i.genetics a. the work of gregor mendel 1. monohybrid crosses 2. dominant and recessive alleles 3....
TRANSCRIPT
I. Genetics
A. The work of Gregor Mendel
1. Monohybrid crosses
2. Dominant and recessive alleles
3. Law of Segregation
B. Mendel and meiosis
Who was this Mendel and what the heck is he doing in a monastery?
• born in 1822• trained himself to be a naturalist early in life• worked as a substitute science teacher
• failed the qualifying exams to be a regular high school teacher!• joined a monastery in Brunn, Austria• sent to Vienna U. to study science and math
Mendel’s first published work: "Versuche über Pflanzen-Hybriden“ or Experiments in Plant Hybridization was a landmark in clarity and insight!
Trained as a mathematician and a biologist, he figured out the laws of inheritance… mathematically!!
MendelWeb
The work of Gregor Mendel
…he called them his children!
• worked with pea plants…
Why pea plants???There was a long-standing tradition of breeding pea
plants at the monastery where Mendel lived and worked
So…they were readily available and they come in lots of varieties!
…there were plants with different flower colors, seed color, flower position etc..
‘Brother Greg... We grow tired of peas again!!!’
And best of all…Pea plants flowers can reproduce by themselves
This allowed Mendel to see if strains were true breeding and to produce hybrids
How Mendel made hybrids…
He’d then tie little bags around the flowers to prevent contact with stray pollen.
Mendel’s hybridization experiments…
Monohybrid crosses:
Parental Generation
True-breeding purple flower x
True-breeding white flower
F1 generation All purple flowers (the hybrids)
F2 generation
Allowed F1 offspring to self-fertilize
705 purple224 white
The results of Mendel’s monohybrid crosses led him to propose…
1. All organisms contain two “units of heredity” for each trait (alleles).
2. Dominant and recessive alleles……and organisms can have any combination of the two alleles (2 dominants, 2 recessives or a mixture 1 dominant and 1 recessive).
3. The Law of Segregation – during gamete formation, alleles separate randomly into separate gametes.
A bit of genetic jargon…
phenotype vs. genotype
What the organism looks like
What alleles the organism has - its genetic makeup
More jargon…
homozygous vs. heterozygous
2 of the same
alleles:
PP or pp 2 different alleles:
Pp
P
p
A Punnett square
A Punnett square…
Gametes from one parentP p
Gametes from other parent
P
p
PPpurple
Pp
Pp pp
purple
purple
white
Ratio: 3:1 or ¾ purple, ¼ white
Let’s relate Mendel’s findings to what we now know about gamete formation
True-breeding purple flower
x True-breeding white flower
P P p
PPP
p
pppp
all purpleP
P
p
F1 generation purple hybrid x purple hybrid
P p P p
P
PP
P pp
pp
PP pp
PP (purple)
Pp (purple) Pp - purple pp - whiteF2
Join to your partner and together, work on the following…
Determine the phenotypic and genotypic ratios for each of the following monohybrid crosses.
Genotypic ratio
Phenotypic ratio
0:1:0 (hd:h:hr)1:0 (dom:rec)or all dominant
AA x aa
0:1:1 (hd:h:hr)1:1 (dom:rec)aa x Aa
1:1:0 (hd:h:hr)1:0 (dom:rec)or all dominant
AA x Aa
1:2:1 (hd:h:hr)3:1 (dom:rec)Aa x Aa
hd = homozygous dominant; h = heterozygous; hr = homozygous recessive
SO, NOW IT’S YOUR TURN TO WORK ALONE
http://www.mendel-museum.com/eng/1online/experiment.htm
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