Download Genetic Principles

Genetic Principles
Advanced Genetics
1/21/15
Zuzana Kocsisova
Mendel’s principles of segregation and
independent assortment
• Alleles segregate from each other
in the formation of gametes.
• Genes for different traits assort
independently during the
formation of gametes.
Besides peas…
• Hieracium
– Seeds produced by apomixis; of maternal origin
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Mirabilis
Honeybees
Mice
Cirsium
Geum
Maize
stocks
Pea weevil (Bruchus pisi)
Mendel’s experimental approach
• Defined phenotypes
• Separate generations
• Quantitative and statistical
relationships
• Simple interpretation of ratios
• Follow-up experiments to back
hypotheses
Fisher: counts too good to be true?
• e.g. 6022:2001 is too close to 3:1
• The probability of a fit this good by chance is
.00007
• Other investigators have repeated Mendel’s
experiments and report rations closer and
further than Mendel’s
Muller: mutations
• Autosomal recessive mutations are harder to
study in diploid organisms because both alleles
must be present to observe the phenotype
• Autosomal dominant and sex-linked mutations
are easier to study in diploid organisms.
• Prior to the use of mutagens, spontaneously
arisen mutations were used in genetic studies.
The ClB chromosome
• Allowed easier counting of lethal X-linked
mutations
Ionizing radiation induces mutations
• Muller used Drosophila
• X-rays
• Radiation affects the
germline, not only the
soma
• Stadler used barley
• X-rays and radium exposure
• Linear relationship between
dose and mutation rate
(both groups)
Sutton: Chromosomal Hypothesis
• Chromosomes are positioned independently
• Homologous chromosomes segregate away
• If multiple traits are on the same
chromosome, they are inherited together
(linked)
Chromosomes in Heredity
Creighton and McClintock:
Genetical and Cytological Crossing Over
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Two genetic loci
Two cytological loci
Heterozygous
All on the same chromosome
A second plant for test-cross
Genetics vocabulary
• Homozygous –
the two alleles at a
locus are identical
• Heterozygous –
the two alleles at a
locus are different
• Aneuploidy –
the presence of an
abnormal number
of chromosomes
Genetics vocabulary
• Linkage – the close
proximity of two or
more loci on a
chromosome
• Linkage disequilibrium
– the non-random
association of alleles at
two or more loci that
descend from a single,
ancestral chromosome
Genetics vocabulary
• Synteny – the conservation of blocks of order
within two chromosomes that are being
compared, usually between species
Genetics vocabulary
• Expressivity – The degree to which a
phenotype is displayed in individuals of a
given phenotype
• Penetrance – the percentage of individuals of
a given genotype that display a phenotype
above the cutoff
Genetics vocabulary
• Pleiotropy – a single gene may contribute to
multiple phenotypes
• Epistasis – a gene may interact with or modify
the phenotype of another gene
Genetics vocabulary
• Epigenetics – persistent and heritable (through
mitosis or meiosis) changes in gene regulation rather
than changes in the DNA sequence itself
Genetics vocabulary
• Inheritance – the way
in which genes are
passed to the next
generation
• Heritability – the
proportion of the
parental phenotypic
variance passed on
genetically to the
offspring
Genetics vocabulary
• Hardy-Weinberg
equilibrium – in the
absence of evolutionary
influences (selection,
drift, migration, etc.), the
genotype and allele
frequencies in a
population will remain
constant
• Evolution – the change in
the frequency of alleles in
a population over time
Pea crosses
• F1
– Rr
– red
• F2
– RR:Rr:rr 1:2:1
– Red:white 3:1
Incomplete dominance
• F1
– Rr
– pink
• F2
– RR:Rr:rr
1:2:1
– Red:pink:white 1:2:1
Questions?
Image Sources
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http://www.teleflora.com/about-flowers/sweetpea.asp
https://commons.wikimedia.org/wiki/File:43_Hieracium_pilosella.jpg
http://strongbrains.com/images/MendelNotebook.jpg
http://imgc.allpostersimages.com/images/P-473-48890/64/6471/OGRH100Z/posters/solvin-zankl-white-type-fruit-fly-drosophilamelanogaster-eyes-lack-pigmentation-and-appear-white.jpg
http://link.springer.com/referenceworkentry/10.1007%2F978-1-4020-67549_3131
https://62e528761d0685343e1cf3d1b99a743ffa4142d9d7f1978d9686.ssl.cf2.rackcdn.com/files/22985/wide_articl
e/width926x450/kbtnk9dz-1367209643.jpg
http://upload.wikimedia.org/wikipedia/commons/4/40/Korea-Barley-01.jpg
http://www.phschool.com/science/biology_place/biocoach/images/meiosis/mem
et1.gif
http://www.geologyclass.org/550px-Punnett_square_mendel_flowers.svg.png
http://www.mpietrangelo.com/hbio/unit/10_inheritance/Chapter_09/B_Jpegs_of
_Art_and_Photos/09_Labeled_Art_and_Photos/09_11aIncompleteDominanceL.jpg
Image Sources
• http://upload.wikimedia.org/wikipedia/commons/5/53/NHGRI_hu
man_male_karyotype.png
• http://www.frontiersin.org/files/Articles/9947/fpsyt-02-00017HTML/image_m/fpsyt-02-00017-g002.jpg
• http://biologos.org/uploads/static-content/synteny_5.jpg
• http://o.quizlet.com/uRq5rOj7JtrzBMeR84aRPA_m.png
• http://beacon-center.org/wpcontent/uploads/2012/09/BEACON_epistasis_fig2.png
• http://www.intechopen.com/source/html/44560/media/image1.jp
eg
• http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/H/heritabil
ity75.gif
• http://bayesianbiologist.files.wordpress.com/2011/06/hw.png