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Biology 1 > evolution key terms > Flashcards

evolution key terms Flashcards

1
Q

inherited characteritics of organisms that enhance their survival and reproductionin specific environments; a trait, or integrated suite of traits, that increases the fitness of its possessor

A

adaptation

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2
Q

bad design that loops around the aortic arch and controls the voice box

A

left recurrent laryngeal nerve

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3
Q

a supposition or proposed explanation made on the basis of limited evidence as a starting point for further investigation

A

hypothesis

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4
Q

darwin’s term for evolution

A

descent with modification

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5
Q

potential for existing adaptations to limit within a given lienage the evolution of subsequent adaptations

A

historical constraint

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6
Q

viewed species as fixed and arranged them on a scala naturae

A

aristotle

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7
Q

binomial nomenclature, inanimate objects, plants, animals, people

A

linneaus, C

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8
Q

found watch in the meadow and thought this is too complex to be here by chance (evolution is bc of god)

A

paley, w

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9
Q

argued that, at best, the AFD supports the need for a designer, it does not show that the designer must be god

A

hume, d

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10
Q

introduced the concept of uniformitarianism

A

hutton, j

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11
Q

theory that changes in the earth’s crust during geological hsitory have resulted from the action of continuous and uniform processes, same natural laws that operate in the universe now have always been applied everywhere and anytime

A

uniformitarianism

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12
Q

5 things of lamarckian evolution

A
  1. different living things have descended from common ancestors
  2. spontanous generation of simple organisms
  3. inherent trend from simple to complex (and less to more perfect)
  4. use/disuse
  5. envioronmental influence
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13
Q

production of living organisms from nonliving matter, as inferred from the apparent appearance of life in some supposedly sterile environments

A

spontaneous generation

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14
Q

“an essay on the principle of population” about limits to human population expansion

A

thomas malthus

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15
Q

proposed that the same geologic processes are operating today as in the past, at the same rate, uniformitarianism

A

lyell, c

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16
Q

born into wealth, medical school and theological training, voyage of HMS beagle, completed essay on “selection”

A

charles darwin

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17
Q

pea pod guy

A

mendel, g

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18
Q

independently developed concept darwin termed natural selection

A

wallace, a

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19
Q

a typical example or pattern of soemthing

A

paradigm

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20
Q

ladder of life

A

scala naturae

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21
Q

great chain of being

A

scala naturae

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22
Q

role of natural history, catalog the ‘links’ as a means of revealing and appreciating the wisdom of god=natural theology

A

aquinas, T

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23
Q

wisdom of god; knowledge of god based on observed facts and expereince apart from divine

A

natural theology

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24
Q

argument for the existence of god or, more generally, for an intelligent creator ‘based on percieved evidence of deliberate design in the natural or physical world

A

teleology/ Arguement from Design (AFD)

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25
Q

challenbes the fundamental idea of “natural theology”

A

empircal

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26
Q

ship Darwin went on when he went to galapogos islands and all of his other research

A

HMS beagle

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27
Q

civil engineer, blending inheritance modifies traits on which natural selection might act, “Natural selection has no power”

A

jenkin, f

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28
Q

archbishop said creation 4004 BC; sunday the 23rd of october by reading the bible

A

ussher J

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29
Q

heat conduction estimate for age of the earth 20-100 million years ago

A

w, thomson (lord kelvin)

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30
Q

disocovered radioactivity

A

becquerel

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31
Q

conducted pioneer research on radioactivity

A

m curie

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32
Q

process in which individual that have certian inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits

A

natural selection

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33
Q

refers to the difference between indivudals in a given generation and how many offspring they are able to leave. the “fittest” leave more offspring while those not suited to the environment leave fewer or even none

A

differential reproductive success

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34
Q

intentional reproduction of individuals in a populaiton that have desirable traits; ex: dogs

A

artificial selection

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35
Q

wild cabbage that underwent artificial selection; the species of plant that includes many common foods as cultivars, including cabbe, broccoli, cauliflower, kale, brussells sprouts, collard greens, savoy, etc

