CH11-TheBasicPrinciplesofHereditypart-01 - CHAPTER 11:...

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Unformatted text preview: CHAPTER 11: GENETICS - BASIC 3.3—: . PRINCIPLES of HEREDITV 7 Gregor Mendel: the “Father of Genetics” -Mende| studied inheritance by breeding pea plants ~Character — attribute (eg. flower color, height, shape) -Trait — version of a character (29 purple, tall, smooth) -Anther — male part of flower m> pollen °Stigma — female part of flower m> ovules -Pea plants naturally self-pollinate (self fertilize) ~Hybrid offspring are produced by cross fertilization - . remove anthers and transfer pollen from another plant SEVEN CHARACTERS STUDIED in MENDEL'S EXPERIMENTS l ffieum "m.- ;‘m. m :fi-Fam. "m:.;-m. m ffieum "m.- :- Each character varies in an “either-or” fashion (dominant is boldface) — Figure 11-2 p 236 Flower color Seed color Pod color -_ Purple 1 V" . .I, __ A r .»"-\-I (33?" 0 Yellow Green Se ed 5 hope 00 Smooth Wrinkied White Tail Green Stern length Short Pod shape 'i \ Inflated Pinched Flower position Axial Terminal MONOHYBRID CROSS A monohybrid CPOSS sTudies The inheriTance of a single characTer - P generaTion are The parenTaI planTs being crossed (= maTed) °True-br‘eeding planTs self-pollinaTe To produce offspring wiTh The same visible TraiT(s) P generaTion (True-breedingfl Tall plan! Shon plant I EEI F1 = 13T generaTion of offspringj ShorT planTs “disappear” in F1 generaTion - DominanT — TraiT seen in F1 generaTion (Tall) - Recessive — TraiT hidden in F1 generaTion (shorT) All [all plants E i Self-pollinaTe or cross F1 F2 : 2nd generaTion of offspring ‘ I,4 ShorT planTs "reappear" in F;2 generaTion — “shorT” herediTary facTor masked by Tall buT noT IosT in F1 TABLE 11-1 Mendel's Model of Inheritance 1. Alternative forms of a "factor" {what we now call a gene]I account for variations in inherited traits. Although Mendel only observed two forms {what we now call alleles} for each factor he studied, we now know that many genes have more than two alleles. 2. Inherited traits pass from parents to offspring as unmodified factors. Mendel did not observe offspring of intermediate appearance, as a hypothesis of blending inheritance would have predicted. Excep- tions to this concept are known today. 3. Each individual has two sets of factors. one of each pair inher- ited from the mother and one from the father. It does not matter which parent contributes which set of factors. 4. The paired factors separate during the formation of reproduc- tive cells {the principle of segregation). Because of meiosis, which was discovered after Mendel's time, each parent passes one set of factors to each offspring. 5. Factors may be expressed or hidden in a given generation. but they are never lost. For example. factors not expressed in the F1 generation reappear in some F2 individuals. 6. Each factor is passed to the next generation independently from all other factors I{the principle of independent assortment}. Research since Mendei's time has revealed that there are exceptions to this principle. Figure 11-5 p 239 HOMOLOGOUS C'SOMES, GENE LOCI and THEIR ALLELES A gamete has one set of chromosomes, the n number. It carries one chromosome of each homologous pair. A given gamete can only have one gene of any particular pair of alleles. When the gametes fuse, the resulting zygote is diploid (2n) and has homologous pairs of chromosomes. For purposes of illustration, these are shown physically paired. (a) One member of each pair of homologous chromosomes is of maternal origin (red), and the other is paternal (blue). 1) Gene: segment of DNA on a chromosome which contains the instructions for producing a protein; MEdiploid cells contains two copies of each gene” 2) Locus - location of a particular gene on a chromosome - Nonhomologous chromosomes Gene loci -I (b) These chromosomes are nonhomologous. Each chromosome is made up of hundreds or thousands of genes. A locus is the specific place on a chromosome where a gene is located. - Homologous c’somes - Alleles are alternative versions of the same gene . Apairot . I II ilk. These genes are not allelic to one another (c) These chromosomes are homo- logous. Alleles are members of a gene pair that occupy corresponding loo on homologous chromosomes. 0 A Dominant allele is expressed even when only one copy is present ' A Recessive allele is only expressed when two copies are present . . Alleles controlling fur color: Black Brown \- I/ I l Alleles controlling turlength: /._ong Short ' s S ' ld) Alleles govern the some character but do not necessarily contain the same information. 4) Genotype: combination of alleles carried by an organism (eg. BB, bb, Bb, 55, 55, 5s, BBSS, Bst, bbss, bst, etc.) ' Homozygous: having identical alleles at a locus eg. homozygous dominant or homozygous recessive ' Heterozygous: having different alleles at a locus - dominant trait is displayed 5) Phenotype = morphological, physiological, or behavioral traits displayed by an organism (2.3. tall, black fur, etc.) ...
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