Lecture 4 BIO 311D 2nd Edition Outline of Last Lecture I Mendelian Inheritance Outline of Current Lecture I Interactions gene loci trait II Linked genes III Sex linked traits Current Lecture I Interactions A One gene locus one trait in phenotype B Gene gene interactions 1 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 color C Gene environment interactions 1 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 problems 1 Cat genes not X linked B black fur unstriped b striped pattern H short hair h long hair A 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 2 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 recessivedominant trait 1 double recessive traits i e 9 AABB AABb AaBB 3 AAbb Aabb 3 aaBB aaBb 1 aabb E Trait determined by more than one gene locus 1 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 trait II III Linked genes A Different homologous pairs sort independently into gametes B 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 ab C 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 Sex Linked Traits A Y linked disorders Some 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 linked B 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 alleles
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