A

brassica oleracea

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36
Q

e mayr observations

A
  1. all species have high reproductive potentional
  2. populations tend to remain stable
  3. environmental resourcdes limited
  4. members of pop vary
  5. much of variation is inheritable
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37
Q

e mayr inferences

A
  1. production of more individuals than the environment can support leads to a struggle for existence, with only a fraction of offspring surviving
  2. survival depends in part on inherited traits and differential reproductive success
  3. change in allele frequencies over time
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38
Q

scientist interbred foxes to domesticate thema nd they turned otu almost like dogs; have a spot on their forehead like other domesticated animals; failure

A

belyaev’s foxes

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39
Q

the area surronding an animal that if encroached upon by a potential predator or threat, including humans, will cause alarm and escape behavior

A

flight initiation distance

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40
Q

a dark brown to black pigment occuring in the hair, skin, and iris of the eye in people and animals. it is responsible for tanning of skin exposed to sunlight

A

melanin

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41
Q

a hormone secreted by teh adrenal glans, especially in conditions of stress, increasing rates of blood circulatio, breathing, and carb metabolsim and preparing muscles for exertion

A

adrenaline

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42
Q

the process of adaptating wild platns and animals for human use

A

domestication

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43
Q

similarity resulting from common ancestry

A

homology

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44
Q

represents variations om a structural theme that was present in their common ancestor; share common ancestry but not necessarily similar function

A

sturtural homology

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45
Q

embryos to similar species look similar

A

ebryological homology

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46
Q

similar dna in common ancestry

A

molecular homology

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47
Q

in the embryonic development of vertebrates, these form on the endothermal side between the pharyngeal arches. the pharyngeal grooves (or clefts) form the lateral ectodermal surface of the neck region to separate arches. the pouches line up with the clefts, and these thin segments become gills in fish

A

phayngeal pouches

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48
Q

in animal anatomy, it is a flexible rod made out of a similar material to cartilage. if a species has one, they are, by definition, a chordate; provide rigid structure for msucle attatchment

A

notochord

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49
Q

is an extension of the spinal chord that extends beyond the animal’s anus. they are a feature of all chordates, which is a phylum that includes vertebrates. all chordates have one at some point, but they might not their whole life

A

post-anal tail

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50
Q

one of the embryonic features unique to chordatesl it is a hollow chord dorsal to the notochord

A

dorsal hollow nerve chord

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51
Q

a feature that appears similar in two taxa which have originated from two different ancestors

A

analogy

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52
Q

similarities between fossil extant taxa from the same geological region; clift/darwin

A

law of succession

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53
Q

similarities which have arisen independently in two or mroe organisms that are not closely related

A

convergence

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54
Q

scientific study of the geographic distrubution of species

A

biogeography

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55
Q

any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group.

A

transitional fossil

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56
Q

thought to be the “first whale.” Straddling the two worlds of land and sea, the wolf-sized animal was a meat eater that sometimes ate fish, according to chemical evidence. Pakicetus also exhibited characteristics of its anatomy that link it to modern cetaceans, a group made up of whales, porpoises, and dolphins

A

pakicetus

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57
Q

one of the most distinctive and highly specialized orders of mammals. They include the largest animal that has ever lived, the blue whale; the highly intelligent and communicative dolphins; the tusked narwhals and blind river dolphins and singing humpback whales — nearly eighty living species in all

A

cetacea

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58
Q

a structure formed early in development

A

limb buds

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59
Q

a feature of an organsims that is a historical remnant of a structure that served as a function in the organism’s ancestors

A

vestigial

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60
Q

each organ and tissue of an organism throws off tiny contributions of itself that are collected in the sex organs and determine the configuration of the offspring; developed by darwin

A

pangenesis

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61
Q

a variant form of a gene. some genes have a variety of different forms, which are located at the same position, or genetic locus, on a chromosome. humans are called diploid organisms because they have two of these at each genetic locus, with one from each parent

