2014 CHROMOSOMAL SEX DETERMINATION Výukový materiál MB Tvůrce: Mgr. Šárka Vopěnková Tvůrce anglické verze: ThMgr. Ing. Jiří Foller Projekt: S anglickým jazykem do dalších předmětů Registrační číslo: CZ.1.07/1.1.36/ Tento projekt je spolufinancován ESF a SR ČR

 in use by gonochorists  they have one sex chromosome = heterochromosome (gonosome)  the other chromosomes are called autosomes  one sex chromosome is geminate  according to the sex there exist either:  in a non-homologic pair with a non-geminate chromosome  or as a pair of homologic chromosomes CHROMOSOMAL SEX DETERMINATION

 the geminate heterochromosome is marked X- chromosome  non-geminate heterochromosome (so called allosome) is marked Y- chromosome CHROMOSOMAL SEX DETERMINATION

 by mammals and by humans is present:  by females a couple of homologic chromosomes XX  by males non-geminate chromosomal couple XY  females produce only eggs  eggs contain chromosome X = homogametic sex CHROMOSOMAL SEX DETERMINATION

 males produce one half of sperms with chromosome X  one half of sperms with chromosome Y = heterogametic sex CHROMOSOMAL SEX DETERMINATION

 after the fertilization of the egg by the sperm with chromosome X => male zygote  after the fertilization of the egg by the sperm with chromosome Y => female zygote CHROMOSOMAL SEX DETERMINATION

 this type of chromosomal sex determination also occurs by dioecious plants, insects except for butterflies  it is named male type or type Drosophila CHROMOSOMAL SEX DETERMINATION

 By birds and butterflies (and also by some fish species, amphibians and reptiles):  There is one pair of chromosomes XX in male somatic cells = males are homogametic sex Bird type: (Abraxas) homozygotic XX heterozygotic XY CHROMOSOMAL SEX DETERMINATION

 Non-geminate pair XY is in female cells = females are heterogametic sex  this type of chromosomal sex determination is named bird type or Abraxas type CHROMOSOMAL SEX DETERMINATION Bird type: homozygotic XX (Abraxas) heterozygotic XY

 heterogametic sex produces:  a half of gametes with chromosome X  a half of gametes with chromosome Y  through their fertilization necessarily develops a half of males and a half of females CHROMOSOMAL SEX DETERMINATION

 main evolutionary advantage:  keeping the same relation of males and females in generations  it ensures the maximum possible amount of descendants by gonochorists in natural populations CHROMOSOMAL SEX DETERMINATION

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 CHALUPOVÁ-KARLOVSKÁ, Vlastimila. Obecná biologie: středoškolská učebnice : evoluce, biologie buňky, genetika : s 558 řešenými testovými otázkami. 2., opr. vyd. Olomouc: Nakladatelství Olomouc, 2010, 206 s. ISBN SOURCES