GENETICS CH 7

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in animals, including humans, differentiation of sexes is evident via
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Terms in this set (44)
which chromosome determines malenessyTwo human abnormalities- Characterized by aberrant sexual development - Both syndromes result from nondisjunction ▪ Failure of X chromosomes to segregate during meiosisklinefelter and turner syndromeboth klinefelter and turner syndrome result fromnondisjunctionfailure of x chromosomes to segregate during meiosisnondisjunction47 chromosomes, xxy - Tall, long arms and legs - Large hands and feet - Internal ducts are male, rudimentary testes fail to produce sperm - Feminine development not suppressed - Enlarged breasts common, rounded hipsklinefelter syndrome45 chromosomes, x Phenotypically female - Female external genitalia and internal ducts - Ovaries are rudimentary - Underdeveloped breasts - Short stature - Cognitive impairmentturner syndrome47 chromosome, xxx Three X chromosomes - Normal set of autosomes - Results in female differentiation - Sometimes women are perfectly normal - Sometimes underdeveloped secondary sex characteristics occur ▪ Sterility and mental retardationtriplo-x47 chromosomes, ___ Only consistently shared characteristic —males are over 6 feet tall - Subnormal intelligence - Personality disordersxyytissues that will form from the gonadgonadal primordiaby the fifth week of gestation, a pair of ___ associated with each embryonic kidneygonadal ridgesgonadal phenotype is sexually indifferent primordial germ cells migrate to ___ridgesgonadal ridges can form either ovaries or testesbipotential gonadsdoes the y or x chromosome have more genesx- Present on both ends of Y chromosome - Share homology with regions on X chromosome - Synapse and recombine with X during meiosisPARspars stands for :pseudoautosomal regionsnonrecombining region of y chromosomemsyLocated adjacent to P A R of the short arm of Y chromosome - Controls male development - Encodes protein: Testis-determining factor (T D F)srytdftestis determining facotr- At 6-8 weeks of development, S R Y gene becomes active in X Y embryos - Encodes protein that triggers testes formationtdfmsy divide into what three regionsx transposed region x degenerative region ampliconic region15% of msyx transposed20% of msyx degenerative region30% of msyampliconic regionencodes proteins specific to development and function of testisampliconic- Genetic mechanism - Balances dose of X chromosome gene expression in males and females - Prevents excessive expression of X-linked genes in humans and other mammalsdosage compensationgenetic mechanism compensates for x dosage disparities inactive x chromosome is highly condensed random inactivation occurs in early embryonic developmentbarr bodiesExplains dosage compensation - Follows N − 1 rulex inactivation- Inactivation of X chromosome is random - Occurs in somatic cells at early stage of embryonic development - All descendant cells have same X-inactivation - Example: Calico cats and fur color/patternslyon hypothesissynthesis of ___ enzyme controlled by x-linked genes provides strong support of the lyon hypothesisG6PDc. elegans have two sexual phenotypesmales and hermaphroditeshermaprodite c. elegans have bothovaries and testesEggs are fertilized by stored sperm - Vast majority produced are hermaphrodites - Less than 1 percent of offspring are males - As adults, males can mate with hermaphrodites ▪ Produce half male and half hermaphrodite offspringself fertilizationControls sex determination in reptiles - Three different patterns of temperature sex determination in reptiles Crocodiles, most turtles, and some lizards: incubation temperature of eggs during embryonic development determines sextsdtsdtemperature-dependent sex determination