BI111 Study Guide - Comprehensive Final Exam Guide - Speciation, Phenotype, Natural Selection

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20 Nov 2018
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BI111 – L1
Genetics Review (Continued)
Felis Catus: (Cats)
2 alleles
oL (dominant, short hair)
ol (recessive, long hair)
Manx cats
oMutation originated in populations of cats on the Isle of Mann
oTailless mutation is dominant and homozygous lethal
“All white” fur controlled by “white masking” gene
o2 alleles:
W (dominant, all white hair)
w (recessive, colored hair possible)
oW allele has “epistatic”(effects different showing of a phenotype) and “pleiotropic”
(multiple effects in different systems) properties
Another pleiotropic effect on phenotype: sickle cell anemia
The dense pigment gene, D codes for melanophilin, a protein involved in the transportation and
deposition of pigment into a growing hair
o2 alleles:
D - functional melanophilin
d - less-functional melanophilin (dilutes hair colour)
Not all genes are 100% dominant or recessive
oIncomplete or partial dominance:
s (recessive) - homozygous has no white hair (ss)
S (incomplete dominance) - some white hair (sS)
Sex Chromosomes:
The “red” gene, O, located on the X-chromosome determines whether or not there will be red
variation in fur colour
o2 alleles:
O - production of phaeomelanin (red)
o - production of eumelanin (browns and blacks)
oWhat are the possible genotypes?
oPhenotypes?
Homogametic and Heterogametic sex chromosomes
oSex chromosomes often determine sex
oX and Y chromosomes in some species
oXX: female XY: male
oW and Z chromosomes in others (birds)
oWZ: female ZZ: male
Consequences of Sex Chromosomes:
Hetergametic sex has only one copy of each type of sex chromosome
oOne copy of a recessive allele results in expression of the trait
Homogametic sex have 2 copies of sex chromosomes
oHeterozygote: recessive allele hidden (carrier)
oHomozygote recessive: trait expressed
Dosage compensation
oRegulatory process that ensures that males and females have = amounts of X-
chromosomes gene products
oIn female mammals, inactivation of one X chromosome makes the dosage of X-linked
genes the same as males
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oRandom inactivation of either X chromosome during embryonic development
oSame X chromosome inactivated in all descendents of a cell
oIs this the only way to compensate for differences between the sexes in the number of
sex chromosomes?
Ex. fruit flies → increase rate of transcription and translation instead of
inactivating an X chromosome
Mutations:
Deletion - broken segment lost from chromosome
Duplication - broken segment inserted into homologous chromosome
Translocation - broken segment attached to non-homologous chromosome
Inversion - broken segment reattached in reverse orientation
Nondisjunction - failure of homologous pair separation in meiosis I, failure of chromatid
separation during meiosis II
Changes in Chromosome Numbers:
Euploids - normal number of chromosomes
Aneuploids - extra or missing chromosomes
Polyploids - extra sets of chromosomes (triploids, tetraploids), spindle fails during meiosis
Terms:
Phenotype - outward appearance
Genotype - type of alleles, genetic constitution of an organism
Lecture 3: Jan. 9, 2017
Population Genetics: Heritable Variation in Populations
The Hardy-Weinberg Principle:
Mathematical model that predicts genotype frequencies: used as a null/control against which
observed data can be compared
All models have assumptions:
1. Random mating
2. Large population size
3. No migration/emigration/mutation
4. No selection
Is our population at H-W “equilibrium”?
First we need to calculate the frequency of each allele
oLet p=freq. Of b allele
oLet q=freq. Of B allele
Refer to calculations in notebook
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