exam 1 BIO 311d

asexual reproduction

a single individual passes genes to its offspring without the fusion of gametes

• genetic variation only arises from mutations- slow process

• beneficial in non-changing environments

clone

group of genetically identical individuals from the same parent, produced asexually by mitosis

sexual reproduction

re-shuffling of alleles through meiosis and fertilization produces genetic variation in the next generation

• beneficial in changing environments

mutuation

origin of genetic variation, mutations can give rise to new alleles

recombinant chromosomes

produced by crossing over, combines DNA from each parents of the individual making gametes

complete dominance

occurs when phenotypes of the heterozygote and dominant homozygote are identical

incomplete dominance

phenotype of F1 hybrids is somewhere between phenotypes of the 2 parental varieties

co-dominance

both alleles from each parent are fully and equally expressed resulting in a phenotype displaying both traits

polygenetic inheritance

additive effect of 2 or more genes on a single phenotype, traits will vary in a population along a continuum

phenotype

set of observable characteristics of an individual resulting from the interaction of its genotype and the environment

genotype

specific genetic makeup of an organism defining the 2 alleles present at a particular locus in the genome

character

a heritable feature that can vary

homozygous

diploid organism with 2 identical alleles for a gene

heterozygous

diploid organism with 2 different alleles for a gene

alleles

alternative versions of a gene

dominant allele

allele that is fully expressed as a single allele in the phenotype of a heterozygote

recessive allele

allele whose phenotypic effect is not observed in a heterozygote, need 2 copies to express it

monohybrid cross

cross between 2 organisms that are heterozygotes or hybrids for one character (gene)

test cross

genetic method used to determine the genotype of a dominant phenotype by crossing it with a homozygous recessive one

dihybrid cross

cross between F1 dihybrids, can determine whether 2 characters are transmitted to offspring as a package or independently

population

local group of individuals of the same species capable of interbreeding and producing fertile offspring (gene pool)

population genetics

study of the distribution of alleles in populations and how they can change in evolution

mircoevolution

small scale evolution within a population of a species, change in allele frequencies for a trait over time

allele frequency

proportion of a certain allele at a given locus in all individuals within a population

geneotype frequency

proportion of a given genotype at a given locus within a population f

founder effect

few individuals are isolated from larger source population often due to gene flowf

bottleneck effect

sudden reduction in population size due to a change in the environment (disease, disaster, etc.)

sexual selection

natural selection specific to mating success

sexual dimorphism

difference in secondary sexual charcteristics between males and females of the same species

adaptation

inherited characteristics of organisms that enhance their survival and reproduction in specific environments

speciation

the origin of new species, bridges mirco and macro evolution and occurs when populations become genetically isolated

• requires stopping gene flow between 2 isolated groups

biological species concept

a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring

reproductive isolation

existence of biological factors (barriers) that impede 2 species from producing viable, fertile offspring

polyploidy

presence of extra sets of chromosomes due to accidents during cell division, can produce new biological species in sympatry within a single generation

sympatric speciation

takes place in geographically overlappun population

• can occur if gene flow if reduced by factros including

  • polypoidly

  • habitat differenttiation

  • sexual selection

allopatric speciation

geographic isolation restricts gene flow between population

• reprodutive isolation may then arise after divergence

• even if contact is restored between population interbreeding is preventing

biological species concept limitations

• does not apply to all organisms (fossils, asexual organisms)

• emphasizes absence of egen flwo, yet some gene flow can occur between distinct species

  • grizzly bear and polar bear = pizzly bear

hybrids

• hybrid germ line cells need to produced balanced gamets via meiosis (must pairup)

• there must be the same number of chromosomes in the 2 species and the chromosomes must be similar in base pair sequence

• all the gene products of the two parents must work together to make a single new organism gene flow is prevented in many hybrids

prezygotic barriers

blocks reproduction and fertilization from taking place

habitat isolation, temporal isolation, behavioral isolation, mechanical isolation, gametic isolation

habitat isolation

• organisms live in different habitats

• part of a population moves to a new habitat and no longer mixes with original population

temporal isolation

organisms reproduce at different times of the year

behavioral isolation

• males and females not only look but also behave different

• these behaviors help species recognize each other and mate

mechanical isolation

• physical differences prevent mating

• for some species, genitals do not line up

gametic isolation

• differences in gamete celles prevent fertillization from taking place

• mating takes place, but egg and sperm cannot fuse

postzygotic barriers

occurs after fertilization/ zygote formation

reduced hybrid viability, hybrid infertility, hybrid breakdown

reduced hybrid viability

hybrids are produces, but fail to develop to reproduce maturity

hybrid infertility

hybrid are viable, but are sterile

hybrid breakdown

2 species can mate and the 1st hybrid generation is viable and fertile, however the successive generations suffer low viability

morphological species concept

defines a species by body form and structure features

• applies to sexual and asexual species, but relies on subjective criteria

biodiversity

the number of species is key to ecosystem stability

• new species form form pre-existing species and species are lost through extinction

hardy-weinburg equation definition

• describes the genetic makeup of a population that is not evolving at a particular locus

• when gametes contribute to the next generation randomly and mendelian inheritance occurs, alleles and genotype frequencies remian constant from generation to generation

hardy-weinburg equation

p + q = 1

p² + 2pq + q²

p²

expected frequency homozygote AA

2pq

expected frequency heterozygote Aa

q²

expected frequency genotype aa

hardy-weinburg equilibrium

if normal sexual reproduction results in the same allele and genotype frequencies in the next generation

assumptions for hardy-weinburg equilibrium

• no natural selection

• no mutations

• no migration

• large population size (no genetic drift)

