17. Sex. Being Male and Female

Transcription

1 17. Sex Being Male and Female

2 Reproduction Asexual: more efficient (Only 1 sex) Low genetic variation Sexual: prevalent (2 sexes, separate or not) High genetic variation Need 2 members of the same species Approaches: External fertilization (aquatic organisms: corals) Don t need to find mate, produce lots of gametes Internal fertilization (land animals) Need to find mate, fewer gametes, assure reproduction

3 Primitive Sex First reproduction: in water Sperm and eggs synchronous release More sperm than egg Sperm swims using a flagella to the egg Size difference between gametes Corals: use cycle of the Moon coordinate release zygotes free to settle

4 Generalities: Males typically larger, stronger, flashier Reality: males may be small, dull, and weak Definition: organism possessing sperm Characteristics: testes: organs producing sperm mammals: Y chromosome (XY) s/thumb/9/9b/male_and_female_a._appensa.jp g/521px-male_and_female_a._appensa.jpg

5 Generalities: typically smaller, weaker, dull Reality: Females many females are large, strong Definition: organism possessing eggs Characteristics: ovaries: organs producing eggs mammals: lack of a Y chromosome (XX) o/articles/ /amplectantbullfro gs1-main_full.jpg

6 SRY Gene Sex-determining Region Y Gene on the Y chromosome testes development to testosterone production to male secondary characteristics XX: can be male if they have SRY gene XY: can be female if they lack SRY 10 to 12 other sex determination genes

7 Reproductive Organ Development Y presence Testes Kidney Wolffian duct Gonads Mullerian duct Y absence Ovaries Cloaca Bladder Testosterone6 wk Probladder Oviduct Uterus Male 14 wk Urethra Testis Penis 14 wk Ovary Female Uterus

8 Human sexual differentiation Mullerian ducts Female gonads Wolffian ducts Male gonads Humans: Each sex starts off as undifferentiated Default is female Y chromosome: may lead to a male

9 Sexual Characteristics Primary Characteristics Female Male Gonads Ovaries Testes Internal genitalia Vagina, Uterus, Fallopian tubes Prostate, Seminar vesicles External genitalia Secondary Characteristics Glans clitoris, labia, vulva Breasts, low muscle mass, high fat Glans penis, scrotum Facial hair, high muscle mass, low fat

10 External Reproductive Organ Development Limb bud 6 wk Cloaca Y presence 9 wk Glans penis 4 wk Glans Urogenital groove Anus Urogenital Groove Y absence 9 wk Scrotum 14 wk Foreskin Glans clitoris Vagina Labium major Labium minor 14 wk

11 Sex Chromosome Disorders Syndrome Frequency Characteristics Turner Syndrome Kleinfelter s Syndrome XYY Syndrome or Super male Triple X Syndrome 1:4,000 female birth XO Infertile Abnormal 2 nd sex characteristics Webbed neck 1:1,000 male birth XXY Infertile Abnormal 2 nd sex characteristics Long limb physique 1:850 male birth XYY Fertile Normal 2 nd sex characteristics 1:1,500 female birth XXX Fertile Normal 2 nd sex characteristics

12 Sex Chromosome Disorders Turner Syndrome XO Klinefelter s XXY Webbed neck

13 Sex and Hormones Testosterone: male hormone (testes) facial hair, muscle development, deep voice, sperm production Estrogen: female hormone (ovaries) breast formation, lower muscle mass, egg maturation Males and females have both hormones ex: Testerone in women maintains sex drive and bone density Estrogen made from Testosterone (1 carbon difference)

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15 Sex Determination Systems System Male Female Examples XY System XY XX Mammals (humans) XO System X XX Insects, such as crickets ZW System ZZ ZW Fish, birds, and insects Temperature Hi Lo Turtles, alligators, and crocodiles 2n System n 2n Bees and ants Sequential Wrasses and clown fish

16 Crocodile Sex Determination Incubating temperature 30 o C all female 32 o C all male 31 o C 50% female, 50% male _ssh.jpg

17 Begin life as females One dominant male Protogyny One female replaces the dominant male in succession Harem Wrasses, other fish gs_webcams_videos_and_more/blogs/giant_ocea n_tank_blog/uploaded_images/bluehead jpg

18 Begin life as a male Breeding pair > 2 fish Protandry Dominant fish will become female If she dies, the next dominant male changes to female Crown fish (Nemo!) ansclownfish_1.jpg

19 Next time: Union Reading: 17.8