Evolutionary Bio Exam 2

Allele Frequencies in Hardy-Weinberg are represented by?

p and q

Genotype frequencies in Hardy-Weinberg are represented by?

p² + 2pq + q² = 1

What does H-W equation tell you?

Given a set of observed allele, the H-W equation tells you the expected genotype frequencies

Hardy-Weinberg equilibrium assumptions

Population allel frequencies do not change when: population is infinitely large (no genetic drift), genotypes do not differ in fitness (no selection), there are no new mutations (no new alleles), there is no migration (no new alleles) and mating is random (with respect to genes of interest)

If a population is not in Hardy-Weinberg equilibrium then why? What is causing it to evolve?

Is the population small? Do genotypes differ in fitness? Are there new mutations? Is mating random? Is there significant migration?

A population not in Hardy-Weinberg Equilibrium will reach Hardy-Weinberg genotype frequencies after…

a single round of random mating

In the absence of evolutionary processes…

allele frequencies will remain constant

gene

Unit of heredity that carries instructions for making proteins; segments of DNA located on chromosomes; responsible for determining traits and characteristics in living organisms.

allele

A variant form of a gene that determines a specific trait. Alleles can be dominant or recessive, and individuals inherit two alleles for each gene, one from each parent. Alleles can interact to produce different phenotypes, and variations in alleles contribute to genetic diversity within a population.

locus/loci

The set of all points that satisfy a given condition or property.

phenotype

physical traits

genotype

genetic code for traits

homozygous

two same alleles

heterozygous

two different alleles

Law of Segregation (Mendel’s First Law)

only one of the two gene copies present in an organism is distributed to each gamete that it makes and the allocation of the gene copies is random

Law of Independent Assortment (Mendel’s Second Law)

The alleles of two (or more) different genes get sorted into gametes independently of one another

dominant allele vs. recessive allele

Dominant alleles are shown in the phenotype over the recessive

incomplete dominance

a form of gene interaction in which both alleles of a gene at a locus are partially expressed often resulting in an intermediate or different phenotype (red flower + white flower = pink offspring)

Sex-linked

genotypes are carried on an X or Y chromosome making them more likely to be present in females or only present in males

mitosis

cell division that occus in eukaryotic cells where parent cell divides into two identical daugter cells

meiosis

a type of cell division in sexually reproducing organisms that reduces the number of chromosomes in gametes

crossing over

a cellular process that happens during meiosis when chromosomes of the same type are lined up, occurs during meiosis prophase 1

Haploid individuals carry one allele at every locus where are diploid individuals…

carry two alleles at every locus (homozygous vs. heterozygous)

polyploids

more than two alleles at every locus

evolution

change in allele frequencies from one generation to the next

percentage of coding exons

0.008 (less than one precent)

generation sources of genetic variation

mutation

redistribution sources of genetic variation

recombination, independent assortment, hybridization, horizontal gene transfer

point mutations

one different codon

Insertion

a section inserted into existing codons

deletion

section deleted from original strand

gene duplication

repeat gene section

inversion

flipped section of genes

chromosome fusion

chromosomes are fused

genome duplication

completely duplicated genome

Germ-line mutations are

heritable (only germ-line)

somatic mutations

affect cells in the body of an organism (not heritable in most cases, except no separate germ line in single-celled organisms, except totipotency in plants)

germ-line mutations

affect gametes, heritable and relevant to evolution

possible consequences of single point mutations

albino-ism, extra digits, fused digits, hyper-/hypo- pigmentations, misshaped skeleton, large brain

sickle-cell anemia

most common inherited blood disorder in the USA, non-synonymous point mutations in hemogloin beta gene

synonymous vs. nonsynonymous mutations

synonymous mutations are DNA mutations that do no change the amino sequence of a protein (minor) vs. nonsynonymous mutations are nucleotide mutations that change the animo acid sequence of a protein (evolutionary important)

insertions and deletions are important in protein genes when…

not in multiples of 3 and in-frame (outside of protein genes: anything goes)

transposable elements

specific form of genetic recombination that moves transposable elements from one place to another (jumping)

Alu insertions can insert themeselves within genes, implicated in many human diseases. What are examples?

breast cancer, ewing’s sarcoma, familial hypercholesterolemia, hemophilia, neurofibromatosis, disbetes mellitus type II

genomes are dynamic entities

genes are constantly undergoing duplications and loss; genes and genomes are continuously turning over

divergence

when duplication event results in different outcome than redundancy

Susumu Ohno, Evolution by Gene Duplication quote

“natural selection merely modified, while redundancy created”

neofunctionalization

duplicate takes on an entirely new function

sunfunctionalization

the duplicate takes on a specialized role similar and complementary to the ancestral function

