Chapt 04 genetics

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Chapter 4The Chromosome Theory of Inheritance

Fill in the Blank

1. The process of two consecutive cell divisions in the diploid progenitors of sex cells is

called ______________________________.Ans: meiosis

Difficulty: 1

2. _________________________ is the term that describes a single set of chromosomes.

Ans: haploid

Difficulty: 1

. !n _______________________ chromosomes" the centromere is closer to one end than

to the middle.

Ans: acrocentric

Difficulty: 2

#. $hromosomes that match in si%e" shape and banding pattern are called_________________________________.

Ans: homologs

Difficulty: 2

&. A ____________________________ is an image of all the chromosomes of an

organism cut from a micrograph" arranged based on staining pattern into pairs and" by

convention" in decreasing si%e followed by sex chromosomes.Ans: 'aryotype

Difficulty: 1

(. ______________________________ occurs when chromosomes fail to separate

properly during meiosis.

Ans: nondis)unctionDifficulty: 2

*. The smaller diploid sister cell that results during meiosis ! in females is called

______________________________.Ans: polar body

Difficulty: 2

+. A ________________________ is an animal cell with two or more nuclei.

Ans: syncytium

Difficulty: 2

,. A multinucleate plant tissue is called a _____________________________.

Ans: coenocyte

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Difficulty: 2

1. The process of matching chromosomes becoming %ipped together during the %ygotenestage of prophase ! is called ______________________________.

Ans: synapsis

Difficulty: 1

Multiple Choice

11. !nDrosophila virilis" nuclei of somatic cells contain 12 chromosomes while nuclei of

sperm cells contain only ( chromosomes. /hat does 0n eual for this species3

A4

54 ($4 12

D4 2#

64 ( or 12" depending on cell type

Ans: 5Difficulty: 1

12. The stage of mitosis when chromosomes condense to form rod7shaped structures visible

under the microscope is called:

A4 interphase.54 prophase.

$4 metaphase.

D4 anaphase.

64 telophase.Ans: 5

Difficulty: 1

1. The stage of mitosis when sister chromatids separate from each other and migrate to

opposite poles of a cell is called:

A4 interphase.54 prophase.

$4 metaphase.

D4 anaphase.

64 telophase.Ans: D

Difficulty: 1

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1#. During which of the following stages of the cell cycle would a chromosome consist of

only a single chromatid3

A4 8154 82

$4 mitotic prophase

D4 mitotic metaphase64 all of the above

Ans: A

Difficulty: 1

1&. /hich of the following statements applies to homologous chromatids3

A4 They are attached to the same centromere

54 They are genetically identical$4 They segregate from each other at anaphase of mitosis

D4 They contain the same genes in the same order but may have different alleles of some

genes

64 9ore than one of the above statements applies to homologous chromatidsAns: D

Difficulty: 2

1(. Drosophila melanogasterhas four pairs of chromosomes. perm from this species are

formed by a meiotic process in which homologous chromosomes pair and segregate butdo not undergo crossing over. ;ow many genetically different 'inds of sperm could be

produced by aDrosophila melanogastermale3

A4 #

54 +$4 1(

D4 (#

64 2&(Ans: $

Difficulty:

1*. >

individuals would most li'ely arise from nondis)unction at the ______ meiotic division

in the ______.

A4 first" mother54 second" mother

$4 first" father

D4 second" father64 more than one of the above could give rise to =>> individuals

Ans: D

Difficulty:

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1+.

individuals could arise from nondis)unction at the ______ meiotic division in the

______.A4 first" mother

54 second" mother

$4 first" fatherD4 second" father

64 more than one of the above could give rise to ==> individuals

Ans: 6Difficulty:

1,. $rossing over between homologous chromosomes occurs at which of the following

stages of meiosis3A4 phase

54 prophase !

$4 metaphase !

D4 anaphase !64 prophase !!

