Biology Solutions 100% A+

Exam 3 Biology 1307

1. True or False. All protists are eukaryotic.

A. true

B. false

2. Chloroplasts arose via _____.

A. endosymbiosis of dinoflagellates

B. endosymbiosis of cyanobacteria

C. endosymbiosis of fungi

D. endosymbiosis of euglenids

3. According to the endosymbiosis theory, how many membranes should a mitochondrion have?

A. One

B. Three

C. Two

D. Zero

4. You are given an unknown organism to identify. It is unicellular and heterotrophic. It is motile, using many short extensions of the cytoplasm. It has well-developed organelles and two nuclei, one large and one small. This organism is most likely to be a ________.

A. foraminiferan

B. diatom

C. ciliate

D. dinoflagellate

E. slime mold

5. Which of the following statements is consistent with the assertion that protists are paraphyletic?

A. There is no common set of synapomorphies that define a protist

B. Protists all share a common set of synapomorphies.

C. Protists are all more primitive than land plants and animals.

D. Protists do not share a single common ancestor.

6. Encouraging the growth (via nutrient fertilization) of photosynthetic protists in marine environments may help reduce global warming because _____.

A. the increased oxygen consumption by large populations of photosynthetic protists will increase photosynthesis in land plants

B. photosynthetic protists are primary consumers in many marine food chains

C. photosynthetic protists fix atmospheric carbon dioxide, decreasing atmospheric carbon dioxide levels

7. Encouraging the growth (via nutrient fertilization) of photosynthetic protists in marine environments may help reduce global warming because ________.

A) photosynthetic protists are primary consumers in many marine food chains

B) photosynthetic protists fix atmospheric carbon dioxide, decreasing atmospheric carbon

dioxide levels

C) the increased oxygen consumption by large populations of photosynthetic protists will increase photosynthesis in land plants

D) photosynthetic protists would release a lot of oxygen, and fertilizing them would increase levels of oxygen in the atmosphere

8. Which of these taxa contains species that produce potent toxins that can cause extensive fish kills, contaminate shellfish, and poison humans?

A. red algae

B. dinoflagellates

C. diplomonads

D. euglenids

9. Which of the following might be a result of adding a secondary consumer to the aquatic ecosystem in the accompanying illustration?

A. a decrease in the number of primary consumers

B. a decrease in the population of decomposers

C. an increase in atmospheric carbon dioxide

D. an increase in the population of scavengers

E. a decrease in the carbon sink

10. The Irish potato famine was caused by an organism that belongs to which species?

A. Phytophtorainfestans

B. Trichomonas vaginalis

C. Giardia spp.

D. Trypanozomacruzi

11. Which of the following eukaryotic lineages contains species that all lack functioning mitochondria?

A. Excavata

B. Rhizaria

C. Amoebozoa

D. Stramenopila

12. Pseudopods that can perform phagocytosis and have the ability to change their shape are generally characteristic of which group?

A. radiolarians

B. amoebas

C. slime molds

D. oomycetes

13. Which of the following is a synapomorphy that defines all green algae and land plants?

A. Seeds B. Vascular tissue C. Cell walls D, Photosynthetic chloroplasts

14. One of the fish in your aquarium dies. Adding which protist to the water would allow you to avoid flushing the dead fish by speeding its decay?

A. an apicomplexan

B. a dinoflagellata

C. a water mold

D. a ciliate

E. a euglenid

15. According to the endosymbiotic theory, why was it adaptive for the larger (host) cell to keep the engulfed cell alive, rather than digesting it as food?

A. The engulfed cell provided the host cell with adenosine triphosphate (ATP).

B. The engulfed cell provided the host cell with carbon dioxide.

C. The engulfed cell allowed the host cell to metabolize glucose.

D. The host cell was able to survive anaerobic conditions with the engulfed cell alive.

E. The host cell would have been poisoned if it had digested the engulfed cell.

16. Alternation of generations occurs in some protists. Which of the following represents the correct sequence of events for this mode of reproduction?

