Genetics part 2 Flashcards
Overall basic timeline of meiosis?
Pre-meiotic S-phase (DNA is doubled), so each now each chromosome has 2 sister chromatids attached at centromere
Recombination (crossing over)
Meiosis I homolog segregation (homologous pairs are seperated)
Meiosis II, sister chromatid separation (seperates the pairs)
What occurs in prophase I?
Chromosomes condense
Homologous pairs form
Forming a synaptonemal complex
Recombination occurs
What occurs in metaphase I?
Each pair of homologues (tetrad) line up at equator
Centromers don’t divide (unlike in mitosis)
Orientation of pairs is random with respect to one another (so can end up on either side of the equator)
What occurs in anaphase I?
Chromosomes, each with 2 chromatids move to separate poles
What occurs telophase I?
2 new daughter cells will each contain one of each chromosome, however the chromosomes still consist of 2 chromatids
So products are haploid, as there is only one of each chromosome
What occurs in Metaphase II, then anphase II, then telophase II?
Individual chromosomes line up at metaphase plate
Centromers split, chromatids separate to opposite poles
Each daughter cell contains one chromosome of each type, so 4 daughter haploid cells are produced from the 2 haploid cells
What is the genotype?
The combination of specific alleles that they carry
The alleles at the locus
What is phenotype?
Observable characteristics
What is an allele?
Alternate forms of a gene
What’s a homozygote?
Identical, eg YY, or yy
What’s a heterozygote?
Different, eg. Yy
What’s a gene?
Basic unit of biological information, specific segment of DNA that encodes a protein
What’s it called if we look at 2 genes instead of 1?
Dihybrid cross
How do you find the gametes in a dihybrid cross?
If parents are Aa, and Bb
Gametes will be, AB, Ab, aB, ab
Due to independent assortment during metaphase I, they line up on potentially different sides of the equator
What ratio does a dihybrid cross produce, when both parents are heterozygous (F1)?
9:3:3:1
In diploids wild type alleles are normally?
Dominant
In diploids mutant alleles are normally?
Recessive
What’s incomplete dominance?
When heterozygoes shown an intermediate phenotype, eg red x white = pink
Genotypic ratio = phenotypic ratio
What is Co-dominance?
Where heterozygoes show phenotype of both alleles
What are multiple alleles?
When there are more than 2 alleles for a gene
What is pleiotropy?
Where one gene contributes to more than one trait
What’s an example of the complications of dominance and pleiotropy?
Sickle-cell syndrome
Normal - no symptoms
Carrier - Some symptoms, not affected by malaria
Diseased - all symptoms, not affected by malaria
What can gene combinations cause?
Novel phenotypes, a new unique apperance the parents didn’t have
Alleles of one gene can mask effects of alleles at another gene (epistasis)
How to see of mutants are mutants in the same gene?
If breed them together and all offspring show mutant trait, then they are
If they aren’y won’t get the mutant trait = complementation, genes have helped each other as one set is recessive in each
What is penetrance?
Measures the percent of individuals with a given genotype who exhibit the phenotype associated with the genotype
What is expressivity?
Measures the extent to which a given genotype is expressed at the phenotypic level
(large variety of possible phenotypes)
What’s linkage?
When have both genes on same chromosome so when you segregate will only get 2 gametes
Unless recombination occurs between the genes during meiosis 1
What’s a testcross?
When you cross the F1 with a double recessive to find out the gametes
What does a greater number of parental offspring suggest?
Linkage
Describe an example of a testcross
So will have 2 genes eg. Pl pl (on the same chromosome) crossed with a testcross pp ll
On the Pl pl, there will be occassional crossing over meaning instead of just getting the parental genotypes (PL and pl), can get the recombinant genotypes (Pl and pL)
The recombinant ones will occur a lot less frequently
What’s a linkage map?
Measure the frequency of recombination between 2 genes on the same chromosome will represent the distance between them
What is one genetic map unit?
The distance between genes per 1% of recombinance = centimorgans (cM)
Are genetic maps linear and additive (can work distances out from other ones?)
Yes
How to map chromosomes?
Count the parental types and recombinant types Between 2 of the genes that you want to find out distance and see if they are linked or not
Work out frequency of recombinants (add them all together), and found out the map units by dividing this by the total amount of offspring (only of the 2 genes you are looking at), if it’s bellow 50 by a lot then they are linked, if it’s around 50 they will be unlinked
What do getting the 3 classes of offspring tell you from a triple cross (common, uncommon and rare)?
All 3 genes are linked
Sometimes gene map units don’t add up to equal distances how come?
