Evolution BIOS3240 Flashcards
(126 cards)
1
Q
What are the three mechanisms of Genome evolution
A
Polyploidy, Chromosomal Rearrangements, Gene duplication and divergence.
2
Q
Who introduced the concept of non-coding DNA
A
Susumu Ohno
3
Q
What are major non-coding elements of the DNA called
A
Exons (coding)
Regulatory sequences (enhances, promoters)
Reptitive DNA: >50% of human genome.
4
Q
What are the repetitive DNA elements and what are the types and examples?
A
Tandam Repeats: repeated sequences directly adjacent to each other,
Types: Microsatellites (2-10bp/unit)
Minisatellites (10-60bp/unit)
Satellites (>60bp/unit)
Examples:
Telomeric Repeats TTAGGG
Centromeric Repeats
Microsatellite expansions can cause diseases
5
Q
What are Interspersed repeats and what are the types of those?
A
Repeats scattered throughout the genome.
Segmental Duplications
sequences>1kb
High sequence identity (90-100%),
some include functional genes.
associated with disease susceptibility.
Transposable Elements: discovered by Barbara McClintock, DNA that can move within the genome
6
Q
What are transposons
A
Copy and paste mechanism: new copy added elsewhere
Cut and paste mechanism: original moves to new site
7
Q
What are retrotransposons?
A
Move via RNA intermediate
Trancribed to RNA -> Reverse transcribed to DNA -> inserted into Genome .
8
Q
Polyploidy is a mechanism of genome evolution describe what it is and its features.
A
Whole genome duplication (multiple sets of chromosomes)
common in plants often fatal in animals
occurs during faulty meiosis when homologues fail to separate.
9
Q
Describe mechanisms of genome evolution including chromosomal rearrangements
A
Structural changes to chromosomes (inversions, translocations, fusions)
impact genome architecture and function.
10
Q
Other mechanisms of genome evolution include gene duplication and divergence.
A
occurs during misaligned meiosis,
one chromosome gains a duplicate the other may lose the gene, provides raw material for evolution
examples: HOX genes: gene family from duplication, Globin gene clusters
11
Q
What are other mechanisms of genome evolution such as intragenic rearrangements.
A
Exon shuffling and duplication during recombination, generates novel protein architectures.
12
Q
What is genome sequencing and comparative genomics?
A
How are genomes sequenced: covered in subsequent lectures.
Bioinformatics tools are essential to:
assemble and annotate genomes
compare synteny, gene families and regulatory elements.
Comparative genomics reveals conserved and lineage-specific features.
13
Q
Explain what is meant by the C-value paradox>
A
The observation that genomic size (C-value) does not correlate with organismal complexity as many simpler organisms have much larger genomes than more complex ones due to the abundance of non-coding and repetitive DNA
14
Q
What is the difference between Genome and C-value?
A
Genome: complete DNA content of an organism
C-value = Haploid DNA content (pg or bp)
1pg DNA = 1Gbp
15
Q
What actually is the C-value Paradox?
A
Observed disconnect between genome size and organismal complexity.
Some simpler organisms e.g amphibians, plants have larger genomes than complex organisms like humans. originated from Thomas Jr. 1971
Caused by extensive non-coding DNA, repetitive elements and transposable elements in eukaryotes.
16
Q
What are the types of Gene composition?
A
Gene number vs complexity
Protein-coding vs non-coding DNA
Transposable Elements
17
Q
With reference to the genome composition explain what is meant by Gene Number vs Complexity
A
In prokaryotes: Gene number correlates with genome size.
In eukaryotes: weak correlation due to non-coding DNA
18
Q
Describe with reference to genome composition what is meant by protein coding vs non-coding DNA
A
Coding DNA: Small fraction of total genome (~1-2% in humans), exons as coding regions of a gene. They remain in the fina messenger RNA (mRNA) after processing and are translated into proteins.
Non-coding DNA: includes regulatory regions, introns, (which are removed from pre-mRNA during splicing so do not appear in final mRNA), structural DNA and repetitive elements.
19
Q
In terms of Genome composition explain what is meant in terms of transposable elements (TEs)
A
common in multicellular eukaryotes: rare in unicellular eukaryotes, significant contributors in genome size and evolution
20
Q
Types of TEs
A
Transposons (cut and paste): move directly as DNA
Retrotransposons (copy and paste: transcribed to RNA reverse transcribed into DNA.
21
Q
What is the impact of Transposable elements on the genome?