A. gametophyte → gamete → fusion → sporophyte → spore → gametophyte

B. sporophyte → spore fusion → gametophyte → gamete → sporophyte

C. gametophyte → fusion → sporophyte → spore → gamete → gametophyte

D. gamete → fusion → gametophyte →spore → sporophyte → gamete

17. In examining a protist, you notice that it lacks a cell wall, and has movement with cytoplasmic streaming. These data allow you to infer that the species belongs to which of the following protist groups?

A. Excavata

B. Stramenopila

C. Rhizaria

D. Alveolata

E. Amoebozoa

18. Chagas disease is spread by the “kissing bug”. This disease affect 16-18 million people around the world and causes about 50,000 deaths annually and is caused by which protist?

A. Giardia

B. Trichomonas vaginalis

C. Trypanosoma cruzi

D. Plasmodioum

19. Dysentery is caused by _______________ and causes severe diarrhea. It is mostly prevalent in countries with a warm climate and poor sanitary conditions. In some places it is known as “Montezuma’s revenge”. Which of the following protists causes dysentery

A. Entamoeba histolytica

B. Phytophthora infestans

C. Plasmodioum

D. Dinoflagellates

20. What impact will the loss of land plants have on the soil?

A. Increase soil stability

B. Increase soil erosion

C. Increase nutrient levels

D. Decrease surface temperature

21. The major function of the medicinal compounds in plants is to _____.

A. as defense against herbivores

B. attract pollinators for seed dispersal

C. attract insects and birds to spread seeds and fruits

D. defend the plant against microbes

22. The most direct ancestors of land plants were probably _____.

A. liverworts and mosses B. green algae C. kelp (brown alga) D. cyanobacteria

23. What evidence indicates the movement of plants from water to land?

A. sporopollenin to inhibit evaporation from leaves

B. loss of structures that produce spores

C. remnants of chloroplasts from photosynthesizing cells

D. waxy cuticle to decrease evaporation from leaves

24. Which of these time intervals, based on plant fossils, came last (most recently)?

A. carboniferous swamps with giant horsetails and ferns

B. rise and diversification of angiosperms

C. colonization of land by early liverworts and mosses

D. extensive growth of gymnosperm forests

25. Angiosperms are the most successful terrestrial plants. Which of the following features is unique to them and helps account for their success?

A. embryos enclosed within seed coats

B. sperm cells without flagella

C. fruits enclosing seeds which contain the plant embryo

D. wind pollination

26. Protists and bacteria are grouped into different domains because _____.

A. bacteria are not made of cells

B. protists have a membrane-bounded nucleus, which bacterial cells lack

C. protists eat bacteria

D. protists are photosynthetic

27. The term gymnosperm refers to plants _____.

A. with “naked seeds” that do not produce flowers

B. that are non-vascular

C. that flower

D. with seeds protected within a fruit

28. What trait gives seeds an advantage over spores?

A. Protected from the environment

B. Small in size

C. Contain nutrients

D. Long-lived

29. Which of the following was a challenge to the survival of the first land plants?

A. desiccation

B. too much sunlight

C. a shortage of carbon dioxide

D. animal predation

30. _____ are angiosperms.

A. Roses

B. Fiddlehead ferns

C. Sphagnum mosses

D. Pine trees

31. Primary producers such as plants and green algae ____________.

A. Convert solar energy (light) to chemical energy (sugars)

B. Decompose decaying material in soil to produce energy

C. Consume other organisms to produce chemical energy (sugars) and solar energy (light)

D. Produce CO2 by performing photosynthesis

32. Plants provide many ecosystem services including production of oxygen and holding the soil. What is an ecosystem?

A. All the organisms or biotic factors in a particular area

B. All the living and nonliving components in a particular area

C. The nonliving or abiotic components in a particular area

D. All plants and animals in a given region

33. Stoma (plural: stomata) are____________.

A. Small openings called pores surrounded by specialized guard cells

B. Watertight sealants produced by plants to avoid desiccation

C. Specialized organelles in plant cells to perform photosynthesis

D. Modified leaves in a plant to avoid predation by herbivores

34. Flowers, the reproductive organ of a flowering plant, has two key reproductive structures called:

A. Seed and pistil

B. Stamen and fruit

C. Stamen and pistil

D. Seed and anther

35. The three main ways in which pollen is transported from plant to plant or flower to flower are:

A. Animals, wind, water

B. Wind, fungi, water

C. Animals, bees, wind

D. Fungi, water, insects

36. _____________ is a process by which pollen is transferred in plants.

