BIO 123 Chapter 9 Extra Credit
BIO 123 Chapter 9 Extra Credit BIOL 123
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This 3 page Class Notes was uploaded by Amber Logan on Monday November 23, 2015. The Class Notes belongs to BIOL 123 at University of New Mexico taught by Dr. Dorothy C. Scholl in Fall 2015. Since its upload, it has received 20 views. For similar materials see Biology for Health Related Sciences and Non-Majors in Biology at University of New Mexico.
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Date Created: 11/23/15
Ch 9 Extra Credit pg 213 De nitions 110 1 9995 10 Monohybrid cross breeding trial that looks at the offspring of 2 individuals that differ with respect to a particular gene pair Dihybrid cross breeding trial that looks at the offspring of 2 individuals that differ with respect to 2 particular gene pairs Homozygous when an individual has the same alleles for a given trait ie AA or aa Heterozygous when an individual has different alleles for a given trait ie Aa Phenotype an individual s physical expression of its genes Genotype an organism s entire DNA molecule that codes for genes Law of segregation states that you receive 2 alleles 1 from each parent which sort independently during gamete formation Independent assortment states that genes for different traits are inherited separately from each other because genes segregate during meiosis Law of dominance states that an allele can be dominant or recessive and that the dominant allele will always be expressed when it is present Mendelian inheritance Mendel s theory of gene inheritance which includes the concepts of the law of segregation the law of independent assortment and the law of dominance pg 215 Applications 13 1 If 2 genes were on the same chromosome they would not be inherited independently of each other because they would not be subject to the law of independent assortment Meiosis explains Mendelian inheritance because meiosis is the reason why there is genetic variability Mendelian inheritance explains the inheritance of genes and the probability of inheriting certain genes This genetic variability would not be possible without meiosis because the production and fusion of genetically different gametes is what leads to the inheritance and variability of genes Mendel s laws of inheritance do not apply to prokaryotes because prokaryotes do not reproduce sexually and therefore do not undergo meiosis Instead prokaryotes undergo binary ssion where they copy their DNA and divide producing 2 genetically identical daughter cells pg 222 De nitions 18 1 Codominance occurs when the phenotypic affect of both alleles is completely expressed in a heterozygote individual Incomplete dominance occurs when no single allele completely dominates the other instead the offspring will have an intermediate phenotype of the genes it inherits from its parents Hypercholesterolemia a condition that results in high cholesterol levels in an individual Pleiotropy where a single gene affects multiple traits Epistasis when the phenotypic effect of alleles of 1 gene depends on the presence of certain alleles for another Polygenic trait occurs when a trait is coded for by multiple alleles Phenotypic plasticity occurs when the environment affects how a gene is expressedregulated Extensions to Mendelian inheritance types of gene inheritance that do not follow the laws of Mendelian inheritance include codominance incomplete dominance pleiotropy epistasis polygenic traits and phenotypic plasticity pg 223 Understanding 14 6 10 l Mendelian inheritance is important because it is the foundation for modern genetics Mendel s work was the rst to demonstrate that there are alternative versions of genes called alleles and that these alleles are either dominant or recessive that alleles segregate and gametes fuse randomly during meiosis and that offspring inherit 1 copy of each gene from each parent It s possible to have more than 2 alleles in a population because a population of individuals can express more than 2 traits For example a population does not simply have brown and blueeyed people it can have greeneyed and hazeleyed people as well In an individual however there are only 2 alleles because an individual only inherits 2 alleles 1 allele from each parent lO A and B blood types are dominant because they will be phenotypically expressed by the production of cellmarker proteins when they are present On the other hand the 0 blood type is recessive because you will not produce any of these cellmarker proteins when it is expressed Both incomplete dominance and codominance are examples of nonMendelian genetics where both alleles of a gene will be expressed to an extent However incomplete dominance is when neither allele completely dominates the other resulting in an intermediate phenotype On the other hand codominance occurs when both alleles will be completely expressed like in the case of AB blood type where both types of cell marker proteins are produced in an individual with this allelic combination Hypercholesterolemia is an example of incomplete dominance because the heterozygous allele combination will result in only half of the LDL receptors required for normal functioning If hypercholesterolemia was an example of codominance then all of the required LDL receptors would be produced because codominace is the complete expression of both alleles Pleiotropy is when 1 gene affects multiple traits like with the gene that controls melanin production which affects the coloring of the skin eyes hair etc A multigenic trait on the other hand is when l trait is coded for by multiple alleles like in the case of skin color The 0CA2 gene exhibits both pleiotropy and epistasis because it affects the expression of several traits in melanin production for determining eye color making it pleiotropic and is in uenced by the activity of the HERC2 gene making it epistatic Eye color exhibits epistatic inheritance because blue eyes are the result of a mutation in the HERC2 gene which affects the expression of the 0CA2 gene which affects melanin production in determining eye color Without this epistatic relationship between the HERC2 and 0CA2 genes a mutation in the HERC2 gene would not have caused the 0CA2 gene to express the melanin production that resulted in blue eyes Skin color exhibits both phenotypic plasticity and multigenic inheritance because the amount of sunlight that an individual is exposed to will in uence the amount of melanin being produced and therefore affect skin color illustrating phenotypic plasticity also skin color is in uenced by multiple genes making it multigenic