Transcript Lecture 5a

[review]
Facultative adaptations
(e.g., sun tanning, mate guarding):
track environmental variation and
adjust phenotype to maximize fitness
prospects.
Heritability
Norm of reaction:
Evolved pattern of response to
environment.
Melanin synth.
Different from susceptibility.
Ambient UVb
Two nature/nurture questions!
1.Why is my skin this color?
causes of development
(interaction)
2. Why do people differ in skin color?
causes of variation
(partition the variance)
If we want to know how heritable a trait
is…
h2 = Vg/Vp, thus
h2 = Vg/(Vg+Ve)
h2 varies from 0 to 1.
Selection is more effective when
heritability is significant; but selection
typically reduces heritability as it works.
Today Goals:
1. Gain an understanding of basic
Mendelian genetics.
2. Gain a basic understanding of
molecular genetics.
Mendel’s Peculiar results:
Bred pure strains of wrinkled and
round together.
wrinkled x round
Offspring were all round
Hence, no blending…
Breed these round offspring among
themselves.
round x round
¾ round : ¼ wrinkled
What the heck!?!
Mendel’s hypothesis about the stuff
of heredity:
1. Particles, not fluids (genes).
2. Adults have a double dose of
particles (diploid adults).
3. Adults give only half of their double
dose to each offspring (haploid
gametes).
4. Some particles have stronger
effects than others (dominance).
The model:
1. Particles
2. Diploid adults
3. Haploid gametes
4. Dominance
Model able to predict other outcomes:
F1 hybrid x pure wrinkled ?
Model able to predict other outcomes:
F1 hybrid x pure wrinkled ?
s
s
S
s
Ss
ss
Ss
ss
wrinked:round
1:1
Not the same
result as the initial
wrinkled x round
cross.
Why not?
What does that
show?
genotype: the genes
themselves.
phenotype: the
outward expression
of those genes.
allele: variant of a
gene, for example:
wrinkled allele and
round allele of the
seed-shape gene
homozygous: two
matching alleles.
heterozygous: two
different alleles.
recessive allele:
expressed only
when homozygous
dominant allele:
expressed even
when
heterozygous
M2
P2
Diploidy: Each
chromosome is paired,
with one from Mom and
one from Dad.
Loci match, but alleles
may not
But sex cells
(gametes, eggs and
sperm) are haploid,
not diploid.
Sex cells (gametes) could be
formed by simply giving either
your paternal or maternal
chromosome to each gamete.
But they aren’t…
Gamete formation
involves recombination
(crossing-over):
Exchange of genetic
material between
maternal and paternal
chromosomes
Result is increased
genetic diversity