Transcript The Science of Inheritance

The work of Gregor Mendel
• Austrian monk
• Father of Genetics
• Previous views of
Inheritance
– Blending
– Spermists
– Ovists
“Father of Genetics”
• Mendel performed
breeding experiments
with garden peas
• Found mathematical
patterns of inheritance
• His work was not
appreciated until
1900, 16 years after
his death
Mendel’s work
• Why breed peas?
• They were available in many varieties,
inexpensive, short life cycle, simple
procedures, easy to grow.
• The use of plants also allowed strict control
over the mating.
• He chose to study only characters that
varied in an ‘either-or’ rather than a ‘moreor-less’ manner.
Tracking heritable
characteristics
• Mendel tracked
heritable characters
for 3 generations.
• When F1 hybrids were
allowed to selfpollinate a 3:1 ratio of
the 2 varieties
occurred in the F2
generation.
Interpreting Mendel’s Data
Parent
Cross
F1
generation
F2
Actual Probability
generation Ratio
Ratio
Round x 100% round 5,474 round 2.96:1
wrinkled
1,850 wrink.
3:1
Yellow x
green pea
100%
yellow
3:1
Long x
short
stem
100% long
stem
6,022 yell 3.01:1
2,001 green
787 long
277 short
2.84:1
3:1
Mendel’s Observations
• “dominant” vs “recessive”
• Before “genes” and “meiosis” was thought
of, Mendel theorized that “inheritance
factors”…
– are in the pollen and ova of peas as alternate
forms for different traits.
– occur in pairs, (equal contribution from both
parents)
– separate during gamete formation and pair up
again at fertilization
Mendel’s Law of Segregation
• Each hereditary characteristic is
controlled by two factors (alleles) that
separate and pass into reproductive cells
(gametes).
Mendel’s Law of Independent
Assortment
• Pairs of inheritance factors (alleles)
segregate independently of each other
when sex cells (gametes) are formed.
Mendelian Inheritance in Humans
dominant
recessive
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Tongue Roller (T)
Free Earlobes (F)
Dimples (D)
Widow’s Peak (P)
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Can’t roll tongue (t)
Attached lobes (f)
No dimples (d)
Straight hairline (w)
Genetics and Probability
 See handout and discuss…
 Coin flipping
 Card picking
 Grab colored marbles
Some Vital Vocab.
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Genetics
Gene vs Chromosome
Alleles
Dominant vs Recessive
Some Vital Vocab.
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Genotype vs Phenotype
Homozygous vs Heterozygous
Diploid vs Haploid
Mitosis vs Meiosis
Zygote
Problem Solving from Mendelian Genetics
• Consider inheritance patterns for
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–
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Cystic fibrosis
Huntington’s disease
Hemophelia
Colorblindness pedigree
Exceptions to Complete Dominance
• Polygenic Traits
• Intermediate Expression (aka incomplete
dominance)
• Multiple Alleles
• Several described at this link!