A
TEs can insert into genes (disrupting function), duplicate genes (potential for new functions copy then paste concept lol
alter gene expression
22
Q
What was the case study that was found to be caused by Transposable Elements.
A
Roma Tomato
TE RIDER duplicated the SUN gene (affects fruit shape during retrotransposition
Rider then disrupted DEFL1 rendering it non-functional
Illustrates TEs as agents of phenotypic innovation and genomic rearrangement.
23
Q
Give the 4 Genome evolution Mechanisms
A
1) Polyploidy: whole genome duplication (common in plants), Leads to speciation and increased gene redundancy
2) Chromsomal Rearrangements: Inversions, translocations, fusions, fissions, reshape genome architecture and gene regulation.
3) Gene duplication and divergence, drives innovation in gene function example: evolution of gene families like globins, HOX genes
4) Exon shuffling: recombination mediated rearrangement of exons, produces novel protein domains and functions
24
Q
What are the genome sequencing techniques:
A
- Sanger sequencing (1977)
- Whole Genome Shotgun (WGS)
- Next-generation sequencing NGS
25
Explain what is meant by Sanger sequencing
Chain termination method using ddNTPs
Basis of early large scale genome projects (e.g Human Genome project)
26
Whole Genome Shotgun (WGS)
DNA fragmented -> cloned into plasmids -> sequenced -> assembled via overlap
used in 2001 for the first draft of the human genome
27
Explain what is meant by Next generation sequencing
No plasmid cloning; fragments amplified and sequenced in parallel, faster, cheaper, higher throughput (post 2005)
28
Bioinformatics what is the purpose?
Process and interpret large scale sequence data, identify genes, regulatory elements, structural variations
29
What is comparative Genomics?
Between Distant Species, identifies conserved genes and ancestral gene sets.
Highly conserved genes help infer deep evolutionary relationships.
Between closely related species; highlights lineage specific changes e.g human vs chimpanzee ~1.2% SNP difference, 2.7% indels
FOX2 Gene (Speech Devlopment): Human specific evolution, mutation leads to speech impairments, present in neanderthals - suggests capacity for speech
Within Species variation:
Variation due to SNPs, indels, CNVs, inversions, Explored in large scale projects like the 1000 genome project and Cancer Genome Atlas
30
What is population Genetics?
Population genetics is the study of genetic structure of populations and how it changes over time and space
31
What does population genetics focus on?
Frequencies of alleles and genotypes
forces that affect these frequencies: mutation, selection, genetic drift, gene flow and non-random mating
bridges mendelian genetics and evolutionary biology by quantifying evolutionary processes in populations.
32
What is the gene pool
The complete set of alleles in a population at any one time.
Allele frequency (p,q) = proportion of alleles at a locus accounted for by a specific allele.
If 70% of alleles at a locus are A and 30% are a: p(A) = 0.7, q (a)=0.3
33
Hardy-Weinberg Principle?
If no Evolutionary forces act on a population, allele and genotype frequencies remain constant from generation to generation.
34
What assumptions are made when using the Hardy Weinberg Principle:
Assumptions:
No mutation, no migration (gene flow), infinite population size (no genetic drift), random mating, no natural selection.
35
What is the equation for the Hardy Weinberg Principle? and what does each of the letters mean?
p^2+2pq+q^2 = 1
p^2: frequency of homozygous dominant (AA)
2pq: Frequency of heterozygotes (Aa)
q^2: frequency of homozygous recessive (aa)
where p + q = 1
36
What are evolutionary Mechanisms that alter allele frequencies?
Mutation: source of genetic variation, alone it is a weak evolutionary force (low mutation rates) but provides material for selection and drift to act on.
Natural Selection: differential reproductive success:
Types:
Directional selection - favors one extreme
Stabilizing selection - favors intermediate phenotype
Disruptive Selection: favors extremes over the mean.
37
What is meant by Genetic Drift:
Random changes in allele frequencies especially in small populations can lead to fixation or loss of alleles.
38
What are two examples of Genetic Drift?
Bottleneck effect - sudden reduction in population size
Founder effect - small subset migrate to new location
39
Describe what is meant by Gene Flow (migration)
Movement of alleles between populations, increases genetic similarity between populations, can introduce new alleles.
40
Describe what is meant by non-random mating
Inbreeding increases homozygosity, may expose deleterious recessives, Assortative mating: individuals mate with those with similar phenotypes
41
What are the sources and types of Genetic Variation in Populations
Sources: mutation, recombination, Gene flow
Types: Single nucleotide polymorphisms, microsatellites, insertion/deletions, chromosomal rearrangements.