Ans: 5Difficulty: 1

2. ;umans have 22 pairs of autosomes plus one sex chromosome pair. ;ow manyautosomes are present in a normal human primary spermatocyte3

A4 22

54 2

$4 ##D4 #&

64 #(

Ans: $Difficulty: 2

21. -remeiotic germ cells that divide mitotically in females are referred to as:A4 primary oocytes.

54 secondary oocytes.

$4 ootids.

D4 oogonia.64 ova.

Ans: D

Difficulty: 1

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22. The cells in which meiosis occurs in males are referred to as:

A4 spermatocytes.

54 spermatogonia.$4 spermatids.

D4 oocytes.

64 sperm.Ans: A

Difficulty: 1

2. A chromosome with two arms of eual length is referred to as:

A4 acrocentric.

54 homologous.

$4 telocentric.D4 meta%oan.

64 metacentric.

Ans: 6

Difficulty: 1

2#. At which of the following stages of meiosis would homologous chromosomes bepaired3

A4 prophase of meiosis !

54 prophase of meiosis !!$4 metaphase of meiosis !

D4 metaphase of meiosis !!

64 a and c are correct

Ans: 6Difficulty: 2

2&. /hich of the following events occurs during mitosis but not meiosis3A4 egregation of sister chromatids.

54 -airing of homologous chromosomes.

$4 $rossing7over between homologous chromosomes.D4 Alignment of chromosomes on the metaphase plate.

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2*. !f a geneticist were to closely examine the ma'e7up of a single autosomal chromosome

from one of your cells" that chromosome would be found to be:A4 derived entirely from genes from )ust one of your grandparents.

54 a mosaic of genes derived from your mother and father.

$4 a mosaic of genes derived from all four of your grandparents.D4 a mosaic of genes derived from )ust two of your grandparents ? either your two

grandfathers or your two grandmothers.

64 a mosaic of genes derived from )ust two of your grandparents ? either your maternalgrandparents" or your paternal grandparents.

Ans: 6

Difficulty: #

2+. !f you are a male" your = chromosome contains genes derived from:

A4 your paternal grandfather only.

54 your maternal grandfather only.

$4 both your paternal and maternal grandfathers.D4 both your paternal grandfather and grandmother.

64 both your maternal grandfather and grandmother.Ans: 6

Difficulty: #

2,. The chromosomal structure to which spindle fibers attach during the mitotic divisions is

referred to as a:

A4 chromatid.

54 centrosome.$4 'inetochore.

D4 metaphase plate.

64 centromere.Ans: $

Difficulty: 1

. 9icrotubules that attach to centrosomes but not chromosomes and that interdigitate with

microtubules emanating from the centrosome at the opposite pole are 'nown as:

A4 'inetochore microtubules.

54 polar microtubules.$4 astral microtubules.

D4 interdigitating microtubules.

64 none of the aboveAns: 5

Difficulty: 1

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1. 9itosis results in _______ in chromosome number while meiosis results in ______

chromosome number.

A4 a doubling of" no change in54 no change in" no change in

$4 a reduction by half in" no change in

D4 no change in" a doubling of64 no change in" a reduction by half in

Ans: 6

Difficulty: 2

2. $ells said to be in the 8 stage:

A4 have two chromatids per chromosome.

54 are replicating their chromosomes.$4 are about to enter the mitotic phase of the cell cycle.

D4 are in an extended 81 phase and no longer cycling.

64 are dead.

Ans: DDifficulty: 1

. $ells in 82 stage of the cell cycle have ______ as cells of the same species in the 81

stage.

A4 twice as many chromosomes54 twice as many chromatids

$4 half as many chromatids

D4 the same number of chromatids

64 half as many chromosomesAns: A

Difficulty: 1

#. A cross between a white7eyed female fruit fly and a red7eyed male would generate

which of the following types of progeny3

A4 @ed7eyed females and white7eyed males.54 /hite7eyed females and red7eyed males.

$4 All red7eyed females and a &:& mixture of white7eyed and red7eyed males.

D4 All red7eyed males and a &:& mixture of white7eyed and red7eyed females.

