Chapter 3: biological foundations, genetics and prenatal development Flashcards Preview

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Flashcards in Chapter 3: biological foundations, genetics and prenatal development Deck (36):

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 



segments of DNA that code for individual traits



• Storage structures for DNA

• Rod-like structures visible in cell nucleus

• 46 chromosomes in 23 pairs

• Sex Chromosomes

    • Males = XY
    • Females = XX 



  • 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

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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 




  • 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


• 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

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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 

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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


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

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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 



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 

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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