102 MEIOSIS 267(clockwise from top) (1ndash4 7 9)John D CunninghamVisuals Unlimited (5 6 8)Carolina Biological SupplyPhototake NYC
Figure 1012Compare these diagrams of meiosis with those of mitosis in Chapter 8 After telophase IImeiosis is finished and gametes form Compare and Contrast In what other ways aremitosis and meiosis different
It is estimated that during prophase Iof meiosis in humans there is an aver-age of two to three crossovers for eachpair of homologous chromosomes
This exchange of genetic material is diagrammed in Figure 1013BCrossing over results in new combina-tions of alleles on a chromosome asyou can see in Figure 1013C Youcan practice modeling crossing over inthe MiniLab at the left
Metaphase IDuring metaphase I the centromere
of each chromosome becomes attachedto a spindle fiber The spindle fiberspull the tetrads into the middle orequator of the spindle This is animportant step unique to meiosisNote that homologous chromosomesare lined up side by side as tetrads Inmitosis on the other hand they lineup on the spindlersquos equator independ-ently of each other
Anaphase I Anaphase I begins as homologous
chromosomes each with its two chro-matids separate and move to oppositeends of the cell This separation occursbecause the centromeres holding thesister chromatids together do not splitas they do during anaphase in mitosisThis critical step ensures that each newcell will receive only one chromosomefrom each homologous pair
Telophase IEvents occur in the reverse order
from the events of prophase I Thespindle is broken down the chromo-somes uncoil and the cytoplasmdivides to yield two new cells Each cellhas half the genetic information of theoriginal cell because it has only onechromosome from each homologouspair However another cell division isneeded because each chromosome isstill doubled
268 MENDEL AND MEIOSIS
Formulate ModelsModeling Crossing OverCrossing over occurs duringmeiosis and involves onlythe nonsister chromatidsthat are present duringtetrad formation Theprocess is responsible forthe appearance of newcombinations of alleles ingamete cells
Procedure Copy the data table Roll out four long strands of clay at least 10 cm long to
represent two chromosomes each with two chromatids Use the figure above as a guide to joining and labeling
these model chromatids Although there are four chro-matids assume that they started out as a single pair ofhomologous chromosomes prior to replication The figureshows tetrad formation during prophase I of meiosis
$ First assume that no crossing over takes place Model theappearance of the chromosomes in the four gamete cellsthat will result at the end of meiosis Record your modelrsquosappearance by drawing the gametesrsquo chromosomes andtheir genes in your data table
Next repeat steps 2ndash4 This time however assume thatcrossing over occurs between genes B and C
Analysis1 Predict What will be the appearance of the chromosomes
prior to replication2 Compare Are there any differences in the combinations
of alleles on chromosomes in gamete cells when crossingover occurs and when it does not occur
3 Analogy Crossing over has been compared to ldquoshufflingthe deckrdquo in cards Explain what this means
4 Think Critically What would be accomplished if crossingover occurred between sister chromatids Explain
5 Evaluate Does your model adequately represent crossingover in a cell
Data Table
No Crossing Over Crossing Over
Appearance of chromosomes Appearance of chromosomes
2 chromosomes with chromatids
Nonsister chromatids
Twist tie
Mark geneswith a pencilpoint
0263-0279 C10S2 BDOL-829900 8304 747 PM Page 268
The phases of meiosis IIThe newly formed cells in some
organisms undergo a short restingstage In other organisms howeverthe cells go from late anaphase ofmeiosis I directly to metaphase ofmeiosis II
The second division in meiosis issimply a mitotic division of the prod-ucts of meiosis I Meiosis II consists ofprophase II metaphase II anaphase IIand telophase II During prophase II aspindle forms in each of the two newcells and the spindle fibers attach to thechromosomes The chromosomes stillmade up of sister chromatids arepulled to the center of the cell and lineup randomly at the equator duringmetaphase II Anaphase II begins as thecentromere of each chromosome splitsallowing the sister chromatids to sepa-rate and move to opposite polesFinally nuclei re-form the spindlesbreak down and the cytoplasm dividesduring telophase II The events ofmeiosis II are identical to those youstudied for mitosis except that thechromosomes do not replicate beforethey divide at the centromeres
At the end of meiosis II four hap-loid cells have been formed from onediploid cell Each haploid cell con-tains one chromosome from eachhomologous pair These haploid cellswill become gametes transmittingthe genes they contain to offspring
Meiosis Provides forGenetic Variation
Cells that are formed by mitosis areidentical to each other and to the par-ent cell Crossing over during meiosishowever provides a way to rearrangeallele combinations Rather than thealleles from each parent stayingtogether new combinations of allelescan form Thus variability is increased
Genetic recombinationHow many different kinds of sperm
can a pea plant produce Each cellundergoing meiosis has seven pairs ofchromosomes Because each of theseven pairs of chromosomes can lineup at the cellrsquos equator in two differ-ent ways 128 different kinds of spermare possible (2n 27 128)
102 MEIOSIS 269
pro- from theGreek word promeaning ldquobeforerdquometa- from theGreek word metameaning ldquoafterrdquoana- from theGreek word anameaning ldquoupback againrdquotelo- from theGreek telosmeaning ldquoendrdquoThe four phases ofcell division areprophasemetaphaseanaphase andtelophase
Homologous chromosomesCrossing over in tetrad
Gametes
Tetrad
A A
Sister chromatids Nonsister chromatids
B B
a a
b b b
a a
B Bb b
b
AA
BB
a a
A AFigure 1013 Late in prophase I the homologouschromosomes come together to formtetrads (A) Arms of nonsister chro-matids wind around each other (B) andgenetic material may be exchanged (C)
AA BB
CC
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270 MENDEL AND MEIOSIS
Figure 1014 If a cell has two pairs ofchromosomesmdashA and aB and b (n 2)mdashfourkinds of gametes (22)are possible dependingon how the homologouschromosomes line up atthe equator duringmeiosis I (A) This eventis a matter of chanceWhen zygotes areformed by the union ofthese gametes 22 22
or 16 possible combina-tions may occur (B)
ab
aB
Ab
AB
AB
AABB AABb AaBB AaBb
AABb AAbb AaBb Aabb
AaBB AaBb aaBB aaBb
AaBb Aabb aaBb aabb
Possible combinations ofchromosomes in zygotes (in boxes)
Poss
ible
com
bina
tion
ofch
rom
osom
es in
egg
s
Possible combination ofchromosomes in sperm
Ab aB ab
Possible gametesPossible gametes
MEIOSIS I
MEIOSIS II
Chromosome A Chromosome aChromosome B Chromosome b
In the same way any pea plant can form 128 different eggs Becauseany egg can be fertilized by anysperm the number of different possi-ble offspring is 16 384 (128 128) A simple example of how geneticrecombination occurs is shown inFigure 1014A You can see that thegene combinations in the gametesvary depending on how each pair of homologous chromosomes lines up during metaphase I a randomprocess
These numbers increase greatly asthe number of chromosomes in thespecies increases In humans n 23so the number of different kinds ofeggs or sperm a person can produce ismore than 8 million (223) When fertil-ization occurs 223 223 or 70 trilliondifferent zygotes are possible Itrsquos nowonder that each individual is unique
In addition crossing over can occuralmost anywhere at random on a chro-mosome This means that an almostendless number of different possiblechromosomes can be produced bycrossing over providing additionalvariation to the variation already pro-duced by the random assortment ofchromosomes This reassortment of
chromosomes and the genetic infor-mation they carry either by crossingover or by independent segregation ofhomologous chromosomes is calledgenetic recombination It is a majorsource of variation among organismsVariation is important to a speciesbecause it is the raw material thatforms the basis for evolution
Explain how cross-ing over increases genetic variability
Meiosis explains Mendelrsquos resultsThe behavior of the chromosomes
in meiosis provides the physical ba-sis for explaining Mendelrsquos resultsThe segregation of chromosomes inanaphase I of meiosis explains Men-delrsquos observation that each parentgives one allele for each trait at ran-dom to each offspring regardless ofwhether the allele is expressed Thesegregation of chromosomes at ran-dom during anaphase I also explainshow factors or genes for differenttraits are inherited independently ofeach other Today Mendelrsquos laws andthe events of meiosis together formthe foundation of the chromosometheory of heredity
AA BB
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271
NondisjunctionAlthough the events of meiosis usu-
ally proceed accurately sometimeschromosomes fail to separate correctlyThe failure of homologous chromo-somes to separate properly duringmeiosis is called nondisjunctionRecall that during meiosis I onechromosome from each homologouspair moves to each pole of the cell Innondisjunction both chromosomesof a homologous pair move to thesame pole of the cell
