10-15 Lecture Notes

7/30/2019 10-15 Lecture Notes

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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

.



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.





M. lewisii

Purple; “landing platform;” low Red; long “spur” (behind); high

concentration;

“naughty

bits”

in

corolla.

concentration; “naughty bits”

project from corolla.



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.



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.



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.



3. (Crossing over and) Recombination


• What is the physical cause?

It creates variation

within chromosomes.

Creates new

combinations of

allele.

During prophase I.

The chromosomes are synapsing.



4.

Outcrossing (versus

“selfing”)


• 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.



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



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.



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

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10-15 Lecture Notes