Lecture 4 BIO 311D 2nd EditionOutline of Last Lecture I. Mendelian InheritanceOutline of Current Lecture I. Interactions: gene loci traitII. Linked genesIII. Sex-linked traitsCurrent LectureI. InteractionsA. One gene locus one trait in phenotypeB. Gene-gene interactions1. One gene locus w/ several traits- Marfan Syndrome, a dominant gene (but highly variable in expression) demonstrates pleiotropy (cardiovascular, skeletal, eyes) - PKU (lack of enzyme to build one amino acid from another) also demonstrates pleiotropy (affects pigment, neurotransmitters, etc.) - Pleiotropy: one gene locus multiple aspects of phenotype 2. Several traits for one gene locus - Quantitative traits: alleles at several gene loci have an additive effect on the same trait in the phenotype e.g. hair colorC. Gene- environment interactions1. The effect of environment on phenotype- Hydrangea color depends on shade, pH and aluminum content of the soil- Siamese cats and Himalayan rabbits depends on the temperature in the environment; their extremities are cooler than their internal body temperature; the dark fur is only expressed at low temperatures - To test this: you could pluck out all the fur on the rabbit and place an ice pack on top of the rabbit to see if the darker fur will be expressed D. Practice problems1. Cat genes (not X-linked): B=black fur, unstriped; b=striped pattern; H=short hair; h=long hairA black, short-haired dihybrid male cat mates with a striped, long-hair female cat.(a) What is the genotype of the female cat? bbhh(b) What are possible gametes from the male cat? Bh, BH, bH, bh(c) What fraction of their offspring is expected to be black? ½2. A dihybrid cross is a mating between two individuals each heterozygous for two different traits. What’s the genotype of the individuals? [Use letters A and B]A 9:3:3:1 ratio 9 double-dominant traits, 3 dominant-recessive trait, 3 recessive-dominant trait, 1 double-recessive traitsi.e. 9 (AABB, AABb, AaBB), 3 (AAbb, Aabb), 3 (aaBB, aaBb), 1 (aabb)E. Trait determined by more than one gene locus1. Skin color of corn snakes are primarily determined by 2 gene loci. One locus affects the synthesis of black pigment (rings) and one independently affects the synthesis of orange pigment (background color)2. Epitasis: genes at one locus affect or mask expression of genes at another locus two independent gene loci and a homozygous recessive genotype at one masked the appearance of the other traitII. Linked genesA. Different homologous pairs sort independently into gametesB. Alleles at different gene loci on the same chromosome are “linked”; they move together in meiosis i.e. AaBb individual with AB linked and ab linked only two types of gamete, type AB and abC. Linked genes tend to be inherited together because they are located near each other on the same chromosome. (Crossing over could unlink some linked genes)III. Sex-Linked TraitsA. Y-linked disordersSome Y-linked disorders, only on Y not X- SRY mutant gonadal dysgenesis, XY type- SHOXY short stature, mesomelic dysplasia- USP9Y Azoospermia- RPY Retinitis pigmentosa, Y-linkedB. X-linked traits- Many gene loci are located on the X chromosome and have no homologous region on the Y chromosome- Recessive, X-linked: color blindness, Fabry’s disease, hemophilia A,B, Lesch-Nyhan syndrome, Muscular dystrophy - Punnett Squares for X-linked traits must show X and Y as well as X-linked
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