42
What is the Inbreeding coefficient (F) and, Inbreeding and its consequences are:
Inbreeding coefficient (F), probability that 2 alleles at a locus are identical by descent, increases homozygosity, Can lead to inbreeding depression - reduced fitness due to expression of deleterious alleles.
43
How do you measure genetic diversity?
Through Heterozygosity:
Which is observed heterozygosity Ho: proportion of heterozygotes in a population
expected heterozygosity: predicted under HWP
Difference between Ho and He indicate departure from HWP.
44
What is Polymorphism?
Proportion of loci that are polymorphic (multiple alleles exist)
45
What does the fixation index measure?
Measures population differentiation due to genetic structure.
46
What is the equation for the fixation index:
FST = (HT - HS)/HT
HT: Expected heterozygosity in total population
HS: Expected heterozygosity within subpopulations
Interpretation:
FST = 0 no differentiation
FST = 1: complete separation
Values > 0.25 suggest significant population structure
47
What are the applications of population genetics:
conservation biology: maintain genetic diversity
Epidemiology: track pathogen evolution
Anthropology: study Human Migration and ancestry
Forensics: identity testing, population assignment
Breeding programs: manage inbreeding and selection.
48
What is the def of Hard- Weinberg Equilibrium?
HWE described the genetic makeup of a population that is not evolving. It provides a baseline expectation for allele and genotype frequencies under ideal conditions
49
What are the application steps to using the Hardy Weinberg Equilibrium?
1) Determine observed genotype frequencies
2) calculate allele frequencies from observed counts
3) Use HWE to calculate expected genotype frequencies.
4) Compare observed vs expected frequencies
Match -> Population in HWE
Mismatch -> Potential evolution
50
Describe the types of natural selection and give the definition
Definition: differential survival or reproduction based on heritable traits, types include: directional: favors one extreme phenotype
stabilizing: favors intermediate phenotype
Disruptive: favorsd both extremems
51
Def of incomplete dominance
The heterozygote shows a mix of both alleles - neither is fully dominant
52
Describe what is meant by Genetic Drift
Definition: random fluctuations in allele frequencies in small populations.
53
What are the subtypes of genetic drift:
Bottleneck Effect: Drastic population reduction e.g disaster
Founder effect: small group colonizes new area
Effects: reduce genetic variation, may cause alleles to become fixed or lost
54
What is Gene flow
Movement of alleles among populations, increases genetic similarity, can introduce new variation
Sexual selection: Definition forms of natural selectrion related to mating success
Types: Intrasexual: compeitition within the same sex (e.g male dee fating)
Intersexual: mate choice e.g birds of paradise
55
What is intrasexual selection
Members of one sex compete with each other for a member of the opposite sex. The victor will be able to mate and pass on their genes
56
What is inrtersexual selection
There is a preference for a trait in a member of the opposite sex e.g a brightly colourled tail. By mating with individuals with the chosen trait, the trait will be passed on to future generations.
57
Sexual selection outcomes:
Leads to sexual dimorphism, trade-off between attractiveness and survival
58
What is the definition of Balancing selection
Definition: selection that maintains multiple alleles in a population
Mechanisms: Frequency dependent selection: fitness depends on allele frequency.
Heterozygote advantage: heterozygotes have greater fitness.
59
What is an example heterozygote advantage in a case study:
Sickle cell Anemia: caused by mutation in heamoglobin beta chain
if Homozygous (ss): sickle cell disease (high mortality)
Heterozygous (Ss): mild symptoms + resistance to malaria
Homozygous (SS): susceptible to malaria.
This maintains the s allele in populations where malaria is endemic, a classic case of heterozygote advantage.
60
What is phylogeny
Phylogeny refers to the evolutionary history and relationships among inidviuals or groups of organisms e,g species or populations.
Relationships shown in phylogenetic trees which map out how lineages diverged over time from common ancestors
61
Why do we study phylogeny what does it help us do?
Clarify organisms based on evolutionary relationships not just physical similarity.
allows us to understand evolutionary processes
track trait evolution e.g feathers placenta
study origins of specific genes gene families or pathogens
infer ancestral states
improve comparative genomics and taxonomy
62
Explain the anatomy of a phylogenetic tree:
root represents the most recent common ancestor of all taxa in the tree, branches represent lineages evolving throught time.
nodes show common ancestors and branching events (speciation)
Tips (leaves) show current species or taxa.
