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Genetics Problems

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Genetics Problems

1. Fill in the punnett square representing the cross between two purebred parent plants (parental cross). The wild type green allele is G and albino allele is g. One parent was purebred albino and the other was purebred green.

+ Parent Allele 1 +Parent Allele 2

> Parent Allele 1

Gg

Gg

> Parent Allele 2

Gg

Gg

a. What are the genotypes and phenotypes of the progeny (F1)? 1 pt

The genotype is Gg, and the phenotype is wild type green

b. Fill in the punnett square representing a cross between two F1 progeny on the next page.

+ Parent Allele 1G +Parent Allele 2 g

> Parent Allele 1 G

GG

Gg

> Parent Allele 2 g

Gg

gg

c. What are the genotypes and phenotypes of the progeny (F2)? 1 pt

GG- green

Gg- green

Gg- green

gg- albino

d. Actual number of albino plants in the F2____1__ Number of green plants ____3___

Out of twenty plants how many would you expect to be albino and how many green? 1 pt

Five will be albino and fifteen will be green

e. Why was your result “probably” different from the expected? 1 pt

Since both parents have recessive genes, it is expected that there would be more albino offspring, which is not the case. The phenotypic ratio in the case above is 3:1. When this ratio is applied to 20 offspring, the result is indicated above.

2. The condition of dwarfism is dominant (D) over normal height (d). Draw a punnett square for what would happen if a woman who is a dwarf marries a man who is not, and they have children. a. What are the chances (probability) that the children will have the dwarf condition? (Assume there are no homozygous dwarf individuals). 3 pts

Normal Height allele dNormal Height allele dDwarf female allele DDdDdDwarf female allele ddddd

The probability for the off spring having a dwarf condition is 50 % as can be identified by the two dwarf offspring.

b. Use the Table below to determine and record your individual traits.

Table 1 Individual Traits 2 pts

Trait

Dominant Form

Recessive Form

My phenotype

hands clasped

left thumb over right

right thumb over left

R

hair texture

curly

straight

R

forehead hair

widows peak

straight hairline

R

chin dimple

present

absent

R

ear lobes

free

attached

D

tongue

can roll

Cannot roll

D

hair whorls

clockwise

counter-clockwise

D

ptc taste

taste

no taste

R

thiourea

taste

no taste

D

sodium benzoate

taste

no taste

D

c. How many dominant traits in Table 1 do you have? __5_recessive? __5_1 pt

d. Use Table 2 to record and determine the frequency of these different alleles in lab class. Each percentage equals the number of students with the dominant OR recessive trait divided by the total number of students times 100%. Total number of students is _16___.

hands clasp

hair texture

forehead hair

chin dimple

ear lobes

leftrightcurlysmoothwidow’sstraightdimplenonefreeattached

1

x xx xx

2

xx x xx

3

x x x xx

4

x x x xx

5

x xx xx

6

x x x x x

7

x x xx x

8

x x x x x

9

xx x xx

10

x x x xx

11

x xx xx

12

x xx xx

13

x xx xx

14

x x x x x

15

x x x x x teacherx x x x x

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

teacher

tongue

PTC

thiourea

sodium benzoate

rollno rolltasteno tastetasteno tastetasteno tastex x x xx x x xx x x x x x x x x x x x x xx xx x x xx x xx x x x xx x x x x x x xx xx x x x x xx x x xx x x x xx x x

Table 2 Class Data Table 4 pts

Trait

# students

dominant form

% students

dominant form

# students

recessive form

% students

recessive form

hands clasped

11

68.75

5

31.5

hair texture

5

31.5

11

68.75

forehead hair

6

37.5

10

62.5

chin dimple

2

12.5

14

87.5

ear lobes

12

75

4

25

tongue

14

87.5

2

12.5

hair whorls

ptc taste

12

75

4

25

thiourea

12

75

4

25

sodium benzoate

7

43.75

9

45.25

e. Why do you think some traits have more of the dominant alleles and some have more of the recessive alleles in your class population? 1pt

The varying presence of dominant and recessive alleles is as a result of the diversity of the human species in the class that can be attributed to race.

f. Do you think these patterns would be the same if you analyzed all AU students? Why or why not? 1 pt

The diversity is expected to be similar in the rest of the AU population. This is because the classroom is a replica of the larger population of the school.

g. Why do you think that some alleles like cystic fibrosis and Huntington’s persist in the human population? 1 pt

The recessive gene that allows the existence of these disorders is hereditary. Even if the condition is not observable, the gene can be passed down from generation to generation hence the persistence of these diseases in the human population.

The earliest records of hemophilia were documented by Dr. John Conrad Otto in the year 1803 (Freedman 15). Hemophilia is a condition that inhibits blood clotting in human beings. Hemophilia is characterized by fibrin deficiency that is vital for the clotting of blood. The effects of hemophilia makes an injured person to bleed more than is normal and leads to loss of a lot of blood(Bradley-Smith et al. 137).This gene allele is mostly inherited from the mother since the gene is carried in the X chromosome. Therefore, the condition is referred to as a sex-linked disorder.

Since the recessive gene for hemophilia is carried in the X chromosome, then males are more likely to get it than women are. This is because if a hemophilic gene is found in the XY combination of the male offspring then it guarantees that the child is going to be hemophilic. However, since the female’s species have to X chromosomes, the rare nature of the condition makes it extremely difficult for females to have two recessive genes (Bradley-Smith et al. 138). Such relationships can best be exemplified in a pedigree diagram as below.

Fig. 1

(Pedigree Analysis, http://faculty.clintoncc.suny.edu)

A pedigree diagram is used to describe the family relationships by using symbols to show people and linear representations that signify genetic relationships. The diagrams help one to identify the occurrence and the phenotypes of a gene and trace its ancestry from one generation to the other (Hartl 97). However, a pedigree diagram only has basic information about a gene and cannot capture the full genetic composition of an organism and this serves as its major limitation.

Works Cited

Bradley-Smith, Guy et al. Oxford Handbook of Genetics. New York, NY: Oxford University Press, 2010. Print.

Freedman, Jerry. Hemophilia. New York, NY: The Rosen Publishing Group, 2006. Print.

Hartl, Daniel. Genetics. Bloomfield, NJ: Jones & Bartlett Publishing, 2011. Print.

Pedigree Analysis, The State University of New York. Pedigree Analysis. Retrieved from faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio 101/Bio 101 Laboratory/Pedigree Analysis/PEDIGREE.HTM

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