A

allele

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62
Q

the specific location or position of a gene’s dna sequence on a chromosome

A

locus/loci

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63
Q

the genetic makeup of an organism or group of organisms with reference to a single trait, set of traits, or an entire complex of traits; the sum total of genes transmitted from parent to offspring

A

genotype

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64
Q

a mature haploid male or female germ cell that is able to unite with another of the opposite sex in sexual reproduction to form a zygote

A

gametes

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65
Q

a threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes

A

chromosome

66
Q

production of offsrping with combination of traits that differ from those foundin either parent. in eukaryotes, this during meiosis can lead to a novel set of genetic info that can be passed on from the parents to the offspring

A

recombination

67
Q

stronger allele

A

dominant

68
Q

weaker allele

A

recessive

69
Q

an individual having two identical alleles of a particular genes and so breeding true for the corresponding characteristic

A

homozygote

70
Q

an individual having two different alleles ofa particualr gene or genes, and so giving rise to varying offspring

A

heterozygote

71
Q

a mathmatical description of a population that is not evolving

A

hardy-weinberg theorem

72
Q

chance fluctions in allele frequencies over generation tend to reduce variation

A

genetic drift

73
Q

genetic drift that occurs when a few individual become isolated from a larger population and for a new populatoin whose gene pool composition is not reflection of taht of the original population

A

founder effect

74
Q

genetic drift that occurs when the size of a population is reduced, as by a natural disaster or human actions. typically, the surviving popoulation is no longer geneticallly representitive of the original population

A

bottleneck effect

75
Q

a mating pattern and a form of sexual selection in which individual with similar phenotypes mate with one another more frequently than would be expected under a random mating pattern

A

assortive mating

76
Q

random mating

A

panmixis

77
Q

the production of offspring from the mating or breeding of individuals or organisms that are closely related genetically

A

inbreeding

78
Q

the transfer of alleles between populations, tends to reduce genetic differences between populations over time

A

gene flow

79
Q

the process of individuals moving into a range from elsewhere

A

immigration

80
Q

the process of individuals moving out of the population range

A

emigration

81
Q

the changing of the structure of a gene, resulting in a variant form that may be transmitted to subsequent generations, caused by the alteration of a single base units in DNA, or the deletion, insertion, or rearragement of larger section of genes or chromosomes

A

mutation

82
Q

a type of mutation caused by a single nucelotide base substiution, insertion, or deletion of the genetic material, DNA or RNA

A

point mutation

83
Q

is the addition of one or more nucelotide base pairs into a DNA sequence. can be anywhere in size from one base pair to a section of one chromosome inserted into another. this can happen due to unequal crossover during meiosis

A

insertion

84
Q

a mutation in which a part of a chromosome or a seuqnce of DNA is lost during DNA replication. any number can be deleted, from a single base to an entire piece of chromosome. can be caused by errors in chromosomal crossover during meiosis, which casues several serious genetic diseases

A

deletion

85
Q

a molecule that carries the genetic instructions used in the growth, development, function and reproduction of all known living organsims and many viruses

A

dna

86
Q

what does dna stand for

A

deoxyribonucleic acid

87
Q

organic molecules that serve as the monomers, or subunits, of nucleic acids like DNA and RNA. the building blocks of nucleic acids are composed of a nitrogenous base, a 5-carbon sugar (ribose or deoxyribos), and at least one phosphate group

A

nucleotides

88
Q

biological process of producing two identical replicas of dna from one original dna molecule; begins with the “unzipping” of the parent molecule as the hydrogen bonds between the base pairs are broken. once exposed, the sequence of bases on each of the separated strands serves as a template to guide the insertion of a complementary set of baseson the strand being synthesized

A

dna replication

89
Q

large biomolecules, or macromolecules, consisting of oone or more long chains of amino acid residues. perform a vast array of functions within organisms, including catalyzing metabolic reawctions, dna replication, responding to stimuli, and transporting molecules. differ primarily in their sequnce of amino acids, which is dictated by the nucelotide sequence of their genes, which usually results in protein folding into a specific 3d structure that determiens its activity

