Lecture 1: Prenatal Development Flashcards

Question

Sex Determination How does sex determination work?

Answer 1

It is the Y chromosome that leads to the development of a male, so sex is determined by which sperm X or Y fertilises the egg

Answer 2

It is the Y chromosome that leads to the development of a male, so sex is determined by which sperm X or Y fertilizes the egg Sperm that carry a Y chromosome (as this is smaller) tend to be lighter and swim faster than those that carry an X, as a result 120-150 males are conceived to every 100 females HOWEVER the ratio at birth is only 106 males to every 100 females... WHY?

Answer 3

Boys are more vulnerable in the womb... - more susceptible to stress - more likely to be miscarried/ birth complications This may be because they have only have one X chromosome. Therefore, if they have a defective gene on the X chromosome, they do not have a functioning copy to balance this out (as their other chromosome is Y).

Answer 4

Sometimes a growing cell cluster breaks apart early in development and results in with identical genes - the clusters develop into identical twins (they come from the same zygote)

Answer 5

Sometimes two different eggs are fertilized at the same time, leading to non-identical twins

Answer 6

2-8 weeks - core organs develop Once the zygote has attached to the uterine wall it develops into an embryo (inner cell mass becomes embryo and the rest becomes the amniotic sac and placenta) Amniotic sac - membrane filled with fluid for even temperature and cushioning Placenta - allows exchange of materials from the mother to the embryo/foetus through blood via blood vessels that make up the umbilical cord

Answer 7

The inner cell mass divides into three layers: 1. Ectoderm (top layer) - becomes the nervous system, nails, teeth, inner ear, lens of the eyes and skin 2. Mesoderm (middle layer) - becomes the muscles, bones, circulatory system, inner layers of the skin and internal organs 3. Endoderm (bottom layer) - becomes the digestive system, lungs, urinary tracts and glands After the three layers differentiate, a U-shaped groove forms down the centre of the top layer and the top of the groove fuses forming the neural tube - this becomes the brain and spinal cord

Answer 8

9 weeks to birth This period is all about growth and further development. Areas near the head develop earlier than those further away from the head

Answer 9

9 weeks to birth This period is all about growth and further development. Areas near the head develop earlier than those further away from the head. last five months - lower parts develop more rapidly and so do the foetuses movements. Development of sexual organs takes place early in this period. All humans (regardless of whether they are male or female) can develop either male or female genetalia (intersex etc) It is the presence or absence of androgens (hormones that include testosterone) that cause male genitalia to develop

Answer 10

Mainly, the zygote’s genetic code (nature). But the environment (nurture) also plays a role.

Answer 11

Environmental - agents (such as drugs), - diseases (such as German measles) - physical conditions (such as malnutrition) that can affect the growing embryo/foetus. Teratogens can impair prenatal development, leading to birth defects or prenatal death. The effect of teratogens depends on timing and the dose-response relationship (the greater the exposure the more likely the damage)

Answer 12

When alcohol crosses the placenta (into the foetuses bloodstream and amniotic sac) concentrations quickly equalize BUT alcohol stays in the foetuses bloodstream for longer (and in the fluid in the amniotic sac). This can lead to heightened activity reflexes and abnormal startle reflexes. Consuming a lot of alcohol while pregnant can lead to FOETAL ALCOHOL SYNDROME Symptoms include: - facial defects - hyperactivity - behavioural problems