Root of the phylogenetic tree = common ancester
internal branch (internode) = ancestral species
63
What does each internal node on a phylogenetic tree represent?
represents a divergence event and te tuos are labelled with extant species names, the relative length of branches may or may not indicate evolutionary distance depending on the tree type (e.g cladogram vs phylogram)
64
What do unrooted trees show and not show
they show relationships but do not show the direction of time, also no indication of ancestral lineage.
65
if two trees have the same topology what does that mean
the branching pattern of the phylogenetic tree is the same.
66
What are the types of phylogenetic trees
1) Cladogram
2) Phylogram
3)Chronogram
67
What is a Cladogram
branch lengths are arbitrary only show topology (branching pattern)
68
What is a phylogram
branch lengths are proportional to the amount of character change or molecular distance.
69
Chronogram does what and show what?
Branch lengths are scaled to time (calibrated with fossils or molecular clock data)
70
Describe what is meant by homologous traits
inherited from a common ancestor e.g vertebrate and limbs
71
What is a clade?
group of species that includes an ancestral species and all its descendants, nested in larger clades but not all groupings of organisms qualify as clades
72
What does monophyletic suggest
it consists of the ancestor species and all its descendants
73
What does paraphyletic mean?
group consisting of an ancestral species and some but not all, of the descendents
74
Polyphyletic meaning?
Grouping includes distantly related species but does not include their most recent common ancestor.
75
How do we infer phylogenies
gather info about morphologies, genes and biochemistry
76
What are analogous traits:
Similar due to convergent evolution, not common ancestry e.g wings in birds and insects
only homolgous traits should be used in tree construction
77
Phylogenetic inference
1) data types what are they?
2) Molecular Phylogenetics explain?
Morphological characters (less common now)
Molecular data: DNA, RNA, Protein sequences
Molecular genetics: uses sequences alignments and evolutionary models to build treats, assumes mutations accumulate over time, and requires orthologous sequences (genes derived from common ancestor via speciation).
78
What is convergent evolution when does it occur
when similar environemental pressures and natural selection produce similar (analogous) adaptions in organisms from different evolutionary lineages.
79
Explain what sequence alignment allows for?
1) molecular phylogeny
2) Align homologous positions in sequences
3) MUSCLE, MAFT, CLUSTALW
4) Gaps represent insertions/deletions (indels)
80
What are the two types of tree building methods
distance based methods: convert alignments into pairwise distance matrices, UPGMA (algorithms)
Character Based methods: examine each site in alignment. includes maximum parismony: find trees requiring fewest evolutionary changes, assumes simplicity, maximum likelihood: uses statistical models, evaluates the probability of observed data given the tree and model
bayesian inference: similar to ML but incorporates prior probabilities.
81
What are the causes of the differing phylogenetic trees, 1 physical issue and 2 molecular issues, possibly due to:
Incomplete lineage sorting
gene duplication/loss
horizontal gene transfer
consensus trees or species trees help resolve conflicts .
82
What is synapomorphy
a derived state shared by two or more lineages which was present in their common ancestor and is not found in other organisms.
synapomorphies diagnose monophyletic groups.
83
What is a symplesiomorphy = shared ancestral character
ancestral state shared by two or more lineages which was present in their common ancestor but is not found in all of its descendants.
symplesiomorphies diagnose paraphyletic groups
84
What are the key assumptions in cladistics
Traits in both outrgroup and ingroup are ancestral.
derived traits arose once
traits in subsets of ingroups evolved in those specific lineages
85
What are the methods for building tress
Maximum Parismony (MP)
Select tree with fewest evolutionary changes.
Maximum Likelihood
uses probabilistic models of DNA evolution, calculates which tree is most likely given the sequence data and a model of mutation
Bayesian Inference
Distance based approaches - UPGMA (unweighted pair group method with arithmetic mean, uses pairwise sequence distances only, good for long sequences
86
Explain the distance based approach UPGMA
Uses pairwise sequence distances only, good for long sequences
1) align sequences
2) create distance matrix
3) group taxa with least differences
4) Recalculate distances using averages
5) Construct tree step by step
Key Assumption: constant rate of evolution (Molecular clock): often violated in real data
87
What do molecular clocks do?
Convert genetic distance into time estimates for divergence, assumes rate of molecular change is constant over time,
calibrated using: fossil record dates, known divergence points
applications: dating species divergence, studying gene duplication events.
