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Sex Determination

Sex Determination. Sexual Differentiation. The process of development of the differences between males and females, from an un differentiated zygote. Sexual Differentiation. Autosomes Sex chromosomes Heterogametic sex (2 types of gametes) Homogametic sex (1 type of gamete)

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Sex Determination

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  1. Sex Determination

  2. Sexual Differentiation • The process of development of the differences between males and females, from an un differentiated zygote

  3. Sexual Differentiation • Autosomes • Sex chromosomes • Heterogametic sex (2 types of gametes) • Homogametic sex (1 type of gamete) • Males are not always heterogametic sex - females are heterogametic in birds, moths, fish and chickens XX/XY – male heterogametic sex ZZ/ZW – female heterogametic sex

  4. Sexual Differentiation • Primary Sexual Differentiation – gonads • Secondary Sexual Differentiation – overall appearance of the organism • Unisexual, Dioecious, Gonochoric – containing only male or female reproductive organs • Bisexual, Monoecious, Hermaphorditic – both male and female reproductive organs

  5. Sexual Differentiation Chlamydomonas (Green algae) • Most of life in haploid stage • Asexually reproduce daughter cells by mitotic division • Unfavorable conditions – (such as nitrogen depletion) function as gametes to produce zygotes • Diploid Zygotes – withstand unfavorable conditions

  6. Sexual Differentiation • Meiosis occurs then returns to the haploid state • Isogametes – gametes are indistinguishable (isogamous is the species producing the isogametes) • When forming zygotes, only “+” and “-” isogametes mate • Chemical difference between cells but no morphological difference

  7. Sexual Differentiation Zea mays A. Stamen - Male 1. Produce diploid microspore mother cells 2. Each mother cell undergoes meiosis to produce 4 haploid microspores 3. Each haploid microspore develops into a mature male microgametophyte (pollen grain)

  8. Sexual Differentiation B. Pistil (Female) 1. Produce diploid megaspore • After meiosis, only 1 haploid megaspore survives • Megaspore divides 3 times producing a total of 8 nuclei in one embryo sac • Two nuclei in the middle – endosperm nuclei

  9. Sexual Differentiation • Micropyle end (where two sperm nuclei enter) – 3 nuclei/1 oocyte, 2 synergids • Antipodal nuclei – the three nuclei opposite from micropyle end • One sperm fertilizes endosperm nucleus; the other sperm fertilizes oocyte nucleus • Double fertilization – diploid zygote/triploid endonucleus • Each ear of corn contains as many as 1000 of these structures

  10. Sexual Differentiation C. elegans • Only 1000 cells • 2 sexual phenotypes • Males – testis (functional) • Hermaphrodite – XX • Males – X (No Y chromosome)

  11. Sexual Differentiation 6. Hermaphrodite – testis and ovaries a. During larval stage, testis produce sperm (stored) b. Ovaries produced but no oogenesis until adult stage c. Able to self fertilize d. If hermaphrodite mates with male – ½ hermaphrodite, ½ males

  12. Sexual Differentiation Protenor (insect) • 1906 Edmund Wilson found female somatic cells contained 14 chromosomes, including 2 X sex chromosomes • Gametes from female contains 7 chromosomes, including 1 X chromosome

  13. Sexual Differentiation • Gametes from the male contains 6 chromosomes without 1 X chromosome • Gametes from the male contains 6 chromosomes with 1 X chromosome • Fertilization by male containing X sperm – FEMALE 6. Fertilization by male containing O sperm – MALE Protenor Mode of Sex Determination– XX / XO

  14. Sexual Differentiation Lygaeus turicus • Insect has 14 chromosomes • 12 autosomes and 2 X chromosomes – Female • 12 autosomes and 1 X + 1 Y - Male • Females produce only X chromosomes • Males produce X and Y chromosomes Lygaeus Mode of Sex Determination (XX/XY)

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