Most common is parental type
Least common is double recombinant type
Double recombinants need to be counted in twice as crossing over has occurred twice
Feature of independent segregation of alleles on DIFFERENT chromosomes?
Equally likely to get the 4 gametes
eg. Ac, aC, AC, ac
Organisms with multiples of the basic chromosome set, are referred to as?
Euploid
What does haploid mean?
Only has one chromosome set, but is part of a life cycle phase
What’s a diploid organism?
Has 2 chromosome sets, one from each parent
What does monoploid mean?
Only has one chromosome set, but isn’t a part of the life cycle, and the rest of the species are diploid
How do cells end up with more or less chromosomes?
Non-disjunction
During meoisis 1, if the chromosomes don’t segregate correctly (too many go to one pole)
All offspring will be abnormal
Why does having extra chromosomes affect the phenotype?
Gene balance - genes have evolved to function in a diploid genetic background and disrupting that background disrupts their function.
Expression of deleterious alleles on monosomic autosomes, because now we only have one allele it can’t be hidden by the dominant allele
Normally leads to death, but can be tolerated in sex chromosomes to a certain degree
What are autosomes?
Non sex chromosomes (not X or Y)
What sex chromosomes do males have, and what do females have?
Males = XY (heterogametic) Females = XX
Features of the Y chromosome?
It pairs with X chromosome, and determines maleness (SRY gene)
Very few genes, a mostly repeated series, and very small compared to X
Inheritance father to son
Features of the X chromosome?
Has many genes unrelated to ses-determination or sex function
Males are hemizygous for X linked genes (effectively dominant as single copy, nothing to cancel it out)
What prevents X-chromosome gene dosage differences having significant effect (the amount of X chromosomes, eg. XXY, XY, XX, XO, XXX
In female mammals all but one X chromosome is epigenetically inactive in early development = lyonisation
They are condensed so much, they form a “Barr” body
Inactivation is random, maternal or paternal can be inactivated
Therefore the female body is mosaic for genes on X chromosome ( as each cell randomly has the the maternal or paternal X chromosome)
What’s the ZW system?
Males are ZZ
Females are ZW
What are forward genetics approaches?
Seek to find the genes encoded by DNA that are responsible for a phenotype of interest
So phenotype to genotype
it’s a classical strategy as starts with phenotype
Enables the wild-type genes for this pathway to be identified and studied
What are CDKs?
Found in all eukaryotes
Control the cell cycle
If mutated can result in cancer
What is BLAST?
Basic Local Alignment Search Tool
Used for analysis of genes
What is phylogenetics?
Estimating relatedness between species based on sequence data
What are homologous genes?
Genes related by evolutionary descent
What are paralogous genes?
Homologous genes in the same species
What are orthologous genes?
Homologous genes but in different species
What is reverse genetics approach?
Seek to find the phenotypes linked to specific sequences of DNA (including genes)
Genotype to phenotype
What can you use for gene targeting?
Homologous recombination
Disruption or deletion
So Make sure trans gene is homlogous to DNA
What’s a knockout mouse?
Had one or more genes knocked out
Careful to not knockout essential genes or will die
What is CRISPR (Clustered Regulary Interspaced Short Palindromic Repeats) in Bacteria? And what do they do?
- Short viral DNA sequence is intergrated into CRISPR locus
- RNA is transcribed from CRISPR locus, processed and bound to Cas protein forming crRNAs
- small crRNA in complex with Cas seeks out and destroys viral sequences
How can CRISPR be used for gene editing?
Make CRISPR target your DNA sequence instead of viral DNA
Have to have guide RNA and Cas9 protein
Modes of inheritance?
Dominant
Vertical patterns
Recessive
Horizontal patterns
Autosomal recessive
Consanguinity (related) often present between parents
Autosomal
Males and females affected with equal probability
X linked recessive
Males affected, female carriers
X linked dominant
All daughters of affected males are affected
Mitochondrial
Non-mendelian (don’t go by normal laws)
Maternal inheritance
Features of autosomal recessive?
Makes and females equally likely to be affected
25% chance of each child of an effected parent
Trait found in siblings not parents
Parents of effected children are likely to be related
Trait may appear as an isolated event
Features of x linked recessive?
Males far more likely to have disease
Trait never passed father to son
All affected males in a family are related though their mothers (carriers)
Features of mitochondrial inheritance?
Non Mendelian
Everyone inherits the condition through the maternal line
What can affect interpretations of pedigrees?
