biol 3301 - genetics ch2a - monohybrid cross st
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Mendelian Genetics
• Around 1857, Mendel began breeding garden peas tostudy inheritance.
• Pea plants have several advantages for genetics. Pea plants are available in !any varieties "ith distinctheritable features #traits$ "ith different variants#characters$.
• %sed &uantitative #yes'no$ characters
• %sed pure lines(
)hite "hite "hite "hite
*ed red red red
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Mendelian Genetics
• +o analye the trans!ittance of traits, !ade
crosses bet"een garden peas varieties "ith
discrete traits( "hite flo"ers'purple flo"ers
• %sed se-ual reproduction in plants yes,
plants have se- too
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Mendelian Genetics
• /irst pair of plants na!ed parental
generation, P.
• *e!oved anthers fro! one #purple flo"er$
plant, used pollen fro! another variety
#"hite flo"er$
• 0elf pollination cross pollination
• *eciprocal crosses
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true-breeding,
purple-flowered
plant
true-breeding,
white-flowered
plant
cross-fertilize
pollen
pollen
all purple-flowered
plants
Parental
generation (P)
First-generation
offspring (F1)
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Monohybrid 2ross
• 2ollected seeds, planted the! and obtained
ne-t generation 33333333333333333333
• All flo"ers on these plants "ere 33333333
• 4et the! 333333333333333333333
• 2ollected seeds, planted the! and obtained
ne-t generation 33333333333333333333
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!"# purple $"# white
Second-
generation
offspring (F2)
First-
generation
offspring (F1)
self-fertilize
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Monohybrid 2ross
• Plants in / generation had
33333333333333 flo"ers in proportion
appro-i!ately 33333333333333333
• All other crosses that follo"ed the
inheritance of one trait produced si!ilar
results and the sa!e ratio
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Mendel6s conclusions
• ach character is deter!ined by 33333333333333333333333333333333333
• ach organis! has 33333333333333 discrete
factors per character • +"o units 333333333333 during ga!etesfor!ation
• +he units do not !i- in hybrid, but one unit can 333333333333 the develop!ent of another
• id not !atter if the particulate factor "as contributed bythe !other or the father #reciprocal crosses i.e. fe!ale or!ale !eiosis$ not always!
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*ule of 0egregation 9r /irst 4a"
• uring the for!ation of ga!etes, the paired
unit factors 3333333333333333333333333,
rando!ly so that each ga!ete receives oneor the other "ith e&ual li:elihood
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Modern ter!inology
• +he trait #or character$ is coded by 333333333333
• Gene is located on 33333333333333, the location
of the gene on the chro!oso!e is called 33333333333333333333
• ach organis! has a pair of each chro!oso!e
33333333333333, n
• ach chro!oso!e contains the gene, but !ay
contain different variant of a gene ; 3333333333
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Modern ter!inology
• 0ince each organis! has a pair of chro!oso!es
#one fro! the !other and one fro! the father$,
alleles !ay be the sa!e 3333333333333333333or different 333333333333333333333333
• 9ne allele can !as: the appearance of another
gene 333333333333333333333
• Allele that is !as:ed ; 333333333333333333
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Modern ter!inology
2apital letter A 3333333333333333333
0!all letter a 333333333333333333333
AA 333333333333333333333333333333
Aa 333333333333333333333333333333
aa 3333333333333333333333333333333
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l
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PP P P
purple parent
all P sper& and eggs
pp p
white parent
all p sper& and eggs
p
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'$offspring
p
p
P p
P p
sper& eggs
P
P
or
ga&etes fro& '
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pp p
P p p
p
ga&etes fro&
'$ plants
eggs
'2
offspring
p
P P
P
P
PP
sper&
P p
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ho&ozygous parent
A A A A
ga&etes
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heterozygous parent
A a a A
ga&etes
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• A Punnett square
predicts the results
of a genetic cross bet"een
individuals
of :no"n
genotype.
Copyright© 2002 Pearson Education, Inc., publishing as Benjamin Cummings
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P p
PP
P
p
pp
P p
eggs
P p
self-fertilize
pP
$
2
$
2
$
2
$
2
$
# s p
e r &
$
#
$
#
$
#
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Branch diagram
Parent 1 Parent Phenotype
= P
= p
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+est cross
•
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Figure 3-4a Copyright © 200% Pearson Prentice Hall, Inc
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4oss of function