A

protein

90
Q

building blocks of protien

A

amino acid

91
Q

an important mechanism for acquiring new genes and creating genetic noevelty in organisms. many new gene functions have evolved through gene duplication adn it has contributed tremendously to the evolution of developmental programms in various organisms. can result from unuequal crossing over, retrooposition, or chromosomal duplication

A

gene duplicaiotn

92
Q

those containing more than 2 paired (homologous) sets of chromosomes. most species whose cells have nuceli (eukayotic) are diploid, meaning they have two sets of chromosomes–one set inherited from each parent

A

polyploidy

93
Q

having a single set of unpaired chromosomes

A

haploid

94
Q

containing two complete sets of chromosomes, one from each parent

A

diploid

95
Q

the transfer of alleles between populations, tends to reduce genetic differences between populations over time

A

gene flwo

96
Q

the aggregate of all the alleles in the population; population united by thsi

A

gene pool

97
Q

natural selection in which the intermediate phenotypes survive or reproduce more successfully than do extreme phenotypes

A

stabilizing selection

98
Q

natural selection in which individuals on both extremes of a phenotypic range survive or reproduce more successfully than do individuals with intermediate phenotypes

A

disruptive selection

99
Q

natural selection in which individuals at one end of the phenotypic range survive or reproduce more successfully tahn do individual with intermediate phenotypes

A

directional selection

100
Q

influences changes in secodnary sex characteristics that can give individuals advantages in mating

A

sexual selection

101
Q

an enzyme used to generate complementary DNA from an RNA template, a process termed this. it is mainly associated with retroviruses

A

reverse transriptase

102
Q

species become species because they reproduce cohesive with other species until they can become the same species, opposite of speciation

A

reproductive cohesion

103
Q

a collection of mechanisms, behaviors and psycholgical procdesses that prevent the members of two different species taht cross or mate from producing offspring, or which ensure that any offspring that may be produced are sterile

A

reproductive isolation

104
Q

types of pre-zygotic isolation

A

spatial, behavioral, mechanical and temporal

105
Q

the preferred locations of reproductive events are not compatiable. can live in different areas or just not have the same preffered place of reprodcution. for ex: different kinds of trees or different parts of the same tree

A

habitat isolation

106
Q

different species tend to have differetn breeding seasons. the timing of when females are fertile. similar species may be phsyically compatiable but may not reproduce due to mating season being at different times.

A

temporal isolation

107
Q

maitng rituals, along with other necessary mating behaviors like mating calls, are necessary for males and females of the same species to indicate it is time to sexually reproduce. if the mating ritual is rejected or not recognized, the mating will nto occur

A

behavior isolation

108
Q

incompatibility of sexual organs

A

mechanical isolation

109
Q

prevents the formation of fertile offspring

A

post-zygotic isolation

110
Q

types of post zygotic isolation

A

hybrid viability, hybrid fertility, hybrid breakdown

111
Q

gene of different parent species may interact and impair the hybrid’s development

A

hybrid viability

112
Q

a viable hybrid individual is sterile and often due to the inability to produce normal gametesin meiosis

A

hybrid fertitility

113
Q

the first generation hybrids are viable and fertile, but when they mate the offspring are feeble and steril

A

hybrid breakdown

114
Q

the formation of new species in populations taht are geogrphically isolated from one another

A

allopatric specieation

115
Q

the formation of new species in populations in the same area

A

sympatric speciation

116
Q

a fertile individual that has mroe than two chromosomes as a result of two different species interbreeding and combining their chromosomes

A

allopolyploidy

117
Q

a method of dating geological or archological specimens by determining the relative proportions of particular radioactive isotopes present in a sample

A

radiometric dating

118
Q

the time required for a quantity to reduce to half its initial value

A

half life

119
Q

a radioactive form of an element that undergoes decay and produces daughter isotopes, which may in turn decay to produce other daughter isotopes

