Chapter 3: biological foundations, genetics and prenatal development Flashcards
Pre and Early Life Cells
-
Gametes:
- reproductive cells: sperm and ova
- Only contain 1⁄2 normal complement of DNA
-
Zygote: new cell formed by conception.
- Full complement of DNA (1⁄2 from sperm + 1⁄2 from egg)
- All other cells are derived from the zygote by Mitosis
Deoxyribonucleic acid (DNA):
Genetic information for each cell
Genes:
segments of DNA that code for individual traits
Chromosomes
- Storage structures for DNA
- Rod-like structures visible in cell nucleus
- 46 chromosomes in 23 pairs
• Sex Chromosomes
- Males = XY
- Females = XX
Mitosis
- Mitosis is the process that ensures that the duplicate cell is identical in genetic makeup to the original cell
- The replication of genetic material during cell multiplication and the transfer of genetic information during reproduction are central to understanding development and growth
Meiosis
Genotype vs Phenotype
• Genotype
– The genetic code of the individual; sum of all genes
– Together with the environment determines phenotype
• Phenotype
– Traits as displayed or expressed
– Examples: height, eye colour or IQ
Phenotype = Genotype + Environment
Alleles
- There are two alleles for each gene, one from each parent
- Different alleles can produce variation in inherited characteristics
- Some alleles are dominant, some are recessive, and some are co-dominant
Dominant and Recessive Inheritance
Dominant alleles
- Always expressed in phenotype
- e.g., brown eyes, curly hair, facial dimples, type A blood, Huntington’s disease
- Possible genotypes: DD, Dd or dD (capitalisation indicates dominant allele)
Recessive alleles
- Must be paired with another recessive allele (aka one from each parent) to be expressed
e. g., blue eyes, colour-blindness, baldness, type O blood, PKU
Possible genotype: dd
Co-dominance:
• Both alleles expressed • Example of blood group
Homozygous alleles
Heterozygous alleles
Polygenic traits
- Homozygous: alleles for a trait are identical
-
Heterozygous: alleles for a trait are different
- Can be a carrier for a recessive allele (e.g., haemophilia)
- Polygenic traits: many genes as well as environment influence character (most traits are polygenic)
Summary of concepts
Determination of sex
- Ova - X; Sperm - X or Y
- Sex of zygote determined by which type of sperm fertilises the ovum
- 30% more male than female zygotes
- 6% more live male births
- Some traits are inherited in a sex linked manner
Genetic abnormalities
- Chromosome abnormality
- e.g., Down syndrome
- Dominant gene disorders
- e.g., Huntington’s disease
- Recessive gene disorders
- e.g., Sickle-cell disease
- Multifactorial
- e.g., congenital heart disease
Down syndrome
- Trisomy 21 – an extra 21st chromosome
- Most common autosomal disorder
- Responsible for 40% of moderate to severe mental retardation
- Symptoms include distinct facial features, mental retardation, speech problems, and slow motor development.
