IB Topic 10 Genetics Notes.notebook
November 05, 2015
Topic 10 ­ Genetics and Evolution
10.1 ­ Meiosis
Essential Idea: Meiosis leads to independent assortment of chromosomes and unique composition of alleles in daughter cells.
Oct 13­5:35 PM
Oct 13­5:36 PM
Vocabulary Review
Review: Meiosis is a reduction division of the nucleus to form haploid gametes.
http://www.stolaf.edu/people/giannini/flashanimat/celldivision/meiosis.swf
gametes
heterozygous
homozygous
haploid
diploid
homologous chromosomes
sister chromatids
centromere
allele
chromosome
replicated
Oct 13­5:44 PM
Oct 13­5:38 PM
10.1 Learning Targets
Chromosomes replicate in interphase before meiosis
Crossing over is the exchange of DNA material between non­sister homologous chromosomes
Crossing over produces new combinations of alleles on the chromosomes of haploid cells
10.2 Inheritance
Essential idea: Genes may be linked or unlinked and are inherited accordingly
Chiasmata formation between non­sister chromatids can result in an exchange of alleles
Homologous chromosomes separate in meiosis I
Sister chromatids separate in meiosis II
Independent assortment of genes is due to the random orientation of pairs of homologous chromosomes in meiosis I
Oct 13­6:41 PM
Oct 21­5:34 PM
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IB Topic 10 Genetics Notes.notebook
Completion and analysis of Punnett squares for dihybrid traits
Review: Punnett squares for monohybrid traits
November 05, 2015
Dihybrid cross of unlinked genes
EX: Yellow pea color is dominant to green and smooth texture is dominant to wrinkled. Cross two heterozygous individuals.
Alleles
Parent phenotypes
Y = Parent genotypes
y = S =
In a certain plant yellow fruit is dominant to white fruit. A heterozygous plant with yellow fruit is crossed with a plant with white fruit. Determine the probable offspring. Possible gametes
s = Brown hair is dominant over light colored hair. Cross two light haired people. Oct 21­6:57 PM
Mendel stated that individual traits are inherited independently from other traits
Oct 22­7:53 PM
Oct 21­7:09 PM
Thomas Hunt Morgan discovered an exception to this rule of independent assortment
His experiments uncovered sex­
linkage of eye color in fruit flies (Drosophila)
Oct 22­8:00 PM
Warm­up: What are linked traits?
independent assortment
linked genes
sister chromatids
Homologous Gametes
chromosomes
crossing over
Oct 23­8:55 AM
Oct 30­1:25 PM
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IB Topic 10 Genetics Notes.notebook
Gene loci are said to be linked if on the same chromosome
Loci = the location of a gene on a chromosome
November 05, 2015
I can identify recombinants involving two linked genes
Normally we see dihybrid traits like this: AaBb ­ heterozygous or homozygous?
To show the same genes as linked:
A B
a
b
Rarely, linked genes that are located far apart on the same chromosome are exchanged during crossing over ­ this is called recombination
Linked genes are often inherited together
Oct 21­5:38 PM
Oct 30­1:24 PM
Chi Squared Practice
Normal teeth (T) are dominant to fangs (t)
Use of chi­squared test on data from dihybrid crosses
Check if your experimental results are what is expected from theoretical data
Smooth fur (F) is dominant to fuzzy (f) Mr. and Mrs. Mouse are both heterozygous for both traits (TtFf), then their offspring should follow the 9:3:3:1 ratio. So if they had 160 babies, what fraction would you expect for each type? all normal
fanged
fuzzy
fuzzy and fanged
Mr. and Mrs. Mouse have 80 normal, 33 fanged, 33 fuzzy, and 14 fuzzy fanged babies. Does this data support the double hybrid model of the data?
Phenotype
Observed number
Expected ratio
Expected number
(obs # ­ exp #) / exp #
Degrees of Freedom = Oct 30­1:45 PM
Nov 1­4:42 PM
Variation can be discrete or continuous
Warm­up: Take out your Chi­Square practice sheet ­ make sure you have the first problem done.
Phenotype Obs #
Exp Exp #
ratio
(obs #­Exp #)^2
Exp #
So far we have looked at traits with a definite form ­ this is discrete variation
The phenotypes of polygenic characteristics tend to show continuous variation
Polygenic traits, such as human height, may also be influenced by environmental factors
TEDTalk
Nov 3­7:41 AM
Nov 2­5:27 PM
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IB Topic 10 Genetics Notes.notebook
November 05, 2015
10.3 Gene Pools and Speciation
What do you recall about evolution?
Essential Idea: Gene pools change over time
Nov 2­7:33 PM
Nov 2­6:13 PM
A gene pool consists of all the genes and their different alleles, present in an interbreeding population.
Evolution requires that allele frequencies change with time in populations
Allele frequency: New combinations of alleles lead to new phenotypes that may be selected for or against by the environment.
Nov 2­7:21 PM
Evolution (selection) can be directional, stabilizing or disruptive
Nov 2­7:26 PM
Stabilizing Selection
EX: Human Birth Weight
Nov 2­7:32 PM
Nov 2­7:27 PM
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IB Topic 10 Genetics Notes.notebook
Directional Selection
EX: Beak shape and size in Medium Ground Finch
Nov 4­7:35 AM
Warm­up: Briefly describe the three types of selection we learned about yesterday.
Nov 4­6:58 PM
Isolation can be temporal, behavioral or geographic
Temporal Isolation
Behavioral Isolation
November 05, 2015
Disruptive Selection
EX: Grass growing near mines that contaminate soil
Nov 4­7:37 AM
For speciation to occur, populations must be reproductively isolated
Nov 4­7:44 AM
If populations are isolated, they may evolve into separate species ­ this is called speciation
Speciation can be gradual, or it may occur abruptly
Gradualism is the theory of speciation at a slow constant pace ­ differences build up over a long period of time
Geographic Isolation
http://www.hhmi.org/biointeractive/anole­lizards­example­speciation
Nov 4­6:24 PM
The theory of punctuated equilibrium states that species have long periods of stability until events disrupt (punctuate) the balance (equilibrium)
Nov 4­6:59 PM
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IB Topic 10 Genetics Notes.notebook
November 05, 2015
Nov 2­7:27 PM
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