Chapter 2 Mendelian genetics 

(We will not study the Chi-square test.)


Genotype and phenotype

Phenotype - description of the appearance of an individual

Genotype - symbols used to represent the genes of an individual

Mendel's experimental design

About Mendel

Picture (Fig. 2.2)

Important dates


First Page Mendel's paper

Access to Mendel's paper

recent papers/book:

Lander, E. S. and R. A. Weinberg. 2000 Journey to the center of Biology. Science 287(5459): 1777-1782.

Burghes, A. H. M., H. E. F. Vaessin, and A. de la Chapelle. 2001 GENETICS: The Land Between Mendelian and Multifactorial Inheritance. Science 293(5538): 2213-2214.

Carlson, E. A. (2004). Mendel's legacy : the origin of classical genetics. Cold Spring Harbor, N.Y., Cold Spring Harbor Laboratory Press.

Koenig, R. 2000 Genetics. Uphill battle to honor monk who demystified heredity. Science 288(5463): 37-9.

Balter, M. 2000 Genetics. Was Lamarck just a little bit right? Science 288(5463): 38.

Burghes, A. H. M., H. E. F. Vaessin, and A. de la Chapelle. 2001 GENETICS: The Land Between Mendelian and Multifactorial Inheritance. Science 293(5538): 2213-2214.

May, R. M. (2004). "Uses and abuses of mathematics in biology." Science 303(5659): 790-3.

the point: Mendelian genetics is old stuff but is important in current discussions of genetics.

4 October 2004

the flow of information goes both ways, from me to you and from you to me.
thanks to Majed Khalifa for reference to an article in Nature (?) relative to a discovery of possible natural selection and a new major gene, both dealing with adaptation of humans in Tibet. "Tibetan mothers have provided anthropologists with a prime example of ongoing human evolution. Researchers have found that women who are able to store more oxygen in their blood have more offspring that live to maturity."

This is the work of Cynthia Beall.  You may hear an interview with her at:

Today is the day for the Nobel Prize in physiology or medicine.  The award this year is give to Richard Axel and Linda B. Buck for their work on the physiology of smell.  See:
On with Mendel.

Choice of organism

pea flower

flower dissection ..Text figure 2.3... Figure2x3.gif

Seven character differences

Seven characters picture see text figure 2.4 ... Figure2x4a.gif.... Figure2x4b.gif

Mendel's experiments

The crosses (general)

Concept of true breeding.. TrueBreeding.GIF

reciprocal crosses

TB purple female x TB white male

TB purple male x TB white female

Dominance and recessiveness

F-1, the cross of two true breeding individual;  F2, the cross of the F-1's; and test cross, the cross of an F-1 with a homozygous recessive individual.

The crosses

for one gene pair... MonoCross.GIF

for two gene pairs.. DiCross.GIF

The conclusions

general..... Conclusions1.GIF

segregation .... 1segregation.GIF

independent assortment..... 2independentAsst.GIF

Segregation animation...SegrMovie.gif

Independent assortment animation....IndAsstMovie2.gif

Analysis by Punnett Square

instruction (see workbook pages: 8 and 9)

example...... MonoPunnet.GIF

Problem with the way the text does Punnett squares: There are too many rows and columns........see: PunnettCorrection.gif

Examples of F-2 and test crosses

Monohybrid series ....  ../MonoHybridSeries.html

Dihybrid series ...../DihybridSeries.html


comparison of segregation and inpependent assortment......3segrandindasst.GIF 


List of terms...... importantwords.gif

6 October 2004

complete chapter 2 and on to chapter 3

Biology Seminars:  tomorrow, Vince Eckhart on How pollinators (and pests) paint Clarkia xantiana flowers, room 223, noon

Free music events Tuesdays at noon 75 LH

We may summarize the basic Mendelian ratios in a table (table of ratios) see page 10 in workbook..... MonoDihybridRatios.gif; workbook page 10

Table filled in ...  ../MonoDiTableFilled.gif

Analysis by fraction method of working problems for simple and complex problems

see pages 11 12, 13 in workbook

Product rule: "....the probability of independent events occurring simultaneously is the product of their individual probabilities" text: page 37

of great importance is the term independent events

Break problem down to analysis of single gene pairs

Based on single gene pair ratios


To get 9:3:3:1 ratio

Slide show......./FractionSeries.html

example...... FractionExample1.GIF

example...... FractionExample2.GIF

We discussed segregation and independent assortment.  An exception to the segregation work is "segregation distortion"  See:  Pennisi, E. (2003). "Meiotic drive. Bickering genes shape evolution

Mendelian genetics in humans

Pedigree analysis ....dealing with human genetics

symbols for males and females and others; mating and progeny lines, Fig 2.15, 2.16

Pedigree for recessive trait... 2x17.gif...Figure 2.17 in text; note use of the dash

Pedigree for dominant trait... DominantPedigree.gif...not on web; see Fig 2.19

how to determine mode of inheritance (dominant and recessive)

        assume abnormal allele to be rare

        more than one model may explain mode of inheritance

        may assume people who mate into the family are homozygous normal

        sometimes best to test the pedigree for different modes of inheritance

Text examples

Albinism..Fig 2.18a..Fig 2.18b

Wooly hair...........2.19a... Fig 2.19b

Problem of abundance of gene in population and Dominance/recessiveness

 Another pedigree (Huntington's; Nancy Wexler story)..see Bishop book


Introduction to OMIM (Online Mendelian Inheritance in Man)

started by Victor McKusick at The Johns Hopkins University

first edition, 1966 .....

Online Mendelian Inheritance in Man....OMIM

Some words about Lysenko    In USSR 1948 - 1965 (  

 Medvedev, Z. A. 1969. The Rise and Fall of T. D. Lysenko. Columbia University Press, New York.

Hossfeld, U. and L. Olsson. 2002 PORTRAITS OF SCIENCE: From the Modern Synthesis to Lysenkoism, and Back? Science 297(5578): 55-56.

Can it happen here? ...the politics of science...Ferber, D. (2002). "Science and government. HHS intervenes in choice of study section members." Science 298(5597): 1323

          HHS = Health and Human Services

Current events

Review basic Mendelian crosses

True breeding; P-, F-1, F-2 generations; phenotype and genotype; alleles; homozygous and heterozygous; monohybrid and dihybrid; cross pollination and selfing; dominance and recessiveness; Punnett square;

reciprocal crosses (purple female x white male; purple male x white female)

test cross: In a Mendelian sense the cross of an F-1 with a homozygous recessive individual.

Major point: Segregation and Independent Assortment are events of meiosis. They occur even if an individual does not have offspring.

  to chapter 3