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LAB-AIDS@ #70 _ GENETICS CONCEPTS KIT
Part 1 - Student Worksheet and Guide
ln the last third of the 19th century an Augustinian monk named Gregor Mendel involved himself in a series of years long
er---riments which eventually resulted in the branch of Biology called Cenetics.
Mendel did breeding experiments with pea plants and was more successful than his predecessors because he worked with only one
variable at a time and used mathematics to reach conclusions and predict future events. In this regard, he was the first modern scientist.
Scientists today use similar methods, working with one variable at a time and transposing observations into numerical quantities, which are then compared with the branch of Mathematics called Statistics.
The series of experiments that follow, duplicate much of Mendel's work but reduce years of work to minutes, uses devices which simulate
gametogenesis and fertilization, and produces random genotype combinations with the same mathematical results as pea plants.
The first device called a CAM-ETO-DISCTM is programmed to represent a pair of alleles (genes) and therefore depicts a diploid parent.
To simulate gametogenesis, the CAM-ETO-DISC is tossed from the shaker. The symbol which appears face up represents a gamete,
containing that allele. When two CAM-ETO-DISCS are tossed simultaneously, a pair of alleles appear, simulating fertilization, and represent the genotype of a zygote that will grow into a mature organism expressing the genetic information contained in those alleles.
SIMULATION OF CENETIC EXPERIMENTS WITH ONE ALLELIC PAIR
Procedure:
l. Working in pairs, obtain two GAM-ETO-DISCS with upper case "Y" on each face. These represent parent pea plants with the
genotype "YY" and the phenotype-yellow seed; i.e., the seed will look yellow. lt is called homozygous because both alleles are the
same.
1
ll.
.
Shake both CAM-ETO-DISCS in the shaker and toss them on the table. The result is the genotype of a possible zygote
(offspring) from the two simulated parent pea plants. Repeat four times and write the results here:
2.
What genotypes were produced and in what percentage?
3.
What is the phenotype of the offspring of homozygous parents with the genotypeYY?
4.
ls there any difference between parents and offspring?
ln paragraph I it was found that offspring of homozygous yellow seeds looked like the parents. Would this be true if the parents
were homozygous green seed?
Obtain two CAM-ETO-DISCS with the lower case "y" on each face. These represent parent pea plants with the genotype "yy"
and the phenotype green seed.
5. Shake both GAM-ETO-DISCS
in the shaker and toss them on the table. Repeat four times and write the results here.
6.
What percentage of the offspring have the same genotype combination
7.
Write a statement describing the genotype and phenotype of offspring from homozygous parents.
as the parents?
WouIdthestalementinquestion7alwaysbetruewithanytypeofhomozygousparents?Mendel bred homozygous plants by allowing them to self-pollinate (pea plants normally self-pollinate) through many generations
and discovered that a pure strain always breeds true, i.e., they always produce plants like themselves. He called these plants
purebred.
r\--. Fasten a "YY" CAM-ETO-DISC to a "yy" one with a small piece of double-sided tape. Fill the clear plastic vial halfway with water
and drop the unit into it. Place the cover on the vial.
B.
Shake the vial
with the unit inside five times. Record the results of the top face.
9.
Whichsymbol always appears face
up?
TheseCAM-ETo-DlSCShavebeenmanufacturedsothatonealwaysoVerpowerSo'do.t
certain characteristics dominate others, i.e., when cros.sbreeding occurs, only one characteristic is expressed or appears in the
phenotype. ln this case, when yellow seed plants are bred with-green seed ones, allof the offspring'will appearwith yellow
seeds, because "Y" gametes dominate over'iy" Bametes. However, their genotype will be "Yy." Ceneiics shorihand indicates a
dominant-recessive relationship with capital and lower case letters,
tull
is dominant over short (t) in pea plants.
10. What phenotype would be expressed with the
tt_,
Yy
tv.
[
".g.
following genotypes? yy
, Tt _
(l
vv
Place one GAM-ETO-DISC marked "Y" on each face and another with "y" on each face in the shaker. These represent purebred
yellow seed and green seed parents.
-,
11. Shake and toss the two GAM-ETO-DISCS on the table five times. Write the results here.
12. Write the genotypes produced and their relative percentages.
13. What is the phenotype of the offspring from purebred parents with the contrasting characteristics ,,yy,, and',yy,,?
14.
