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Intro to Genetics
11.1 The Work of Gregor
Mendel
Mendel
• Austrian Monk
• Born in 1822 in the Czech Republic
• Studied at University of Vienna
– Math and Science
• Worked in a monastery and school for 14
years
– In charge of garden in the monastery
Mendel’s work
• Fertilization
– Process of male and female reproductive
cells joining together.
• Used pea plant
• Pea are True breeding
– If allowed to self pollinate they would
produce identical offspring
Mendel’s work
• Produced Hybrids
– Offspring that has parents with different
traits
– He saw that : ↓ ( fig 11-3 on pg 264)
• Seed Shape
– Round + Wrinkled  Round
• Seed Color
– Yellow + Green  Yellow
• Seed Coat Color
– Gray + White  Gray
• Pod Shape
– Smooth + Constricted  Smooth
• Pod Color
– Green + Yellow  Green
• Flower position
– Axial + Terminal  Axial
• Height
– Tall + Short  Tall
Mendel's Conclusion
1. Inheritance is determined by traits
passed generation to generation. Now
known as Genes each gene has
different forms called ALLELES
2. Principle of Dominance: Some Alleles
are recessive and some are dominant.
• Segregation: alleles are separated
• Gametes: Sex cells
• Genes are separated into alleles to form
gametes
Segregation
• The splitting of a gene into alleles to
form the gamete.
– P = parents
– F1 = 1st generation
– F2 = 2nd generation
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TT
P
segregation
F1
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Tt
T
tt
X
T
Tt
t
tT
t
tT
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Tt
F1
segregation
F2
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T
Tt
X
t
Tt
T
Tt
t
tt
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Probability and Punnett Squares
Pg 267-269
Genetics and Probability
• Probability
– The likelihood of a specific outcome
happening
– Ex: Getting tails when flipping a coin ½ or
50%
– If flipping a coin 3 time the probability of it
landing on tails all three time
• ½ x ½ x ½ = 1/8 or 12.5%
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• Genotype
– The genes an organism has.
• Phenotype
– The traits that the organism exhibits.
• Homozygous:
– When an organism has either both
dominate or recessive genes for a given
trait
• Heterozygous
– When an organism has both a dominate
and recessive genes for a given trait
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Punnett Squares
They are used to
show possible
genotypes and
phenotypes
(11-7 on pg 268)
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• Cross a Rr Tt with an Rr Tt
• What % of the genotype is
– RR TT & rr tt (all homozygous)
– All Heterozygous (Rr Tt)
• What is the % phenotype shows
– All dominant traits,
– All recessive traits
Example Aa Bb Dd X Aa Bb Dd
• AaBbDd
– ABD
– ABd
– AbD
– Abd
– aBD
– aBd
– abd
• AaBbDd
– ABD
– ABd
– AbD
– Abd
– aBD
– aBd
– abd
Mitosis
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Meiosis
pg 275-281
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Genome
• Genome: Complete complement of an
organism’s DNA.
– Includes genes (control traits) and noncoding DNA organized in chromosomes.
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Genes
• Eukaryotic DNA is
organized in chromosomes.
– Genes have specific places
on chromosomes.
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Heredity
• heredity – way of
transferring genetic
information to
offspring
• Chromosome theory of
heredity:
chromosomes carry
genes.
• Gene – “unit of
heredity”.
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Chromosome numbers
All are even numbers –
diploid (2n) sets of
homologous
chromosomes!
Ploidy = number of
copies of each
chromosome.
Diploidy
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Meiosis – key differences from mitosis
• Meiosis reduces the number of chromosomes by half.
• Daughter cells differ from parent, and each other.
• Meiosis involves two divisions, Mitosis only one.
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Meiosis 1
First division of meiosis
• Prophase 1: Each chromosome duplicates
and remains closely associated. These are
called sister chromatids. Crossing-over can
occur during the latter part of this stage.
• Metaphase 1: Homologous chromosomes
align at the equatorial plate.
• Anaphase 1: Homologous pairs separate
with sister chromatids remaining together.
• Telophase 1: Two daughter cells are formed
with each daughter containing only one
chromosome of the homologous pair.
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Meiosis II
Second division of meiosis: Gamete formation
• Prophase 2: DNA does not replicate.
• Metaphase 2: Chromosomes align at
the equatorial plate.
• Anaphase 2: Centromeres divide and
sister chromatids migrate separately to
each pole.
• Telophase 2: Cell division is complete.
Four haploid daughter cells are
obtained.
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Animation
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Meiosis creates genetic variation
• During normal cell growth, mitosis produces
daughter cells identical to parent cell (2n
to 2n)
• Meiosis results in genetic variation by
shuffling of maternal and paternal
chromosomes and crossing over.
No daughter cells formed during meiosis
are genetically identical to either mother or
father
During sexual reproduction, fusion of the
unique haploid gametes produces truly
unique offspring.
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Independent assortment
Number of combinations: 2n
e.g. 2 chromosomes in haploid
2n = 4; n = 2
2n = 22 = 4 possible combinations
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Independent assortment
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Crossing over
Chiasmata – sites of crossing
over, occur in synapsis.
Exchange of genetic material
between non-sister chromatids.
Crossing over produces
recombinant chromosomes.
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Mitosis vs. meiosis
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