BIOLOGY 1B Lecture Notes - Lecture 4: Frequency-Dependent Selection, Sickle-Cell Disease, Petrochelidon

33 views2 pages
Lecture 4: Natural Selection
8/30
Evolution by means of natural selection
o Individuals in a population vary in their traits
o There is a struggle for existence that leads to differential survival and reproduction and
preservation of favored, heritable traits
o Fitness: the relative contribution an individual makes to the gene pool of the next generation
Directional selection: an extreme phenotype is favored over other phenotype causing allelic frequency to
shift over time in direction of that phenotype
o Ex: Cliff Swallow- larger wing span favored in the cold season so there is a directional shift
Large individuals are able to stay warmer; larger energy reserves
Little birds die, big birds survive to skew population
Stabilizing selection: Favors intermediate variants and reduces phenotypic variation, maintaining status quo
o Ex. Human population with baby birth weights
Disruptive selection: the extremes are favored
o Ex. Black bellies seedcracker
Heavy beaks favored and small beaks favored because heavy beaks can exploit big seeds
and small beaks can exploit small seeds
Why preserving genetic diversity is important:
o Ex. Malaria
Sickle cell anemia: caused by mutation that changes shape of blood cells
Creates resistance to malaria; not as easily infected in heterozygous condition
In homozygous recessive condition, the cells stick together and result in physical
problems
In homozygous dominant condition, not protected from malaria
High frequency of heterozygotes= beneficial in areas more affected by malaria
Ex. N=30,923. AA=25,374 As=5482 ss= 67
Total number of alleles= 61,846
How many A alleles exist? (25,374)(2) + (5482)= 56,230
Total s alleles= 5616
F(A)= 56230/61846= 0.909=p
F(s)=5616/61846= 0.091=q
p2+2pq+q2=1
plug frequency values into hardy Weinberg
p2 (0.824)+2pq (0.165) +q2 (0.008)
How many heterozygotes predicted? 0.165(30923)= 5102
AA predicted = 25,480
ss predicted= 247
Therefore, population not in Hardy Weinberg equilibrium
Frequency dependent selection: fitness of phenotype depends on its frequency relative to other phenotypes
in a given population
o Ex. Lefty and righty fish mouths
Sexual selection:
o Intersexual selection: MATE CHOICE; members of one sex choose mates of other sex to mate
with; compete with members for mates
Epigamic traits selected for by the opposite sex
Ex. peacock and its feathers, belly of bird
Why is the choice usually up to the female?
Female has limited number of eggs; takes time and effort to lay and hatch and
care of young
o More energetically invested in process
o Needs to pick male who would be good mate for offspring
o Female gametes much larder than male gametes
The ‘good genes’ hypothesis
find more resources at oneclass.com
find more resources at oneclass.com
Unlock document

This preview shows half of the first page of the document.
Unlock all 2 pages and 3 million more documents.

Already have an account? Log in

Document Summary

Lecture 4: natural selection: evolution by means of natural selection. Human population with baby birth weights: disruptive selection: the extremes are favored, ex. Black bellies seedcracker: heavy beaks favored and small beaks favored because heavy beaks can exploit big seeds, why preserving genetic diversity is important: and small beaks can exploit small seeds, ex. Malaria: sickle cell anemia: caused by mutation that changes shape of blood cells, creates resistance to malaria; not as easily infected in heterozygous condition. In homozygous recessive condition, the cells stick together and result in physical problems. In homozygous dominant condition, not protected from malaria: high frequency of heterozygotes= beneficial in areas more affected by malaria, ex. Lefty and righty fish mouths: sexual selection: Intrasexual selection: members of same sex compete with each other in order to mate: long calling males created offspring that lived longer, had shorter time to metamorphosis, sexual dimorphism: distinct characteristics between sexes in a species, ex.

Get access

Grade+
$40 USD/m
Billed monthly
Grade+
Homework Help
Study Guides
Textbook Solutions
Class Notes
Textbook Notes
Booster Class
10 Verified Answers
Class+
$30 USD/m
Billed monthly
Class+
Homework Help
Study Guides
Textbook Solutions
Class Notes
Textbook Notes
Booster Class
7 Verified Answers

Related Documents

Related Questions