88
What are the limitations of molecular clocks
Clock speed varies among genes
Natural selection can bias rates
Gene duplication complicates rate interpretation
different genes yield different divergence times (humans vs chimpanzees)
high uncertainty for pre-fossil divergence events.
89
How are molecular clocks calibrated?
Molecular Clocks are calibrated by plotting the number of genetic differences against the dates of evolutionary branch points that are from the fossil record.
90
Explain the differences in clock speed.
Inidvidual genes vary in how clocklike they are
if most of the evolutionary changes in genes and proteins has no effect on fitness then the rate of molecular change should be regular.
Difference in clock rate for different genes are a function of the importance of the gene and how critical the specific amino acids is to protein function.
91
What are the potential problems with molecular clocks
The molecular clock does not run smoothly as expected if mutations were neutral
irregularities result from natural selection in which some DNA changes are favored over others
estimate of evolutionary divergences older than the fossil record, have a high degree of uncertainty.
92
What is a species?
A species is a group of interbreeding natural popiulations that produce viable, fertile offspring are reproductively isolated from other such groups
93
What is the strengths and limitations of species survival?
Strength focuses on gene flow and reproductive isolation
Limitations: not applicable to asexual organisms, hybridisation can occur e.g ligars, zorses challenging strict reprodutive boundaries.
94
What does temporal isolation involve
reproductive timing differs
e.g eastern and western spotted skunks
95
What does behavioral isolation involve
different courtship rituals e.g blue footed vs red-footed
96
What does mechanical isolation
Morphological differences, opposite shell spirals in bradybaena snail
97
Gametic isolation
gametic isolation -> sea urchin sperm/egg incompatibility
98
Postzygotic barriers (after fertilisation):
Reduced Hybrid Viability: Hybrid fails to develop properly e.g varies.
Reduced Hybrid Fertility: Sterile offspring e.g Mule (horse x donkey).
Hybrid breakdown: F2 or backcross offspring feeble/sterile.
99
The process of speciation
Key components: Gene flow reduction or interruption, reproductive isolation, accumulation of genetic differences
100
What is allopatric speciation ("Other country")
Geographic barrier isolates populations -> genetic divergence
Natural selection, drift, or mutation cause evolutionary change.
Even if populations meet again, they may be reproductively isolated.
101
Peripatric speciation
Allopatric + founder effects
Small isolated populations undergo rapid change due to drift and selection
102
What is Sympatric speciation ("Same country")
Occurs without geographic isolation:
Mechanisms:
polyploidy esp in plants
sexual selection
habitat differentiation
103
What are Hybrid Zones and Outcomes:
When species with incomplete reproductive isolations meet: The things that happen are the following: Reinforcement: hybrids are unfit -> selection strengthens isolation
Fusion -> Barriers weaken -> species merge
Stability -> Hybrids form continuously but species remain distinct.
104
Define Sympatric speciation
Sympatric speciation occurs when reproductive isolation arises within a single interbreeding population without geographic barriers.
105
What are the key mechanisms that drive sympatric speciation?
Polyploidy: sudden changes in chromosome number prevent breeding with the original population e.g many crop species like wheat are polyploid hybrids.
Sexual selection: preference for specific traits leads to mating within subgroups
Habitat differentiation: subgroups within the population exploit different resources or microhabitats e.g apple maggot flies now lay eggs on apples instead of hawthorn: this host shift reduces mating between groups.
106
Explain what the sympatric speciation is driven by in Heliconius Butterflies
Habitat differentiation, prezygotic isolation, sexual selection, natural selection
107
What are the principles that underlie some examples of nonmendelian inheritance
Mitochondrial inheritance
X chromosome inactivation
Genomic imprinting
Meiotic drive
108
pedigree definition
A family history that shows how a trait is inherited over several generations
used to understand the transmission pattern of a particular disorder
can determine whether family has an autosomal or sex-linked disease whether it is dominant or recessive.
109
Give an example of autosomal dominant disorders
Achondroplasia: common cause of restricted growth 1 in 10000 births, mutation in FGFR3 (Fibroblast growth factor receptor 3)
Causes skeletal abnormalities
Shows complete penetrance in heterozygotes.
