Genetics WK1PPTtj
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Transcript of Genetics WK1PPTtj
Basic Course Info • Course Website is on TED
–Course information and syllabus
– Lecture PDF’s
–Announcements
–Discussion Board
–Contact information
• Class is available on videocast @ podcast.ucsd.edu
Required Materials
• Essentials of Genetics by Klug, Cummings, Spencer, and Palladino, 8th edition.
• MasteringGenetics, a web-based resource, available from the textbook publisher (Pearson). – Course ID: MGENREUTHER91695
Section sign up
• Sign up for discussion sections will
be online with your student PID
http://sections.ucsd.edu/ at
5:00pm today
• There are no discussion sections this
week!
• Check syllabus. Not all Blink
sections are listed.
Exams
• ONLY excuse to miss a test is hospitalization or serious family emergency (only unplanned events count with valid documentation)
• Religious conflict/OSD accommodation – you must talk to me this week.
• No weddings, parties, vacations, excuses
GRADING:
Midterm Exams (100 points each) 200 points Final Exam 250 points Problem Sets (15 points each) 105 points Case It Assignment 40 points TOTAL 595 points Extra Credit Surveys!!!! > (85%) A-, A or A+ > (75%) B-, B or B+ > (65%) C-, C or C+ > (55%) D If necessary, these cutoffs will be adjusted downward so
that at least 50% of students in the class receive an A or a B, but they will not be adjusted upward for any reason.
How to do well in this course
• Attend lectures and take notes
• Go over those notes and text soon after lecture.
• Rewrite and organize notes. Supplement with book
• Attend sections and ask questions.
• Practice, practice, practice
Cheating
Final Things
• What can be on the test?
– Anything in lecture.
– Use common sense
– You are not responsible for material received outside of lecture; however, I will test you with application and conceptual questions. Therefore you will need to take the information learned in lecture and be able to use it in new and creative ways.
Evolution
• Evolution is a change in the genetic composition of a population over time (across generations)
Population – group of individuals from the same species that live in the same area and have the potential to mate
Devil’s hole pupfish
Northern flicker
Allele – A specific variant of a gene. Different individuals of a species have the same genes, but may have different alleles.
Example: Sickle cell anemia allele
3 steps of microevolution
1. Variation in a trait exists within populations
2. Traits are heritable (DNA)
3. Not all offspring reproduce equally
Evolution = change in the genetic composition of a population
1 - Variation exists in populations
Peppered moths on a white tree
+
+
=
=
2 – Variation in traits is heritable
Peppered moths on a white tree
3 - Not all individuals reproduce equally
A change in the frequency of a trait that has a genetic basis (black moths
become rarer)
= EVOLUTION!!!
Pre-Industrial Revolution
Industrial Revolution
As the environment changes, so does the benefit of being a black moth
Grant et al. (1996) J. of Heredity 87(5):351
Natural Selection
Differential success in reproduction
Results in favored alleles increasing in frequency in future generations
Adaptation
Darwin and the Voyage of the Beagle 1831-1836
What does Origin… say?
1. All organisms evolved from common ancestor - descent with modification
2. Mechanism - natural selection - differential survival/reproduction
(individuals with certain traits survive/reproduce more than individuals without those traits) Profoundly challenged prevailing world view
In other words…
1. Evolution as fact
– Pattern
– Accepted quickly
2. Natural selection drives adaptation
– Process
– Rejected initially
Summary
1. Evolution as fact – Pattern
– Accepted quickly
2. Natural selection drives adaptation – Process
– Rejected initially
Why was natural selection rejected by the scientific community?
Principles of Natural Selection
1. Variation within a trait
2. Variation is heritable
3. Not all individuals reproduce equally
Why Natural Selection Wasn’t Initially Accepted
1. The earth was too young
2. No mechanism for the creation of novel variation
3. No mechanism for the inheritance of adaptations
Next Step: Resolve these 3 issues and modern evolutionary theory is born
2 - Thomas Morgan and Mutation
• Worked with fruit flies (Drosophila melanogaster)
• Previously, mutations were thought to be large, causing speciation or new morphological features
• Morgan quantified mutation, its mechanism, and its effect on the body
• Received Nobel Prize in 1933.
Wildtype Mutant
3 – Mechanism of inheritence
• Any beneficial adaptation will be diluted and eventually disappear
3 - Weissman and Lamarckism
• Infamous mouse tail clipping experiment
• Debunked “soft inheritance”
• Inherited characters are from genes of successful parents
F1
F1
F2 F2
Experimental genetics began in an abbey garden
Gregor Mendel discovered principles of genetics in experiments with the garden pea
• Mendel showed that parents pass heritable factors to offspring (heritable factors are now called genes)
Copyright © 2009 Pearson Education, Inc.
Gregor Mendel’s breakthrough: principles of inheritance
• Age 21 became a monk
• Returned to school at age 29: University of Vienna
• Returned to the monastery scientifically trained
• Performed well-controlled experiments that revolutionized our understanding of inheritance
• Findings published in 1866
1822-1884
Mendel’s Postulates
Genes are found in alternative versions called alleles
Genotype is the listing of alleles an individual carries for a specific gene
1. For each characteristic, an organism inherits two alleles, one from each parent; the alleles can be the same or different
– A homozygous genotype has identical alleles
– A heterozygous genotype has two different alleles
Copyright © 2009 Pearson Education, Inc.
Mendel’s Postulates
2. If the alleles differ, the dominant allele determines the organism’s appearance, and the recessive allele has no noticeable effect
– The phenotype is the appearance or expression of a trait
– The same phenotype may be determined by more than one genotype
3. Law of segregation: Allele pairs separate (segregate) from each other during the production of gametes so that a sperm or egg carries only one allele for each gene
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Geneticists use the testcross to determine unknown genotypes
Testcross
• Mating between an individual of unknown genotype and a homozygous recessive individual
• Will show whether the unknown genotype includes a recessive allele
• Used by Mendel to confirm true-breeding genotypes
Copyright © 2009 Pearson Education, Inc.
B_
or
Two possibilities for the black dog:
Testcross:
Genotypes
Gametes
Offspring 1 black : 1 chocolate All black
Bb
bb
BB
Bb bb
B
b
Bb
b
b B
Dihybrid cross = following 2 traits (yellow and round = dominant)
Figure 3-7
Draw a Punnett square of a GgWw X GgWw dihybrid cross
• figure out gamete combinations for top and side of square
• fill in possible outcomes of fertilization of those gametes
Dihybrid cross Punnett square
Figure 3-7
Mendel’s 4th postulate
• Independent assortment
– During gamete formation, segregating pairs of unit factors (genes) assort independently of each other.*
* sometimes
How many gametes can be made
by F1 of dihybrid cross?
2 independently assorting genes, 2 alleles each
4 different types of gametes can be made
2 X 2 = 4
GW gW Gw gw
Trihybrid cross: 3 independent
monohybrid crosses
How many different kinds of gametes can be made
by the F1 population? Phenotypes?
Independent assortment creates
extensive genetic variation
• number of possible gametes, each with different chromosome compositions:
–2n, where n is the haploid number of chromosomes
– for humans (n=23), this is 8 million!
– fertilization is two gametes
• 8 million X 8 million – 64 X 1012 combinations
Question: How many different
types of gametes can be
formed by the genotype
DdEeFF ? a) 2
b) 3
c) 4
d) 6
e) 8
