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Kinesiology 3347A/B

1 Unit 3: Prenatal Growth Readings: Chapter 2 Introduction o Tends to follow chronological timelines much more strictly than postnatal growth far more predictable Cell Theory: o All living things are composed of cells o The cell is the basic functional, structural and organizational unit of life o Cells only arise from pre-existing cells o Cells carry genetic info in the form of DNA. This material is passed from parent cell to daughter cell. o How we grow via hyperplasia o Prenatal period: conception (when zygote is formed) birth (around 40 weeks) o Gestation - carrying of an embryo/fetus; multiple (simultaneous = twins) o Pregnancy - fertilization and development of an embryo/fetus in a female uterus o Gestation and prenatal growth are highly species-specific o Mice 25 day gestation 2g at birth Growth rate = 2/25 = 0.08g/day o Blue whale 300 day gestation 3,000,000g at birth Growth rate = 10 kg/day 2 o Humans 259-294 day gestation (266 days on average) 37-42 weeks ~3,250g birth weight ~3.3kg ~Growth rate = 12.2g/day Most of the mass that a human fetus accumulates is from the 4 month of pregnancy onward Human Gestation: o In utero growth and development requires 266 days o Conceptional/ fertilizational age o Menstrual/gestational age (relative to last menstruation of mother, 280 days) - 10 lunar months o Lunar month = 4 weeks (28 days per month) o Approximate DOB: Beginning of last menstruation (b/c difficult to determine exactly when conception happened early on) Deduct 3 months Add 7 days o 95% of babies born +/- 2 weeks (of this predicted DOB) o Weight increases several billion fold (as embryo develops) Huge increases during prenatal period Gestation Pediatricians guide to estimate fetal length: o Lunar month = 28 days o Lunar month until 5 months E.g., at 3 months = 3 = 9cm 3 o Multiply lunar month by 5 after 5 months o Difficult to measure b/c curled up in the uterus Karyotyping and Sex determination: o Human genome, 46 chromosomes arranged in pairs o Bottom: X and Y chromosomes = male genome o Somatic cells = All body cells except those involved in reproduction Diploid 46 chromosomes 44 autosomes (non-sex related chromosomes, men and women share between each other) 2 sex chromosomes (23rd pair) o Similar in size and shape, same genes for same set of traits = homologues But traits carried on the genes are often different (one from father and one from mother) Homologous pairs - same size and shape One from each parent o Karyotyped by size and shape o Karyotyping = method used to organize and classify chromosomes Sex Cells: o Haploid o Random assortment of traits o 23 chromosomes Contain DNA from mother or father 4 XX vs XY Trends: o Y chromosome Smaller, lighter Androsperm (a sperm carrying a Y chromosome) faster, longer tail sperm will generally reach ovum faster than a sperm carrying an X chromosome o Primary sex ratio up to 1.25:1 (males:females) conception Ratio of males to females conceived, number of eggs fertilized by male DNA is greater than that carrying female DNA o X chromosome Carries more genetic info More durable, heavier, slows down gynosperm XX more likely to mature on track (for fetus and human, don't know why) More stable Gynosperm = sperm carrying female chromosomes o Fewer XY survive full term o Secondary sex ratio 1.06:1 (male:female) More spontaneously aborted (mothers often dont know this is happening), ratio of males to females born Effectively stored to around 1:1 at birth o Born males are longer and heavier (bigger, stronger, fitter) - survival of the fittest, perhaps? o Androsperm > Gynosperm by a large margin; probably offsets poor survival rate and relatively fragile construction However, families predominated by females tend to have gynosperm outnumbering androsperm (therefore not a steady rule)
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