A. Pollen grains

B. Style

C. Pollination

D. Translocation

37. True or False. The female part of the flower is the stamen.

A. True B. False

38. True or False. The main function of the endosperm is to provide nutrients for the embryo plant.

A. True B. False

39. True or False. Plants and not algae are the main primary producers in Earth’s oceans.

A. True B. False

40. True or False. Bryophytes such as mosses lack vascular tissue (xylem and phloem).

A. True B. False

41. Root hairs are most important to a plant because they ________.

A. anchor a plant in the soil

B. store starches

C. increase the surface area for absorption

D. provide a habitat for nitrogen-fixing bacteria

E. contain xylem tissue

42. As fuels, wood and coal ________.

A) are the main fuel sources in industrialized countries today.

B) are both formed from living or fossil plants.

C) are both formed under pressure deep in the Earth.

D) are sustainable as they are even now being made at high rates.

43. Molecular phylogenies show all land plants are a monophyletic group. This suggests ________.

A) there were many different transitions from aquatic to terrestrial habitats

B) wind-pollinated plants arose first

C) land plants have undergone a diversification since they first colonized terrestrial habitats

D) there was a single transition from aquatic to terrestrial habitats

44. Which of these time intervals, based on plant fossils, came last (most recently)?

A) extensive growth of gymnosperm forests

B) Silurian-Devonian explosion with fossils of plant lineages containing most of the major morphological innovations

C) colonization of land by early liverworts and mosses

D) rise and diversification of angiosperms

E) carboniferous swamps with giant horsetails and lycophytes

45. Why are seedless vascular plants considered paraphyletic rather than monophyletic?

A) Some of the groups within the seedless vascular plants are more closely related to each other than to other groups (such as Lycophyta).

B) They share a more recent common ancestor with seeded plants than they do with the non-vascular plants.

C) All of the groups contained within the seedless vascular plants do not have the same ancestor.

D) The group includes their common ancestor but also the seeded descendants of that same ancestor.

46. Which set contains the most closely related terms?

A) megasporangium, megaspore, pollen, ovule

B) microsporangium, microspore, egg, ovary

C) megasporangium, megaspore, egg, ovule

D) microsporangium, microspore, carpel, ovary

47. In the process of alternation of generations, the ________.

A) sporophyte is haploid and produces gametes

B) sporophyte is diploid and produces spores

C) gametophyte is haploid and produces spores

D) gametophyte is diploid and produces gametes

E) spores unite to form a zygote

48. Where are you LEAST likely to see green algae?

A) as pink snow in the mountains in summer

B) growing symbiotically with fungi in lichens or with some invertebrate animals

C) growing independently on dry rock in meadows

D) growing independently on wet rock in ponds and lakes

E) floating in seas and oceans

49. When a mosquito infected with Plasmodium first bites a human, the Plasmodium ________.

A) gametes fuse, forming an oocyst

B) cells infect the human liver cells

C) cells cause lysing of the human red blood cells

D) oocyst undergoes meiosis

50. Carbon dioxide enters the inner spaces of the leaf through the ________.

A) cuticle

B) epidermal trichomes

C) stoma

D) phloem

E) walls of guard cells

51. Which part of a plant absorbs most of the water and minerals taken up from the soil?

A) root cap

B) root hairs

C) the thick parts of the roots near the base of the stem

D) storage roots

E) sections of the root that have secondary xylem

52. When an animal cell is placed in a hypotonic solution and water enters the cell via osmosis, the volume of the cell increases until it bursts. This does NOT happen to plant cells, because ________.

A) they have large central vacuoles, which provide abundant space for storage of incoming water

B) the composition of their plasma membranes differs from that of animal-cell plasma membranes in a way that provides much greater strength

C) they have cell walls, which prevent the entry of water by osmosis

D) they have cell walls, which provide pressure to counteract the pressure of the incoming water

E) certain gated channel proteins embedded in their plasma membranes open as osmotic pressure decreases, allowing excess water to leave the cell

53. Compared to a cell with few aquaporins in its membrane, a cell containing many aquaporins will ________.

A) have a faster rate of osmosis

B) have a lower water potential

C) have a higher water potential

D) have a faster rate of active transport

E) be flaccid

54. Which cells in a root form a protective barrier to the vascular system where all materials must move through the symplast?