Loss

mutational decay or wholesale loss (most common)

most genes do not exist as a ______ within and across species

single copy (most genes are part of larger gene “families”)

Terpene synthases

terpenoids (in resins, essentual oils, and aromas) more than 2-fold increase in number in grapes, directly related to aromatic features of wine

examples of gene families and number of copies per

actins (5-30), tubulins (5-15), histones (100-1000), immunoglobin (more than 500), heat-shock proteins (3-5)

ploidy

number of copies of unique chromosomes in a cell

polyploidy can result in

instantaneous sympatric speciation

diploid X tretraploid results in

sterile triploid (seedless fruits)

gemone duplications

whole-gemone duplications are important driver of evolution in several diverse lineages, gene duplication on a grand scale

What percent of all speciation events in flowering plants involve whole-genome duplications?

15% (all flowering plants are ancient polyploids)

independent assortment

creates novel combinations of alleles, alleles of different genes assort independently of one another (as long as they’re not linked)

recomination reshuffles chromosomes, where and when does this occur?

germ-line, meiosis: prophase I

genetic linkage

the physical proximity of alleles at different loci, loci that are physically close are less likely to be separated by recomination during meiosis, they are said to be genetically “linked”

linkage equilibrium

alleles at one locus segregate randomly with respect to alleles at the other

linkage disequilibrium

alleles at different loci are nonrandomly associated, they are segreating together more often than expected by change

bottom line of genetic linkage?

recomination is an important source of genetic variation

evolution is _______ in allele frequencies from one generation to the next

change

evolution does not occur under what kind of conditions?

hardy-weinberg

how do populations evolve?

genetic drift, natural selection, migration (gene flow), mutation

when are sampling errors higher?

smaller sample sizes

evolution by drift

reduces genetic variation in small populations, more dramatic fluctuations in small populations, alternative alleles become fixed, less overall standing variation in small populations

in a finite population allele frequencies fluctuate…

overtime, even in the absence of natural selection

random, nonrepresentative allele (gamete) sampling…

leads to changes in allele frequencies

what is the primary cause of random allele sampling?

meiosis

why is each reproductive event an “independent role of the dice”?

independent assortment and recominations

why do individuals only pass on some (not all) of their alleles?

they only reproduce a finite number of times (some don’t reproduce at all)

some alleles are fixed and others are lost causing

a decreasing fraction of heterozygotes over time

functionally deleterious alleles can become fixed…

in a population by genetic drift

what is a result of genetic drift?

seperate populations diverge in allele frequencies and presence/absence of certain alleles

genetic drift is _____ in small populations

the predominant evolutionary mechanism

bottlenecks

reduce genetic variation

what happens to rare alleles during a bottleneck?

they are likely to be lost

northern elephant seals

hunted and nearly extinct in 1800s, “last” 8 were found in 1892 and killed to be in a museum, now 100,000 exist

bottleneck significance of northern elephant seals

post-bottleneck very little detectable heterozygosity, more found in pre-bottleneck specimens

cheetahs bottleneck significance

very little genetic heterozygosity, no polymorphic loci, similar to lab-bred mice

pingelapese islanders

high incidence of complete color blindness

founder effects cause genetic drift

new popilations started by a small number of individuals

american amish populations

2 waves of immigrations: 500 german immigrants in the 1700s, 3000 german immigrant in the early 1800s

Ellis-van Creveld syndrome

genetic disorder with autosomal recessive transmission

key concept for bottlenecks

even brief bottlenecks can lead to a drastic reduction in genetic diveristy that can persist for generations

fitness

the reproductive success of an individual with a particular phenotype

components of fitness

survival to reproductive age, mating success, fecundity (number of offspring produced)

relative fitness

fitness of a genotype standardized by comparison to other genotypes

average excess fitness

difference in fitness between average fitness of individuals with a given allele vs. the average fitness of the population as a whole

this equation describes the change in allele frequency due to selection

p(o) > 0 if allele is present at all, effectiveness of selection is directly porportional to the frequency of the allele

delta p is greater than 0: allele increase in frequency, delta p is less than 0 < allele decreases in frequency

w > 0 if population exists

natural selection is more powerful in large populations

drift weaker in large populations, small advantages in fitness can lead to large changes over the long term

the strength of selection influences…

how quickly a trait will increase in frequency within a populations over time

selection occurs when genotypes differ in…

fitness

what do outcomes of selection depend on?

frequency of allele of effects on fitness

population size influences power of drift and selection

drift more powerful in small populations and selection more powerful in large populations

additive

allele yields twice the phenotypic effect on two copies present

dominance

dominate allele masks presence of recessive in heterozygotes