In one form of nondisjunction twokinds of gametes result One has anextra chromosome and the other ismissing a chromosome The effects ofnondisjunction are often seen aftergametes fuse For example when agamete with an extra chromosome isfertilized by a normal gamete thezygote will have an extra chromo-some This condition is called trisomy(TRI soh mee) In humans if a gametewith an extra chromosome number 21is fertilized by a normal gamete theresulting zygote has 47 chromosomesinstead of 46 This zygote will developinto a baby with Down syndrome
Although organisms with extrachromosomes often survive organ-isms lacking one or more chromo-somes usually do not When a gametewith a missing chromosome fuseswith a normal gamete during fertil-ization the resulting zygote lacks achromosome This condition is calledmonosomy In humans most zygoteswith monosomy do not survive If azygote with monosomy does survivethe resulting organism usually doesnot An example of monosomy that isnot lethal is Turner syndrome inwhich human females have only a single X chromosome instead of two
Another form of nondisjunctioninvolves a total lack of separation ofhomologous chromosomes When thishappens a gamete inherits a completediploid set of chromosomes like thoseshown in Figure 1015 When agamete with an extra set of chromo-somes is fertilized by a normal haploidgamete the offspring has three sets ofchromosomes and is triploid Thefusion of two gametes each with anextra set of chromosomes producesoffspring with four sets of chromo-somesmdasha tetraploid
Male parent (2n)
Meiosis
Abnormalgamete (2n)
Nondisjunction
Zygote(4n)
Female parent (2n)
Meiosis
Abnormalgamete (2n)
Nondisjunction
Figure 1015 Follow the steps to seehow a tetraploid plantsuch as this chrysanthe-mum is produced
RB Satterthwaite
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Chromosome MappingFigure 1016Crossing over the exchange of genetic material by nonsisterchromatids provides information that can be used to make chro-mosome maps Crossing over occurs more frequently betweengenes that are far apart on a chromosome than between genesthat are closer together Critical Thinking Why is the fre-quency of crossing over related to the distance betweengenes on a chromosome
272 MENDEL AND MEIOSISB JohnCabiscoVisuals Unlimited
AA BB50
AA DD BB CC10 5
DD AA CC BB510
or or
CC DD
DD CC35
35
or
AA BBCCDD
50
10 35 5
Crossing over In prophase I ofmeiosis nonsister chromatids crossover as shown in the photo aboveEach X-shaped region is a crossover
AA
Mapping Crossing over produces new allele combinationsGeneticists use the frequency of crossing over to map the relativepositions of genes on a chromosome Genes that are farther aparton a chromosome are more likely to have crossing over occurbetween them than are genes that are closer together
BB
Frequencies and distance Suppose there are four genesmdashA B C and Dmdashona chromosome Geneticists determine that the frequencies of recombination amongthem are as follows between A and Bmdash50 between A and Dmdash10 between Band Cmdash5 between C and Dmdash35 The recombination frequencies can beconverted to map units AndashB 50 AndashD 10 BndashC 5 CndashD 35 These map unitsare not actual distances on the chromosome but they give relative distancesbetween genes Geneticists line up the genes as shown above
CC
Making the mapThe genes can bearranged in thesequence that reflectsthe recombinationdata This sequence is a chromosome map
DD
Stained TEM Magnification 1905
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Understanding Main Ideas1 How are the cells at the end of meiosis different
from the cells at the beginning of meiosis Usethe terms chromosome number haploid anddiploid in your answer
2 What is the significance of meiosis to sexualreproduction
3 Why are there so many varied phenotypes withina species such as humans
4 If the diploid number of a plant is 10 how manychromosomes would you expect to find in itstriploid offspring
Thinking Critically5 How do the events that take place during
meiosis explain Mendelrsquos law of independentassortment
6 Get the Big Picture Compare Figures 1012 and813 of meiosis and mitosis Explain why crossingover between nonsister chromatids of homolo-gous chromosomes cannot occur during mitosisFor more help refer to Get the Big Picture in theSkill Handbook
SKILL REVIEWSKILL REVIEW
102 MEIOSIS 273Bildarchiv OkapiPhoto Researchers
PolyploidyOrganisms with more than the usual
number of chromosome sets are calledpolyploids Polyploidy is rare in animalsand almost always causes death of thezygote However polyploidy frequentlyoccurs in plants Often the flowers andfruits of these plants are larger thannormal and the plants are healthierMany polyploid plants such as the ster-ile banana plant shown in Figure 1017are of great commercial value
Meiosis is a complex process andthe results of an error occurring aresometimes unfortunate However theresulting changes can be beneficialsuch as those that have occurred inagriculture Hexaploid (6n) wheattriploid (3n) apples and polyploidchrysanthemums all are availablecommercially You can see that a thor-ough understanding of meiosis andgenetics would be very helpful toplant breeders In fact plant breedershave learned to produce polyploidplants artificially by using chemicalsthat cause nondisjunction