64 The result can not be predicted because it depends on whether the female ishomo%ygous or hetero%ygous.

Ans: A

Difficulty: 2

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&. A female fruit fly with singed bristles was mated with a male from a true7breeding wild

type stoc' with long bristles. All of the 1 females had wild7type bristles and all of the

1 males had singed bristles. !f the 1 flies are intercrossed" the expected ratio of longto singled bristles in the 2 flies is:

A4 1: in both sexes Bi.e. males and females will all have long bristles4.

54 :1 in both sexes.$4 :1 in females" while all the males will have singed bristles.

D4 1:1 in females" while all the males will have singed bristles.

64 1:1 in both sexes.Ans: 6

Difficulty: 2

(. @ed7green color7blindness is controlled by an = chromosomal gene in humans. Anormal man and woman whose fathers are both color7blind marry. /hat is the

probability that their first child will be color7blind3

A4 1C2

54 1C#$4 1C+

D4 1C64

Ans: 5

Difficulty: 2

*. ;emophilia is caused by an =7lin'ed mutation in humans. !f a woman whose paternal

uncle Bfathers brother4 was a hemophiliac marries a man whose brother is also a

hemophiliac" what is the probability of their first child having hemophilia Bnote: assumeno other hemophilia in the pedigree and no hidden carriers4.

A4

54 1C#$4 1C2

D4 1C+

64 1Ans: A

Difficulty:

+. A white7eyed female fruit fly is mated to a red7eyed male. Ene of their progeny is awhite7eyed female. /hat is the li'ely 'aryotype of this white7eyed daughter3

A4 ==

54 ==>$4 =E

D4 ===

64 =>>Ans: 5

Difficulty: 2

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,. A white7eyed female fruit fly is mated to a red7eyed male. Ene of their progeny is a

white7eyed female. This white7eyed daughter li'ely arose from nondis)unction of the

sex chromosomes during _________ in the __________.A4 meiosis !" mother

54 meiosis !!" mother

$4 meiosis !" fatherD4 meiosis !!" father

64 meiosis ! or !!" mother

Ans: 6Difficulty:

#. 9ales with one copy of an =7lin'ed gene are said to be _________ for that gene.

A4 homo%ygous54 heteroallelic

$4 hetero%ygous

D4 hemi%ygous

64 deficientAns: D

Difficulty: 1

#1. !n chic'ens" it is the females that have two different sex chromosomes BF and /4 while

the males have two F chromosomes. A F7lin'ed gene controls the pattern of the featherswith the dominant 5 allele causing the barred pattern and the b allele causing non7barred

feathers. rom which of the following crosses would all of the daughters be of one type

Bbarred or non7barred4 and all of the sons the other type3

A4 barred females G non7barred males54 non7barred females G barred males

$4 non7barred females G non7barred males

D4 barred females G barred males64 more than one of the above

Ans: A

Difficulty: #

#2. !nDrosophila" the recessive allele for for'ed bristles is sex7lin'ed" and the recessive

allele for purple eyes is autosomal. The wild7type alleles are for straight bristles and red

eyes" respectively. A female hetero%ygous for both pairs of alleles is mated with a malewith for'ed bristles and purple eyes. /hat percentage of the daughters will have for'ed

bristles and purple eyes3

A4 1H54 *&H

$4 &H

D4 2&H64 H

Ans: D

Difficulty:

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#. !n what proportion of a mans sperm will all 2 chromosomes have centromeres

inherited from the same parent Beither his mother or his father43

A4 1C254 B1C242

$4 B1C24#(

D4 B1C242264 B1C#4#(

Ans: D

Difficulty: #

##. uppose you discover a new species of worm that exists in two forms ? slimy and non7

slimy. >ou find that when slimy females are mated to non7slimy males the offspring

consist of slimy males and non7slimy females" whereas when non7slimy females aremated with slimy males" the offspring of both sexes are all slimy. >ou would conclude

that the _________ allele is dominant and that ________ are the heterogametic sex Bthe

sex with two different sex chromosomes4 in this species of worm.