A) pericycle

B) cortex

C) epidermis

D) endodermis

E) exodermis

55. You are conducting an experiment on plant growth. You take a plant fresh from the soil that weighs 5 kilograms (kg). Then you dry the plant overnight and determine the dry weight to be 1 kg. Of this dry weight, how much would you expect to be made up of oxygen, carbon, and hydrogen?

A) 1 gram

B) 4 grams

C) 40 grams

D) 960 grams

E) 1 kg

56. Which of the following statements about essential nutrients are TRUE? Essential nutrients ________.

I. are necessary for plant growth and reproduction

II. are required for a specific structure or metabolic function

III.cannot be synthesized by a plant

IV.are produced by symbiotic bacteria

A) I and IV

B) II, III, and IV

C) I, II, and III

D) I, II, III, and IV

57. Which criteria allow biologists to divide chemicals into macronutrients and micronutrients?

A) molecular weight of the element or compound

B) the quantities of each required by plants

C) how they are used in metabolism

D) whether or not they are essential for plant growth

58. A mineral deficiency is likely to affect older leaves more than younger leaves if the ________.

A) mineral is a micronutrient

B) mineral is very mobile within the plant

C) mineral is required for chlorophyll synthesis

D) mineral is a macronutrient

E) older leaves are in direct sunlight

59.Which of the following elements correctly pairs an essential element in plants with its function?

A) nitrogen–component of nucleic acids, proteins, hormones, coenzymes

B) magnesium–component of nucleic acids, phospholipids, ATP

C) phosphorus–cofactor functioning in protein synthesis

D) sulfur–component of DNA; activates some enzymes

60.Why is nitrogen fixation an essential process?

A) Fixed nitrogen is often the limiting factor in plant growth.

B) Nitrogen fixation is very expensive in terms of metabolic energy.

C) Nitrogen-fixing capacity can be genetically engineered.

D) None of the above

61.Nitrogen fixation is a process that ________.

A) recycles nitrogen compounds from dead and decaying materials

B) converts ammonia to ammonium

C) releases nitrate from the rock substrate

D) converts nitrogen gas into ammonia

E) recycles nitrogen compounds from dead and decaying materials and converts ammonia to ammonium

62.Which of the following, if used as a fertilizer, would be most immediately available for plant uptake?

A) NH3

B) N2

C) CN2H2

D) NO3-

63. In what way do nitrogen compounds differ from other minerals needed by plants? Only nitrogen ________.

A) can be lost from the soil

B) can be provided by symbiotic bacteria

C) is needed for protein synthesis

D) is held by cation exchange capacity in the soil

E) can be absorbed by root hairs

64. What is the correct sequence of steps during infection of plants by nitrogen-fixing bacteria?

A) Rhizobia release Nod factors; roots release flavonoids; rhizobia proliferate inside of root hair; infection thread grows into the root cortex; nodule forms.

B) Rhizobia release flavonoids; roots release Nod factors; rhizobia proliferate inside of root hair; infection thread grows into the root cortex; nodule forms.

C) Roots release flavonoids; rhizobia release Nod factors; rhizobia proliferate inside of root hair; nodule forms; infection thread grows into the root cortex.

D) Roots release flavonoids; rhizobia release Nod factors; rhizobia proliferate inside of root hair; infection thread grows into the root cortex; nodule forms.

E) Nodule forms; infection thread grows into the root cortex; rhizobia proliferate inside of root hair; rhizobia release flavonoids and Nod factors.

65. Carnivorous plants have evolved mechanisms that trap and digest small animals. The products of this digestion are used to supplement the plant’s supply of ________.

A) water

B) carbohydrates

C) lipids and steroids

D) nitrogen, nutrient, and other minerals

66. Which of the following statements about nitrogen fixation in root nodules is correct?

A) The plant contributes the nitrogenase enzyme.

