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Anth 450 Modern Human Biological Variation
Dr. Darlene Applegate
Fall 2007
Lab 2:  Principles of Simple Inheritance

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INTRODUCTION

The mechanisms of simple inheritance, or the transmission of discrete (monogenic) traits from one generation to the next, are well understood.  The transmission of traits from parent to offspring begins with the process of meiosis, or the creation of gametes (sex cells, eggs and sperm).  Meiosis is the process of cell duplication that involves two stages of cell division and results in the production of four gametes, each carrying half of the number of chromosomes for the species.

Chromosomes are significant in inheritance because chromosomes are composed of DNA, which is the genetic code of life.  DNA is composed of sequences of chemical bases (adenine, thymine, cytosine, guanine) and other molecules.  The sequence of bases "carries" the instructions for assembling amino acids into proteins, which are the structural building blocks of living organisms.

Two fundamental laws control the process of simple inheritance, Mendel's laws of segregation and independent assortment. In this lab we will apply these laws of simple inheritance.

• The law of segregation states that the two alleles for a trait are passed to the different gametes during meiosis. In other words, a gamete will not receive both alleles for a particular trait.

• The law of independent assortment states that alleles for different traits are passed to gametes during meiosis independently of each other.

Upon successful completion of this lab, students will

• understand how Mendel's laws of inheritance affect gamete formation.

• collect and analyze data on discrete traits.

• practice pedigree analysis.

• understand ABO blood type inheritance.

READINGS

Read pages 1-22 in France (2004).  Be sure to bring the lab manual as well as this overview to the lab or you will be unable to complete the assignment.

 
ASSIGNMENT

General Instructions

• The lab assignment will be completed in pencil using the answer sheet provided in class and the lab manual questions and instructions.
  

• Show your work, including Punnett squares, on the answer sheet.
  

• Note that the single-letter symbols used to represent alleles for traits are listed on page 12. Be sure to use these particular letters.
  

• When reporting phenotypes, be sure to use the full description. For example, "ear lobes" is not complete, but "attached ear lobes" and "free-hanging ear lobes" are complete.
  

• When reporting genotypes, clearly write the upper- and lower-case letters (especially Cc, Tt, and Ff) so I can easily distinguish them. If I cannot read your answers, they will be counted wrong.
  

• The lab assignment is due at the beginning of class time on Friday, October 12.
  

• We will complete Exercise 1.1 as a group at the beginning of the first lab session.

• With the help of your lab partner, record your phenotypic expression for each of the nine traits. Descriptions of these traits, including the dominant and recessive expressions, are provided on pages 9 and 10 of the lab manual.

• Since we don't have the chemicals for PTC tasting, consider yourself a taster if you think brussel sprouts and turnip greens are bitter and consider yourself a non-taster if you don't think these plants are bitter. 
  

• We will compile the phenotypes for the entire class. 
  

• Using the class data, summarize the class members' phenotypic characteristics.
  

• When calculating percentages, round all of your answers to whole numbers.

• Be careful to distinguish genotypes from phenotypes in completing this exercise.
  

• When reporting genotypes, use the appropriate upper- and lower-case letters, such as EE, Ee, and ee. Do not use the terms "homozygous dominant," "heterozygous," and "homozygous recessive."
  

• Report your answers as percentages for questions 2 through 7. 
  

• For questions 2 through 4, also report possible phenotypes and percentages.
  

• For question 6, assume that "having no ear lobes" means free-hanging (not attached).
  

• When calculating percentages, round all of your answers to hundredths place (0.00 %).
  

• For questions 1 and 2, actually draw two separate pedigree charts (ignore the instructions in question 2 that say to add to the previous chart).
  

• For question 3, prepare your answer as a pedigree chart with genotype labels for each individual.
  

• For all pedigree charts, use the symbols "A" and "a" for the alleles.
  

• For question 1, also answer "why" they can or can't be the baby's parents.
  

• For question 2, your answer can't simply be "O is the universal donor."
  

• For question 3, your answer should relate to antibodies.
  

amino acid - building blocks of proteins

allele - alternate expressions of a gene

antibody - proteins that react to foreign antigens

antigen - blood proteins

chromosome - threadlike structures of DNA found in cell nuclei and bearing genes

discrete trait - trait controlled by one gene locus

dominant - an allele that masks phenotypically other allele(s)

gamete - sex cells (egg and sperm)

gene - part of a chromosome that codes for a particular trait

genotype - the genetic makeup of an individual, usually considered one trait at a time

heterozygote - an individual carrying two different alleles for a trait

homozygous dominant - an individual carrying two dominant alleles for a trait

homozygous recessive - an individual carrying two recessive alleles for a trait

independent assortment - alleles for different traits are passed to gametes during meiosis independent of each other

monogenic trait - trait controlled by one gene locus

pedigree analysis - the study of phenotypes in family lines to discern genotypes

phenotype - outward physical expression of one's genetic makeup

polygenic - traits controlled by more than one gene locus

protein - sequence of amino acids, building blocks of living organisms

recessive - an allele that is masked phenotypically by another allele

segregation - the two alleles for a trait are passed to the different gametes during meiosis

sex-linked trait - trait controlled by a gene(s) on the X chromosome

simple inheritance - transmission of discrete traits from one generation to the next
 

REFERENCE

France, Diane L.
2004 Lab Manual and Workbook for Physical Anthropology (5th ed.). West/Wadsworth, Belmont, CA.