plants:
-Lack of mineral defficiency
-Disease
-Faulty cell division
What are the ways in which meiosis can lead to genetic variation?
Meiosis can lead to genetic variation:
-Corssing over
-Independant assortment of chromosomes or chromatids
-Mutation
-Changes in chromsome number eg polypoidy plants, down syndrome
What is continuous variation?
Continuous variation = quantitative, within a range, polygenic -> diff alleles at a single locus = smaller effect
-Affected by both genes and environment
What is discontinous variation?
Discontinuous variation = qualitative, categories, monogenic - different alleles at a single locus = large effect
-Affected by genes only
What is monogenic inheritance?
Monogenic inheritance is inheritance for a single gene
What is meant by codominance?
Codominance is where two alleles are equally dominant
What is haemophillia?
Haemophillia is an inherited blood disorder caused by a recessive hetereozygous allele - females are the carriers, males express it (as males have only one X chromosome
What is dihybrid cross?
Dihybrid cross considers the inhertiance of two characteristics at the same time - 2 different genes on 2 different chromosomes
What is an autosome?
Autosome = name given to any chromosome that isn’t a sex chromosome (X/Y)
What is meant by genetic linkage?
Genetic linkage = tendency of alleles that are located close together on a chormosome - inherited as one unit during meiosis - no independant assortment
-Linkage crosses -> crossing over = few recombinants where genotype different to parents
What affects frequency of recombinants?
Closer the genes are = less likely to be seperated = fewer recombinants
How to find recombinant frequency?
Recombinant frequency = (number of recombinant offspring x 100%) / (total number of offspring)
What is the chi squared test used for?
The chi squared test is used to see if results fit the pattern expected -> checking different between actual and predicted results are due to chance or due to significant difference
When are results significant/not significant?
-less than critical value = no significance = accept the null hypotheses
-more than critical value = significance = reject the null hypotheses
How to find degree of freedom in the chi squared test
Degree of freedom -> columns - 1
What is meant by epistasis?
Epistasis = gene interaction - when genes on different loci interact to affect one phenotypic characteristic -> so action of one gene modified by another gene
What are the was in which epistasis may work?
Epistasis may work:
-Antagonistic - results in masking, expressed = epistatic, masked gene = hypostatic
-Complementary - works together
What are the three types of epistasis?
3 types of epistasis:
-Recessive
-Dominant
-Complementary
What is recessive epistasis?
Recessive epistasis = homozygous recessive allele of one gene locus masks the affect of the allele at another gene locus
What is dominant epistasis?
Dominant epistasis = dominant allele of one gene masks the effect of an allele at another gene
What is complimentary epistasis?
Complimentary epistasis = both dominant alleles of a pair of genes are required to produce a given phenotype
What is meant by population genetics?
Population genetics investigate how allele frequencies change over time
What is a gene pool?
Gene pool refers to the sum of all genes in a population
What is meant by allele frequency?
Allele frequency = relative frequency of an allele - in diploid ppulations with two potential alleles frequency is always 1 (Hardy-Weinberg Principle)
What is meant by the Hardy-Weinburg principle?
The Hardy-Weinburg Priniciple = In a stable population, with no disturbing factors, the allele frequencies remains constant -> no evolution between generations
What are the factors affecting evolution?
Factors affecting evolution:
-Mutation (different alleles)
-Sexual selection (increase in allele frequency)
-Gene flow (movement of alleles between populations due to immigration/emmigration
-Genetic drift (change in allel frequency due to mutation - greater impact in smaller populations
-Natural selection (increased characteristics that aid survival
What affects population stability
Factors that affect population stability:
-Selection pressures
-Predation
-Natural seelction
-Variation
-Survival of the fittest
What are the three types of selection?
Three types of selection:
-Stabilising
-Directional
-Disruptive
What is meant by stabilising selection?
Stabilising selection = selection in favour of the norm eg birth weight
What is meant by directional selection?
Directional selection = positive selection for one of the extremes eg peppered moths
What is meant by disruptive selection?
Disruptive selection = norm is selected against eg galapgos finches
What is genetic drift?
Genetic drift is when chance dictates passing of alleles -> becomes common -> not due to survival
What is meant by population bottleneck?
Population bottleneck = large reductions in population size which last for at least one genreation
What is meant by density-dependant factors in evolution
Density-dependant = competition, predation, disease
Density-independant = affect populations at all sizes - natural disasters, seasonal changes
What is meant by the founder effect?
The founder effect = small population can arise due to establishment of new colonies by a few isolated individuals -> small gene pools, less genetic variation, but more advantageous alleles as passed on from original generation
What is speciation?
Speciation is the formation of new species through evolution -> new organisms can’t interbeed to produce fertile offspring with organisms of the original species
What causes speciation?
Speciation occurs due to:
-Organisms isolated isolated and can’t interbreed with rest of population -> no gene flow
-Alleles undergo mutations - different environment / selection pressures - diff mutations
-Accumulations of mutations leads to phenotype changes
What is meant by allotropic speciation?
Allotropic speciation = form of speciation - some members of population seperated by physical barrier - different selection pressures - isolation results in founder effect and genetic drift
-Eg galapagos finches
What is meant by sympatric speciation?
Sympatric speciation = occurs within populations that share the same habitat
-No geographical isolation
-Involves reproductive isolation within a randomly mating population
-Caused by rapid genetic change that alters morphology, behaviour, habitat preference
What are reproductive barriers to speciation?
Prezygotic reproductive barriers prevent fertilisation and formation of a zygote - as a result of hybridisation
What is artificial selection?
Artificial selection - selective breeding of desirable characteristics - closely related = inbreeding of species
What are the limitations of artificial selection?
Limitations of artificial selection:
-Limits gene pool - limits genetic diversity - less adaptations
-Closely related - same recessive alleles - offspring more likely to be affected by homozygous recessive genetic disorders
What are gene banks?
-Seed banks keep seeds
-Gene banks store biological samples other than seeds eg sperms
-Outbreeding - causes genetic diversity - reduces occurrence of homozygous recessives
What is adaptive radiation?
Adaptive radiation = where rapid organism diversification takes place) - eg galapagos finches evolving to adapt to different environments
What is an operon?
An operon is a cluster of genes under control of a promoter
Where does lactose bind to?
Lactose binds to the repressor protein (allows RNA to then bind to the promoter)
Why are Hox genes consistent over every being?
Hox genes are highly conserved - mutation would have large effect potentially lethal
What is a homeobox gene?
A homeobox gene contains a homeobox which is 180 base pairs long, regulates gene expression and is responsible for the development of the body plan
Difference between regulatory genes and structural genes?
Regulator genes - makes transciption factors, regulates gene expression/transcription of the structural genes
Structural genes - makes the protein - transcribed by the regulatory genes