Write a statement describing the dominant-recessive rela_tionship between genes contained in the offspring of purebred
parents with contrasting genetic characteristics such as ,'yy,, and ',yy.,,
Mendel did similar experiments and called the conclusion in question I4, The Law of Dominance. He discovered clominance in
He called the offsp.ring of parents with,contrasting characteristics, hybrids.They are heterozygous because members of
allelic pairs are.different. Hybrid or[anisms always have the sime phenotype as ihe dominant parent buttontain a combination of
alleles from both.
seven traits.
V'
Select two CAM-ETO-DISCS with "Y" on one face and "y" on the other. These represent a pair of hybrid parents with the genotype ,,yv.,,
15. Shake and toss the two on the table
16.
/00 times. Tally the results by genotype and record the final totals
here.
\r'
What are the phenotypes?
17. What is the phenotype ratio?
(Ratio is determined by assuming the smaller number is 1. Dividing it into the other numbers reduces them
to lowest terms, e.g., if
there,wereg0-yellowseed,plantsandl0greenseed.plants,theratio-wouldbegyellowtol
green or9:1,i.e.,90dividedbyf fieq"uats
9 and since 1 0 is assumed to be 1 , the ralio is 9 yeliow to 1 green.)
18. What is the class phenotype ratio?
19. What is the class genotype ratio?
20. ls there a difference in phenotype between purebred parents and their offspring?
21 .
When,purebred yellow seed and green seed plants are crossed, what appears to happen to the phenotype green seed in their
hybrid offspring?
22.Write
a statement which describes what happens to alleles which carry the recessive characteristic as they are passed
from the
purebred recessive parent through its hybrid progeny and to those offspring of the hybrids which have in" alrrOf recessive
genotype.
"
Afterdoingsimilarexperiments, Mendel calledtheconclusion in question 22,fhelawof Segregation (separation) and Recombination.
LAB.AIDS@ #70 - GENETICS CONCEPTS KIT
Part ll - Student Worksheet and Guide
SIMULATION OF GENETTC EXPERIMENTS WITH ONE ALI-EtIC PAIR WHEN DOMINANCE
!S NOT A FACTOR.
r
l'
:edure
obtain two red cAM-ETo-Dlscs.rM These,represent parent Four o clock plants which have red flowers,
i.e., their phenotype
red. They
are homozygous because both alleies are the same (RR).
is
23' Shake both GAM-ETO-DISCS and toss them on the table. Repeat four times. The result is the
genotype of a possible zygote
(offspring) from these simulated parent Four O'clocks. Record the results
here
24.Write the genotypes produced and their relative percentages.
25. What is the phenotype of the offspring from purebred parents with the genotype
26.
ll'
RR?
ls there any difference between parent and offspring?
Obtain two white CAM-ETO-DISCS. These represent homozygous parent Four O'clock plants which
have white flowers (WW).
27. shake both and toss on the table five times. Record the results here:
28. what percentage of the offspring have the same genotype as the parents?
29. Write a statement describing the genotype and phenotype of offspring from homozygous parents.
._'o.What
lll'
term would Mendel have used to describe these homozygous parents and their offspring and
why?
Place the white GAM-ETO-D|SC representing a gamete from a homozygous white flowered parent,
over the red one which
depicts a Bamete from a homozygous red floi,erEd parenu simutatingi!?rliiirrior.
to in" tigt,r.
i";[i";;[th;;i#;tr:; iliJ;p
31. What color appears through the CAM-ETO-DtSCS?
Choosing traits which had the dominant-recessive relationship was of great brenefit to Mendel because
the concept of dominance was basic to the formulation of is laws of genetics. lt is more likEIy though that they
.h
he knew something of their relationshipanf,{id h'is experiments to provii"pi"8r. in fact, dori*n."lr
ii"rltru"rylr[-"-""rt.
we;;; ib;r;i;l;;h"#;;"*;;"
*ffiil:fffiL::i::f ffiff8'.iliti,il;?:li:t;i:f,:lilfJ:'J:il':'nit:|!;:*:fl,Lt:i:ijfr:'rffiti:*xfl?"",",:".;;
different Senotype sy.mbols; red is RR and white r-s wW. The hererozygous or hybrid offiii";; ;h;;h'r';;#li"
[," ,
its parents' characteristics, is given the.letter from each. The genotype"of the hy6rid ir rn"iufoi"
nw. ,rrr"[["i JlJroi
t
studies on incomplete dominance, but it is likely rhat he waf aware of it.
if?"i'.f
6.;;"y
lV' obtainfourCAM-ETo-Dlscs,twored,andtwowhite.Fastentheredandwhitetogetherwithapieceofdoublefacedtape.These
now represent a pair of hybrid parents.
