PBL 1: Development of the Body and Brain:

Behaviour Genetics:

the field that seeks to discover the influence of heredity (genes) and environment on individual differences in human traits and development

• Done through twin experiments and adoption studies

How do Twin Studies and Adoption Studies Work and Problems

Twin: look at behavioural similarities of identical twins (same DNA) compared to fraternal twins (no more genetically similar that siblings)

• Problem: difference in environments of the twins (adults stress the similarities of identical twins and therefore perceive themselves as a ‘set’ and play together more than fraternal twins leading to environment difference)

Adoption: seek to discover whether the behaviour and psychological of adopted children is more similar to adoptive parents (nurture) or biological parents (nature)

• Another form is adopted vs biological siblings

Hereditary Environment Correlations and 3 Types:

our genes do not only influence who we are, but they also influence the environments we experience

Passive GenoEC, Evocative GenoEC and Active GenoEC

What are the Definitions of Passive, Evocative and Active GenEC:

Passive: occur because biological parents provides a rearing environment for the child

Evocative: occur because a childs genetically influence characteristics elicit certain types of environments

Active (Niche Picking): occur when children seek out environments that they find compatible and stimulating.

• Niche Picking refers to finding a setting that is suited to one’s genetically influenced abilities

Shared and Non-Shared Environmental Experiences:

To understand the environments role in difference between people, we should distinguish between shared on nonshared environments with other people in the same household

• Shared Environmental Exp: common experiences (parents personalities or intellectual orientation, socioeconomic status, their neighbourhood)

• Non Shared Environmental Exp: child's unique experiences both within the family and outside the family, that are not shared with a sibling (different peer groups and friends but also how parents interact with each child is different)

Epigenetic View:

development is the result of an ongoing, bidirectional interchange between heredity and environments (how environments can influence which genes are expressed)

• Criticises the Heredity-Environment Correlation because it gives heredity to much of one-sided influence and doesn’t look at prior environmental influences

Gene X Environment Interaction:

the interaction of a specific, measured variation in DNA and a specific, measured aspect of the environment

• Example: 5-HTTLPR gene, people have an elevated risk of getting depression only if they have stressful lives

Prenatal Development:

begins with fertilisation and ends with birth, lasting between 266 days to 280 days (divided into three periods: germinal, embryonic and fetal)

Three Stages of Prenatal Development:

Germinal Period, Embryonic Period and Fetal Period

Conception:

Occur when a single sperm cell unites with an ovum (egg) in the female's fallopian tube in a process called fertilisation

What Happens in the Germinal Period:

• takes place in the first two weeks of conception

• Creates the zygote followed by cell division and attached of the zygote to uterine wall

• Cell specialisation occurs after 1 week (different tasks)

• Blastocyst: A small cluster of internal cells that will develop into the embryo

• Trophoblast: An outer layer of cells that later provides nutrition and support for the embryo because it becomes the placenta

What happens in the Embryonic Period

• from two weeks to two months

• Cell differentiation intensifies, support systems for cells form and organs appear

• This period begins as the blastocyst attaches to the uterine wall and the mass of cells is now called an embryo, and three layers of the cells form

• As the three layers form, life support systems for the embryo develop quickly

• Small molecules pass back and forth between the mother and embryo or fetus (including cigarette smoke that weakens fetal membranes from which the placenta develops)

• Organogenesis occurs

What are the three layers that form in embryonic period

• Endoderm: Inner layer of the cells, which will develop into digestive and respiratory systems (primarily produces inner body parts) 

• Mesoderm: middle layer, becomes circulatory systems, bones, muscles, excretory system and reproductive system (primarily produces parts that surround internal areas) 

• Ectoderm: outermost layer, eventually becomes the nervous system, brain, sensory receptors (ears, nose, eyes etc.) and skin parts (hair and nails etc.) (primarily produces surface parts) and neural tube

What life-support systems forms as the three layers form

Amnion: bag that contains clear fluid in which the embryo floats

• The amniotic fluid provides an environment that is temperature and humidity controlled as well as shock proof

Umbilical Cord: connects the baby and the placenta (made of two arteries, one vein)

Placenta: consists of disk-shaped group of tissues in which small blood vessels from the mother and the offspring intertwine but don’t join

What molecules can and cannot be past back and forth between the mother and embryo

• CAN: Oxygen, water, salt, food from mothers blood and digestive waste from the offsprings blood

• CANNOT: Large molecules that cannot pass through the placental wall include red blood cells and harmful substances (bacteria, maternal waste and hormones)

• Any drug or chemical substance the pregnant woman ingests can cross the placenta to some degree, unless metabolised or altered during passage, or is too large

Organogenesis:

process of organ formation in the first two months of prenatal development

• Third week after conception: Neural tube that eventually becomes the spinal cord develops

  • 21 days: eyes begin to appear, 24 days: the cells for the heart begin to differentiate

• Fourth week: the urogenital system becomes apparent and arm and leg buds emerge, four chambers of the heart take shape and blood vessels appear

• Fifth to Eighth: arms and legs differentiate further, face starts to form but still not recognisable, intestinal tract develops and facial structures fuse

• Eight Weeks: weighs 1/30 ounce and 1 inch long

The Fetal Period:

lasts from 2 months to 9 months (mostly grows and gains. weight)

• Three Months: 3 inches long and weighs 3 ounces, has become active (moves arms, legs and head and opens and closes mouth), face features (and upper/lower arms, hands and lower limbs) are distinguishable, and  the genitals are identifiable (most cases) 

• Fourth Month: 6 inches long and weighs 4 to 7 ounces, the mother can feel arm and leg movements (kicking) and growth spurt occurs in the bodies lower parts 

• Fifth Month: 12 inches long and weighs close to a found, structures of skin have formed, more active (preference for a specific position in womb) 

• Sixth Month: 14 inches and gain another half pound to a pound, eyes and eyelids are completely formed, and a fine layer of hair covers head, grasping reflex is present and irregular breathing movements occur 

  • At 24 to 25 weeks, the fetus has a chance of surviving outside the womb (it’s viable) (very end of second trimester) 

  • Infants born between 24 and 37 weeks usually need help breathing because their lungs are not fully developed but all organs are already there 

• Seventh Month: 16 inches and weighs 3 pounds 

• Eighth and Ninth Month: fatty tissues develop and functioning of various organs systems (heart and kidneys etc) step up, fetus grows longer and gains substantial weight (another 4 pounds) 

• Birth: baby weight 7 ½ proud and about 20 inches long