- Incidence increases with maternal age
- 1 in 1900 births at 20yrs; 1 in 300 at 35yrs; 1 in 30 at 45yrs
Phenylketonuria (PKU)
- Frequently occurring recessive disorder
- By 1 year infants are permanently retarded
- However, if identified early, these children are given a diet low in phenylalanine and usually attain an average level of intelligence and have a normal lifespan
- Inheriting unfavourable genes does not always lead to an untreatable condition if the environment (diet) can be adjusted
Abnormalities of the Sex Chromosomes
- These disorders produce less severe problems and deficits usually result in fewer problems than defects of the autosomes
- Often not recognised until adolescence
- XO = Turner’s syndrome (Female, short, infertile)
- XXY = Kleinfelter’s syndrome (Male, sterile, learning disorders)
- XYY = Male, tall, low IQ (especially verbal IQ)
Genetic counseling
• Helps prospective parents assess risk of bearing a child with a genetic defect
- Especially helpful when:
- Parents already have biological children with a defect
- Family history
- Ethnicity
- Women 35 years or older
Behavioural genetics
• Behaviour genetics: study of the nature/ nurture interaction
- Remembering that:
- Nature = genetics
- Nurture = environment
Phenotype = Genotype + Environment
Examples of behavioural genetics
Examples of how behavioural genetics can be analysed in humans:
Adoption studies: dissimilar nature, similar nurture
Twin studies: identical or fraternal, raised separately or together
Prenatal development
Gestation
Gestational age
• Gestation: The approximately 38-week period of development between conception and birth
• Gestational Age: Age of unborn baby, usually dated from the first day of an expectant mother’s last menstrual cycle
Stages of prenatal development (4)
- Conception
- Germinal (0 - 2 weeks)
- Blastocyst implants in uterus wall
- Embryonic (3 - 8 weeks)
- Umbilical cord connects embryo to placenta
- Amniotic sac develops
- Foetal
- Week 9 to birth
Germinal stage of development
Foetal Stage Development: 8 Weeks to Birth
• Organs and body become more complex
- “Finishing touches” – toenails, eyelids
- Appearance of bone
Two types of multiple births
-
Monozygotic (MZ)
- One egg – one sperm cell
- Identical twins
- Share 100% of genes
-
Dizygotic (DZ)
- Two eggs – two sperm cells
- More common
- Fraternal twins
- Share 50% of genes – just like non-twin siblings
Prenatal influences on the child
Teratogens (prenatal hazards) examples
• Medicinal drugs
–Prescription of drugs such as thalidomide
• Non-medicinal drugs
–Foetal alcohol syndrome, foetal alcohol effect
• Maternal disease
–Viruses, bacteriological and parasitic diseases, STIs, HIV/AIDS
• Environmental hazards
–Physical, biological, chemical, radiation
Maternal and environmental factors that Impact on Prenatal Development
-
Age of mothers
- > 35 years – higher risk of infertility and Down syndrome infant
- Teenage – higher risk for low birth weight babies, stillbirths, birth complications
-
Domestic violence
- Stress, family dysfunction, may be deliberate to terminate pregnancy
Paternal Factors that Impact on Prenatal Development
• May affect quality of sperm:
- Exposure to lead
- Marijuana or tobacco smoke
• Alcohol or radiation
- Pesticides
- Paternal age
Risks to prenatal health
• Risks:
• Weight gain
- Cigarettes, alcohol, drugs
- Signs of pregnancy complication
• Need for:
• Rest, exercise, personal hygiene
- Preparation for labour and birth
- Effective use of health care system
Childbirth settings
- Until 1800s home births most common
- Rising power of medicine saw delivery moved to hospitals by 1900s
- Hospital births account for 90%
–Birthing rooms and rooming in
• Non-hospital
–Birth centres
–Home births
Birth process
Difference between Parturition and Labour
-
Parturition – (before childbirth) brings on labour 2 weeks before delivery
- Uterine contractions
- Cervix becomes flexible
- Stimulated by rising estrogen levels
- Labour refers to uterine contractions that affect dilation of cervix and forces the fetus through birth canal
Birth
Feotal presentation
Stages of labour
-
Foetal presentation
- Cephalic (head first)
- Breech (bottom and feet first)
- Transverse (sideways)
-
Stages of labour
- First stage – up to 10cm cervix dilation
- Transition to full dilation
- Second stage – culminates in birth
- Third stage – expulsion of placenta and umbilical cord
Different methods of prepared childbirth
- Read method
- Lamaze method
- Leboyer technique
Midwives and doulas
- Important role served by the two
- Support from doulas linked to shorter labours and fewer delivery complications
Medication for deliveries
Problems during labour
-
Faulty power (uterus doesnt contract strongly enough)
- Oxytocin can induce labour
-
Faulty passageway
- Placenta Previa (cervix covered by placenta)
-
Faulty passenger
- Breech
- cephalopelvic disproportion (baby is too big)
-
Caesarean section
- When vaginal delivery is unsafe
