evolution key terms

Question 1

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

Answer 1

adaptation

Question 2

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

Answer 2

left recurrent laryngeal nerve

Question 3

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

Answer 3

hypothesis

Question 4

darwin’s term for evolution

Answer 4

descent with modification

Question 5

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

Answer 5

historical constraint

Question 6

viewed species as fixed and arranged them on a scala naturae

Answer 6

aristotle

Question 7

binomial nomenclature, inanimate objects, plants, animals, people

Answer 7

linneaus, C

Question 8

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

Answer 8

paley, w

Question 9

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

Answer 9

hume, d

Question 10

introduced the concept of uniformitarianism

Answer 10

hutton, j

Question 11

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

Answer 11

uniformitarianism

Question 12

5 things of lamarckian evolution

Answer 12

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

Question 13

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

Answer 13

spontaneous generation

Question 14

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

Answer 14

thomas malthus

Question 15

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

Answer 15

lyell, c

Question 16

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

Answer 16

charles darwin

Question 17

pea pod guy

Answer 17

mendel, g

Question 18

independently developed concept darwin termed natural selection

Answer 18

wallace, a

Question 19

a typical example or pattern of soemthing

Answer 19

paradigm

Question 20

ladder of life

Answer 20

scala naturae

Question 21

great chain of being

Answer 21

scala naturae

Question 22

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

Answer 22

aquinas, T

Question 23

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

Answer 23

natural theology

Question 24

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

Answer 24

teleology/ Arguement from Design (AFD)

Question 25

challenbes the fundamental idea of “natural theology”

Answer 25

empircal

Question 26

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

Answer 26

HMS beagle

Question 27

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

Answer 27

jenkin, f

Question 28

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

Answer 28

ussher J

Question 29

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

Answer 29

w, thomson (lord kelvin)