Gene Linkage and MapsGenes sometimes appear to be
inherited together instead of inde-pendently If genes are close togetheron the same chromosome they usually
are inherited together These genesare said to be linked In fact all thegenes on a chromosome usually arelinked and inherited together It is thechromosomes rather than the individ-ual genes that follow Mendelrsquos law ofindependent assortment
Linked genes may become sepa-rated on different homologous chro-mosomes as a result of crossing overWhen crossing over produces newgene combinations geneticists canuse the frequencies of these new genecombinations to make a chromosomemap showing the relative locations ofthe genes Figure 1016 illustratesthis process
Figure 1017The banana plant is anexample of a triploidplant Think CriticallyWhy do you think thebanana plant is sterile
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Before YouBegin
Itrsquos difficult to predict thetraits of plants if all thatyou see is their seeds Butif these seeds are plantedand allowed to grow cer-tain traits will appear Byobserving these traits youmight be able to deter-mine the possible pheno-types and genotypes ofthe parent plants that pro-duced these seeds In thislab you will determinethe genotypes of plantsthat grow from twogroups of tobacco seedsEach group of seeds camefrom different parentsPlants will be either greenor albino (white) in colorUse the following geno-types for this cross CC green Cc greenand cc albino
How can phenotypes and genotypes of plants be determined
ProblemCan the phenotypes and genotypes of the parent plants thatproduced two groups of seeds be determined from the phe-notypes of the plants grown from the seeds
HypothesesHave your group agree on a hypothesis to be tested that willanswer the problem question Record your hypothesis
ObjectivesIn this BioLab you will Analyze the results of growing two groups of seeds Draw conclusions about phenotypes and genotypes based
on those results Use the Internet to collect and compare data from other
students
Possible Materialspotting soil light sourcesmall flowerpots or seedling thermometer or
flats temperature probetwo groups of tobacco seeds plant-watering bottlehand lens
Safety PrecautionsCAUTION Always wash your hands after handling plantmaterials Always wear goggles in the lab
Skill HandbookIf you need help with this lab refer to the Skill Handbook
1 Examine the materials provided by your teacher As agroup make a list of the possible ways you might testyour hypothesis
2 Agree on one way that your group could investigate yourhypothesis
PLAN THE EXPERIMENTPLAN THE EXPERIMENT
PREPARATIONPREPARATION
Matt Meadows
274 MENDEL AND MEIOSIS
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102 MEIOSIS 275
ANALYZE AND CONCLUDEANALYZE AND CONCLUDE
1 Think Critically Why was it necessary to grow plants from the seeds inorder to determine the phenotypes of the plants that formed the seeds
2 Draw Conclusions Using the information in the introduction describehow the gene for green color (C) is inherited
3 Make Inferences For the group of seeds that yielded all green plants areyou able to determine exactly the genotypes of the parents that formed theseseeds Can you determine the genotype of each plant observed Explain
4 Make Inferences For the group of seedsthat yielded some green and some albinoplants are you able to determine exactlythe genotypes of the plants that formedthese seeds Can you determine the geno-type of each plant observed Explain
5 Use the data posted onto
compare your experimental design withthat of other students Were your resultssimilar What might account for the differences
ERROR ANALYSIS
Find this BioLab using the link below andpost your results in the table providedBriefly describe your experimental design
3 Design an experiment that will allow you to collect quanti-tative data For example how many plants do you thinkyou will need to examine
4 Prepare a numbered list of directions Include a listof materials and the quantities you will need
5 Make a data table for recording your observations
Check the Plan1 Carefully determine what data you are going
to collect How many seeds will you need Howlong will you carry out the experiment
2 What variables if any will have to be con-trolled (Hint Think about the growing condi-tions for the plants)
3 Make sure your teacher has approved your experi-mental plan before you proceed further
4 Carry out your experiment Make any needed obser-vations such as the numbers of green and albino plantsin each group and complete your data table
