BOLOGY 107 Lecture 23Outline of Last Lecture I. Geneticsa. Punnett square b. Laws of independent assortmentc. Probabilityd. Test crossOutline of Current Lecture II. Test Cross MisconceptionsIII. Extensions of Mendelian GeneticsIV. Pedigree AnalysisV. Chromosomal Basis of InheritanceCurrent LectureTest Cross Misconceptions1) Probability vs. outcomea) With a few number of progeny, it is possible to have a heterozygous parent and only progeny showing the dominant phenotypei) A greater number of progeny helps correct thisii) Once there is one progeny with the recessive phenotype, the parent is deemed heterozygous2) Dominance vs. predominancea) Frequency of a genotype in a population does not mean the allele is dominant or recessivei) Genetic dominance is determined by the biochemical process of the geneii) Predominance is decided by fitness, selection, and/or genetic drifExtensions of Mendelian Genetics3) Incomplete dominancea) Neither allele is completely dominanti) Heterozygote intermediate- blending?4) Codominance a) More than two alleles for a gene, more than one is dominanti) Example: blood types(1) A and B are both dominant genotypes over O, AB is a possible blood typeThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.5) Epistasis a) One gene affects the expression of anotheri) Example: Labrador retriever(1) One gene determines coat color (brown or black) while another determines if the color pigments are deposited in the hairs. If the pigments are not deposited, a white haired, or “yellow lab” is observed.6) Polygenetic inheritancea) Two or more genes affect the same phenotypei) Only happens with quantitative traits such as skin color or height where a spectrum occurs rather than this-or-that basis7) Environmental effectsa) Expression of a gene can be determined by environmental factorsi) Example: flower color(1) Some flowers of the same plant with the same genotype show a different phenotype for petal color in different pH environments8) Pleiotropya) One gene affecting multiple phenotypesi) Example: pea genetics(1) Petal color and color of seed casing are determined by the same geneb) Different from polygenici) One gene for many phenotypes vs. many genes for one phenotype9) Mosaicism and related phenomenaa) Rise from cells with different dominant genotypes in the same individuali) Causes:(1) Mutation afer initial cell division(2) Zygotes or embryos fuse(3) Chromosomal inactivation(a) Inactivating one of the copies of a chromosomePedigree Analysis10) Analysis of inheritance patterns based on extended family informationa) Draw pedigree based on phenotypes and, if any, know genotypesb) Deduce dominant vs. recessive traits and genotypes of individualsi) Used when test crosses cannot be preformedii) Dominant traits do not skip a generation11) Inherited disordersa) Recessive disordersi) No functional copy of a gene for a parent to show the phenotypeii) Heterozygotes show normal phenotype, but carry the affected geneiii) Example: Albinismb) Dominant disordersi) Only one affected gene is required to show the phenotype(1) Protein is created that actively creates the problemii) Can be no carriersiii) Rare in population(1) Affect reproductive fitness so not likely to be passed (excludes Huntington’s disease)(2) Homozygotes are severely affected, high fatality earlyc) Partial dominancei) Sickle-cell anemia(1) Shown by β-globin misshape(2) Heterozygotes only show signs in a low O2 environment(3) Resistant to malaria- explains retentionChromosomal Basis of Inheritanced) Genes are DNA sequences at loci (specific locations on chromosome)e) Explains violations to Mendel’s laws12) Fruit flya) Thomas Morgan discovered sex-link traits and crossing over of chromosomesb) Drosophilia modeli) Easy to breed, many progeny, sort generationii) Easy to induce and identify mutationsiii) Only 8 chromosomes(1) Three variant pairs and one sex determining pairiv) Have polytene chromosomes(1) Salivary glands make 1000+ copies of chromosomes(2) Self associate to form chain with visible banding(3) Easily view deletions and mutationsv) Wild-type, phenotype shown in the wild population, denoted with a +, like W+c) Parent generation- crossed Red-eyed female with a white-eyed malei) F1 generation- all had red eyesii) F2 generation- 3:1 ratio with red eyes, female had a 2:0 red-eye ratio, male had a 2:1 red-eye ratioiii) Morgan determined red-eye gene was on female chromosomed) Sex determinationi) XY- human, female is XX, male is XYii) XO- grasshoppers, female is XX, male is Xiii) ZW- chicken, female is ZW, male is ZZiv) Diploid vs. haploid, bees, female is diploid, male is haploid13) Human sex genesa) Male determines sex of the childi) Autosomal- exist in homologous pairs no matter the sexii) X chromosome- 800+ genes unrelated to sexiii) Y chromosome- 40-80 individual genes(1) Pseudoautosomal regions- pair wit X chromosome during meiosis(2) Two genes have homologous pairs on the X, but do not pair or cross over(3) A dozen genes are unique to Y chromosome, relate to male differentiationand developmentiv) X-inactivation(1) Only one X chromosome is active in mammals, random inactivation(2) Possibly used as dosage compensation of
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