Lecture_8_-_Sex_Determination-1

Lecture_8_-_Sex_Determination-1 - Lecture 8 Lecture Sex...

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Lecture 8 Lecture 8 Sex Determination and Sex Determination and Sex Chromosomes Sex Chromosomes
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Reproduction Reproduction Sexual Reproduction – two haploid gametes usually from two different individuals unite to form a new diploid individual Asexual Reproduction – mitotic division of either haploid or diploid cells within a single individual Some species exhibit only one or the other and some species exhibit both
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Reproduction Reproduction Sexual Reproduction – implies successful mating between two individuals and relies on differentiation of primary sex organs in each individual organism. This differentiation occurs in species considered low on the evolutionary scale such as bacteria and single-celled algae as well as in higher eukaryotes In more highly differentiated eukaryotes this differentiation is evident as morphological or phenotypic differences
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Reproduction Reproduction In higher eukaryotes, a dissimilar pair of homologous chromosomes, the X-Y pair or the sex chromosomes, is often characterized as determining the sex of the individual In some species such as mammals, individuals that are heteromorphic for this X-Y pair are often characterized as males In other species such as some fowl, reptiles and amphibians, heteromorphic individuals (ZW) are females and homomorphic individuals (ZZ) are males
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Sexual Differentiation Sexual Differentiation In fact, genes not chromosomes determine sexual differentiation Some of the genes that determine sex are located on the sex chromosomes and some are located on the autosomes Primary sexual differentiation refers to the presence of the primary sexual organs; the testes or the ovaries Secondary sexual differentiation refers to the presence of secondary organ such as mammary glands and external genitalia
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Sexual Differentiation Sexual Differentiation In plants and animals several terms ( unisexual , dioecious , gonochoric ) refer to individuals that contain only one type of reproductive organ Conversely, the terms bisexual , monoecious and hermaphroditic refer to individuals which contain both sets of primary sexual organs. These individuals are often capable of producing both types of fertile gametes and are fairly common in many plant and animal species A third type called intersex individuals have partially developed primary sexual organs and are usually infertile
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Sexual Differentiation Sexual Differentiation Different species of plants and animals have evolved highly different sexual life cycles Chlamydomonas , a blue-green algae spends most of its life in a haploid form and reproduces asexually thru mitotic division of its haploid cells. During periods of stress some of the haploid
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Lecture_8_-_Sex_Determination-1 - Lecture 8 Lecture Sex...

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