B) The process is relatively inexpensive in terms of ATP costs.

C) Leghemoglobin helps maintain a low oxygen concentration within the nodule.

D) The process tends to deplete nitrogen compounds in the soil.

E) The bacteria of the nodule are autotrophic.

67. Most of the dry mass of a plant is derived from ________.

A) NO3- and CO2

B) K+ and CO2

C) PO4 and K+

D) H2O and K+

E) H2O and CO2

 
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Masters In Biomed

>Bovine-L liver form (87)

MSQAEFDKAAEEVKHLKTKPADEEMLFIYSHYKQATVGDINTERPGMLDFKGKAKWDAWNELKGTSKEDAMKAYIDKVEELKKKYGI

>Chick-L liver form (86)

mseaafqkaaeevkelksqptdqemldvyshykqatvgdvntdrpgmldfkgkakwdawnalkgmskedamkayvakveelkgkygi

>Dog-L Liver form (86)

MSQAEFDKAAEDVKHLKTKPADDEMLYIYSHYKQATVGDINTERPGLLDLRGKAKWDAWNQLKGTSKEDAMKAYVNKVEDLKKKYGI

>Chimpanzee-L liver form (87)

MSQAEFEKAAEEVRHLKTKPSDEEMLFIYGHYKQATVGDINTERPGMLDFTGKAKWDAWNELKGTSKEDAMK

AYINKVEELKKKYGI

>Human-L liver form (87)

MSQAEFEKAAEEVRHLKTKPSDEEMLFIYGHYKQATVGDINTERPGMLDFTGKAKWDAWNELKGTSKEDAMKAYINKVEELKKKYGI

>Duck-L Liver form (86)

MAEAAFQKAAEEVKQLKSQPSDQEMLDVYSHYKQATVGDVNTDRPGMLDFKGKAKWDAWNALKGMSKEDAMKAYVAKVEELKGKYGI

>Bovine-B brain form_(88)

MSLQADFDKAAKDVRKLKTRPDDEELKELYGLYKQSVIGDIDIECPALLDLKGKAKWEAWNLQKGLSKEDAMNAYISKAKELIEKYGI

>Chick-B brain form -ACBP) (88)

MALQADFDGAAKDVKKLKTRPTDEELKELYGFYKQATVGDINIECPGVLDVKGKAKWEAW

NLKRGISKEDAMNAYISKAKAMIEKYGI

>Human-B brain form B-ACBP) (88)

MALQADFDRAAEDVRKLKARPDDGELKELYGLYKQAIVGDINIACPGMLDLKGKAKWEAWNLKKGLSTED

ATSAYISKAKELIEKYGI

>Duck-B brain form B-ACBP) (103)

mfqahllrgtltlsfflhqadfdeaaeevkklktrptdeelkelygfykqatvgdiniecpgmldlkgka

kweawnlkkgiskedamnayiskaktmvekygi

>Bovine-T testis form -ACBP)(86)

mcqvefemacaaikqlkgpvsdqekllvysyykqatqgdcnipappatdlkakakweawnenkgmskmdamriyiakveelkkneag

>Dog-T testis form (74) (T-ACBP)

MCQVEFEMACAAIKQLKGPVSDQEKLLVYSFYKQATQGDCNIPAPPATDVKAKAKWEAWNQNKGMSKMDAHEDL

>C.elegans (85)

mtlsfddaaatvktlktspsndellklyalfkqgtvgdnttdkpgmfdlkgkakwsawdekkglakddaqkayvalveeliakyga

>Barley (93)

MGLKEEFEEYAEKAKTLPDTTTNESKLCLYSLYKQATVGPVNTDRPGLFDLAGKAKWDAW

KSVEAKSKEEAMADYITKVKQLLEEAAAASASS

>Fruitfly1 (86)

MVSEQFNAAAEKVKSLTKRPSDDEFLQLYALFKQASVGDNDTAKPGLLDLKGKAKWEAWNKQKGKSSEAAQQEYITFVEGLVAKYA

>S.cerevisiae (86)

mvsqlfeekakavnelptkpstdellelyalykqatvgdndkekpgifnmkdrykweawenlkgksqedaekeyialvdqliakyss

>A.thaliana (92)

mglkeefeehaekvntltelpsnedllilyglykqakfgpvdtsrpgmfsmkerakwdawkavegksseeamndyitkvkqllevaas

Pabio 536 Lab session and Homework Week 8 Multiple Alignment

1. Perform a multiple alignment using the ACBP liver forms and the ACBP brain forms from this week’s sequence file and show the alignment (ALN file) you obtained (10 points).