New mutations
Penetrance ( either the carrier does express gene or not in phenotype)
Expressivity (all carriers express phenotype, but severity varies)
Delayed onset (takes time for disease to develop)
Anticipation (as you have more generations, the onset of the disease)
Imprinting (genes that are only affected by one of the parents as the other one can’t cancel them out)
Google all definitions
What’s lod score?
lod score = log10 (odds loci are linked / odds loci are unlinked)
statistical estimate of whether two genes, or a gene and a disease gene, are likely to be located near each other on a chromosome and are therefore likely to be inherited.
What are discontinuous traits?
Eg. Tongue roll or no tongue roll
Not many genes
No environmental factors
Quadratics traits?
Eh, height or weight
Effected by multiple genes and alleles
Strongly influenced by envirnonemnets
What are the 3 types of poly genetic traits?
Metric
Meristic
Threshold
All rely on normal distribution
Feature of metric trait?
Mean is centre of distribution
Has a variance to measure spread
Features of meristic traits?
Eg. Amount of hairs on nuckle
Features of threshold traits?
Discrete phenotypes that are multifactorial
Have to tick over threshold to be classified
How are quantitive traits different to Mendelian laws?
Now have to consider environment
Patterns of inheritance are the same
Word equation for phenotypic variation?
= genetic variance + environmental variance + genetic and environmental interaction variance
What does VG (genetic variance£?
Alleles present + dominance interactions + epistaxis interactions
All of these are variances
What does the heritability of a trait describe?
How much variation is genetic
Broad sense- tells you how much is related to genetics and how much to the environment
Narrow sense - tells you how much is allleles and how much is environmental
Add equations
H^2 represents how heritable it is will be between 0 and 1
How to predict genotype frequencies?
Put the allele frequencies into ur punnet square and multiply them to find genotype frequencies
Hardy Weinberg equation for a 2 allele locus?
p + q = 1
p = dominant allele
q = recessive allele
Therefore
p^2 + 2pq + q^2 = 1
RR + Rr + rr = 1
H-W equilibrium only applies when?
Diploid
Random mating ( if not decrease heterozygous individuals)
Allele frequencies same in both sexes
Large population size
No gene flow ( immigration or emigration )
No mutation
No selection
Genetic drift?
Google definition
What is adaptive radiation?
Describes the spread of new species of common ancestry into different niches
What is convergent evolution?
The process wherby organisms not closely related, independently evolve similar traits as a result of having to adapt to similar environments or ecological niches
Features of mammals?
Have efficent respiratory and circulatory traits Larger brain than other vertebrates Mammary glands Hair Fewer, but more differentiated teeth
What are the 3 lineages of mammals?
Monotremes
Marsupials
Eutherians
Features of monotremes?
Warm blooded high metabolic rate
Hair over bodies
Produce milk
Lay eggs
Features of marsupials
Embryos develop within placenta in mothers uterus
Born very early in embryonic development
Complete development nursing in maternal pouch called a marsupium
Features of eutherians?
Complete embryonic development within uterus (mother feeds via placenta)
Compared with marsupials have a longer pregnancy and also a more complicated one
What acts on the variation within populations?
Natural selection
What occurs because of changes in allele frequencies?
Evolution
Divergence of populations leads to?
Speciation
Evolution is considered in terms of?
Changes in allele and gene frequencies over time, and the average action of selection on genotypes
What is genetic drift?
The chance difference in transmission of alleles, leading to fluctuations in allele frequency
Drift most strongly affects rare alleles, affects them more than selection as well
Drift is the primary mechanism for increasing rare recessives
Drift is responsible for changing frequencies of neutral mutations (have no phenotypic effect)
What is a genetic bottleneck?
Bottleneckimg event occurs meaning that there is only a small surviving population
The drift in small populations can then produce biased allele frequencies = founder effect
Describe heterozygote advantage?
Where the heterozygote genotype actually produces the phenotype which is most likely to survive
Will promote frequency of rare alleles
Is also balancing selection as multiple alleles are maintained in the population
Describe frequency dependent selection?
Alleles have an advantage when rare, but not when they are common
Eg. New camouflage which isn’t recognised by predators
Describe fluctuating selection?
Where conditions change very rapidly meaning that allele frequencies fluctuates up and down relative to what the conditions are like
What is fitness?
Survivorship and fecundity
Fitness (W) = 1 - s
s = selection coefficient
When s is high what happens?
Allele frequencies change rapidly
Describe stabilising, directional and disruptive selection?