A4 slimy" females54 slimy" males

$4 non7slimy" femalesD4 non7slimy" males

Ans: A

Difficulty: #

#&. /hich of the following is not a property of homologous chromosomes3

A4 They pair physically during prophase of meiosis !.

54 They exchange genes by crossing over during meiosis.$4 They carry alleles for the same genes at the same chromosomal position.

D4 They are attached to the same centromere during 82 of the cell cycle.

64 They segregate to opposite poles at anaphase of meiosis !.Ans: D

Difficulty: 2

#(. uppose you discover a new variant in which mice have spi'y fur instead of the usual

soft fur. >ou notice that this trait seems only to be present in males. To investigate this

pattern" you cross a spi'y7fur male with a soft7fur female" and find that all of the 1

progeny of both sexes have soft fur. >ou then interbreed the 1 and observe that all ofthe 2 females have soft fur" but 1C# of the 2 males have spi'y fur. >ou conclude that:

A4 the spi'y allele is an =7lin'ed recessive.

54 the spi'y allele is >7lin'ed.$4 the spi'y allele is autosomal recessive with sex7limited expression.

D4 the spi'y allele is an =7lin'ed dominant.

64 the spi'y allele is an autosomal dominant with sex7limited expression.Ans: $

Difficulty:

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#*. !n fruit flies" brown eyes can be caused by the recessive mutations pn Bprune4" bw

Bbrown4 or ry Brosy4" which are on the = chromosome" second chromosome and third

chromosome" respectively. /ild7type alleles for all three genes must be present for eyesto be red. uppose that two brown7eyed flies are crossed and their progeny consist of

brown7eyed sons and red7eyed daughters. /hich mutation is responsible for the brown

eyes in the parental female3A4 pn

54 bw

$4 ryD4 either bw or ry

64 any of the three ? pn" bw or ry

Ans: A

Difficulty: #

#+. $olor vision depends upon the dominant alleles of three genes ? the @ gene and the 8

gene are both on the = chromosome" while the 5 gene is autosomal. @ecessive

mutations in any of the three genes can cause color7blindness. uppose a colorblind manmarries a colorblind woman and all of their offspring have normal vision. /hat is the

genotype of the woman3A4 @@88bb

54 @@gg55

$4 rr88bbD4 @@gg55 or @@88bb

64 rr88bb or rrgg55

Ans: A

Difficulty: #

#,. A variable feature of some chromosomes in corn is the presence or absence of 'nobs at

particular sites. uppose that one member of each of two pairs of chromosomes in acorn plant has a 'nob. !f this plant were crossed with a 'nobless plant" what percentage

of the offspring is expected to be 'nobless3

A4 1H54 *&H

$4 &H

D4 2&H

64 HAns: D

Difficulty:

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&. /hat aspect of chromosome behavior most clearly accounts for 9endels law of

segregation3

A4 9ovement of sister chromatids to opposite poles at anaphase !! of meiosis.54 9ovement of homologous chromosomes to opposite poles at anaphase ! of meiosis.

$4 $rossing over between homologous chromosomes during prophase ! of meiosis.

D4 @eplication of chromosomes prior to meiosis.64 !ndependent alignment of different homologous pairs on the metaphase ! spindle.

Ans: 5

Difficulty: 2

&1. /hat aspect of chromosome behavior most clearly accounts for 9endels law of

independent assortment3

A4 9ovement of sister chromatids to opposite poles at anaphase !! of meiosis.54 9ovement of homologous chromosomes to opposite poles at anaphase ! of meiosis.


D4 @eplication of chromosomes prior to meiosis.

64 !ndependent alignment of different homologous pairs on the metaphase ! spindle.Ans: 6

Difficulty: 2

&2. /hich aspectBs4 of chromosome behavior isCare primarily responsible for the

tremendous amount of genetic variability associated with sexual reproduction3A4 egregation of sister chromatids at anaphase !! of meiosis.

