2: Genetic and Developmental Influences
- Page ID
- 297615
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Clinical Perspectives
- As mentioned previously, the following sections include information on clinical perspectives
Henrietta Lacks (1920-1955)
- Tobacco farm worker; passed away from cervical cancer
- When she was trying to treat it, it was discovered that her cells multiply at a very fast rate
- Cells could be kept alive and continue to grow (after the discovery, these cells were named after her and called HeLa cells)
- Significant amount of research using HeLa cells…polio vaccine, other vaccines, cancer treatments, HIV treatments, in vitro fertilization, first human cells to be cloned, and first human cells to be examined in the first space missions
- Cells were taken and used for research without consent from Henrietta or her family
- Due to systemic prejudice and racial discrimination, her family was not contacted or made aware of the HeLa cell research for several years
Research on Health
- Bioarchaeological – limited information over time
- Historical – limited records exist; not representative of whole population
- Autopsies – higher rates of particular diseases, concerns about ethics in past studies
- Clinical datasets – more data, large sample sizes
- Animal research – rats are far more sensitive to what is tested than humans, and humans are affected in some ways that rats are not affected
Cells
- Somatic – cells other than gametes; divide through mitosis
- Gametes – sperm and ova; divide through meiosis
- If cell growth exceeds cell death, tumors can form (can be benign or malignant)
- Cells can specialize to perform a specific function
- Stem cells are early, undifferentiated cells
- Cells contain a nucleus with pairs of chromosomes
- Chromosomes contain tightly coiled DNA
- A gene is a location on a chromosome with DNA code
Genes
- Gene – region of DNA on chromosome
- Trait – appearance (ex: height, eye color, hitchhiker’s thumb)
- Locus – location of gene on chromosome
- Allele – variant of a gene
- Homozygous – same allele on both chromosomes in the pair
- Heterozygous – different alleles on each chromosome in the pair
- Dominant – always expressed in the presence of a recessive allele; this does not mean it is more common in population
- Recessive – only expressed if there are 2 recessive alleles in the chromosome pair
Genetic Conditions
- Autosomal dominant (D) and autosomal recessive (R) genetic disorders
- Sickle cell anemia: affects hemoglobin of red blood cells (R)
- Cystic fibrosis: causes buildup of mucus in respiratory tract (R)
- Tay-Sachs: causes destruction of nerve cells in brain and spinal cord (R)
- Phenylketonuria (PKU): causes phenylalanine to build up in the body which can lead to brain damage and seizures (R)
- Huntington’s disease: progressive brain disorder; symptoms don’t start until 30s – 40s (D)
- Achondroplasia: stunted growth in long bones (D)
- Anemia: blood clotting disorder (R)
- Chromosomal conditions:
- Down syndrome (Trisomy 21) – 3 copies of 21st chromosome
- Fragile X syndrome – X chromosome is fragmented
- Klinefelter syndrome – extra X chromosome (XXY)
- Triple-X syndrome – 3 X chromosomes (XXX)
- Turner syndrome – only 1 X chromosome (X)
- Intersex
- Genetic conditions that affect spinal column:
- Scoliosis – pronounced curve; genetic link
- Kyphosis – name for the curve in upper and mid-back, but can be painful if the curve is more extreme
- Lordosis – name for the curve in neck or lower back, but can be painful if the curve is more extreme
Skeletal System
- Bones
- Tendons – muscle to bone
- Ligaments – bone to bone
- Surfaces for tendons, ligaments, muscles to attach
- Lever system for mobility
- Fat storage
- White blood and red blood cell production
- Maintains calcium and phosphorus homeostasis
- Hypocalcemia – lack of calcium
- Hypercalcemia – excess of calcium
Bone Cells
- Calcium salts make bone hard and strong
- