Mendel and Mendelian Genetics

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Mendel and Mendelian Genetics Terminology Heredit
ary traits (or characters or characteristics) Th
e outward expression of genes within the limits
of the environment in which the plant is
growing Genotype the genetic make-up of an
individual plant (in some cases we talk in terms
of populations or cultivars) Phenotype the
physical expression of the genotype, what we
see may refer to a single trait of a single or
group of plants or to a population of plants
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Mendel and Mendelian Genetics PG x E the
environment influences the expression of the
phenotype e.g. consider identical twins raised
together or apart diet grooming
habits exercise consider plants nitrogen
level water light Genes then are the starting
point for determining phenotype, they determine
the structure and functions of the organism The
phenotype however is a highly complex organism
with numerous, complex biochemical pathways
capable of being influenced by the environment
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Mendel and Mendelian Genetics Symbols used in
plant breeding Allele The alternate forms of a
gene. Usually written in simple terms as a
capital letter (denoting DOMINANCE) or a lower
case letter (denoting recessiveness). An allele
is found at the gene locus on a chromosome and
the other allele is found at the same locus on
the homologous chromosome. (Together the 2
alleles make up the gene) e.g. Aa where A is
dominant and a is recessive AA and Aa genotypes
could have red flowers aa genotypes could have
white flowers
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Mendel and Mendelian Genetics Symbols used in
plant breeding P parent F filial (Latin
filiusson) used to identify generations past
the mating of two parents (usually homozygous).
Each successive generation is produced by
selfing, natural or artificial. S denotes
generations of selfing such that F1 S0 OR
F2 S0 (heteroz heterog gen.) F2 S1 ,
etc. M denotes generations following use of a
mutagenizing agent P M0 (generation before
mutation) M1 (generation to which the
mutagent is applied) M2 (generation
produced by selfing the M1, etc.)
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Mendel and Mendelian Genetics Symbols used in
plant breeding Systems using the F
notation System I System II P1 x P2
P1 x P2 F1 F1 F2 ?
IPS F2 ? IPS F3
F23 F3 generation F2 derived
F3 Discuss generation growing or in seed
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Mendel and Mendelian Genetics Other terminology
used in plant breeding Harvest seed from 1 plant
and plant to a row the next season Progeny row
(cotton) Ear row (corn) Head row (wheat) Plant
row Nursery row Others?
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Mendel and Mendelian Genetics Mutation
breeding Goal is to do as little damage as
possible while affecting at least 1 gene (point
mutation) Types of damage from mutagent Deletions
of entire chromosome segments Inversions Point
Reading Frame (start code) ACT CCC GTG TCG
TCC (stop code) Gene If we knock out the
A then we shift the reading frame and make the
sequence a nonsense sequence and therefore
knock out the gene
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Mendel and Mendelian Genetics Mutations occur
naturally at very low levels lt 1 most are
deleterious and nature discards them Example of
Mutation Breeding from Dick Auld (TTU) Used EMS
on seeds of Paymaster 200 Selected for fiber
length in the progeny Length Strength Mic. UI TA
M 94L-25 1.29 32.5 4.2 83 TTU 271
1.23 32.2 4.1 83 CAMD-E 1.09 26.9
4.0 83 PM 200 (M0) 1.14 29.8 4.1 83
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The value of Plant Breeding What has contributed
to increased yields over the past 100 years
climate change commercial fertilizer herbicides
power equipment PGR GENETICS We measure the
contribution of genetics in Genetic Gain Corn
1930-1980 92 kg/ha/yr or 89 of the yield gain
in Iowa was attributed to improved
genetics. Wheat 50 attributed to genetic
gain Sorghum 1956-1980 39 of yield inc.
attributable to Genetic Gain Cotton 7 kg/ha/yr
or .74/yr gain in yield pot. from genetic imp.
NOTE Genetic Gain depends on where, when, what
genotypes!! No Hard Numbers.
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Genetic Gain or Gain from Selection Gs i h2
?s2ph i selection index based on percent of
plants selected h2 heritability of the
trait ?s2ph standard deviation of the
phenotypic variance i and h2 are pretty well
fixed ?s2ph this is what we are about creating
variability from which to make selections and
understanding the effect of selection on the
trait of interest be it host plant resistance,
crop quality, or yield. Breeding goal create
variation and identify way to screen for and
select desirable phenotypes
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Characteristics and breeding techniques, selfed
and crossed crops Characteristic
or Self-pollinated Cross-pollinated breeding
techniques species species
Characteristics of Natural Populations Genotypes
of sporophyte Homozygous Heterozygous Gametes of
a single plt. All the same All different Progeny
of a single plt. Homogeneous Heterogeneous Self-in
compatibility None Frequent Inbreeding
depression None Usual
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Characteristics and breeding techniques, selfed
and crossed crops Characteristic
or Self-pollinated Cross-pollinated breeding
techniques species species
Breeding Techniques Introductions Yes Yes Pure-lin
e selections Often only as inbreds Mass
selection Occasionally Frequently Pedigree Yes No
Bulk populations Yes Yes Backcross Yes Yes Hybrids
Occasionally Yes Recurrent selection Occasionally
Yes Synthetic cultivars Occasionally Yes