Introduction to Cell & Molecular Biology (BIOL121) - Dr. S.G. Saupe (; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321

Genetics:  Study Guide

Required Readings
  text, Chapter 16 & 17

Goal of the Unit
 The goal of this unit is to provide an introduction to Mendelian genetics and the mechanisms of inheritance.

Important Terms and Concepts
(Can you use conversationally?  Can you prepare a concept map with these terms?  Make a crossword puzzle?)

  • codominant                      

  • incomplete dominance

  • pleiotropy

  • test cross                  

  • meiosis               

  • allele

  • locus

  • gene

  • P, F1, F2

  • haploid

  • self pollination

  • genotype

  • Punnett square

  • diploid

  • phenotype

  • linkage

  • tetrad

  • dominant

  • segregation

  • homologous chromosome

  • 3:1,  1:1

  • 9:3:3:1,  1:1:1:1

  • recessive

  • independent assortment  

  • homozygous

  • crossing over

  • heterozygous

  • sex chromosome

  • autosome

  • karyotype

  • sex‑linked

  • epistasis

  • true‑breeding

  • fertilization


Some General Study Tips:  The following are a few tips for preparing for the next exam:

  1. Work as many genetics problems as you can

  2. Sketch out non‑disjunction of sex chromosomes during meiosis and predict possible offspring. 

  3. Make a concept map

  4. Work more genetics problems

  5. Do the problems at the end of each chapter

Caution:  The material in this unit is not readily "crammable".  I encourage you to spend some time with this material prior to "exam‑eve". 

Learning Objectives:  Upon completion of this unit you should be able to:

  1. summarize Mendel's contributions to the science of genetics

  2. explain why it can be said that Mendel was `ahead of his time'.

  3. compare and contrast dominant, recessive, incomplete dominance and codominance and give examples of each.

  4. describe the characteristics of the following human traits: tongue rolling (D),  widow's peak (D), wet ear wax (D), L/R interlocking fingers (D), attached earlobes (D), hitchhiker's thumb (D), PTC tasting (D), Chin fissure (D),  Darwin tubercle (D), S‑methylthioester detection (r), pigmented iris (D),  freckles (D), polydactyl (D), dimples (D), achondroplasia = dwarfism (r), albinism  (r),  wooly hair (r), Huntington's disease (D), Marfan's syndrome (D)

  5. describe the law of segregation and relate it to genes, chromosomes,  homozygous, heterozygous,

  6. describe the law of independent assortment and relate it to genes,  chromosomes, homozygous, heterozygous

  7. explain what is meant by "linked genes"

  8. use a Punnett square (or other method) for predicting offspring from a  genetic cross

  9. explain what is meant by multiple alleles and provide an example

  10. describe what is meant by pleiotropy and provide an example

  11. describe what is meant by polygenic inheritance and give an example.

  12. explain the difference between phenotype and genotype. Give an example.

  13. explain how otherwise normal parents can give birth to a child with a  genetic disease

  14. explain what is meant by a testcross and how they are used

  15. what is meant by a `carrier' of a genetic disease

  16. describe two trait crosses

  17. describe the genetics of eye color

  18. indicate the sex chromosome composition of a normal male and female, and individuals with Turner's, Down's, Klinefelter's and Triplo‑X syndromes.

  19. describe the procedure used to prepare a karyotype.  Explain the role of colchicine in the process and why white bloods cells but not red ones are used for the procedure.  Why are the cells put in a hypotonic solution?

  20. describe the procedures of amniocentesis and chorionic villi biopsy.  Indicate the pros and cons of these procedures (not on exam)

  21. predict the offspring resulting from the fertilization of a gamete produced by the non‑disjunction of sex chromosome during either meiosis I or II in both males and females and normally produced gametes.

  22. What is a Barr body?

  23. explain the genetics of coat color in calico cats

  24. explain why there is a 50% probability of any one child being a girl (or boy).

  25. explain what it means that the "father determines the sex of the child".

  26. give the genotypes of the parents if the offspring exhibit a 1:1 ratio of phenotypes.  3:1 ratio? 9:3:3:1 ratio? 1:1:1:1 ratio?

  27. explain why peas were a good choice for an experimental organism

  28. explain what is meant by "true‑breeding"

A Feline Genetics Question:   A question for lovers of beasts with tuna-breath

     Consider a cat cell with a diploid number of two (2).  This cell undergoes meiosis to form egg cells.  Two of the genes in this cell are: (1) Fur Color - the allele for black fur (B) is dominant over the allele for white fur (b); and (2) Fur Thickness - the allele for thick fur (T) is dominant over the allele for thin fur (t).  Prior to meiosis, one chromosome had alleles "B" and "T".  The homologous chromosome had alleles "b" and "t". 

  1. Ignoring crossing over, what are the possible genotypes of the gametes?

  2. Assume this cat (genotype BbTt) is mated with a completely homozygous recessive cat (bbtt).  Give the phenotype, phenotypic frequency and genotype of the expected offspring.

  3. Now, suppose a cross-over occurs between genes 1 and 2 in the individual with the genotype BbTt.  Make a drawing of this cell in the middle of metaphase I of meiosis.  For each chromatid indicate the position of the alleles using the letters "B", "b", "T", and "t".  Put the alleles for gene 1 about onequarter of the way down from the top of the chromatids and those for gene 2 about one-quarter up from the bottom of the chromatids.

  4. Consider the cat with the genotype BbTt.  What are the possible genotypes of gametes that result from crossing over?

  5. Assume the parent cited above, with the genotype BbTt, is mated with a cat that has the genotype, bbtt.  What are the genotypes and phenotypes of the offspring that result from crossing over?


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Last updated: July 14, 2009     � Copyright by SG Saupe