5 Visit to post your data6 Make wise choices in the disposal of
materialsCLEANUP AND DISPOSAL
Ray PfortnerPeter Arnold Inc
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ncbdolglencoecominternet_lab ncbdolglencoecominternet_lab
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276 MENDEL AND MEIOSIS
A Solution from Ratios
In 1866 Gregor Mendel an Austrian monkpublished the results of eight years of experi-
ments with garden peas His work was ignoreduntil 1900 when it was rediscovered
Mendel had three qualities that led to his dis-covery of the laws of heredity First he was curi-ous impelled to find out why things happenedSecond he was a keen observer Third he was askilled mathematician Mendel was the first biol-ogist who relied heavily on statistics for solu-tions to how traits are inherited
Darwin missed his chance About the sametime that Mendel was carrying out his experi-ments with pea plants Charles Darwin was gath-ering data on snapdragon flowers When Darwincrossed plants that had normal-shaped flowerswith plants that had odd-shaped flowers all theoffspring had normal-shaped flowers He thoughtthe two traits had blended When he allowed theF1 plants to self-pollinate his results were 88plants with normal-shaped flowers and 37 plantswith odd-shaped flowers Darwin was puzzled bythe results and did not continue his studies withthese plants Lacking Mendelrsquos statistical skillsDarwin failed to see the significance of the ratioof normal-shaped flowers to odd-shaped flowersin the F2 generation What was this ratio Was itsimilar to Mendelrsquos ratio of dominant to recessivetraits in pea plants
Finding the ratios for four other traitsFigure 103 on page 256 shows seven traits thatMendel studied in pea plants You have alreadylooked at Mendelrsquos data for plant height andseed shape Now use the data for seed colorflower position pod color and pod shape to findthe ratios of dominant to recessive for thesetraits in the F2 generation
Draw Table B in your notebook or journalCalculate the ratios for the data in Table A andcomplete Table B by following these steps
bull Step 1 Divide the larger number by the smaller number
bull Step 2 Round to the nearest hundredthbull Step 3 To express your answer as a ratio
write the number from step 2 followed by a colon and the number 1
RW VanNormanVisuals Unlimited
Think Critically Why are ratios so important inunderstanding how dominant and recessive traitsare inherited
To find out more about Mendelrsquos work visit ncbdolglencoecommath
Table A Mendelrsquos Results
Seed Flower Pod PodColor Position Color Shape
Yellow Axial Green Inflated6022 651 428 882
Green Terminal Yellow Constricted2001 207 152 299
Table B Calculating Ratios for Mendelrsquos Results
Seed Flower Pod PodColor Position Color Shape
Calculation 6022 300
2001
Ratio 31yellow green
0263-0279 C10S2 BDOL-829900 8304 815 PM Page 276
Section 101STUDY GUIDESTUDY GUIDE
CHAPTER 10 ASSESSMENT 277
Section 102
To help you reviewMendelrsquos work use the OrganizationalStudy Fold on page 253
Key Concepts Genes are located on chromosomes and
exist in alternative forms called alleles Adominant allele can mask the expression ofa recessive allele
When Mendel crossed pea plants differingin one trait one form of the trait disap-peared until the second generation of off-spring To explain his results Mendelformulated the law of segregation
Mendel formulated the law of independentassortment to explain that two traits areinherited independently
Events in genetics are governed by thelaws of probability
Vocabularyallele (p 256)dominant (p 256)fertilization (p 253)gamete (p 253)genetics (p 253)genotype (p 258)heredity (p 253)heterozygous (p 259)homozygous (p 258)hybrid (p 255)law of independent
assortment (p 260)law of segregation
(p 257)phenotype (p 258)pollination (p 254)recessive (p 256)trait (p 253)zygote (p 253)
Mendelrsquos Lawsof Heredity
Key Concepts In meiosis one diploid (2n) cell produces
four haploid (n) cells providing a way foroffspring to have the same number ofchromosomes as their parents
In prophase I of meiosis homologous chro-mosomes come together and pair tightlyExchange of genetic material called cross-ing over takes place
Mendelrsquos results can be explained by the dis-tribution of chromosomes during meiosis
Random assortment and crossing over dur-ing meiosis provide for genetic variationamong the members of a species
The outcome of meiosis may vary due tonondisjunction the failure of chromosomesto separate properly during cell division
All the genes on a chromosome are linkedand are inherited together It is the chro-mosomes rather than the individual genesthat are assorted independently
Vocabularycrossing over (p 266)diploid (p 263)egg (p 265)genetic recombination
(p 270)haploid (p 263)homologous chromo-