2. Compare the pattern of identical residues conserved within the liver forms to those conserved within the brain forms. Are there brain or liver specific residues (ie residues conserved in liver but not in brain or vice versa)? Provide a couple of examples (ie brain: A26, liver: W32)(10 points).

3. A) Determine a “pattern” of liver-specific amino acid residues, ie those amino acids conserved in all liver forms but not in the brain forms. Provide your pattern. (10 points) B) Do a PHI-BLAST search using the human ACBP Liver form in the query and your Liver-specific pattern – limit your output to salmonids. Did you detect a putative liver ACBP form in the salmonid “ atlantic salmon salmo” ? provide the BLAST hit. If you obtain no putative salmon ACBP hits try altering your pattern slightly and redo the PHI-BLAST. If all else fails, do a normal BLAST search with no pattern and exam the hits to see if you can detect a putative liver ACBP form in the salmonid “atlantic salmon salmo”? Provide the BLAST hit. In this last case, how did the salmo sequence differ from your pattern (10 points) C) Do a multiple alignment of all of the liver forms in question 2 plus your putative salmon liver ACBP form – provide the alignment (10 points). D) Discuss the alignment with regard to other liver-specific residues that you did not include in your PHI-BLAST pattern, ie are those conserved as well? Would you consider this putative atlantic salmon ACBP to be a liver form? Discuss (10 points).

4. A) Determine a “pattern” of amino acid residues that are conserved in the ACBP brain forms but not in the liver forms. Provide the pattern (10 points) B) Do a PHI-BLAST search using the human ACBP Brain form in the query and

your Brain-specific pattern – limit your output to salmonids. Did you detect a putative brain ACBP form in the Atlantic salmon (Salmo salar)? If you obtain no putative salmon ACBP hits try altering your pattern slightly and redo the PHI-BLAST. If you still get no putative salmon ACBP hit try doing a protein BLAST without the pattern and look at the hits by eye to determine whether there is a brain form in Salmo salar (hint- you should detect one) (10 points)

C) Do a multiple alignment of all of the brain forms in question 2 plus your putative salmon brain ACBP form – provide the alignment. (10 points)

D) Discuss the alignment with regard to the brain-specific residues? Would you consider this salmon ACBP to be a brain form? Discuss in relationship to your PHI-BLAST pattern and other “brain form”specific characteristics. (10 points)

5. EXTRA CREDIT: Do an alignment of all of the liver and brain form ACBP sequences including the salmon sequences. Identify the identical residues

 

 

conserved within all the sequences and discuss with regard to conservation of the previously characterized “ACBP” motifs (10 points). Can you make any conclusion regarding how the brain and the liver forms differ from each other – relying upon what you know of the structure of ACBP? (no right answer here – something to think about). (10 points)

 
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Biology(Hormone)

  1. A patient having renal surgery suddenly develops massive hypertension and dies during surgery. An autopsy shows the presence of a pheochromocytoma. In your own words, explain how this incident might have happened.
  2. Your favorite cousin, who is 20 years old, has just been diagnosed with type 2 diabetes. He is overweight and spends most of his time playing computer games or watching television. As a health professional, what advice will you give him?
  3. Your patient has just been diagnosed with SIADH. His mother is asking you what this condition is and what she should expect next. What will you tell her?
  4. Your patient has been admitted to the hospital in preparation for a total removal of her thyroid gland to reverse her hyperthyroidism. She suddenly develops thyroid storm. What manifestations will you find, and what is the pathophysiologic basis of thyroid storm?

Topic Altereations in hormone regulation**

 
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Meiosis Lab

Cellular reproduction in Eukaryotes involves either mitosis or, in the case of sex cells, meiosis. Mitosis involves the reproduction of a cell into two identical daughter cells. Meiosis, however, is a reduction division where a parental diploid cell produces four haploid gametes. Upon fusion, two haploid gametes (in humans the sperm and the egg) will result in one diploid zygote. In this activity you will track chromosomes through meiosis using colored beads.