A

parent isotope

120
Q

the remaining nuclide left over from radioactive decay

A

daughter isotope

121
Q

a geologic eon, 4,000 to 2,500 million years ago (4-2.5 billion years), that followed the hadeon eon adn is preceded by the proterozoic eon. during this, earth’s crust had cooled enough to allow the formation of continenets; atomospheric oxygen present

A

archean

122
Q

the first traces of life appear nearly 3.5 billion years ago; single and multicellular eukaryotes appeard, including animals at the very end of this period

A

proterozoic

123
Q

the current geologic eon, adn the on during which abudndant animal and plant life existed. it covers 541 million years to the present, and began with the cambrian period when diverse hard-shelled animals first appeared

A

phanerozoic

124
Q

first cells appeared during the

A

proterozoic

125
Q

first atmostpheric oxygen appeared during the

A

archean

126
Q

aka great dying, occured about 252 million years ago, forming the boundary between the permian and the triassic geologic periods, as well as the paleozoic and mesozoic eras most severe known extinction with up to 96% of marine species and 70% terrestrial species becoming exctnct. only mass extinction of insects.

A

permian extinction

127
Q

a global extinction event responsible for eliminating 80 percent of all species of animals at or very close to the boundary between the cretacious and paleogene periods, about 66 million years ago. characterized by the elimination of many lines of animals that were important elements of the mesozoic era, including nearly all dinos and many marine invertebrates

A

cretacious/teriary extinction, k-t

128
Q

crater is an impact crater underneath the yucatan peninsula in mexico, caused k-t extinction

A

chicxulub crater

129
Q

the act or process of growing or causing something to grow or become larger or more advanced

A

development

130
Q

the growth of body parts at different rates, resulting in a change of body porportions

A

allometry

131
Q

evolutionary change in the timing or rate of an organism’s development

A

heterochrony

132
Q

the retention of juvenile features in the adult animal.

A

neoteny

133
Q

example of neoteny

A

axolotl

134
Q

the retention by adults of traits previously seen only in the young,

A

padomorphosis

135
Q

transformation of one organ into another, arising from mutation in or misexpression of specific developmentally critical genes; alteration of major atomical features

A

homeosis

136
Q

control of major developomental programs in animals; any of a class of closely simiar sequences that occur in various genes are involved in regulating embryonic devolopment in a wide range of species

A

homeobox

137
Q

a group of related genes that control the body plan of an embryo along the cranio-caudal (head-tail) axis. After the embryonic segments have formed, (x) proteins determine the type of segment structures (e.g. legs, antennae, and wings in fruit flies or the different types of vertebrae in humans) that will form on a given segment. (x) proteins thus confer segmental identity, but do not form the actual segments themselves.
An analogy for the (x) genes can be made to the role of a play director that calls which scene the actors should carry out next. If the play director calls the scenes in the wrong order, the overall play will be presented in the wrong order. Similarly, mutations in the (x) genes can result in body parts and limbs in the wrong place along the body. Like a play director, the (x) genes do not act in the play or participate in limb formation themselves.

A

hox

138
Q

a theory about how organisms are related to one another through evolutionary time

A

phylogeny

139
Q

the devising of choosing names for things, especially in a science

A

nomenclature

140
Q

puting something into categories

A

classification

141
Q

a formal system of naming species of living things by giving each a name composed of two parts, the first being the genus and the second the species

A

binomial system

142
Q

there are three kingdoms, divided into classes, and they, in turn, into orders, families, genera (singular: genus), and species (singular: species), with an additional rank lower than species.

A

linnean hierarchy

143
Q

a group of one or more populations of an organism or organisms seen by taxonomists to form a unit

A

taxa/ taxon

144
Q

a systematic term from cladistics denoting the closest relative of a given unit of a phylogenetic tree

A

sister taxa

145
Q

a group is a taxon (group of organisms) which forms a clade, meaning that it consists of an ancestral species and all of its descendants

A

monophyly

146
Q

(derived trait) a novel evolutionary trait that is unique to a particular species and all its descendants and which can be used as a defining character for a species or gorup in phylogenetic terms

A

apomorphy

147
Q

an evolutionary trait that is homologous within a particular group of organisms but is not unique to members of that group and therefore cannot be used as a diagnostic or defining character of the group. for example, vertebrae are found in zebras, cheetahs, and gorillas, but the common ancestor in which this trait first evolved is so distant that the trait is shared by many other naimals.