In rare homozygous cases - fatal soon before/after birth "lethal allele"
males and females equally affected 50:50
2 carreier parents 1 in 4 chance of affected children
consanguinity is a factor
carriers much more common than affected patients
110
Another example of Autosomal recessive disorders
1) Sickle cell anaemia
autosomal recessive disease caused by mutation in the haemoglobin gene
2) Sickle cell shape of red blood cells means they can clog capillaries
111
Give another example of autosomal recessive disorders
Autosomal recessive disease caused by mutation in the cystic fibrosis transmembrane receptor Cftr gene
People that lack the receptor ie 2 mutant copies cannot secrete enough liquid in their mucus
Sticky mucus accumulates and harbours infections
112
Explain the concept of mitochondrial inheritance
Mitochondria have their own genome, separate from the nuclear genome (likewise chloroplast in plants)
Mitochondria are passed down in the egg but not in the sperm (only the mother will pass on mutations, not Father)
Many mitochondria per cell = HETEROPLASMY -> if looking you can have a graded fraction of how much of that mitochondrial DNA is damaged. This is why a mother passes on all the diseases to the children.
Mitochondrial diseases affect muscle function, cardiomypothy effect energy hungry tissues.
(mother passes to almost all children but with variable phenotype severity)
113
What is sex-linked inheritance
Females (XX) have two copies of each allele and can therefore be heterozygous or homozygous for an X-linked allele.
Males (XY) have only a single X chromosome, and are described as hemizygous for X linked genes Only have a single X chromosome.
Therefore in the male body any recessive allele present on the X chromosome gets immediately revealed.
e.g females can be carries for colourblindness
thus recessive alleles on the X chromosome are thus uncovered in males -> Hemizygous exposure.
114
What are the key features of X-linked recessive inheritance and why are males more frequently affected?
X-linked recessive traits are caused by mutations on the X chromosome.
Males (XY) have only one X chromosome and are hemizygous, so any recessive mutation on it is immediately expressed.
Females (XX) have two X chromosomes, so a normal allele can mask the effect of a recessive one — they can be carriers without showing symptoms.
This explains why males are more commonly affected.
Examples: Haemophilia A, red-green colour blindness, Duchenne muscular dystrophy.
115
How are X-linked recessive traits passed from parents to offspring
Carrier Mother x Normal Father
50% of sons are affected
50% daughters are carriers
Affected father x normal mother: all sons are unaffected (get Y from dad), all daughters are carriers (inherit Xr from dad)
Fathers pass on their X chromosome only to daughters and Y chromosome to sons
Mothers pass an X to both sons and daughters
116
In X linked recessive traits if you have an affected father what happens to the sons and daughters?
100% of daughters are unaffected carries
Sons do not inherit mutant allele.
117
In X linked recessive traits e.g haemophilia A, red-green colour blindness if you have a carrier mother what happens?
Mutant allele is passed to 50% of daughters and 50% of sons
daughters are unaffected carriers, sons are affected.
118
Give the examples of nonmendelian inheritance
Genomic imprinting
Meiotic Drive
119
Describe aspects of genomic imprinting
Angelman syndrome is a severe genetic disease caused by a de novo deletion on chromosome 15
Causative mutation in always found to have occurred in the maternal genome.
If the exact same mutation occurs in the paternal genome a different disease results prader willi syndrome.
120
Explain what is meant by imprinting
difference in phenotype associated with a mutation depending on whether the mutation is maternally or paternally derived.
Also called a parent of origin effect.
In this Case: Paternal inheritance: Prader-willi syndrome
Maternal inheritance: Angelman syndrome
121
Angel syndrome inherited mutation on chromosome 15 from mum
affects both boys and girls
severe learning difficulties usually non-verbal children
happy demeanour (cconstand smiling and laughing)
Motor difficulties (seizures, gait problems jrky limb movements)
122
Prader Willi Syndrome: inherited mutation no chromosome 15 from dad
affects both boys and girls
mild to moderate learning difficulties
endocrinological disturbance (male sterility, reduced fertility in females)
inability to regulate appetite: sever obesity.
123
What happens in female meiosis:
Only one meiotic product becomes the gamete the other products become polar bodies and degenerate. Some every rare genes cause meiotic drive and are preferentially passed on
124
What happens when a male somatocyte is dividing
The cheating mechanism depends on the details of the division male or female meiosis
Male meiosis: all four meiotic products become gametes
some (very rare genes) can act as gamete killers
125
What is Cas9/CRISPR?
Bacterial adaptive immune system
Bacteria "capture" bits of DNA from bacteriophages and use these to make RNA guides. The gRNA then directs the Cas9 nuclease to cleave the invaders DNA and resist bacteriophage infection.
It is a 2 part system:
If we put the Cas9 on the dad's Y chromosome.. and Mum provides the guide RNA.. then only male embryos will be edited .. so if we target an essential gene, the male embryos will arrest in early development
126
