BOLOGY 107 Lecture 23 Outline of Last Lecture I Genetics a Punnett square b Laws of independent assortment c Probability d Test cross Outline of Current Lecture II III IV V Test Cross Misconceptions Extensions of Mendelian Genetics Pedigree Analysis Chromosomal Basis of Inheritance Current Lecture Test Cross Misconceptions 1 Probability vs outcome a With a few number of progeny it is possible to have a heterozygous parent and only progeny showing the dominant phenotype i A greater number of progeny helps correct this ii Once there is one progeny with the recessive phenotype the parent is deemed heterozygous 2 Dominance vs predominance a Frequency of a genotype in a population does not mean the allele is dominant or recessive i Genetic dominance is determined by the biochemical process of the gene ii Predominance is decided by fitness selection and or genetic drif Extensions of Mendelian Genetics 3 Incomplete dominance a Neither allele is completely dominant i Heterozygote intermediate blending 4 Codominance a More than two alleles for a gene more than one is dominant i Example blood types 1 A and B are both dominant genotypes over O AB is a possible blood type These 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 another i 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 inheritance a Two or more genes affect the same phenotype i Only happens with quantitative traits such as skin color or height where a spectrum occurs rather than this or that basis 7 Environmental effects a Expression of a gene can be determined by environmental factors i Example flower color 1 Some flowers of the same plant with the same genotype show a different phenotype for petal color in different pH environments 8 Pleiotropy a One gene affecting multiple phenotypes i Example pea genetics 1 Petal color and color of seed casing are determined by the same gene b Different from polygenic i One gene for many phenotypes vs many genes for one phenotype 9 Mosaicism and related phenomena a Rise from cells with different dominant genotypes in the same individual i Causes 1 Mutation afer initial cell division 2 Zygotes or embryos fuse 3 Chromosomal inactivation a Inactivating one of the copies of a chromosome Pedigree Analysis 10 Analysis of inheritance patterns based on extended family information a Draw pedigree based on phenotypes and if any know genotypes b Deduce dominant vs recessive traits and genotypes of individuals i Used when test crosses cannot be preformed ii Dominant traits do not skip a generation 11 Inherited disorders a Recessive disorders i No functional copy of a gene for a parent to show the phenotype ii Heterozygotes show normal phenotype but carry the affected gene iii Example Albinism b Dominant disorders i Only one affected gene is required to show the phenotype 1 Protein is created that actively creates the problem ii Can be no carriers iii Rare in population 1 Affect reproductive fitness so not likely to be passed excludes Huntington s disease 2 Homozygotes are severely affected high fatality early c Partial dominance i Sickle cell anemia 1 Shown by globin misshape 2 Heterozygotes only show signs in a low O2 environment 3 Resistant to malaria explains retention Chromosomal Basis of Inheritance d Genes are DNA sequences at loci specific locations on chromosome e Explains violations to Mendel s laws 12 Fruit fly a Thomas Morgan discovered sex link traits and crossing over of chromosomes b Drosophilia model i Easy to breed many progeny sort generation ii Easy to induce and identify mutations iii Only 8 chromosomes 1 Three variant pairs and one sex determining pair iv 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 mutations v Wild type phenotype shown in the wild population denoted with a like W c Parent generation crossed Red eyed female with a white eyed male i F1 generation all had red eyes ii F2 generation 3 1 ratio with red eyes female had a 2 0 red eye ratio male had a 2 1 red eye ratio iii Morgan determined red eye gene was on female chromosome d Sex determination i XY human female is XX male is XY ii XO grasshoppers female is XX male is X iii ZW chicken female is ZW male is ZZ iv Diploid vs haploid bees female is diploid male is haploid 13 Human sex genes a Male determines sex of the child i Autosomal exist in homologous pairs no matter the sex ii X chromosome 800 genes unrelated to sex iii 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 differentiation and development iv X inactivation 1 Only one X chromosome is active in mammals random inactivation 2 Possibly used as dosage compensation of genes
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