Prenatal period: Conception
- human development begins within a fraction of a second when a sperm and an ovum unite (fertilisation)
- the fertilised egg cell is a zygote
- takes place 280 days before birth
Prenatal period: Genetic factors
- normal zygote has 46 chromosomes
- each cell in the body has 23 pairs of chromosomes, except the gametes (ovum and sperm), that have 23 chromosomes each
- genes consist of DNA
- all humans are 99% identical in their genetic makeup
- therefore only 0.1% of our DNA is responsible for all physiological and psychological differences
- body cells (somatic cells) go through mitosis
- germ cells go through meiosis to form gametes
- when the two alleles (gene pair) that a child receives from their parents are homozygous, they will show this characteristic
- when the two alleles are heterozygous, the dominant allele will show
- sex is determined by gametes, specifically the father’s sperm cell
Prenatal period: Multiple births
Factors that may increase the prevalence of twins include family history of twins, high maternal age, race, and a large maternal size
Prenatal period: Infertility
- in a third of infertility cases, the problem can be traced to the man, and a third can be traced to the woman, the remaining third is unknown
- the fertility decline in women begin at 25-30 years of age
- children born through in-vitro have a higher risk for health problems and birth defects
Prenatal period: Genetic abnormalities
- only 2% to 3% of live births show a significant defect
Examples:
- porphyria in Afrikaners: blisters on skin exposed to sun
- Tay-Sachs in Jewish people: affects brain and spinal cord that results in death before the age of five
- Albinism in black South Africans, absence of pigmentation in skin, hair and eyes that are sensitive to light
- Thallasssemia in Greek and Italian South Africans, a deficiency in red blood cells
Chromosomal deficiencies include Down Syndrome
- Trisomy 21 (90% of cases): extra chromosome on 21st pair leads to 27 chromosomes in each cell
- Mosaic Down Syndrome: some cells contain 46 chromosome, while other have 47
Prenatal stage: Germinal
- period of the zygote
- conception - 2 weeks
- cell division begins within 24-36 hours of conception
- as the zygote develops, it travels along the fallopian tube
- day 5 it reaches the uterus
- from day 6, implantation takes place, where the zygote attaches itself to the inner wall of the uterus
- implantation is usually completed by day 9, and is the end of the germinal stage
Prenatal stage: Embryonic
- implantation- 8 weeks
- now referred to as embryo
- rapid growth, and cell and organ differentiation
- embryo develops into three layers:
1. Ectoderm (hair, nails, teeth, sensory organs, skin and nervous system)
2. Mesoderm (muscles, skeleton, inside of skin, blood circulation)
3. Endoderm (digestive system, liver, pancreas, sweat glands, and respiratory system - placenta and umbilical cord develops at start of embryonic stage
- upper part of the body develops faster than the lower part of the body
Prenatal stage: Foetal
- 8 weeks until birth
- further differentiation takes place
- during the third month, sexual organs of the foetus appear
- a connection is formed between the nervous system and the muscles, with the result of spontaneous movement of the arms and legs
- month 4: foetus becomes more human, thumb sucking, hiccuping
- month 5: movements become stronger
- month 6: eyes are fully formed, and they look around in all directions, foetus cries
- month 7: boundary between viability and non-viability, reacts to temperature and can smell and taste
- month 8: fatty tissue is formed
- month 9: more fat tissue is formed, body systems function more effectively, and antibodies are transferred from mother to child
- learning takes place in the womb during the last 3 months of pregnancy
Prenatal environmental influences
- the age of the parents
- nutrition of the mother
- radiation
- infectious diseases during pregnancy
- the use of medication and drugs
- the emotional
Teratogen
Any external factor or process that has a negative effect on the normal development of an unborn child
Polygene heredity
Interaction between genes: temperament, intelligence polygene traits
