BIOLOGY 345 Lecture Problem set #1 January 20, 2003

MENDELIAN GENETICS, PROBABLILITIES, PEDIGREES- review of basic principles of genetics presented in Introductory Biology Courses.

YOU MUST SHOW ALL YOUR WORK TO RECEIVE FULL CREDIT.

 

1. (10 PTS) In humans, hemophilia is caused by an X-linked recessive gene. A woman who is a non-bleeder marries a non-bleeder, and they have a hemophiliac son. What is the probability of hemophilia in their future female and male offspring. Use symbols (circles for females and squares for males) to represent each of the above-mentioned individuals in a pedigree, and indicate their genotypes. (Use the symbol h for the hemophilia mutant allele and H for the normal non-bleeder allele.)

 

 

 

 

 

 

 

2. (15PTS) Consider the pedigree in problem 10, p. 143, in your textbook.
a. Determine the most likely mode of inheritance (autosomal vs sex-linked and dominant vs recessive). Explain your answer.

 

 

 

 

b. Specify the genotypes of mother, father, and first generation offspring. Define your gene symbols.

 

 

 

 

 

c. Does the ratio of third generation children with the trait to third  generation children without the trait match what would be expected based on your knowledge of parental genotypes?

Explain using a Mendelian model.

 

 

 

 

 

 

3. (15PTS) For the autosomal trait, ABO blood group system, the A(IA) and B(IB) alleles are codominant (i.e., IAIB genotype produces both the A and B antigens = AB blood type). The O blood type is homozygous recessive for the O allele (ii).

a. Use a Punnett square to determine what blood types are possible in the children of an AB mother and a type O father.

 

 

 

 

 

b. Two A parents produce an O child. Show this occurrence using genotypes of the two parents and child.

 

 

 

 

 

c. Two parents produce all four blood types among their children (A,B,AB,O). Determine the genotypes of the two parents.

 

 

 

 

4. (15 PTS) Couple #1 have a child with a genetic disease caused by an X-linked recessive allele. Neither parent has the disease. Couple #2 have a normal son, despite the fact that the father has the disease. Several years later, couple 1 sues the hospital claiming that these two newborns were switched in the nursery following their birth. You are called as a genetic counselor to testify at the trial. What information would you give to the jury concerning the allegation? 
Show the pedigrees of these two families and explain your answer using genotypes.

 

 

 

 

 

 

 

 

 

5. (15 PTS) Miniature wings in Drosophila melanogaster results from an X-linked gene (m) that is recessive to an allele for long wings ( m+). Sepia eyes is produced by an autosomal gene (s) that is recessive to an allele for red eyes (s+).

a. A female fly that has miniature wings and sepia eyes is crossed to a male that has normal wings and is homozygous for red eyes. Show the parents’ genotypes, and give the phenotypes and genotypes expected in the F1 flies from this cross.

 

 

 

 

b. The F1 are intercrossed to produce the F2. Use a tree diagram to show the sex and phenotypes of the F2 flies. Indicate the expected frequency of occurrence of each F2 type.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6. (!0 PTS) Phenylketonuria (PKU) is an inherited disease, rare in the population, caused by an autosomal recessive mutant gene. A phenotypically normal woman, whose parents are also normal, plans to marry a normal man, but she is worried about PKU occurring in her children because she has brother with the PKU disorder. How would you counsel her on the possibility of producing PKU children? Include a pedigree of all individuals and their possible genotypes in your discussion.

 

 

 

 

 

 

 

 

7. (10 PTS) Mendel’s Experiments

a. Define Mendelian segregation.

 

 

 

 

 

b. From one of Mendel’s crosses between two pure-breeding lines (P. green seeds X yellow seeds), he observed a 3:1 ratio of yellow to green seeds in the F2 (the offspring of F1 plants that were allowed to self fertilize). He planted several of these F2 seeds and allowed the resulting F2 plants to self fertilize and recorded each of their F3 progeny. Based on his model of inheritance, what are your predictions for these F3 results? Include genotypes in your presentation.

P yellow X green

F1 X F1 (all yellow F1  )

F2 Yellow (selfed) à F3

 

 

 

F2 green (selfed) à F3

 

 

8. (10) Mendel crossed purebred wrinkled, green-seeded plants with purebred round, yellow-seeded plants. Then he crossed (in a backcross) the F1 progeny to purebred wrinkled, green-seeded plants and observed 31 plants with round, yellow seeds, 26 with round, green seeds, 27 with wrinkled, yellow seeds, and 26 with wrinkled, green seeds. Assuming independent assortment, what proportion of these types would be expected? Use a tree diagram to show the derivation of these phenotypes and their expected proportions.

It is helpful to show the genotypes (in the spaces below) of the parental and backcross plants used to produce the above offspring

P round yellow X wrinkled green (parental cross)

__________ ____________

F1 round yellow X P winkled green (backcross)

_____________ _____________

 

 

 

 

 

 

 

 

 

9.  Access the NCBI (National Center for Biotechnology Information) web site from the link on the BIO 345 course web page.  Use information at this web site to answer, in your own words, the following questions.  Short and concise paragraphs will suffice.
a.  What is the history and mission of NCBI?
b.  What is GenBank?
c.  What is Entrez?
d.  What kinds of information can be obtained with the use of BLAST search procedures?
e.  Briefly describe the field of Bioinformatics.
f.  Use OMIM at the NCBI web site to characterize the inherited disorder phenylketonuria.  Include its mode of inheritance, chromsome locaton,  phenotypic effects, possible treatment and its defect in metabolism.