41

 

Meiosis

Lab 4

 

 

 

42

 

 

Lab 4: Meiosis

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Introduc on

Meiosis only occurs in organisms that reproduce sexually. The process generates haploid (1n) cells

called gametes (sperm cells in males and egg cells in fe-

males), or spores in some plants, fungi, and pro sts, that

contain one complete set of chromosomes. Haploid cells

fuse together during fer liza on to form a diploid cell with

two copies of each chromosome (2n).

Genes are the units of heredity that have speciĂžc loci

(loca ons) on the DNA strand and code for inheritable

traits (such as hair color). Alleles are alterna ve forms of the same gene (brown vs. blue eyes). Homol-

ogous chromosomes contain the same genes as each other but o en di erent alleles. Non-sex cells

(e.g. bone, heart, skin, liver) contain two alleles (2n), one from the sperm and the other from the egg.

Mitosis and meiosis are similar in many ways. Meiosis, however, has two rounds of division—meiosis I

and meiosis II. There is no replica on of the DNA between meiosis I and II. Thus in meiosis, the parent

cell produces four daughter cells, each with just a single set of chromosomes (1n).

Meiosis I is the reduc on division– the homologous pairs of chromosomes are separated so that each

daughter cell will receive just one set of chromosomes. During meiosis II, sister chroma ds are sepa-

rated (as in mitosis).

 

 

 

 

 

Concepts to explore:

Meiosis

Diploid cells

Haploid cells

Chromosomal crossover

Concepts to explore:

 

There are over two meters of DNA pack-

aged into a cell’s nucleus. It is coiled and

folded into superhelices that form chro-

mosomes, which must be duplicated be-

fore a cell divides.

Each of the 23 human chromosomes

has two copies. For each chromosome,

there is a 50:50 chance as to which copy

each gamete receives.

That translates to over 8 million possi-

ble combina ons!

 

 

Lab 4: Meiosis

44

 

Meiosis:

Prophase I: The sister chroma ds a ach to their homologous counterparts (same chromo-

some – di erent version). This is the stage where crossing over occurs (homologous chro-

mosomes exchange regions of DNA). Structures which will serve as anchors in the cell

(centrioles) during the division process appear.

Metaphase I: The chromosomes line up in the middle of the cell. The orienta on of each

pair of homologous chromosomes is independent from all other chromosomes. This

means they can “ßip ßop” as they line up, e ec vely shu ing their gene c informa on

into new combina ons. Microtubules (long strands) grow from each centriole and link

them together while also a aching to each pair of homologous chromosomes.

Anaphase I: The microtubules pull the homologous chromosomes apart (the sister chro-

ma ds remain paired).

Telophase I: One set of paired chromosomes arrives at each centriole, at which me a nu-

cleus forms around each set.

Cytokinesis: The plasma membrane of the cell folds in and encloses each nucleus into two

new daughter cells.

Prophase II: Before any replica on of the chromosomes can take place, the daughter cells

immediately enter into prophase II. New spindle Ăžbers form as the nucleus breaks down.

Metaphase II: The sister chroma ds align in the center of the cell, while the microtubules

join the centrioles and a ach to the chromosomes. Unlike metaphase I, since each pair of

sister chroma ds is iden cal, their orienta on as they align does not ma er.

Anaphase II: The sister chroma ds are separated as the microtubules pull them apart.

Telophase II: The chroma ds arrive at each pole, at which me a nucleus forms around

each.

Cytokinesis: The plasma membrane of the cell folds in and engulfs each nucleus into two

new haploid daughter cells.

We brießy discussed “crossing over” in Prophase I. Since the chromosomes of each parent undergoes

gene c recombina on, each gamete (and thus each zygote) acquires a unique gene c Ăžngerprint.

The closeness of the chroma ds during prophase I, creates the opportunity to exchange gene c mate-

rial (chromosomal crossover) at a site called the chiasma. The chroma ds trade alleles for all genes

located on the arm that has crossed.