some (p 264)meiosis (p 265)nondisjunction (p 271)sexual reproduction
(p 266)sperm (p 265)
Meiosis
ncbdolglencoecomvocabulary_puzzlemaker
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Review the Chapter 10 vocabulary words listed inthe Study Guide on page 277 For each set ofvocabulary words choose the one that does notbelong Explain why it does not belong
1 eggmdashspermmdashzygote2 homozygousmdashhybridmdashheterozygous3 phenotypemdashgenotypemdashallele4 nondisjunctionmdashgenetic recombinationmdash
crossing over5 zygotemdashdiploidmdashgamete
6 At the end of meiosis how many haploidcells have been formed from the originalcellA one C threeB two D four
7 When Mendel transferred pollen from onepea plant to another he was ________ theplantsA self-pollinating C self-fertilizingB cross-pollinating D cross-fertilizing
8 Which of these does NOT show a recessivetrait in garden peasA B C D
9 During what phase of meiosis do sister chromatids separateA prophase I C anaphase IIB telophase I D telophase II
10 During what phase of meiosis do nonsisterchromatids cross overA prophase I C telophase IB anaphase I D telophase II
11 A dihybrid cross between two heterozygotesproduces a phenotypic ratio of ________A 31 C 9331B 121 D 169
12 Open Ended On the average each humanhas about six recessive alleles that would belethal if expressed Why do you think thathuman cultures have laws against marriagebetween close relatives
13 Open Ended How does separation of homol-ogous chromosomes during anaphase I ofmeiosis increase variation among offspring
14 Open Ended Relating to the methods ofscience why do you think it was importantfor Mendel to study only one trait at a timeduring his experiments
15 Open Ended Explain why sexual reproduc-tion is an advantage to a population thatlives in a rapidly changing environment
16 Observe and Infer Why is it possible tohave a family of six girls and no boys butextremely unlikely that there will be a publicschool with 500 girls and no boys
17 Recognize Cause and Effect Why is itsometimes impossible to determine the genotype of an organism that has a domi-nant phenotype
18 Observe and Infer While examining a cellin prophase I of meiosis you observe a pairof homologous chromosomes pairing tightlyWhat is the significance of the places atwhich the chromosomes are joined
19 Several humangenetic disorders result from nondisjunctionin meiosis including Down syndromeKleinfelterrsquos syndrome and Turner syn-drome Visit to inves-tigate these disorders What characteristic iscommon to each Choose one of these dis-orders or another human disorder causedby nondisjunction and prepare a visual dis-play that explains the disorder Explain thedisorder to your class
REAL WORLD BIOCHALLENGE
278 CHAPTER 10 ASSESSMENT
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ncbdolglencoecomchapter_test
0263-0279 C10S2 BDOL-829900 8304 813 PM Page 278
Multiple ChoiceUse the diagram to answer questions 20ndash23
20 Which of the following is trueA Individual 1 is heterozygousB Individuals 2 and 3 are homozygousC Individual 4 is recessiveD All individuals will be male
21 Which of the following has the Tt genotypeA 1 C 3B 2 D 2 and 3
22 If T is the allele for purple flowers and t isthe allele for white flowers the resultswould be ________A 3 out of 4 are purpleB 3 out of 4 are whiteC equal numbers of white and purpleD all of the same color
23 Which of Mendelrsquos observations woulddescribe the results of the experimental cross in question 22A rule of dominanceB law of segregationC law of independent assortmentD rule of unit factors
24 Recessive traits appear only when an organism is ________A matureB different from its parentsC heterozygousD homozygous
25 The stage of meiosis shown here is ________A anaphase IB metaphase IIC telophase ID telophase II
Study the diagram and answer questions 26ndash28
26 What name is given to the process shownaboveA fertilization C meiosisB zygote D gametes
27 What name is given to the cells shown inthe diagram aboveA fertilization C meiosisB zygotes D gametes
28 If each of the cells shown in the diagram has16 chromosomes how many chromosomeswould you expect to find in a skin cell of theresulting organismA 16 C 32B 64 D 8
T
T 1 2
43t
t
CHAPTER 10 ASSESSMENT 279
Constructed ResponseGrid InRecord your answers on your answer document
29 Open Ended Explain the difference between trisomy and triploidy Describe a way that eachcondition could occur Use diagrams to clarify your answer
30 Open Ended Compare metaphase of mitosis with metaphase I of meiosis Explain the significance ofthe differences between the two stages in terms of sexual reproduction and genetic variation
The assessed North Carolina objective appears next to the question
303
303
303
303
303
303
ncbdolglencoecomstandardized_test
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