Lecture 11 Reading Chapter 14 1 Concepts Be able to explain the importance of inheritance to biology and evolution in particular In biology inheritance is very important as it can predict the genotypes of future offspring This is important when considering reproducing and for diagnosing individuals in reference to family history Evolutionarily inheritance is very important as we can track the inheritance patterns to learn which traits are favored and which traits eventually die out throughout evolution Be able to explain how Mendel did his experiments Mendel used pea plants to do his experiments probably for many reasons including they have many varieties have short generation time and have large numbers of offspring Mendel chose to track traits that had two clearly visible alternate forms and also made sure these traits that over many generations would produce the same variety as the parent plant means they were true breeding Mendel cross pollinated two different true breeding peas for example purple flowered crossed with white flowered This is called hybridization with the parent generation being P generation Their offspring were the F1 generation and allowing F1 to self pollinate cross pollinate leads to an F2 generation Mendel followed through to the F2 generation which allowed him to deduce the law of segregation and the law of independent assortment Be able to distinguish between Mendelian inheritance and blending inheritance The idea of blending inheritance says that traits are passed on as a blend of the two parents genes similar to how blue and yellow mix to make green This idea would mean that over time we would see a population uniform in traits which we have not seen and this idea also does not account for the reappearance of traits after they have skipped a generation Mendelian inheritance states that there are alternative versions of genes called alleles and an organism inherits two copies alleles of a gene one from each parent If the two alleles are different Mendelian inheritance says that the dominant allele determine s the organism s appearance and the recessive allele has no noticeable effect on the organism s appearance Mendel s model also includes the law of segregation as explained below Be able to explain the significance of the Law of Segregation The law of segregation states that the two alleles for a heritable character segregate or separate from one another during gamete formation and end up in different gametes This corresponds with the distribution of the genes of a pair of homologous chromosomes into the four different gametes at the end of meiosis Terms Gene a discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA or some RNA usually in viruses Allele any of the alternative versions of a gene that may produce distinguishable phenotypic effects Locus a specific place along the length of a chromosome where a given gene is located Heterozygote having two different alleles for a given gene Homozygote having two identical alleles for a given gene Genotype the genetic makeup or set of alleles of an organism Phenotype the observable physical and physiological traits of an organism which are determined by its genetic makeup Dominant an allele that is fully expressed in the phenotype of a heterozygote Recessive an allele whose phenotypic effect is not observed in a heterozygote F1 the first filial hybrid heterozygous offspring arising from a parental cross F2 the offspring resulting from interbreeding or self pollination of the hybrid F1 generation Monohybrid an organism that is heterozygous with respect to a single gene of interest all offspring from a cross between parents homozygous for different alleles are monohybrids Lecture 12 Reading 13 1 and 13 2 Concepts Be able to distinguish between the genetic consequences of sexual and asexual reproduction In asexual reproduction a single individual is the parent and passes copies of all its genes to its offspring without the fusion of gametes The genomes of the offspring are exact copies of the parent s genome gives rise to a clone or group of genetically identical individuals Genetic differences that arise are due to mutations In sexual reproduction two parents give rise to offspring that have a unique combination of genes inherited from the two parents The offspring vary genetically from their sibling and from their parents they are variations of a common theme of family resemblance but not exact replicas Be able to distinguish the cellular processes behind asexual mitosis and sexual meiosis reproduction Mitosis Takes place in somatic cells Occurs in sexual and asexual organisms Cell divides once Interphase occurs prior to each division DNA replication in interphase DNA replicates once for one division Prophase is short few hours Chromosomes divide once No synapsis Meiosis Takes place in germ cells Occurs only in sexually reproducing Cell divides twice Interphase is only before meiosis 1 DNA replication in interphase 1 DNA replicates once for two divisions Prophase is long few days Chromosomes divide once even though 2 cell divisions Synapsis of homologous chromosomes Chromatids do not exchange segments during prophase No crossing over or chiasmata Centromeres line up at same metaphase plate Daughter cells are identical to parent Centromeres divide in anaphase Similar chromosomes move towards opposite poles in anaphase Spindle fibers disappear and nucleoli reappear in telophase Cytokinesis follows every mitosis and produces two cells Chromosome number remains constant Take part in healing and repair and helps in multiplication of cells takes place during prophase Chromatids of homologous chromosomes exchange segments during prophase Chiasmata and crossing over are present Centromeres line up in two plates that are parallel to each other Daughter cells contain a mixture of maternal and paternal genes Centromeres divide in anaphase 2 Dissimilar chromosomes move towards opposite poles in anaphase 1 and 2 Spindle fibers do not disappear completely and nucleoli do not reappear in telophase Cytokinesis occurs after second division and results in four cells Chromosome number is reduced from the diploid to haploid Takes part in formation of gametes and maintenance of chromosome number in race multiplication of cells not involved Know that chromosomes exist as homologous pairs in diploids Be able to explain why meiosis produces haploid daughter cells from diploid parents Meiosis
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