Stabilising = intermediate variants are selected for, reduces variance for a trait
Directional selection = individuals at one extreme are selected for, shifts the mean value of the trait. Tends to be associated with changing environments
Disruptive selection = individuals at both extremes are selected for, leading to a bimodal distribution
What’s kin selection?
Refers to changes in gene frequency across generations driven by interactions between related individuals
Equation for coefficent of relatedness?
r = (0.5)^n
n = connection removed from self
Children will be 50, so will parents
grandfather would be 25 and so on
rB > C
What are the values?
r = the genetic relatedness to the recipient of the altrustic act as the probability that a gene picked randomly from each locus is identical by descent
B = The additional reproductive benefit gained by the recipient of the altrusitic act
C = the reproductive cost to the individual of performing the act
Basically relatedness x benefit > cost
What is adaptation?
The change or process of change by which an organism or species becomes better suited to its environment
What’s mullers ratchet?
Accumulation of deleterious mutations (which can be removed by sexual reproduction and recombination)
What can make a population seem like it’s not under selection?
If rate of mutation or drift balances it
What are body plans?
Common basic body plan for different groups of organisms
Use to be a lot more of them
What is saltation?
Huge major changes in body plan over one generation (just a theory)
What are homologous structures and analogous structure?
Homologous structures:
Similarity by common descent
Similar form and function
Similar developmental trajectory
Analogous structures:
Different ancestry
Same function
Different developmental trajectory
What is speciation and the 2 types?
Allopatric - in different environment so new species is created due to evolution
Sympatric - new species evolving even though in same environment and time
New species mean cant breed and produce fertile offspring
Why animals can no longer breed together?
Pre mating isolation:
Behavioural choices Temporal isolation (mate at different times) Mechanical incompatilbillity
Post-zygotic isolation
Hybrid sterility
What is Co-evolution?
The evolution of reciprocal adaptations of 2 or more species that have prolonged close interactions
Eg. Mutualism, benefits both, eg bees getting pollen off plants
Parasitsm, predation, driven adpaptions in each other to catch or escape
Competition drives to adapt to out compete other
What’s mimicry in butterflies?
One unpalatable model butterfly which is most abundant will have a certain pattern and other butterflies will copy it to avoid predation
Batesian mimicry is when palatable butterfly just copies pattern
What’s adaptive radiation?
Describes the spread of new species of common ancestry into different niches involving an excess of caldogenesis (formation of branches on evolutionary tree) over extinction
What’s convergent evolution?
The process wherby organisms not closely related, independently evolve similar traits as a result of having to adapt to similar environments or ecological niches
What is ecological release?
When a species expands its niche within it’s own habitat or into a new habitat where there is little competition for resources, which remain abundant
What’s evolutionary capacitance?
Living systems have the ability to accumulate genetic variation that has no phenotypic effect until the system is disturbed
This mechanism allows rapid phenotypic change in a population and rapid adaptation to new environmental conditions
What is evolutionary relay?
Independent species acquiring similar characterisitcs through their evolution in similar eco-systemsbut not at the same time
What is parallel evolution?
Independent species evolving together at the same time in the same ecospace and acquiring similar characteristics
Homologous structures are evidence of?
Radiation
Eg. limbs of mammals
Analogous structures are evidence of?
Convergent evolution
Eg. wings of birds and insects
What are the conclusions from the paper which examined ecological oppurtubity and competition in driving genetic diversification?
Ecological opportunities promoto morphological diversification
Homogoenous environments do not promote adaptation
Mutation and selection alone are sufficient to promote new designs
Competition amongst niche variants maintains variation
Trade-offs in competitive ability drive adaptive radiation
Quick desciption of paper?
Had cultures of bacteria shaken or unshaken
Put on lab bench
Smooth colony was found throughout
Wrinkly spreader was found at surface
Fuzzy spreader was found at bottom of broth
Had a control in a shaken beaker
After 7 days found heterogenous environment (not shaken) had produced a lot of biodiversity, Whereas the homeogenous shaken produced no biodiversity
Fuzzy spreader can’t invade wrinkly spreader
Wrinkly spreader may cut off oxygen to fuzzy spreader
Good example of convergent evolution?
Marsupials vs eutherians
2 important jaw closing muscles of mammals?
Temporalis and masseter
Dentition pattern in mammals?
Molars Pre molars Cannes Incisors Cannes Premolars Molars
What are flightless birds known as?
Ratites
How are birds adapted for flight?
Hollow bones
Lack urinary bladder
Small testicles, females only have one ovary
How to know which gene is in the middle in a test cross?
It will be the one when it’s the only variable that is in the rare and the parental genotype