• random mating

mircoevolution

when hardy-weinburg assumptions are not met

mechanisms of evolution

forces of evolution can change allele frequencies, gene flow, genetic drift, natural selection

gene flow

transfer of alleles due to migration of fertile individuals or gamete between population

• tends to reduce variation between populations over time (homogenizer)

• can increase or decrease fitness to benefit population

genetic drift

change in the gene pool of a small population due to random chance

• small populations have lower random matings, more genetic drift

• tends to reduce genetic variation through random loss of alleles

• can cause harmful alleles to become fixed

natural selection

nonrandom differential succes in survivorship and reproduction of individuals can cause adaptations in populations

• traits are shaped by abiotic and biotic factors in an ecosystem (selective pressures)

intrasexual selection

direct competition among individuals of one sex, often males, for mates of the opposite sex

intersexual selection

mate choice, occurs when individuals of one sex, often females, are choosy in selecting their mates

selection strength

zero- allele does not affect fitness

positive- allele increases fitness, benefits those who carry it, passed on to offspring

negative- alllele decreases fitness, disadvantages those who carry it, lower offspring

why do females prefer showy males?

good genes hypothesis- less disease, better offspring

sensory exploitation bias hypothesis

darwin

discovered a mechanism for evolution, not the idea of evolution

descent with modification

evolution by natural selection

struggle for existence

due to competition for resources

how evolution by natural selection works

• individuals in a population vary in their heritable characteristics

• organisms produce more offspring than the environment can support

• individuals that are well suited to their environment tend to survive long enough to leave more offspring than other individuals, differential reproductive success

• over time, favorable traits or adaptations accumulate in the population

3 types of natural selection

directional, disruptive, stabilizing

directional selection

favors 1 direction, depends on environment

disruptive selection

favors both extremes, average is selected against

stabilizing selection

favors the average, extremes are selected out

sex-linked traits

x and y linked traits

x linked traits

follow a specifc pattern of inheritance

for a recessive x linked trait to be expressed

• a female needs 2 copies of the allele

• a male needs only 1 copy of the allele

• x linked recessive disorders are much more common in males than in females because they only have 1 x

• mother to son inheritance is common

y linked traits

will follow the father to son only

• a father will pass trait to all sons, who will pass to all of their sons

mendelian genetics

blending vs particulate inheritance

• inherited as average of parents traits vs inheritance as units of heredity

mendel’s 1st law

law of segregation

• the 2 alleles for a heritable character separate during gamete formation and end up in different gametes (3:1 phenotypic ratio)

mendel’s 2nd law

independent assortment

• each pair of alleles assorts independently from other pairs of alleles during meiosis (9:3:3:1 phenotypic ratio)

dominance

a relationship between alleles of one gene, in which the effect of phenotype of one allele masks the contribution of a 2nd allele at the same locus

dominance does not equal prevalence

crossing of purple flower and white flower

p generation- true breeding parents PP x pp

step 1- cross breeding produces f1

f1 generation- hybrids Pp x Pp

step 2- self fertilization produces f2

f2 generation- PP, Pp, Pp, pp

crossing over- recombination

• contribites to genetic variation by combining DNA from 2 parents into a single chromosome

• in humans an average of 1-2 crossover events occurs per chromosome

independent assortment

• each pair of homologs orient randomly at metaphase 1 of meiosis

• each pair of chromosomes sorts maternal and paternal homologs inot daughter cells independently of others

• number of combinations possible is 2^n (n= the haploid number/ number of chromosomes in gametes

random fertilization

• adds to genetic variation because any sperm can fuse with any egg

• fusion of 2 gametes (4 - 8 million chromosome combinations) produces a zygote with any of the about 70 trillion diploid combinations

• each zygote has a unique genetic identity

3 types of mircotubules

• kinetochore- attach to each chromatid

• polar/non-kinetochore- overlap with each other

• astral- attach to the centrosome to the cell pole

requirements for cell division

• receipt of signal

• DNA replicayion

• DNA redistribution- mitosis

• cytokinesis- cell division

5 phases of mitosis

prophase, prometaphase, metaphase, anaphase, telophasem

mitosis

one diploid cell forms two diploid cells, number of chromosomes says the same

• DNA replication- occurs during interphase, before mitosis begins

• number of divisions- 1 including PPMAT

• synapsis of homologs- does not occur

• 2 daughter cells, each genetically identical to the parent cell with the same number of chromosomes

role of mitosis in animals, plants, and fungi

• enables multicellular animal, fungus, or plant to arise from a single cell,

• produces cells for growth, repair and in some species asexual reproduction

• produces gametes in the plant gametophyte

interphase- mitosis

• G1- cell growth and differentiation

• S- synthesis and replication of chromosomes

• G2- synthesis of molecules, other than DNA, needed for cell division

• G0- cells that never divide, nerve cells

cytokinesis

• process of cells dividing

• animals- the membrane pinches as the cleavage furrow forms two membranes from it

• plants- cell plate made of cell wall materials form in between the nuclei and expands to form cell wall and divides

meiosis 1

in the first division at meiosis, the homologous pairs separate

meiosis 2

in the second division of meiosis, the sister chromatids separate, resulting in four haploid cells. Each contains just one copy of each chromosome, rather than a homologous pair

meiosis

• DNA replication- occurs during interphase before meiosis 1, but not meiosis 2

• number of divisions- 2, each including PPMAT

• synapsis of homologous chromosomes- occurs during prophase 1 alonge with crossing over between nonsister chromatids, resulting chiasmata hold pairs together due to sister chromatid cohesion

• number of daughter cells- 4, each haploid, genetically different from parent cell and each other

role of meiosis in animals, fungi, and plants

• produces gametes in animals or spores

• reduces number of chromosome sets by half and introduces genetic variablity among the gametes or spores