Biology 205 Principles of Segregation/Independent Assortment

Chapter 2

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I.  Gregor Mendel

A. Discuss the importance of Mendel

• Clear distinction between phenotype and genotype
• Derived his principles without knowledge of chromosomes
• Use of mathematics/quantitative methods

B. Give examples of Mendel's traits in peas

C. Describe Mendel's experimental design

• Explain Mendels's procedure for crossing pea plants. See fig 2.3
• Distinguish between self and cross fertilization (selfing vs cross)

D. Define the vocabulary related to Mendel's work

• True Breeding
• Parental Generation
• Hybrid
• F1, F2(First and Second Filial Generations)

II. Principle of Segregation

A. Outline the procedure for the Monohybrid Cross

B. Explain how to set up a test Cross

C. State the principle of segregation and Mendel's conclusions

• Factors controlling traits are inherited as indivisible units
• Factors controlling traits remained unchanged from parent to offspring
• These factors occur in pairs in each parent
• Traits can be either dominant or recessive; that is expressed in the F1 or not
• When gametes formed each gamete gets one of each factor but not both: principle of segregation

D. Define the following concepts:

• Gene
• Allele
• Homozygous vs Heterozygous Dominant Vs Recessive
• Phenotype Vs genotype
• Locus (or gene locus)

Comment: There are standard sets of terminology used to name and represent genes and alternate forms of a gene and we will see several in this course. Often, the combinations of letters and numbers used as lables for genes and alleles are often Italicized to clearly distinguish them from phenotypes.

E. Explain and use approaches to Monohybrid cross problems

• Punnett Square
• Branch or Tree diagrams

Comment: At first glance the Punnett square technique seems easier to do but a little thought will show otherwise.

F. Note conventions for labeling alleles for simple dominant and recessive alleles

Make sure you understand all the genetics terminology pp 36 - 37

III. Principle of independent assortment

A. Explain the basic procedure for doing a dihybrid cross

B. Explain what Mendel concluded:

• Alleles of each gene pair segregate independently of each other when gametes are formed
• Explain how he concluded this from his dihybrid cross results

C. Be able to solve dihybrid cross problems using

• Punnett Square
• Branch diagram approaches. See fig 2.13 p. 41
• Behavior can sometimes be inherited in a relatvely simple Mendelian fashion: Hygienic Bee Example.

D. Be able to use probability reasoning to do more complex Mendelian problems (i.e. trihybrid crosses etc.)

IV Modern interpretation of Mendel's pea results

A. Explain the Chromosomal theory of inheritance

B. Compare behavior of genes and chromosomes

• Genes are at different positions on the chromosome. The position or location of a gene is called the gene's locus
• Members of each gene pair segregate during meiosis because that is what the chromosomes do.
• Members of each gene pair segregate independently because that is what each pair of chromosomes do (ignoring linkage)

V Genetics Problems

A. Simple Monohybrid Cross: Problems 2.1 - 2.11

B. Simple Dihybrid Cross Problems 2.12, 2.14 - 2.15

C. Using principles of probability to solve genetics problems. 2.16 - 2.19; 2.21

VI Activities

Explore these links.

• Assortment of Chromosomes in Meiosis: http://wsrv.clas.virginia.edu/~rjh9u/meiosis1.html
• Pea Soup Investigate monohybrid crosses and then dihybrid crosses. Note the correct link as of 09/03/01is: http://www.sonic.net/~nbs/projects/anthro201/exper/
• Genetics Science Learning Center: http://gslc.genetics.utah.edu/
• MendelWeb Has simulations and references for Mendelian Genetics including links to Mendel's original paper.

From the Entangled Bank

• Monohybrid Crosses
• Principle of Independent Assortment/Dihybrid Crosses
• Probability Tutorial (may be hard to understand at first reading)

pgd 08/28/02 revised 01/21/05