Question 30

disocovered radioactivity

Answer 30

becquerel

Question 31

conducted pioneer research on radioactivity

Answer 31

m curie

Question 32

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

Answer 32

natural selection

Question 33

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

Answer 33

differential reproductive success

Question 34

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

Answer 34

artificial selection

Question 35

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

Answer 35

brassica oleracea

Question 36

e mayr observations

Answer 36

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

Question 37

e mayr inferences

Answer 37

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

Question 38

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

Answer 38

belyaev’s foxes

Question 39

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

Answer 39

flight initiation distance

Question 40

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

Answer 40

melanin

Question 41

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

Answer 41

adrenaline

Question 42

the process of adaptating wild platns and animals for human use

Answer 42

domestication

Question 43

similarity resulting from common ancestry

Answer 43

homology

Question 44

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

Answer 44

sturtural homology

Question 45

embryos to similar species look similar

Answer 45

ebryological homology

Question 46

similar dna in common ancestry

Answer 46

molecular homology

Question 47

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

Answer 47

phayngeal pouches

Question 48

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

Answer 48

notochord

Question 49

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

Answer 49

post-anal tail

Question 50

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

Answer 50

dorsal hollow nerve chord

Question 51

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

Answer 51

analogy

Question 52

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

Answer 52

law of succession

Question 53

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

Answer 53

convergence

Question 54

scientific study of the geographic distrubution of species

Answer 54

biogeography

Question 55

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

Answer 55

transitional fossil

Question 56

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

Answer 56

pakicetus

Question 57

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

Answer 57

cetacea

Question 58

a structure formed early in development

Answer 58

limb buds

Question 59

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

Answer 59

vestigial

Question 60

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

Answer 60

pangenesis

Question 61

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

Answer 61

allele

Question 62

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

Answer 62

locus/loci

Question 63

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

Answer 63

genotype

Question 64

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

Answer 64

gametes

Question 65

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

Answer 65

chromosome

Question 66

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

Answer 66

recombination

Question 67

stronger allele

Answer 67

dominant

Question 68

weaker allele

Answer 68

recessive

Question 69

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

Answer 69

homozygote

Question 70

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

Answer 70

heterozygote

Question 71

a mathmatical description of a population that is not evolving

Answer 71

hardy-weinberg theorem

Question 72

chance fluctions in allele frequencies over generation tend to reduce variation

Answer 72

genetic drift

Question 73

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

Answer 73

founder effect

Question 74

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

Answer 74

bottleneck effect

Question 75

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

Answer 75

assortive mating

Question 76

random mating

Answer 76

panmixis

Question 77

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

Answer 77

inbreeding

Question 78

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

Answer 78

gene flow

Question 79

the process of individuals moving into a range from elsewhere

Answer 79

immigration

Question 80

the process of individuals moving out of the population range

Answer 80

emigration

Question 81

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

Answer 81

mutation

Question 82

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

Answer 82

point mutation

Question 83

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

Answer 83

insertion

Question 84

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

Answer 84

deletion

Question 85

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

Answer 85

dna

Question 86

what does dna stand for

Answer 86

deoxyribonucleic acid

Question 87

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

Answer 87

nucleotides

Question 88

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

Answer 88

dna replication

Question 89

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

Answer 89

protein

Question 90

building blocks of protien

Answer 90

amino acid

Question 91

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

Answer 91

gene duplicaiotn

Question 92

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

Answer 92

polyploidy

Question 93

having a single set of unpaired chromosomes

Answer 93

haploid

Question 94

containing two complete sets of chromosomes, one from each parent

Answer 94

diploid

Question 95

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

Answer 95

gene flwo

Question 96

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

Answer 96

gene pool

Question 97

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

Answer 97

stabilizing selection

Question 98

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

Answer 98

disruptive selection

Question 99

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

Answer 99

directional selection

Question 100

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

Answer 100

sexual selection

Question 101

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

Answer 101

reverse transriptase

Question 102

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

Answer 102

reproductive cohesion

Question 103

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

Answer 103

reproductive isolation

Question 104

types of pre-zygotic isolation

Answer 104

spatial, behavioral, mechanical and temporal

Question 105

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

Answer 105

habitat isolation

Question 106

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.

Answer 106

temporal isolation

Question 107

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

Answer 107

behavior isolation

Question 108

incompatibility of sexual organs

Answer 108

mechanical isolation

Question 109

prevents the formation of fertile offspring

Answer 109

post-zygotic isolation

Question 110

types of post zygotic isolation

Answer 110

hybrid viability, hybrid fertility, hybrid breakdown

Question 111

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

Answer 111

hybrid viability

Question 112

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

Answer 112

hybrid fertitility

Question 113

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

Answer 113

hybrid breakdown

Question 114

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

Answer 114

allopatric specieation

Question 115

the formation of new species in populations in the same area

Answer 115

sympatric speciation

Question 116

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

Answer 116

allopolyploidy

Question 117

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

Answer 117

radiometric dating

Question 118

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

Answer 118

half life

Question 119

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

Answer 119

parent isotope

Question 120

the remaining nuclide left over from radioactive decay

Answer 120

daughter isotope

Question 121

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

Answer 121

archean

Question 122

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

Answer 122

proterozoic

Question 123

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

Answer 123

phanerozoic

Question 124

first cells appeared during the

Answer 124

proterozoic

Question 125

first atmostpheric oxygen appeared during the

Answer 125

archean

Question 126

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.

Answer 126

permian extinction

Question 127

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

Answer 127

cretacious/teriary extinction, k-t

Question 128

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

Answer 128

chicxulub crater

Question 129

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

Answer 129

development

Question 130

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

Answer 130

allometry

Question 131

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

Answer 131

heterochrony

Question 132

the retention of juvenile features in the adult animal.

Answer 132

neoteny

Question 133

example of neoteny

Answer 133

axolotl

Question 134

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

Answer 134

padomorphosis

Question 135

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

Answer 135

homeosis

Question 136

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

Answer 136

homeobox

Question 137

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.

Answer 137

hox

Question 138

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

Answer 138

phylogeny

Question 139

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

Answer 139

nomenclature

Question 140

puting something into categories

Answer 140

classification

Question 141

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

Answer 141

binomial system

Question 142

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.

Answer 142

linnean hierarchy

Question 143

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

Answer 143

taxa/ taxon

Question 144

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

Answer 144

sister taxa

Question 145

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

Answer 145

monophyly

Question 146

(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

Answer 146

apomorphy

Question 147

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.

Answer 147

plesiomorphy

Question 148

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

Answer 148

ingroup

Question 149

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

Answer 149

OUTGROUP

Question 150

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

Answer 150

erv (endogenous retroviruses)

Question 151

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

Answer 151

AZT

Question 152

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

Answer 152

gp41

Question 153

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

Answer 153

integrase

Question 154

an enzyme that breaks down proteins and peptides

Answer 154

protease

Question 155

the cabability of an organism to defend itself against a disease

Answer 155

resistance

Question 156

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

Answer 156

HAART, highly active antireroviral therapy

Question 157

the number of simultanous mutations required to produce resistance

Answer 157

genetic barrier

Question 158

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

Answer 158

CCR5

Question 159

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

Answer 159

CCR5D32

Question 160

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.

Answer 160

mitosis

Question 161

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).

Answer 161

meiosis