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Bio 308 Lec 2

by: Kiara Reyes

Bio 308 Lec 2 Bio 308

Kiara Reyes
GPA 2.9

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Hello Everyone, here are Lecture 2 notes, they are color coded to make it easier to remember. Red- Important Info/Vocabs Green- Examples Purple-Keep in mind Blue-Side notes Hope these notes ...
M. Johns
Class Notes
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This 5 page Class Notes was uploaded by Kiara Reyes on Saturday September 3, 2016. The Class Notes belongs to Bio 308 at Northern Illinois University taught by M. Johns in Summer 2016. Since its upload, it has received 5 views. For similar materials see Genetics in Biology at Northern Illinois University.


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Date Created: 09/03/16
Lecture 2: Basic Mendelian Principles Mendel’s Big Idea Particulate Inheritance- The determinate of inherited traits are discrete units that are passed between generations unaltered, not blended together  Count large numbers of offsrpings. Offspring ratios observed are imperfect reflections of underlying simple ratios Ex: ¾ , ¼ , etc Experimental Organism  Mendel working with peas  Plants have sexual processes very similar to animals -Male gamete= sperm, pollen grain -Female gamete= egg, ovule  Pea plants have both sexes on the same plant, and they can be self- pollinated: pollen from one plant is used to fertilize ovules from the same plant Monohybrid Cross Monohybrid Cross: Only one trait is examined (possible genetic variation present)  1 seeing what happens when plants with different traits are crossed, then go through Mendel’s explanation  Purple Flowers vs White Flowers The original parental lines are true-breeding or pure-breeding. All offsprings within the lines give the same flower color for an arbitrary numbers of generation ~Frist Cross~  True-breeding purple x True-breeding White All offsrpings are purople. The parents line are the P generation; the offsprings are the F1 (first filial) generation  All the F1’s are purple regardless of which parent (father or mother) was purple and which was white -No Blending occurs, purple F1 plants look exactly like the purple parentals  Purple Dominant because it appears in the F1 hybrid  White Recessive because it doesn’t appear in the F1 hybrid ~Selfing the F1~  Self-pollinate the F1 plants to get F2 (second filial) generation  F2 appear in a ratio ¾ purple to ¼ white Note: White has re-appeared in the F2, unchanged despite having been in a purple F1 plant. Genes are not affected by the organism that carries them ~Selfing the F2~  Each F2 plant is selfed to produce a group of F3 offspring  F3 offspring of the white F2 are all white. The F2 white plants were all true-breeding -Some F2 purple have all purple F3 offspring. These F2 purple plants are true breeding -Other F2 purple give purple and white F3 in a ratio of ¾ Purple to ¼ White  F2 Behavior: They can be distinguished by the offspring they produce, but not by their physical appearance Explanation Diploid- 2 copies of each gene; 1 from the mother and 1 from the father  A gene can have many different versions called alleles P= Purple alleles (Big Purple) p= White alleles (small purple)  True breeding line are Homozygous for gene being examined: both copies of the gene are the same alleles -Initial Cross: one parent= PP, other parent= pp  Hybrid lines are Heterozygous: two copies of the gene being examined are different -Initial: Different= Pp  When diploid organisms reproduce, they make gametes (sperms and egg) that are haploid: they have only 1 copy of each gene. Copy goes into the gamete is a random process  The male and female gametes combined at random to form Zyotes, the first diploid cells of the next generations  These plants have the same phenotype (physical appearance) but different genotype (genetic constitution). Much of genetics is an attempt to determine the relationship between phenotypes and genotype ~F1 -> F2~  When the F1 (Pp) plant makes gametes, each gametes gets either a P allele or p allele. This happens randomly, so ½ of the gametes are P and ½ are p ~F2~  In summary: ¼ PP, ½ Pp, ¼ pp (White)  Since P is dominant, both PP and Pp plants are purple. ¾ phenotype is Purple and ¼ are White  Mendel found that this rule worked for all 7 of his traits, to within what he considered reasonable accuracy Law of Segregation Mendel’s 1 Law of Genetics: two members of a gene pair segregate randomly and equally into the gametes, which then combine at random to form that next generation  Backcross involves mating the F1 hybrid to one of the parental types. There are 2 possible backcrosses in the system: -Backcrossing to the Dominant parent (Pp x PP) Pp producing ½ P gametes and ½ p gametes where PP producing only P gametes. Thus the offspring being ½ PP and ½ Pp both being purple -Backcrossing to the Recessive parent (Pp x pp) all producing ½ P gametes and ½ p gametes where pp producing only p gametes. Thus the offspring being ½ Pp (purple) and ½ pp (white)  Test Cross is a mating between a heterozygous (unknown) to the recessive homozygous (tester). For monohybrid crosses, the test cross is the same as a backcross to the recessive parental type. The offspring of a test cross are in the same ratio as the gametes from the organism being tested: ½ P (purple) and ½ p (white) -Cross unknown to recessive parental offspring appear to be gene ratio as gametes from unknown Dihybrid Cross Dihybrid Cross examines 2 different genes -Yellow (Y) is Dominant to green (y) -Round (R) is Dominant to wrinkled (r) Initial Cross:  These combine to make F1 plants that are YyRr. Note: that neither parents has this phenotype ~F1 -> F2~  When the YyRr plant is mated, it makes 4 kinds of Gametes: ½ Y, ½ R, ½ y, ½ r  ¼ YR, ¼ yR, ¼ yr, ¼ Yr  The gametes combine randomly. The combinations are shown in a 16 cell Punnett square  This is the fundamental ratio for the F2 from dihybrid cross: 9/16 show both dominant traits, 3/16 show one dominant and the other recessive, 3/16 show one recessive and the other dominant, and 1/16 show both recessive traits  F2 dihybrid results are the combination of 2 monohybrid crosses Law of Independent Assortment nd Mendel’s 2 Law: For unlinked genes, alleles from each gene segregate into the gametes independently of one another  Some genes are linked, which means that they don’t segregate independently of each other and thus don’t give the 9:3:3:1 ratio of F2 offsrpings. Linked genes are close together on the same chromosome


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