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Unformatted text preview: Development and Sex Determination
Chapter 7 7th week of development Sexual Differentiation in Humans Until then, we're all female Genetic and environmental factors Male Reproductive System Fig. 7.1 Female Reproductive System Fig. 7.3 Oogenesis Fig. 7.4 Sperm and Oocyte Production
Sperm: When are they made? How often? How many? Sperm and Oocyte Production
Oocytes: When are they made? How often? How many? Fertilization to Implantation Fertilization = Zygote = Occurs in fallopian tube moved to uterus Mitosis 1 cell becomes blastocyst Fig. 7.5 Blastocyst ~ 100 cells It has two parts: Inner cell mass = embryo/embryonic stem cells Trophoblast = placenta, etc Implantation Trophoblast implants in endometrium After 12 days: trophoblast forms the chorion human gonatotropic hormone (hGH) Pregnancy tests Placenta What does the placenta do? Separates mom's blood from baby's blood Umbilical cord Day 1 Day 2 Day 3 Day 4 Day 5 Days 67 Fig. 7.6 Fig. 7.6 Day 12 Day 14 Trimesters of Development First trimester: organ formation Second trimester: organ maturation Third trimester: growth How long is the gestation period for humans? Human Embryo at 4 Weeks Fig. 7.7 Human Embryo at 46 Weeks Fig. 7.7 Human Embryo at 8 Weeks Fig. 7.7 Human Fetus at 16 Weeks Fig. 7.7 Congenital Malformations 97% of babies are "normal" Birth defects: disruptions in embryonic development genetic disorders exposure to environmental agents Teratogens What are these? Examples include Radiation Viruses Chemicals The Effects of Teratogens Fig. 7.8 Fetal Alcohol Syndrome (FAS) Alcohol = teratogen 1.9/1,000 births Preventable No level of alcohol consumption is known to be safe Fetal Alcohol Syndrome
Common problems in FAS: Growth retardation Mental retardation Facial abnormalities Learning disabilities Fig. 7.10 Defining Sex Chromosomal sex = Gonadal sex = Phenotypic sex = Formation of structures: gene action, environment, interactions within embryo and between embryos Sex Determination
Fig. 7.12 Genes on the Y Chromosome SRY gene = male gene Gene product causes testis development Autosomal genes too Testes secrete testosterone No Y chromosome = female Hemaphrodites = Mutations that Alter Phenotypic Sex Androgen insensitivity = Pseduohermaphroditism = Gender ambiguity Ok, but... Females = 2 X chromosomes, males = 1 X chromsome Do genes on X chromosome get expressed twice as much in females? X Inactivation To compensate, one X is inactivated Called dosage compensation Males don't have them Inactivated X = Barr Body Males & females express X linked genes equally Female Mosaics X inactivation is random Some cells mom's X, others dad's X Conrolled by X inactivation gene (XIST gene) Females can be mosaics Woman Heterozygous for Anhidrotic Ectodermal Dysplasia
Normal sweat glands Fig. 7.17 No sweat glands Female Are Mosaics for XLinked Genes Fig. 7.16 SexLimited Traits Sex limited trait = Secondary sexual characteristics ...
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- Fall '07