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At the beginning of the ninth week, the embryo is termed a fetus (spelled "foetus" in British English). In comparison to the embryo, the fetus has more recognizable external features and a more complete set of developing organs. Human embryology is the study of this development during the first eight weeks after fertilization.
The embryo and subsequent early fetus appear to be sexually indifferent, looking neither like a male or a female. Over the next several weeks, hormones are produced that cause undifferentiated tissue to transform into either male or female reproductive organs. This process is called sexual differentiation.
Sexual differentiation is the process of development of the sex differences between males and females from an undifferentiated zygote. [1] [2] Sex determination is often distinct from sex differentiation; sex determination is the designation for the development stage towards either male or female, while sex differentiation is the pathway towards the development of the phenotype.
Genetic factors may be the most significant cause of autism. Early studies of twins had estimated heritability to be over 90%, meaning that genetics explains over 90% of whether a child will develop autism. [1] This may be an overestimation, as later twin studies estimate the heritability at between 60 and 90%.
Occasionally a human birth is anything but ordinary. A recent report highlighted a rare case from 2010, in which a baby girl born in Hong Kong was found to be carrying twin fetuses. The study ...
An embryo is the initial stage of development for a multicellular organism.In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm cell.
Drawing on some transsexualism cases, Garcia-Falgueras and Swaab state that "[f]rom these examples it appears that the direct action of testosterone on the developing brain in boys and the lack of such action on the developing brain in girls are crucial factors in the development of male and female gender identity and sexual orientation".
The girls will spend the next several weeks in the NICU at Mercy, but other than some monitoring, they are expected to be okay. "They're both just little miracles, it could have been so many ...