A

plesiomorphy

148
Q

in a cladistic analysis, the set of taxa which are hypothesized to be more closely related to each other than any are to the outgroup

A

ingroup

149
Q

in a cladistic analysis, any taxon used to help resolve the polarity of characters, and which is hypothesized to be less closely related to each of the taxa under consideration than any are to each other

A

OUTGROUP

150
Q

endogenous viral elements in the genome that closely resemble and can be derived from retroviruses. they are abundant in the genomes of jawed vertebrates, and they compirse 5-8% of human genome; these genes can mutate and instead of moving to another location in the genome they can become exogenous or pathogenic. this means that not all ERVs may have originated as an insertion by a retrovirus but that some may have been the source for the genetic info int eh retrovirus they resemble. when integration of viral DNA occur in the germ-line, it can give rise to this, which can later become fixed in the gene pool of the host population

A

erv (endogenous retroviruses)

151
Q

belongs to a group of drugs called nuceloside analogues. interferes with an enzyme called revere transcriptase (RT), which is used by HIV-infected cells to produce fewer viruses; can be used to help the baby not have it

A

AZT

152
Q

a subunit of the envelope protien complex of retroviruses, including HIV. a transmembrane protein that contains several sites within its ectodomain that are required for infection of host cells

A

gp41

153
Q

is an enzyme produced by a retrovirus that enables its genetic material to be integrated into the DNA of the infected cell

A

integrase

154
Q

an enzyme that breaks down proteins and peptides

A

protease

155
Q

the cabability of an organism to defend itself against a disease

A

resistance

156
Q

a customized combo of different classes of medications that a physician prescribes based on such factors as the patient’s viral load (how much virus is in the blood), the particular strain of the virus, the CD+4 cell count, and other considerations (e.g. disease symptoms). cannot rid body of HIV, it must be taken every day for life. can control viral load, delaying or preventing onset of symptoms or progression to AIDs, thereby prolonging survival. used since 1996, changed from fatal to chronically managed

A

HAART, highly active antireroviral therapy

157
Q

the number of simultanous mutations required to produce resistance

A

genetic barrier

158
Q

a protein on the surface of white blood cells that is involved in the immune system as it acts as a receptor for chemokines. this is the process by which T cells are attracted to specific tissue and organ targets

A

CCR5

159
Q

mutation of the normal CCR5 gene (co-receptor)– this mutation is found largely in peoples of northern Europe and of northern europena descent. the mutation largely prevents infection by HIV

A

CCR5D32

160
Q

During mitosis one cell? divides once to form two identical cells.
The major purpose of mitosis is for growth and to replace worn out cells.
If not corrected in time, mistakes made during mitosis can result in changes in the DNA? that can potentially lead to genetic disorders?.
Mitosis is divided into five phases:
1. Interphase:
The DNA in the cell is copied in preparation for cell division, this results in two identical full sets of chromosomes?.
Outside of the nucleus? are two centrosomes, each containing a pair of centrioles, these structures are critical for the process of cell division.
During interphase, microtubules extend from these centrosomes.
2. Prophase:
The chromosomes condense into X-shaped structures that can be easily seen under a microscope.
Each chromosome is composed of two sister chromatids, containing identical genetic information.
The chromosomes pair up so that both copies of chromosome 1 are together, both copies of chromosome 2 are together, and so on.
At the end of prophase the membrane around the nucleus in the cell dissolves away releasing the chromosomes.
The mitotic spindle, consisting of the microtubules and other proteins, extends across the cell between the centrioles as they move to opposite poles of the cell.
3. Metaphase:
The chromosomes line up neatly end-to-end along the centre (equator) of the cell.
The centrioles are now at opposite poles of the cell with the mitotic spindle fibres extending from them.
The mitotic spindle fibres attach to each of the sister chromatids.
4. Anaphase:
The sister chromatids are then pulled apart by the mitotic spindle which pulls one chromatid to one pole and the other chromatid to the opposite pole.
5. Telophase:
At each pole of the cell a full set of chromosomes gather together.
A membrane forms around each set of chromosomes to create two new nuclei.
The single cell then pinches in the middle to form two separate daughter cells each containing a full set of chromosomes within a nucleus. This process is known as cytokinesis.