54 egregation of homologous chromosomes at anaphase ! of meiosis.


D4 !ndependent alignment of different homologous pairs on the metaphase ! spindle.64 5oth c and d contribute to the generation of variability.

Ans: 6

Difficulty: 2

&. /hich sex chromosomes are limited to only one sex3

A4 = and F54 = and /

$4 > and F

D4 > and /

64 = and >Ans: D

Difficulty: 1

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. !n the following pedigree" the indicated trait is caused by what type of allele3

A4 autosomal recessive54 autosomal dominant

$4 =7lin'ed recessive

D4 =7lin'ed dominant

64 >7lin'edAns: $

Difficulty: 2

&&. !n the following pedigree" the indicated trait is caused by what type of allele3



D4 =7lin'ed dominant64 >7lin'ed

Ans: D

Difficulty: 2

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&(. !n the following pedigree" the indicated trait is caused by what type of allele3

A4 autosomal recessive

54 autosomal dominant$4 =7lin'ed recessive


64 >7lin'edAns: 5

Difficulty: 2

&*. !n the following pedigree" the indicated trait is caused by what type of allele3

A4 autosomal recessive

54 autosomal dominant

$4 =7lin'ed recessiveD4 =7lin'ed dominant

64 >7lin'ed

Ans: ADifficulty: 2

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&+. !n the following pedigree" the indicated trait is caused by what type of allele3




64 >7lin'ed

Ans: 6Difficulty: 2

&,. A female fruit fly with vermilion eyes and normal wings is crossed to a male with

normal red eyes and cut wings. The 1 progeny consist of females with red eyes and

normal wings" and males with vermilion eyes and normal wings. /hen the 1 progenyare interbred" the 2 consists of two types of females ? vermilion eyes" normal wings

B1C24 and red eyes" normal wings B1C24" and two types of males ? vermilion eyes"

normal wings B1C24 and red eyes" cut wings B1C24. Are the genes for eye7color and wing7

type =7lin'ed or autosomal3A4 The eye7color gene is =7lin'ed and the wing7type gene is autosomal.

54 The eye7color gene is autosomal and the wing7type gene is =7lin'ed.$4 5oth genes are =7lin'ed.D4 5oth genes are autosomal.

64 9ore than one of the above is consistent with the data.

Ans: $Difficulty: #

(. !n fruit flies" an =7lin'ed dominant mutation B


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(1. The following is a list of mitotic events out of order.

A4 $hromosomes align on the midplate of the cell.

54 Iinetochores begin attaching to spindle fibers.$4


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(#. A cell with three pairs of chromosomes has the genotype Aa5b$c" such that each pair of

alleles is on a different pair of chromosomes. !f this cell were to undergo a mitotic

division" how many genetically different types of gametes could be produced3A4 1

54

$4 (D4 +

64 ,

Ans: ADifficulty: 2

(&. !n humans" =E individuals are females with Turners syndrome and ==> individuals

are males with Ilinefelters syndrome. /hich of the following events could not give riseto a Ilinefelters male3

A4


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(+. !n animal gametogenesis" a single primary spermatocyte generates ______ sperm" while

a single primary oocyte generates ______ eggBs4.

A4 1" #54 1" 1

$4 #" 2

D4 #" 164 #" #

Ans: D

Difficulty: 1

Matching

(,. 9atch the event with the appropriate stage of mitosis.1. ister chromatids separate and move to opposite poles. a. prophase

2. $hromosomes begin attaching to spindle fibers. b. prometaphase

. $hromosomes decondense and nuclear membrane reforms. c. metaphase

#. $hromosomes condense and spindle forms. d. anaphase&. ister chromatids attached to opposite spindle poles. e. telophase

Ans: 17b" 27d" 7e" #7a" &7c

Difficulty: 2

*. 9atch the chromosomal event with the appropriate stage of meiosis.1. ;omologous chromosomes pair and cross over. a. prophase

. ;omologous chromosomes segregate to opposite poles. b. metaphase

. ister chromatids segregate to opposite poles. c. anaphase !#. -airs of chromosomes align on the spindle. d. metaphase !!

