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This document covers various topics related to genetics including Mendelian genetics, pedigree analysis, autosomal recessive and dominant disorders, multiple gene inheritance, sex determination systems, prenatal genetics, chromosomal aberrations, and more. It discusses the experiments and conclusions of Gregor Mendel, the use of Pisum sativum as a model organism, and the principles of dominance and random segregation of alleles. It also covers various genetic disorders such as phenylketonuria and achondroplasia, and the different sex determination systems in different species. The document also explains prenatal genetic testing and chromosomal aberrations that can occur spontaneously or be induced by certain chemicals or radiation.
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Genetics Exam 2 Gene = trait, allele = code Mendel
Same genotype, expressed differently Epistasis A product of one gene influences the expression of another gene Modification of dihybrid cross 9: 3: 3: 1 ratio Dominant series C series / rabbits C+ = full color Cch^ = chinchilla Ch^ = himalayan C = albino X – lined Genes Factor VIII Alleles Xh^ = hemophilia XH^ = normal Generally, when looking at a pedigree, when only men are affected it is x – linked “criss - cross” inheritance Morgan’s Experiment on X – Linkage Fruit fly nomenclature Allele key W+ = wildtype red allele W= mutant white allele Wingless mutant (Wg allele) (wildtype is Wg+) Dosage Compensation (mammals) Having too much or too little genetic info can affect how tissues develop Bar Bodies – one X active in every cell X chromosome inheritance Very early on in embryonic development, one X becomes inactive Inactive X becomes very condensed Epigenetic inheritance Cells “remember” which X chromosome it had active and tells its progeny which X to use as the embryo develops Bar Body Every mammal cell has only one activated X XX – one inactivated (one Bar Body) XXX – two inactivated (two Bar Bodies) Calicos < Orange male = XoY Black male = XBY Black female = XBXB
Orange female = XoXo Calico female = XBXo Y – linked genes Not technically homologous to X chromosome, but do share some genes Pseudo autosomal region of X and Y Small region of code that X and Y both have Mammalian Sex Structure Determination (Y system) 7 weeks gestation (human) embryo has bipotential gonads (have both male + female tissue) Y chromosome signals for male sex tissue development SRY gene Encodes TDF Sex determining region of Y encodes Testes Determining Factor = a transcription factor (protein) Y chromosome -> SRY -> TDF -> development of testes -> testosterone hormone -> sperm ducts, penis, brain “sensitization” If no signal, typical female structures develop Mutation in SRY: 46, XY Gonadal Dysgenesis No TDF – gonadal tissue is minimal Develop uterus, vagina, oviducts Hormone therapy at puberty 46, XX Testicular Difference of Sex Development Crossing over of SRY gene to X chromosome Develop male characteristics No sperm development genes Sperm development is on Y chromosome Chimerism 46, XX / 46, XY Two early embryos fuse into a single embryo Effects on development variable Tetra gametic 4 gametes involved that fuse into one embryo Other Sex Determination Systems Drosophila Ratio of X to sets of autosomes Y not related to sex XX / 2 sets of autosomes = 2/2 = 1 (female) XY / 2 sets of autosomes = ½ = 0.5 (male) ZW System (birds) Females = ZW Males = ZZ Some reptiles also use the ZW system (Ex. Kimono dragons)
o 45, X (10)/ 46, XX (90) Mosaic Down o 45, 21+ / 46 Ploidy = sets of chromosomes Diploid – many animals, fungi, + plants Monoploid – sterile insects (ex. Worker bees) Tetra, hexa, octoploid – common in plants o Polyploid Toads are tetraploid Chromosomal Aberration (chromosomal “mistake”) Spontaneous Induced o X – rays, certain chemicals Can occur in gamete, embryo, or somatic cell in adults