A

mitosis

161
Q

During meiosis one cell? divides twice to form four daughter cells.
These four daughter cells only have half the number of chromosomes? of the parent cell – they are haploid.
Meiosis produces our sex cells or gametes? (eggs in females and sperm in males).
Meiosis can be divided into nine stages. These are divided between the first time the cell divides (meiosis I) and the second time it divides (meiosis II):
Meiosis I
1. Interphase:
The DNA in the cell is copied resulting in two identical full sets of chromosomes.
Outside of the nucleus? are two centrosomes, each containing a pair of centrioles, these structures are critical for the process of cell division?.
During interphase, microtubules extend from these centrosomes.
2. Prophase I:
The copied chromosomes condense into X-shaped structures that can be easily seen under a microscope.
Each chromosome is composed of two sister chromatids containing identical genetic information.
The chromosomes pair up so that both copies of chromosome 1 are together, both copies of chromosome 2 are together, and so on.
The pairs of chromosomes may then exchange bits of DNA in a process called recombination or crossing over.
At the end of Prophase I the membrane around the nucleus in the cell dissolves away, releasing the chromosomes.
The meiotic spindle, consisting of microtubules and other proteins, extends across the cell between the centrioles.
3. Metaphase I:
The chromosome pairs line up next to each other along the centre (equator) of the cell.
The centrioles are now at opposites poles of the cell with the meiotic spindles extending from them.
The meiotic spindle fibres attach to one chromosome of each pair.
4. Anaphase I:
The pair of chromosomes are then pulled apart by the meiotic spindle, which pulls one chromosome to one pole of the cell and the other chromosome to the opposite pole.
In meiosis I the sister chromatids stay together. This is different to what happens in mitosis and meiosis II.
5. Telophase I and cytokinesis:
The chromosomes complete their move to the opposite poles of the cell.
At each pole of the cell a full set of chromosomes gather together.
A membrane forms around each set of chromosomes to create two new nuclei.
The single cell then pinches in the middle to form two separate daughter cells each containing a full set of chromosomes within a nucleus. This process is known as cytokinesis.
Meiosis II
6. Prophase II:
Now there are two daughter cells, each with 23 chromosomes (23 pairs of chromatids).
In each of the two daughter cells the chromosomes condense again into visible X-shaped structures that can be easily seen under a microscope.
The membrane around the nucleus in each daughter cell dissolves away releasing the chromosomes.
The centrioles duplicate.
The meiotic spindle forms again.
7. Metaphase II:
In each of the two daughter cells the chromosomes (pair of sister chromatids) line up end-to-end along the equator of the cell.
The centrioles are now at opposites poles in each of the daughter cells.
Meiotic spindle fibres at each pole of the cell attach to each of the sister chromatids.
8. Anaphase II:
The sister chromatids are then pulled to opposite poles due to the action of the meiotic spindle.
The separated chromatids are now individual chromosomes.
9. Telophase II and cytokinesis:
The chromosomes complete their move to the opposite poles of the cell.
At each pole of the cell a full set of chromosomes gather together.
A membrane forms around each set of chromosomes to create two new cell nuclei.
This is the last phase of meiosis, however cell division is not complete without another round of cytokinesis.
Once cytokinesis is complete there are four granddaughter cells, each with half a set of chromosomes (haploid):
in males, these four cells are all sperm cells
in females, one of the cells is an egg cell while the other three are polar bodies (small cells that do not develop into eggs).

A

meiosis

Biology 1 (14 decks)

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