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)
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."
http://www.nature.com/news/2004/040913/full/040913-20.html
This is the work of Cynthia Beall. You may hear an interview
with her at: http://www7.nationalacademies.org/interviews/Cynthia_Beall_Interview.html
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: http://nobelprize.org/medicine/laureates/2004/
On with Mendel.
Choice of organism
pea flower
flower dissection ..Text figure 2.3... Figure2x3.gif
Seven character differences
Mendel's experiments
The crosses (general)
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
The conclusions
Independent assortment animation....IndAsstMovie2.gif
Analysis by Punnett Square
instruction (see workbook pages: 8 and 9)
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
summary
comparison of segregation and inpependent assortment......3segrandindasst.GIF
terminology
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
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
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
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
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
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.