BIO Chapter 11 Notes
BIO Chapter 11 Notes BIO 101
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This 5 page Class Notes was uploaded by Natalie Berry on Sunday October 16, 2016. The Class Notes belongs to BIO 101 at Missouri State University taught by Kyoungtae Kim in Fall 2016. Since its upload, it has received 3 views. For similar materials see Biology in Your World in Science at Missouri State University.
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Date Created: 10/16/16
Key: Light Blue = main idea Purple = important parts of the main idea Green = examples Orange = key terms Pink = the definition of the key term Red = especially important Chapter 11: Mendel and his discoveries Mendel’s main inferences were correct: 1. The basic units of genetics are material elements 2. The elements come in pairs 3. These elements (genes) can retain their character throughout many generations 4. The gene pairs separate during the formation of gametes Experimental subjects: Pisum Sativum Pisum sativum = pea plant he used Peas in a pod = seed in the plant’s ovary Each begins as an unfertilized egg until sperm bearing pollen lands on the plant’s stigma and set fertilization in motion Pisum plants can self-pollinate They can also cross pollinate; one plant can pollinate the other Mendel did cross pollination with tweezer and paintbrushes Mendel could control certain attributes in the pea plants each of the characters came in two varieties Such character variations are called traits He labeled each variation as dominant or recessive Phenotype and genotype Traits represent phenotype Phenotype: a physiological feature, bodily characteristic, or behavior of an organisms Ex. In our pea plant, phenotype means visible characteristics Purple flowers are one, white another Yellow seeds vs green seeds Phenotype is determined by an organisms underlying genotype Genotype: and organism’s genetic make up Starting the Experiments: Yellow and Green peas Mendel began by making sure his plants “bred true” or purebreds basically Parental F1 and F2 generations Parental generation (p gen): the generation that begins an experimental cross between organisms The offspring of the p gen are called the first filial generation F1: short hand for first filial generation Fx: any succeeding generation nd Ex. F2 for 2 generation, F3 for third and so on Mendel took plants that bred true for yellow seeds and plants that bred true for green seeds for his p gen Then he took pollen from one variety of the plants and fertilized the other variety The plant fertilized this way produced their own seeds – all of them were yellow (F1 generation) Key: Light Blue = main idea Purple = important parts of the main idea Green = examples Orange = key terms Pink = the definition of the key term Red = especially important This indicated yellow was dominate while green was recessive He took his F1 seeds and let plants grow from them He let them self-pollinate instead of cross pollinating them From self-pollination in the F2 generation, he got 6,022 yellow seeds and 2,001 green Important to note Green seeds disappeared in F1 but reappeared in F2 From these results, he saw that inheritance for his peas was not a matter of blending their characteristics Ex. They were either purple or white; there was no lavender from blending the two In other words, no intermediate phenotypes This was contrary to the belief at the time. People though traits blended to make a homogenous third entity It was also apparent that plats could retain potential for recessive phenotypes even it skips a generation He also hypothesized these elements (genes) came in pairs since his phenotypes did Its accurate to think of matched pairs of genes as alternative forms of a single gene Allele: one alternative for of a single gene Another generation After he saw the recessive genes reappear, Mendel decided to extend his breeding He took a set of all yellow F2 seeds, planted them, and let those self-pollinate Then he looked at the color of the F3 seeds in the pods of the F2 plants. Out of 519 plants, 166 were only yellow and 353 had a mix of both But when he took a set of green F2 plants and planted them, all of them were green He concluded that there were two types of yellow plants: pure and mixed Pure yellow has nothing but yellow alleles Mixed yellow has one yellow and one green allele Green seeds had nothing but green alleles It was a lot of info, let’s review the experiment by generation F1 generation To start let’s refer to alleles in capital and lowercase letters Dominate = capital, recessive = lowercase Ex. A pure yellow plant would be YY because yellow is dominate Pure green would be yy because green is recessive A mix would be Yy Let’s say for the purpose of this breakdown the female gametes are supplied by a plant that is YY while male gametes come from a plant that is yy Remember in meiosis homologous chromosomes separate Key: Light Blue = main idea Purple = important parts of the main idea Green = examples Orange = key terms Pink = the definition of the key term Red = especially important This happens in the pea plants, meaning that each plant will contribute one member of its gene pair to its gametes The female will give a Y gamete and the male a y gamete When the gametes fuse in fertilization the result is a Yy hybrid in F1 Note because Y is dominant, all seeds in F1’s offspring will have a yellow phenotype even though every see has a mixed genotype (Yy) It only takes one Y for a seed to be yellow by 2 y (yy) for it to be green F2 generation The starting point here is the F1 seeds that are