&. ister chromatids attach to opposite poles of spindle. e. anaphase !!

Ans: 17a" 27c" 7e" #7b" &7dDifficulty: 2

*1. 9atch the event with the cell division process in which it occurs. B


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*2. 9atch the event with the type of cell in which it occurs during spermatogenesis. B


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True or False

*(. ister chromatids are identical chromosomes" duplicated during metaphase and stillattached to each other.

Ans: True

Difficulty: 1

**. The nonsex chromosomes are called autosomes.

Ans: TrueDifficulty: 1

*+. A female that is ==E has Turner yndrome.

Ans: alseDifficulty: 2

*,. A chromatin7laden nucleus is uiescent.


+. The period between cell cycles is called interphase.

Ans: True

Difficulty: 1

+1. During the and 82stages of interphase" the centrosomes replicate" producing two

centrosomes that remain in extremely close proximity.

Ans: TrueDifficulty: 1

+2. $hromosomes attach to these microtubules through lin'age groups.Ans: alse

Difficulty: 1

+. -olar microtubules are short and unstable and extend out from the centrosome toward

the cells periphery.

Ans: alse

Difficulty: 2

+#. A somatic cell is a cell destined for a speciali%ed role in the production of gametes.


+&. During pachytene" structures called recombination nodules begin to appear along thesynaptonemal complex" and an exchange of parts between nonsister chromatids occurs

at these nodules.

Ans: True

Difficulty: 2

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Short Answer

+(. !n humans" why is pattern baldness seen only in men3

Ans: -attern baldness is an example of sex7limited expression. !t is caused by

hetero%ygosity for an autosomal baldness gene" which when homo%ygous causesbaldness in both sexesJ in the hetero%ygous condition" pattern baldness is

expressed only in males and is thus sex7limited.

Difficulty: 2

+*. 8ive examples of three different methods by which chromosomes can determine sex.

Ans: == females" => males ? humans" fruit fliesJ == females" =E males ? some

moths and other insectsJ FF males" F/ females ? birds and butterflies.Difficulty: 2

++. /hat are the conseuences of a mutation that disrupts cyto'inesis for cells that are

actively dividing3Ans: 9itosis without cyto'inesis leads to multinucleate cells with multiple copies of

each chromosome.Difficulty: 1

+,. /hat is the ma)or cause of Downs syndrome3Ans: Trisomy Bthree copies4 of chromosome 21" which results from nondis)unction of

chromosome 21 in meiosis of the mother B+H of cases4 or father B2H of cases4.

Difficulty: 1

,. /hat is meant by the term 0chec'point with respect to regulation of the cell cycle3

Ans: A chec'point is a moment when cell cycle progress can be stopped temporarily if

a preceding step is not yet complete.Difficulty: 2

,1. /hat was the evidence that led /alter utton to conclude that the = and >chromosomes determine sex3

Ans: utton studied the chromosomes of grasshoppers and showed that males always

had one = and one > while females always had two =s.

Difficulty: 2

,2. 5ridges crossed white7eyed female and red7eyed male fruit flies and recovered rare

exceptional white7eyed females and red7eyed males in addition to the usual red7eyedfemales and white7eyed males. ;ow did 5ridges observations lend support to the

chromosome theory of inheritance3

Ans: 5ridges showed that the exceptional flies also had exceptional 'aryotypes forthe sex chromosomes B=E males and ==> females4. o" a reversal in the normal

pattern of transmission of a genetic trait is perfectly correlated with a mista'e in

the pattern of transmission of a particular pair of chromosomes Bthe sex

chromosomes4" such that the exceptional sons inherit their = Band their eye color4

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from their father" and the exceptional daughters inherit both of their =s Band their

eye color4 from their mother" proving that the eye color gene must be on the =

chromosome.Difficulty: #

,. /hat are two important functions of meiosis3Ans: To reduce chromosome number by half in preparation for fertili%ation so that

biparental inheritance does not lead to an increase in chromosome numberJ to

generate offspring that differ genetically from their parents and from each other.Difficulty:

,#. /hy are recessive =7lin'ed traits more commonly seen in men than in women3

Ans: 5ecause expression of an =7lin'ed trait in a man reuires only that he inherit onecopy of the allele from his mother" whereas expression in females reuires

inheritance of two copies" one from each parent.

