Download Mendelian Genetics

Gregor Johann Mendel
• 1822- 1884
• Austrian monk
• Experimented with pea
plants
• He thought that
‘heritable factors’ (genes)
retained their
individuality generation
after generation
Time Line
• 1831 Charles Darwin joins crew of Beagle
• 1839 Schleiden and Schwann propose the Cell Theory
• 1847 Semmelweiss proposes that infection is spread by contaminated hands of
physicians.
• 1856 Mendel begins hybridization studies with garden peas
• 1857 Louis Pasteur (France) introduces the Germ Theory of Disease.
• 1859 Darwin publishes Origin of Species
• 1865 Mendel presents presents his results in transmission of phenotypic traits
between the generations to the Brünn Society of Natural Sciences.
• 1900 Hugo de Vries in Holland, William Bateson in Great Britain, Franz
Correns in Germany, and Erich Tschermak in Austria acknowledged
Mendel's legacy, and hailed him as the true father of classical genetics.
Terms to Know and Use
• Gene – A DNA blueprint controlling
synthesis of a protein
• Trait - variant for a gene: i.e. a purple
flower, determined by alleles
• Dominant trait - expressed over recessive
trait when both are present
• Recessive trait - not expressed when the
dominant trait is present
• Co-Dominant – expressed as blended traits
• Allele - a variation of a gene responsible for
different traits, often represented as A or a
• Locus - location of a gene,or allele, on a
chromosome
• Chromosome - strand of DNA containing
the genes
• Haploid - one copy of a chromosome
• Diploid - two copies of a chromosome
• Gamete - a spermatozoa or oocyte (egg)
cell, they are haploid
• Zygote - cell resulting from the fusion of
two gametes, they are diploid
• Genotype - the type of alleles on a
chromosome: genetic makeup
• Phenotype - The way a genotype is
expressed: i.e. the color of a flower
• True breeding line - organisms that always
pass the same genotype to their offspring
• Hybrid - offspring resulting from
crossbreeding two true breeding lines: F1
Garden Pea Experiments
1856-64
• Mendel disagreed with
the “Blending Theory”
of inheritance.
• Started with 34 kinds
peas Pisium sativum
• After 2 years he had
22 purebreds
http://www.dnaftb.org/dnaftb/1/concept/index.html
Pea Characteristics
Trait on the left is dominant. Trait on the right is recessive.
Flower Parts
Mendel’s Hypotheses
• There are alternate forms
of ‘genes’=alleles
• For each trait, organisms
have 2 genes, one from
mom & one from dad
• Pollen and egg each carry
1 allele/trait because
alleles segregate
• When only one allele is
expressed & other has no
noticeable effect, it is
dominant
•
http://www.sumanasinc.com/webcontent/anisamples/
nonmajorsbiology/independentassortment.html
Mendel’s Experiments
1. Plants must possess constant
differentiating characteristics.
2. The hybrids of such plants
must, during the flowering
period, be protected from the
influence of all foreign pollen,
or be easily capable of such
protection.
3. The hybrids and their offspring
should suffer no marked
disturbance in their fertility in
the successive generations.
Mendel's Laws of Inheritance
• Law of Segregation during gamete
formation allele pairs separate or segregate,
into different gametes (Demonstrated with a
“test cross”).
• Law of Independent Assortment
suggested that each allele pair segregates
independently of other gene pairs during
gamete formation (Demonstrated with a dihybrid cross).
•
http://www.sumanasinc.com/webcontent/anisamples/majorsbiology/independentassortment.html
Mother contributes:
True Breeding
A
or
A
A
AA
AA
A
AA
AA
Mother contributes:
Cross Breeding
a
or
a
A
Aa
Aa
A
Aa
Aa
Monohybrid Cross
Test Cross
Mendel's Laws of Inheritance
• Law of Segregation during gamete
formation allele pairs separate or segregate,
into different gametes (Demonstrated with a
“test cross”).
•
http://www.sumanasinc.com/webcontent/anisamples/nonmajorsbiology/independentassortment.html
• Law of Independent Assortment
suggested that each allele pair segregates
independently of other gene pairs during
gamete formation (Demonstrated with a dihybrid cross).
•
http://www.sumanasinc.com/webcontent/anisamples/majorsbiology/independentassortment.html
Dihybrid Cross
Smooth Tall
Smooth
Tall
Smooth wrinkled
short
Tall
wrinkled
short
Two chromosomes of one parent are represented on the left.
Possible alleles passed on to the offspring are on the right.
(Consider smooth or wrinkled peas AND tall or short plants)
Dihybrid Cross
Mother contributes:
SB Sb
SB
SSBB
sB
sb
SSBb
SsBB
SsBb
Sb
SSbB
SSbb
SsbB
Ssbb
sB
sSBB
sSBb
ssBB
ssBb
sb
sSbB
sSbb
ssbB
ssbb
Chromosomes = DNA
Meiosis I
One diploid sex cell divides……
Meiosis II
Result: One diploid cell = four haploid cells
Crossing Over in Meiosis I
DO ALL GENES ASSORT
INDEPENDENTLY?
• Genes on the same chromosome tend to be
inherited together = linked
• Sex-linked genes: color blindness, MD,
hemophilia.
X
Y
•
X
X
Credits
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Mendel Image: pw1.netcom.com/~aguldo/ agga/bt/txt/bt1899.htm
Pea trellis: http://www.floridata.com/ref/p/images/pisu_sa1.jpg
Experiments in Plant Hybridization (1865)
by Gregor Mendel Read at the meetings of February 8th, and March 8th, 1865
to the the Natural History Society of Brünn (paper can be read at:
http://www.mendelweb.org/home.html
MendelWeb, edited by Roger B. Blumberg.
(http://www.netspace.org/MendelWeb/, Edition 97.1 1997)
The Biology Project: http://www.biology.arizona.edu/default.html
Meiosis Images: www.micro.utexas.edu/.../bio304/ genetics/meiosis.4.gif
Crossing Over image:
http://medlib.med.utah.edu/block2/biochem/Formosa/Figures/Lecture5/515%20Meiosis.JPG
Monohybrid, dihybrid, test cross & pea flower: ntri.tamuk.edu/homepagentri/lectures/ biology/test-cross.gi