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Genetics 300 Ch. 4

Sex Determination and Sex linked Characteristcs

QuestionAnswer
Sex balance each partner contributes 50% of genes, any genes making the rare sex partner better fit will be spread at greater %. eventually # of sex partners will equalize
Armadilidium Vulgar due to environment, bacteria infect convert males into females, causing unbalance, however, isopods have evolved mutation preventing bacterial feminization process
Human Chromosomes have 2 sex chromosomes X and Y. other 44 chromosomes are automsomes.
Sex determination in Humans determined by the presence of sex chroms and some genes on those chroms. Males are heterogametic in humans XY and females are homogametic XX
Monoecious organism bearing both male and female reproductive organs
Dioecious carry either male or female reproductive structures. Sex may be determined by chromosomes genetically or environmentally
ZZ - ZW system Male is ZZ homogametic, female is ZW heterogametic. found in birds, snakes and some amphibians
Primary Pseudoautosomal Region X and Y chroms are homologous only at this , essential for chromosome pairing in meiosis in the male.
Haploiddploidy insects with this - males are haploid (unfertilized eggs) and females are diploid (fertilized eggs)
Environemental Sex determination temp can influence which sex an organism develops into such as turtles, alligators, croc. ex. larvae settles as a female and attract other larvae which become male to mate with original female. they then switch sex and attract additional larvae etc..
Sex determination in Drosophilia X:A ratio ratio of 1.0 is female (XX:AA or XXY: AA) ratio less then .5 produce male phenotype. (XY :AA or XO: AA)
XXX : AA ratio of 1.5 phenotype metafemale which is never fully develops.
XX : AAA .67 ratio produces intersex
Turner Syndrome females, contain a single X (called XO) symptoms: short, low hairline, folds of skin around neck, sterile, normal intelligence
Klinefelters Syndrome Male, one or more Y and multiple Xs ex XXY. Symptoms: smaller testes, reduces facial hair, taller, sterile, normal intelligence
Poly-X Females Female, XXX no distinct differences except taller and thinner. most normal intelligence and fetile
SRY gene Sex determining region a region on the Y chrom is responsible for male phenotype.
Androgen insensitivity Syndrome XY Appear female externally. uterus, oviducts and ovaries absent and they contain testes. Due to defective androgen receptor - testosterone can not bind to it and female characteristics develop.
nondisjunction 10% occurrence, 2 X chroms fail to separate if fertilized by a Y a female will be produced. If fertilized by an X a XXX will be produced by die.
Indifferent Stage contain gonads, wolffian duct and mullerian duct
SRY present - indifferent stage Wolffian Duct and gonads transition to testes and vas deferens
SRY absent - indifferent stage Mullerian Duct and gonads transition to ovaries and uterine tube
XYY Karyotype "Super-males" usually tall produce high levels of testosterone, many are unaware of syndrome
Trisomy 3 copies of any chrom instead of 2. Trisomy 21 causes down syndrome Trisome 18 causes Edwards syndrome Risk increases with mothers age
dosage Compensation because of X linked genes, females have twice as much gene product as males. D.C. equalizes amount of protein produced by X linked genes . Doubles the activity of genes on the X chroms of males.
Barr bodies darkly stains structure an inactive X chromosome
Lyon hypothesis in each female, one of 2 X chromosomes become inactive (randomly) females are hemizygous at cellular levels - cells in females are not identical as one X is inactive an therefore code for different protein.
Created by: loveflyny
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