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Bonus #2 due 4/21
Meiosis and
Genetic Diversity
Asexaul
Reproduction
extremely low
genetic diversity
vs.
Sexaul
Reproduction
greater genetic
diversity
How does sexual reproduction generate
genetic diversity?
Gene for
growth
hormone
Gene for
brown hair
pigment
Gene for
blue eye
pigment
Gene for
hemoglobin
Gene for
DNA polymerase
Haploid
chromosomes
Allele for
low express
(short)
Gene for
growth
hormone
Allele for
high express
(tall)
Allele for
black hair
Gene for
hair color
Allele for
black hair
Allele for
sickle cell Hb
Gene for
hemoglobin
Allele for
normal Hb
Diploid
chromosomes
Fig 1.5
Each pair of
chromosomes
is comprised
of a paternal
and maternal
chromosome
Fig 1.11
meiosis
Diploid
Haploid
Fig 3.16
Meiosis splits apart the
pairs of chromosomes.
X 23
in humans
haploid
X 23
in humans
X 23
in humans
diploid
X 23
in humans
Inheritance = The interaction between genes
inherited from Mom and Dad.
sister chromatids= replicated DNA (chromosomes)
tetrad= pair of sister chromatids
Fig 3.12
Fig 3.16
Meiosis splits apart the
pairs of chromosomes.
X 23
in humans
Asexual
Reproduction
extremely low
genetic diversity
vs.
Sexual
Reproduction
greater genetic
diversity
How does sexual reproduction generate
genetic diversity?
Fig 3.10
Crossing-over
(aka Recombination)
DNA cut and
religated
DNA cut and
religated
Crossing-over:
Proteins in the cell cut and religate the DNA,
increasing the genetic diversity in gametes.
Fig 3.10
Crossing-over:
Proteins in the cell cut and religate the DNA,
increasing the genetic diversity in gametes.
Fig 3.10
Crossing-over:
Proteins in the cell cut and religate the DNA,
increasing the genetic diversity in gametes.
Fig 3.10
Asexual
Reproduction
extremely low
genetic diversity
vs.
Sexual
Reproduction
greater genetic
diversity
How does sexual reproduction generate
genetic diversity?
Fig 3.17
Independent Assortment
(aka Random Assortment)
Fig 3.17
Independent Assortment
2 possibilities
for each pair,
for 2 pairs
22 = 4
combinations
Fig 3.17
Independent Assortment
2 possibilities
for each pair,
for 23 pairs
223 =
8,388,608
combinations
Crossingover
Meiosis:
In humans,
crossing-over and
(Ind. Assort.)
independent
assortment lead to
over 1 trillion
possible unique
gametes.
(1,000,000,000,000)
Meiosis I
Meiosis II
4 Haploid cells, each unique
Fig 3.12
Fig 3.12
4 haploid cells
{Producing gametes}
Sexual reproduction
creates genetic
diversity by
combining DNA
from 2 individuals,
but also by creating
genetically unique
gametes.
{Producing more cells}
haploid
X 23
in humans
X 23
in humans
diploid
X 23
in humans
Inheritance = The interaction between genes
inherited from Mom and Dad.
Do parents’ genes/traits blend together in offspring?
Fig 2.6
In many
instances there
is a unique
pattern of
inheritance.
Traits
disappear and
reappear in
new ratios.
Fig 1.6
from DNA to Protein:
from gene to trait
Fig 1.7
from DNA to Protein:
from gene to trait
Molecular
Cellular
Organism
Population
Genotype
Phenotype
Human blood types
Fig 4.11
Fig 4.11
One gene with three alleles controls carbohydrates
that are found on Red Blood Cell membranes
A
A
A
B
A
A
A
A
A
Allele A = A carbs
B
B
B
RBC
A
B
RBC
RBC
B
B
B
B
Allele B = B carbs
Allele O = no carbs
Human blood types
Fig 4.11
We each have two versions of each gene…
A
So
A
A
A
A
RBC
A
A
A
A
Genotype could be
A and A
OR
A and O
Recessive alleles do not show their phenotype
when a dominant allele is present.
A
A
A
A
A
RBC
A
A
A
See Fig 4.2
A
Genotype could be
A and A
OR
A and O
What about…
RBC
Genotype = ??
What about…
RBC
Genotype = OO
What about…
B
A
B
A
A
RBC
B
B
A
B
A
What about…
B
A
B
A
A
RBC
B
B
A
B
Genotype = AB
A
Human blood types
AA or
AO
BB or
BO
AB
OO
Fig 4.11
If Frank has B blood type,
his Dad has A blood type,
And his Mom has B blood type…
Should Frank be worried?
Mom=B blood
possible BB or BO
genotypes
Dad=A blood
AA or AO
possible
Mom=B blood
Dad=A blood
BB or BO
AA or AO
genotypes
Gametes all B / 50% B and all A / 50% A and
50% O
50% O
Mom=B blood
Possible
genotypes BB or BO
Dad=A blood
AA or AO
Gametes all B / 50% B and all A / 50% A and
50% O
50% O
Frank can be BO
= B blood
…no worries
Grandparents
AB and AB
Mom=B blood
possible
BB or BO
Dad=A blood
AA
genotypes
Gametes all B / 50% B and
50% O
Frank can be BO or BB
= B blood
all A
…Uh-Oh
Pedigree, tracing the genetic past
Dom.
Rec.
Rec.
Dom.
Fig 2.11
We can also
predict the
future
Fig 2.6
Inheritance of blood types
Mom = AB
Dad = AB
Inheritance of blood types
Mom = AB
Gametes:
A or B
Dad = AB
A or B
Inheritance of blood types
Mom = AB
Gametes:
A or B
A or B
Dad
A or B
A AA
Mom or
B AB
Dad = AB
AB
BB
Chance of each
phenotype for
each offspring
25% AA
50% AB
25% BB
Single genes controlling a single trait are unusual.
Inheritance of most genes/traits is much more
complex…
Dom.
Rec.
Rec.
Dom.
Genotype
Phenotype
Genes code for
proteins (or RNA).
These gene
products give rise
to traits…
Human blood types
AA or
AO
BB or
BO
AB
OO
Fig 4.11
Genotype
Phenotype
Genes code for
proteins (or RNA).
These gene
products give rise
to traits…
It is rarely this
simple.
Fig 4.3
Incomplete
dominance
Fig 4.4
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