The process of meiosis is complex and highly regulated. There are a series of checkpoints that a cell

must pass before the next phase of meiosis will begin. This ensures any mutated cells are iden Ăžed

 

 

Lab 4: Meiosis

45

 

and repaired before the cell division process can con nue.

 

One of the muta ons that is of par cular concern is a

varia on in the amount of gene c material in a cell. It is

cri cal that the gamete contain only half of the chromo-

somes of the parent cell. Otherwise the amount of DNA

would double with each new genera on. This is the key

feature of meiosis.

Figure 1: The stages of meiosis

Muta ons that are not caught by the cell’s

self-check system can result in chromoso-

mal abnormali es like Down’s syndrome, in

which there are 3 copies of chromosome

21.

 

 

Lab 4: Meiosis

46

 

Experiment 1: Following Chromosomal DNA Movement

Every cell in the human body has two alleles that condense into single chromosomes held together by

a centromere. These “sister” chroma ds replicate and pair with the newly made homologous chromo-

somes. In this exercise we will follow the movement of the chromosomes through meiosis I and II to

create haploid (gamete) cells.

 

 

 

 

 

 

 

Procedure

Meiosis I

A. As prophase I begins, chromosomes coil and condense in prepara on for replica on.

1. a) Using one single color of bead, build a homologous pair of duplicated chromo-

somes. Each chromosome will have 10 beads with a di erent colored centromere

in it.

For example, if there are 20 red beads, 10 beads would be snapped together to

make two di erent strands. In the middle of each of the 10 bead strands, snap

a di erent colored bead in to act as the centromere.

Figure 2: Bead Set-up

Materials

2 sets of di erent colored snap beads (32 of each)

8 centromeres (snap beads)

Blue and red markers*

*You must provide

 

 

Lab 4: Meiosis

47

 

b) Now, repeat these steps using the other color of bead.

2. a) Assemble another homologous pair of chromosomes using only 12 (that’s 6 per

strand) of the Ăžrst color bead. Place another, di erent colored bead in the middle

of each to act is its centromere.

b) Repeat this step (2 strands of 6 beads plus a centromere) with the other color of

beads.

B. Bring the centromeres of two units of the same color and length together so they can be held

together to appear as a duplicated chromosome. Your beads should appear as they do in Fig-

ure 2.

C. Simulate crossing over between the blue and red chromosomes. Bring the two homologous

pairs together (that’d be the two pairs that both have 10 bead strands) and exchange an equal

number of beads between the two. This simulates what occurs during prophase I.

D. ConĂžgure the chromosomes as they would appear in each of the remaining stages of meiosis I.

Use Figure 1 to guide you.

 

Meiosis II

E. ConĂžgure the chromosomes as they would appear in each stage of meiosis II. Use Figure 1 to

guide you.

F. Using the space below, and using blue and red markers, draw a diagram of your beads in each

stage. Beside your picture, write the number of chromosomes present in each cell. This work

will help you answer the ques ons in the lab, but does not need to be submi ed for grading.

 

Meiosis I

Prophase I

 

 

Metaphase I

 

 

 

 

 

Lab 4: Meiosis

48

 

Anaphase I

 

 

 

Telophase I

 

 

 

Meiosis II

Prophase II

 

 

 

Metaphase II

 

 

 

Anaphase II

 

 

 

Telophase II

 

 

F. Return your beads to their original star ng posi on and simulate crossing over again. Track

how this changes the ul mate outcome as you then go through the stages of meiosis I and II.

 

 

Lab 4: Meiosis

49

 

Ques ons

1. Why is crossing over important in heredity?

2. Provide two ways that meiosis I and meiosis II are di erent.

3. a) In this lab, how many chromosomes were present in each cell when meiosis I started?

b) How many chromosomes were present in each daughter cell at the end of meiosis II?

4. If humans have 46 chromosomes in each of their body cells, determine how many chromo-

somes you would expect to Ăžnd in the following:

Sperm ___________________

Egg ___________________

Daughter cell from mitosis ___________________

Daughter cell from meiosis II ___________________

5. Why is it necessary to reduce the chromosome number of gametes, but not of other cells of

an organism?

 
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