Difficulty: 2

,&. /hy are dominant =7lin'ed traits seen in women more commonly than in men3

Ans: There are two reasons: 14 Any = chromosome is twice as li'ely to be present in awoman as a man because women have two = chromosomes and men have oneJ 24

many dominant mutations are recessive lethals" so that for many dominant =

traits" men that inherit them die during development because of hemi%ogosity.Difficulty:

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Eperimental !esign an" Interpretation of !ata

,(. !nDrosophila" vestigial wings Bvg4 is a recessive autosomal mutant allele" and yellowbody By4 is a recessive =7lin'ed mutant allele. The wild7type alleles" vgKand yK control

normal wings and dar'7brown body color respectively. !f a homo%ygous yellow"

vestigial female is crossed to a normal male and the 1 offspring are interbred" what willbe the phenotypes and ratios of the 1 and 23

Ans: 1 ? females: all brown body" normal wings

males: all yellow body" normal wings2 ? females and males: brown body" normal wings ? C+

brown body" vestigial wings ? 1C+

yellow body" normal wings ? C+

yellow body" vestigial wings ? 1C+

Difficulty: #

,*. !nDrosophila" white eyes Bw4 and yellow body By4 are both recessive =7lin'ed

mutations. The wild type alleles" w

K

and y

K

" control red eyes and dar' body color"respectively. !f a homo%ygous yellow body" red eyed female is crossed with a dar' body"white7eyed male" and 1 progeny are interbred" what will the phenotypes and ratios of

the 1 and 2 be3

Ans: 1 ? females: all dar' body" red eyes

males: all yellow body" red eyes2 ? females: yellow body" red eyes ? 1C2

dar' body" red eyes ? 1C2

males: yellow body" red eyes ? 1C2dar' body" white eyes ? 1C2

Difficulty: #

,+. uppose you discovered a new mutation in mice that caused a curved spine. >ou notice

that this mutation is only seen in females. /hen curved7spine females are crossed with

normal males" the progeny are always recovered in the ratio: 1C curved7spine females"1C normal females" 1C normal males. 6xplain the genetic basis for this ratio.

Ans: The gene is =7lin'edJ the curved7spine allele is dominant to the normal allele in

hetero%ygotes but causes lethality in hemi%ygous males.

Difficulty: #

,,. !n crosses of white7eyedDrosophilafemales by red7eyed males" 5ridges recovered

white7eyed daughters and red7eyed sons at a rate of around one per 2" offspring.B9ost of the offspring were white7eyed males and red7eyed females.4 ;e hypothesi%ed

that these exceptional progeny resulted from nondis)unction of the = chromosomes in

meiosis in the female. /hy did he suspect that nondis)unction was occurring in thefemale parent3 /hat types of progeny would result from nondis)unction in the male

parent3

Ans: ==> red7eyed females and =E white7eyed males" so male nondis)unction does

not account for the observed exceptions.

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Difficulty:

1. !n crosses of white7eyedDrosophilafemales by red7eyed males" 5ridges recoveredwhite7eyed daughters and red7eyed sons at a rate of around one per 2" offspring.

B9ost of the offspring were white7eyed males and red7eyed females.4 ;e hypothesi%ed

that these exceptional progeny resulted from nondis)unction of the = chromosomes inmeiosis in the female. /hat is the expected 'aryotype of the exceptional red7eyed

males3 8ive two ways to test this predicted 'aryotype.

Ans: =E" tests ? 14 examine nuclei for > chromosome" 24 test males for fertility.Difficulty:

Chapt 04 genetics

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