32. Shake both sets in the shaker and toss them on the table 100 times.Tally the results. write
the totals here:
33. What genotypes are produced and with what percentages?
34. What is the genotype-phenotype ratio of your results? (See questio n 17 {or ratio explantation)
.
5. What is the genotype-phenotype ration of the class data?
36. write a statement describing the phenotype of offspring from two hybrid parents which have no
dominant-recessive
relationship.
SIMULATION OF GENETIC EXPERIMENTS WITH TWO ALIEIIC PA!RS -A DIHYBRID CROSS
Living things contain many genetic characteristics and it is therefore logical to want to design experiments which involve more
than one at a time. However, the problem with studying multiple variables is tracing causal factors. In the future, computers may
simplify the problem and allow experiments involving many variables simultaneously. Mendel was aware of problems with causal
factors but he did perform some experiments with dihybrids, i.e., pea plants which were hybrid for two traits. Actually he compar'
\-/
data from separate experiments done with different traits on the same plants.
The devices used in this activity to generate data are called TETRADICETM. Each of the four faces is identified to represent a
possible gamete from a double hybrid and therefore aTETRADIE depicts a parent organism. Cametogenesis is simulated by placing
a TETRADIE in a shaker and tossing it on the table. The symbols which are read from the face on the table simulate a gamete from
the diploid parent. When two TETRADICE are tossed simultaneously they simulate fertilization producing sets of alleles for two
traits, which represent the genotype of a new organism.
l.
Obtain two TETRADICE. They have the following sets of alleles:TY, Ty, tl ty. Each TETRADIE depicts a dihybrid pea plant which
has the phenotype tall with yellow seeds. lts Benotype is TtYy and each face represents a possible gamete.
37. Shake both TETRADICE in the shaker and toss them on the table. The result is the genotype of a possible zygote from these
simulated dihybrid pea plants. Make 160 zygote combinations and tally them by phenotype. Write the final totals here:
38. What is the phenotype ratio? (See Question 17)
39. What is the phenotype ratio of the class data?
40. Using the class data:
a. what is the ratio of yellow seeds to green?
b. what is the ratio of tall stems to short?
The cumbersome phenotype ratio generated by a dihybrid cross seems to be two 3:1 ratios, superimposed over one another.
Therefore, in this case at least, it is [ossible to study two variables simultaneously and still trace the causal factors.
Obtain two CAM-ETO-DISCS with the symbols "fY" on one face and "ty" on the other. These symbolize a dihybrid pair of pea
plants with the phenotype tall stem, yellow seeds.
4'l . Shake in the shaker and toss on the table 100 times. Tally the results by genotype and write the
final totals here:
42. Write the genotypes produced and the relative percentages.
43. What is the phenotype ratio?
44. What is the class phenotype ratio?
45. Other than the fact that there are two sets of alleles i nvolved , is there any difference between this phenotype ratio and the
previous ratio studied which had one set of alleles?
46. ln that experiment with one pair of alleles, how many chromosomes were involved?
47. How many chromosomes were therefore involved in the experiment in paragraph ll of this series?
48. How were the alleles arranged on those chromosomes?
49. How many chromosomes were involved in the experiment in paragraph
I
of this series?
50. How were the alleles arranged on the chromosomes?
5'l .
Write a statement describing the behavior of two pairs of alleles which are on separate sets of chromosomes (paragraph
l)
rather than linked to the same set (paragraph ll).
When Mendel did similar dihybrid crosses he called his conclusion, The Law of lndependentAssortment or Unit Characters. l.+-.term U n it Character can be thought of as an allele. lt is remarkable that he was able to formu late his laws because at that time tht
was no knowledge of chromosoi',"t, g"n"t or gametogenesis.
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