1. Define and distinguish between the terms "gene" and "allele".

A gene is a discrete unit of heredity located on chromosomes and a gene consists of DNA.    An allele is an alternate form of a specific gene.  (ex. eye color gene vs blue eye allele)
2. Define and distinguish between the terms "genotype" and "phenotype".

Genotype is the genetic composition of an individual, especially in terms of the alleles for particular genes.  Phenotype is the outward appearance of an organism (the physical and physiological traits of an organism).
3. Define the terms "dominant" and "recessive".

"Dominant" describes an allele that determines the phenotype in the heterozygous condition.  "Recessive" describes an allele that is "masked" by the presence of a dominant allele (see question below).
4. What are the two possible genotypes of an individual that displays the dominant phenotype?    AA or Aa
5. What is the only possible genotype of an individual that displays the recessive phenotype?    homozygous recessive (aa)
6. What does it mean to be:

a) phenotypically dominant?  If an individual is phenotypically dominant, (s)he has at least one dominant allele for a gene, but it is not known if (s)he is genotypically heterozygous or homozygous dominant.
b) homozygous recessive?   If an individual is homozygous recessive for a gene, both alleles are recessive.
c) heterozygous?.    If an individual is heterozygous, (s)he has two different alleles - for example, one dominant allele and one recessive allele.
7. Using terms that you defined above, explain what two types of parent individuals are always used in a test cross.  Explain what specific information is gained in a test cross.

A test cross is a cross between a homozygous recessive individual and a phenotypically dominant individual.  The phenotype(s) and phenotype ratio of their offspring will "reveal" the genotype of the phenotypically dominant parent.  If all of their offspring have a dominant phenotype, then the phenotypically dominant parent was homozygous dominant, but if half of the offspring have a recessive phenotype, then the parent was heterozygous.
(A test cross can also be used to determine the dominance relationship between two alleles, but that could already be known and the cross would still be a test cross.)
8. Match the genetic terms:  (Some have multiple answers and answers can be used more than once.)

a) Dihybrid cross                                     AABB x aabb, or AaBb x AaBb, or AaBb x AAbb
b) Monohybrid cross, two heterozygotes Aa x Aa
c) Homozygous condition                       AA, or aa, or AABB x aabb, or AA x AA, or AA x aa
d) Heterozygous condition                     Aa, or Aa x Aa
e) True-breeding parents                       AA x AA, or AA x aa, or AABB x aabb
9. Two rugrats with brown eyes are mated and have 100 offspring - 76 have brown eyes and 24 have pink eyes.  What is the most likely genotype of each parent?  (Use “E” and “e”.)

   E = brown allele, e = pink allele;  E>e
        parent 1: Ee             parent 2: Ee
10. Answer this question using the results of the previous question.  A rugrat with brown eyes is mated to a rugrat with pink eyes.

a) What are all of the possible genotype(s) for each parent?    brown eyes: EE or Ee,     pink eyes: ee
b) If these rugrats have an offspring with pink eyes, what are the actual genotypes of the parents?
       brown eyes: Ee,         pink eyes: ee
11. Draw one homologous chromosome pair (after replication) for the following linked genotype:  AaBb.

Here are three examples: 
12. I am willing to try to arrange to meet with students who have questions on the course material - all you have to do is ask.  You are also welcome to email questions to me.  boet0027@umn.edu

• Linked genes, being on the same chromosome, cannot assort independently of each other.
• The meiotic basis of Mendel’s principles is seen in the parallel behavior of gene and chromosomes in meiosis I.  The separation of members of each homologous pair of chromosomes during meiotic anaphase I results in the segregation of alleles.
• The independent alignment of each pair of homologues on the spindle at meiotic metaphase I followed by disjunction accounts for the independent assortment of nonallelic genes present on different chromosome pairs.

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