ANNOUNCEMENTS

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ANNOUNCEMENTS

• Exam 1 is Friday. Take-home 1 is due at Exam 1.
• Check the missing iClicker list on the web
  page...
• Q A session tomorrow
• HS411, 530 -700
• Bring questions!

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• This karyotype belongs to a
• male
• female

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Frequency
Why are sex chromosome abnormalities so much more
common than autosomal abnormalities?
X-inactivation reduces the harmful effects of
aneuploidy for the X chromosome.
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Why are males normal at all? Males have only
one-half of the copy number of X-linked genes
that female do. Development in mammals is very
sensitive to an imbalance in the number of genes.
Too much or too little gene product generally
results in abnormal phenotypes. ANSWER One of
the X-chromosomes is inactivated in human
(mammalian) females.
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Chromosomal variation

• Variation in chromosome number
• Aneuploidy
• Euploidy/Polyploidy
• Variation in chromosome structure
• Change in the amount of genetic information
• - deletions
• - duplications
• Rearrangement of gene locations
• - inversions
• - translocations

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• Polyploidy (more than 2 sets of chromosomes)
• Polyploidy is common in plants, occasional in
  fish and amphibians, and rare in mammals
• Polyploidy is thought to be important over
  evolutionary history, since whole genome
  duplications may provide raw material for
  adaptation
• Odd ploidies (3N) are often sterile, but even
  ploidies (4N, etc.) are fertile and often highly
  fit

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Polyploidy

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Diploid Tetraploid Hyla These are essentially
the same frog - it is the balance between the
number of gene copies that is important for
proper development, not necessarily the total
number of gene copies
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Chromosomal variation

• Variation in chromosome number
• Aneuploidy
• Euploidy/Polyploidy
• Variation in chromosome structure
• Change in the amount of genetic information
• - deletions
• - duplications
• 2. Rearrangement of gene locations
• - inversions
• - translocations

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Deletion - loss of a chromosomal segment
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Deletions are often deleterious (bad). The
effects depend on the size of the region
lost. Ex. cri du chat syndrome (missing part of
chrom. 5)
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Duplication - repeating of a chromosomal segment
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Duplications may be deleterious (bad)
ex. bar-eye in Drosophila
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Duplications may also provide raw material for
longer term adaptive evolution of gene families
(good).
Ex. Hox genes
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Inversions - double breakage insertion of
flipped segment
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Translocations
Reciprocal translocation between chromosomes
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Translocations Inversions Generally, inversions
and translocations are not directly harmful to
carriers, but their progeny may inherit
deletions/duplications that are deleterious.
Familial Downs Syndrome a segment of
chromosome 21 translocated to chromosome 14 (3
copies total)
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Chromosomal variation - key points
Variation in chromosome number and structure can
have major effects on individual health and on
evolution Aneuploidy - odd number of 1
chromosome common, harmful to individuals (e.g.
trisomies) Polyploidy - Duplication of all
chromosomes common in many taxa, may result in
changes in size or other traits, thought to
contribute to speciation Chromosomal
rearrangements Duplications, deletions - often
harmful, may be good Inversions, translocations
- not directly harmful
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Maternal effects Maternal effects occur when the
mothers genotype or phenotype affects the
phenotype of her progeny directly.
For example, older salmon produce larger eggs
which have more nutrients so that their fry are
larger at hatching.
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Maternal effects and maternal inheritance

• Mothers can affect offspring phenotype in lots of
  ways in addition to normal Mendelian inheritance
  of her alleles at nuclear genes
• Environmental maternal effects
• Imprinting/epigenetics
• Genetic maternal effects
• Maternal inheritance of mitochondrial
  chloroplast genes

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Genetic maternal effects

• Genes are inherited normally, but trait is
  controlled by mothers genotype
• Maternal effect occurs when the offspring
  phenotype is directly determined by mothers
  genotype (not indirectly via offspring genotype)

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Genetic maternal effects -- Coiling in the snail
Limnea peregra The direction of shell coiling is
controlled by a single gene. Right (dextral)
coiling (D) is dominant to left (sinistral)
coiling (d). The phenotype of an individual is
determined by the genotype of its mother. The
genotype of a mother determines the structure of
the eggs that she produces.
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Maternal genotype
Maternal genotype
DD Dd
dd
Left (sinistral)
Right(dextral)
Progeny DD, Dd, or dd
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P F1 F2
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P F1 F2
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Eukaryotic genomes (not to scale!!) 1 Mb
1,000,000 base pairs of DNA 1 kb 1,000 bp
X
x
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Extranuclear or cytoplasmic inheritance
sperm
egg
Often, organelle genomes are maternally-inherited

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Mitochondrial DNA in humans encodes just 13 genes
- all are necessary for oxidative phosphorlyation
(OXPHOS)

• Haploid, circular DNA molecule (derived from
  bacterial endosymbiont)
• Reproduces via mitosis (many mt per cell)
• Little or no recombination

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All children inherit their mothers mtDNA type
mother
father
m2
m1
m1
m1
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In humans, mitochondrial variation influences
male fertility..
Sperm races H haplotype best, T haplotype worst
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In humans, mitochondrial variation influences
male fertility..
Sperm races H haplotype best, T haplotype worst
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QWhy are infertile haplotypes not eliminated by
natural selection??
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QWhy are infertile haplotypes not eliminated by
natural selection?? A Because human
mitochondria are maternally inherited, reductions
in male fertility do not reduce their own
transmission (fitness). This creates genetic
conflict between mitochondrial and nuclear
genomes.
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Why is only male fertility affected??
Sperm are motile and need lots of energy from
mitochondria -- mutations causing even slight
reductions in OXPHOS efficiency may hurt sperm
motility
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Mitochondria also cause male sterility in many
plants
Silene acaulis
Male sterile (female)
hermaphrodite
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Chloroplasts

• Location of photosynthesis in plant cells
• Haploid (one copy in each individual)
• Maternally inherited in some groups and
  paternally inherited in others (pine trees)

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Table 7.4
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EXAM 1

• Material through Monday
• Format - 10 multiple choice questions (5 pts
  each) 4 problems (10-15 pts each)
• Strategy - Be systematic! Read the questions
  carefully!
• Questions about Take-home exam or In-class exam
  format/logistics?