all mixed Yy Then meiosis happens which results in a separation of cells Now half the gametes contain Y and the other half contain y This cross can now give us back the green phenotype on a 1:3 proportion Note there are now twice as many mixed genotype seeds (Yy) than either pure seeds (YY and yy) F3 generation (check out figure 11.6 in the book for visual representation of the genes) Remember when Mendel planted and self-fertilized his yellow F2 seeds he got 519 plants where 166 were just yellow Now you know why: they were not only phenotypically yellow, they were “pure” yellow in genotype (YY) The mixed plants were genotype Yy Finally when he planted and self-fertilized green F2 plants they were all green because their genotype was yy The law of segregation For inheritance to work Mendel noticed that even though plant cells may have two copies (alleles) of a gene relative to a given character, those copies must separate in gamete formation Law of segregation: differing characters in organisms result from two genetic elements (alleles) that separate in gamete formation such that each gamete only gets one of the 2 alleles The physical basis for this is the separation of homologous chromosomes during meiosis Homozygous and heterozygous conditions There is scientific terminology for genotypically pure and mixed organisms Homozygous: an organism that has two identical alleles of a gene for a given characteristic Ex. YY or yy Heterozygous: an organism that has differing alleles for a given characteristic Ex. Yy You’ll see homozygous combined with the terms dominate and recessive Ex. YY plant = homozygous dominant, yy plant = homozygous recessive Dominant: a term used to designate an allele that is expressed in the heterozygous condition Key: Light Blue = main idea Purple = important parts of the main idea Green = examples Orange = key terms Pink = the definition of the key term Red = especially important Ex. In a heterozygous pea plant (Yy) the Y is expressed meaning it is dominate over y Recessive: a term used to designate an allele that is not expressed in heterozygous condition Ex. the green allele (y) is recessive because it its not expressed when it exists in heterozygous condition with the yellow allele (Yy) Crosses involving two characters Monohybrid: an experimental cross in which organisms are tested for differences in one character Mendel wanted to what happens when you breed for two characteristics Dihybrid cross: an experimental cross in which the plants used differ in two of their characteristics His question was: Do given characters tend together or separately? If you get one characteristic passed on to a plant, do you get the other? One dihybrid cross he performed involved the seed color (yellow and green) and their shape (smooth or wrinkled) Yellow is dominant to green, and smooth is dominant to wrinkled For seed shape alleles we’ll use S and s In F1 gen all seeds were smooth and yellow When F1 seeds were self-pollinated, the F2 phenotypes were 315 smooth yellow, 108 smooth green, 101 wrinkled yellow, and 32 wrinkled green These numbers are a 9:3:3:1 ratio The law of independent assortment This outcome is only possible if Mendel was right: characteristics were being transmitted independently from each other in heredity Law of independent assortment: states that during gamete formation, gene pairs assort independently from one another Remember that in meiosis pairs of homologous chromosomes assort independently from one another at the metaphase plate Mendel’s genes for seed color exist on the plants chromosome 1, see shape on 7 Because they are separate, they assort independently at the metaphase plate meaning they are passed on independently to future generations Reaction to Mendel’s ideas Literally no one cared about all his research until 16 years after he died. The end . Incomplete dominance and codominance Not all Mendel’s rules applied to all instances of inheritance Ex. Even though there were only a choice of purple and white flowers in his pea plants, flowers like the red and white snapdragon can make pink This still isn’t “blending” Incomplete dominance Think about what genes do: they contain info regarding the production of proteins Regarding colors, proteins can bring about the formation of pigments Key: Light Blue = main idea Purple = important parts of the main idea Green = examples Orange = key terms Pink = the definition of the key term Red = especially important This is the case with snapdragons They have a gene for color and one of the alleles of this gene brings out red, the second brings out no pigment (white), it’s not functional Two red alleles make red, while one red allele only makes enough pigment to make pink So neither red or white is completely dominant Incomplete dominance: a genetic condition where the heterozygote phenotype is intermediate between either of the homozygote phenotype Codominance When people talk blood type, they mean types of “glycolipids” that extend from the surface of red blood cells These surface extensions come in variations like A and B Blood types are completely under genetic control with a single gene on chromosome 9 determining your blood type (A, B, AB, or O) There are two copies of this gene because there are two of 9 from the maternal and paternal Two alleles for A= A type Two alleles for B = B type One for both = AB type A person with two alleles that code for neither A or B = O Codominance: a condition in which two alleles of a given gene have different phenotypic effects with both effects manifesting in organisms that are heterozygous for the gene