Upload
caochauvu
View
222
Download
0
Embed Size (px)
Citation preview
7/30/2019 10-15 Lecture Notes
http://slidepdf.com/reader/full/10-15-lecture-notes 1/12
ene c var a on
o ay s ques ons: y are many quan a ve ra s
normally distributed?
Where
does
genetic
variation
.
II. Four sources of genetic variation
.
7/30/2019 10-15 Lecture Notes
http://slidepdf.com/reader/full/10-15-lecture-notes 2/12
I. Polygenic inheritance: Why is variation in so many
traits normally distributed?
Basic assumptions
of
the
model:
1. Many genes are involved in quantitative traits.
3. In a o ulation there are man alleles of each ene.
. e genes assor n epen en y.
4. The effects of each allele add together.
7/30/2019 10-15 Lecture Notes
http://slidepdf.com/reader/full/10-15-lecture-notes 3/12
7/30/2019 10-15 Lecture Notes
http://slidepdf.com/reader/full/10-15-lecture-notes 4/12
M. lewisii
Purple; “landing platform;” low Red; long “spur” (behind); high
concentration;
“naughty
bits”
in
corolla.
concentration; “naughty bits”
project from corolla.
7/30/2019 10-15 Lecture Notes
http://slidepdf.com/reader/full/10-15-lecture-notes 5/12
Dr. Bradshaw’s group planted F2s at random locations in
na ura a a n e erra eva a moun a ns, en
recorded which
pollinators
visited
which
flowers.
1. Circle the individuals that had the most visits from
bumblebees.2. Put a star next to individuals that had the most visits
from hummingbirds.
This is what they measured—frequency and type of
pollinator visits.
7/30/2019 10-15 Lecture Notes
http://slidepdf.com/reader/full/10-15-lecture-notes 6/12
II. Four sources of genetic variation
1. Mutation: based on 2010 sequencing data from humans,
an average gamete contains 1 base‐substitution mutation
in
every ~
10
8
bases.• How many mutations is this?
• ow o ese mu a ons crea e gene c var a on
• When does mutation occur?
•What
is
the
physical
cause?
About 34.
Mutations are changes in genetic base
sequence, so they are variation
themselves. They create new alleles.
This happens in chromosome replication prior to meiosis, and maybe even
mitosis.
Copying errors,
chromosome
abnormalities,
DNA damages.
7/30/2019 10-15 Lecture Notes
http://slidepdf.com/reader/full/10-15-lecture-notes 7/12
2.
Independent
assortment
• How does it create genetic variation?
• When does it occur?
•
It allows for random assortment of parental and maternal chromosome. It
creates variation among chromosome, instead of within.
Meiosis I, during metaphase.
Chromosomes (homologs) aligned randomly on the methapase plate.
7/30/2019 10-15 Lecture Notes
http://slidepdf.com/reader/full/10-15-lecture-notes 8/12
3. (Crossing over and) Recombination
• How does it create genetic variation?
• What is the physical cause?
It creates variation
within chromosomes.
Creates new
combinations of
allele.
During prophase I.
The chromosomes are synapsing.
7/30/2019 10-15 Lecture Notes
http://slidepdf.com/reader/full/10-15-lecture-notes 9/12
4.
Outcrossing (versus
“selfing”)
• How does it create genetic variation?
• When does it occur?
• What is the physical cause?
Allows for combinations of male and female gametes. Including chromosome
from 2 different individuals, form new alleles.
When male and female gametes combine. Happens when mating.
7/30/2019 10-15 Lecture Notes
http://slidepdf.com/reader/full/10-15-lecture-notes 10/12
F1 hybrids between
M. lewisii and
M. cardinalis
let P = petal color genes; S = flower shape genes, N =
‐ ‐1 1
C‐P 2
L‐P 2
L‐
S2 C‐
S2 C‐
N 4L‐
N 4
L‐P 4
C‐P 4
C‐N L‐N
C‐N 2
L‐N 2
L‐P 3
C‐P 3
‐
3‐
3
C‐N 3
L‐N 3
C‐N 5
L‐N 5
L‐S1
C‐S1
7/30/2019 10-15 Lecture Notes
http://slidepdf.com/reader/full/10-15-lecture-notes 11/12
III. The evolution of sex
Why go to all this trouble, just to produce offspring that
are genetically
different
from
each
other
and
from
their
parent(s)?
1. Purifying selection (getting rid of deleterious alleles)
.‐
phenotypes)
Chance of producing offspring without crummy alleles.
Allows us to fight off new environments that may contain harms like
new diseases.
7/30/2019 10-15 Lecture Notes
http://slidepdf.com/reader/full/10-15-lecture-notes 12/12
An experiment with roundworms parasitized by a
acter um.
ompare o gate y se ng to
m xe
mating” (some outcrossing) populations.
Why do college students think that t‐shirts smell nice, if
they were worn by someone with different MHC alleles
t an t ey
ave