The Influence of Genetics and Environmental Factors

Key Terms

  • Genotype

    • Genetic information that determines an organism’s traits

    • Examples: genes for eye color, hair color

  • Phenotype

    • Observable physical characteristics

    • Examples: brown eyes, blonde hair

  • Chromosomes

    • Structures that store genetic information

    • Located in the nucleus (center of the cell)

    • Humans have 23 pairs of chromosomes

    • One chromosome in each pair is inherited from the mother and the other from the father

  • DNA (Deoxyribonucleic Acid)

    • The molecule that makes up chromosomes

    • Carries genetic instructions

  • Genes

    • Segments of DNA

    • Each gene controls a specific trait

  • Sex Chromosomes

    • The 23rd pair of chromosomes determines biological sex

    • XX = female, XY = male

Multiple Offsprings

  • Types of Twins

    • Fraternal (Dizygotic) Twins: formed when two separate eggs are fertilized by sperm

    • Identical (Monozygotic) Twins: formed when one fertilized egg splits into

  • Factors Influencing Multiple Births

    • Family history of twins

    • Geographic region

    • Higher rates reported among populations in Black African

    • Maternal age 35-39 years

    • Maternal body type

      • More common in taller or overweight individuals

    • Previous pregnancies

    • Use of fertility treatments

      • Fertility drugs

      • In vitro fertilization (IVF)

  • Health Outcomes of Multiple Births

    • Higher risk of premature birth

    • Increased likelihood of pregnancy and neonatal complications

Patterns of Gene-Gene Interaction

  • An allele is made up of a pair of genes

  • Homozygous: occurs when both alleles inherited from parents are the same

  • Heterozygous: occurs when the two alleles inherited from the parents are different

Dominant vs. Recessive Pattern

  • In heterozygous pairings, dominant and recessive alleles determine the expressed trait

  • The dominant allele masks the effect of the recessive allele

  • Example

    • Dark hair parent: DD

    • Light hair parent: dd

    • D = dominant (dark hair)

    • d = recessive (light hair)

    • A child with genotype Dd will have dark hair

    • The child is a carrier of the light hair trait

    • Different genotype, same phenotype

  • Incomplete Dominance

    • Neither allele is completely dominant

    • Results in a combined or intermediate trait

    • Sickle cell trait/anemia (heterozygous individuals show partial expression)

X-linked Pattern

  • When an X chromosome carries an allele associated with a disease or abnormality, males are more likely to be affected.

    • Males have only one X chromosome, so there is no second allele to mask the condition.

    • Females have two X chromosomes and are therefore more likely to be carriers rather than affected

    • Examples of X-linked conditions include hemophilia and Fragile X syndrome

Mutation

  • A sudden and permanent change in a segment of DNA

  • Can occur spontaneously (cause not always known)

  • Can also be caused by hazardous environmental agents (mutagens)

Chromosomal Abnormalities

  • Most chromosomal defects occur during meiosis

  • Example: Down Syndrome

    • Usually caused by a failure of the 21st chromosome pair to separate during meiosis

    • This results in an extra copy of chromosome 21 (trisomy 21)

    • Common characteristics

      • Intellectual disability

      • Memory and speech difficulties

      • Delayed motor development

      • Distinct physical features

      • Risk factor: advanced maternal age

Genetic Screening & Counseling

  • Genetic screening

    • Tests used to identify the presence of genetic diseases or abnormalities

  • Genetic counseling

    • A communication process that helps individuals or couples

    • Assess their risk of having a child with a hereditary disorder

    • Understand results and make informed decisions about possible courses of action

Reproductive Technologies

  • Donor Insemination

    • Sperm from a donor is introduced into a woman’s reproductive system to achieve pregnancy

  • In Vitro Fertilization (IVF)

    • Multiple eggs are stimulated to mature and then retrieved surgically

    • Eggs are fertilized with sperm in the lab

    • The fertilized embryo is transferred back into the woman’s uterus

  • Surrogacy

    • Another woman carries and gives birth to a baby for someone who cannot carry a pregnancy

  • Amniocentesia

    • Tests the amniotic fluid

    • Performed around 14 weeks after conception

  • Chorionic Villi Sampling (CVS)

    • Tests the placental tissue for genetic abnormalities

    • Usually performed 10-13 weeks

  • Fetoscopy

    • Direct inspection of limbs, face, and fetal blood

    • Performed 15-18 weeks

  • Maternal Blood Analysis

    • Fetal cells enter the maternal bloodstream

    • Can measure alpha-fetoprotein to detect kidney, esophagus, and neural tube defects

  • Ultrasound

    • High-frequency sound waves produce images of the fetus

    • Assesses size, shape, and position

  • MRI (Magnetic Resonance Imaging)

    • Uses magnetic fields to create detailed images of fetal structures

    • Especially useful for brain abnormalities

Environmental Contexts for Development

Family Dynamic

  • The family is a network of interdependent relationships

  • Negative family dynamics can contribute to developmental problems in children

  • Key Factors in Family Influence

    • Roles and responsibilities of family members

    • Parental decisions regarding having children

    • Parenting styles and approaches to child-rearing

Transmission of Maternal Stress

  • Maternal stress can impact both birth outcomes and long-term development

  • Possible Effects:

    • Low birth weight

    • Infant temperament (ex., irritability, fussiness)

    • Emotional regulation difficulties

    • Shortened attention span

Socioeconomic Status

  • SES: education, employment, and income

  • More time dedicated to children

  • Resources & access

  • Link to family size, parental timing, neighborhood & school

Neighborhood & School

  • SES influences family choices, including:

    • Neighborhood & school selection

    • Crime levels in the neighborhood

    • Housing stability

    • Community resources: Involvement in local organizations and faith communities can provide support

    • Type of school (public vs. private)

    • Access to extracurricular activities

Epigenetics: Interaction between genes and environment

  • The big question: How much?

  • Kinship Studies compare traits and characteristics among family members

  • Heritability Studies

    • Derived from kinship studies

    • Estimate the extent to which individual differences are due to genetic factors

  • Not an exact science

  • Gene-Environmental Interaction

    • Genetic makeup influences responsiveness to the environment

  • Types of Gene-Environment Correlations:

    • Passive correlation - Child has no control; environment matches parents’ genetics

    • Evocative correlation - Child evokes responses from others that reinforce genetic tendencies

    • Active correlation - Child seeks experiences that align with their genetic tendencies

  • Epigenetics

    • Gene expression can be modified by environmental influences and