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Chapter 11

Chapter 11 - Mendel, Genes, and Inheritance.docx

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BIOL 204
Dr.Roland Treu

CHAPTER 11 MENDEL GENES AND INHERITANCESickle cell diseaseo2 copies of gene one from each parent that codes for altered subunit of hemoglobinoO2 supplies lowaltered hemoglobin differs from normal protein by single AA forms long fibrous crystallike structures that push RBC into sickle shapeoSickled RBC too elongatedinflexible to pass t capillariesaar cells block capillaries and surrounding tissue starved for oxygen and saturated w metabolic wastes111 The Beginnings of Genetics Mendels Garden PeasBefore believed blending theory of inheritancehereditary traits blend evenly in offspring t mixing of parents bloodIn his work w peas Mendel studied heritable characteristics characters such as flower colour or seed shapeoVariation in char such as purplewhite flower is called a traitMendel established that characters are passed to offspring in form of discrete hereditary factorsgenes NMendel observed parental traits appear unchanged in offspring whereas others disappear in one gen to reappear in nexthe unknowingly obsvd result of segregation of chromos to gametes in meiosis111a Mendel Chose TrueBreeding Garden Peas for His ExperimentsMale gametes are sperm nuclei contained in pollen in anthers of flowerFemale gametes are egg cells produced in carpel of flowersNormally pea plants selffertilize aka selfpollinateoSperm nuclei in pollen produced by anthers fertilize egg cells housed in carpel of same flowerExpmt prevented selffert by cutting off anthers TF pollen to fertilize must come from diff plantcrosspollinationChose pea plants known to be truebreeding aka purebreedingthat is when selffertilized pass traits wo change from one generation to the next111b Mendel First Worked with SingleCharacter CrossesP generation Pparental plants cross and produce seeds tht dev into F generation Ffilial1Placed pollen of purple flower and placed it in stigma of white flowerF seeds purple flowers as if trait for white flowers disappeared no evidence of blending1F purpleflowered selffertilizedF generation aar 31 ratio of PW12Repeated w other coloursBoth traits present in F gen and w definite predictable proportion 2111c Mendels SingleCharacter Crosses Led Him to Propose the Principle of SegregationH adult plants carry a pair of factors that govern the inheritance of each character1oFor each character an organism inherits one factor from each parentMendels factorsgenes and diff versions of genes that produce diff traits of a character are alleles of the gene H if an indvs pair of genes consists of different alleles one allele is dominant over the other2oAssumes that one allele is dominant and the other recessiveH pairs of alleles that control a character segregate as gametes are formed half the gametes carry one 3allele and the other half carry the other alleleMendels Principle of SegregationoFusion of haploid MF gameteszygote nucleus which receives one allele for character from M gamete and one for same character from F gamete reuniting the pairsIndv w PP or pp combo of alleleshomozygote and is said to be homozygous for P alleleIndv w Pp combo of allelesheterozygote and is said to be heterozygous for the traitF heterozygote produced from cross tht involves single charactermonohybrid monoone and hybrid1offspring of parents w diff traitsoPp x Ppmonohybrid crossMendels hypotheses explain how indvs may differ genetically but still look the sameoEx PP and Ppplants although genetically diff both have purple flowersoGenotypegenetic constitution of organismoPhenotypeoutward appearance oHence PP and Pp produce same purpleflower phenotype111d Mendel Could Predict Both Classes and Proportions of Offspring from His HypothesesProbabilitypossibility that an outcome will occur if it is matter of chanceThe Product Rule in ProbabilityWhen 2more events are independent probability that they will both occur calculated using product ruleindv probabilities are multipliedoEx sex of one child has no effect on sex of next childrenstndrdoProbability of 1 child being a girl is 12 and probability of 23 child being a girl is 1212oTF 12 x 12 x 1218 chance that all three children will be girlsThe Sum Rule in ProbabilitySum ruleseveral diff events all give same outcomeoEx probability of Pp offspringstndstndoPp x Pp can produce Pp in 2 ways P of 1 parentp of 2 parents OR p of 1 parentP of 2 parentoTF 141412 chance that Pp x Pp will produce Pp offspringProbability of Mendels CrossesPunnett square method dtrmns genotypes of offspring and their expected proportions
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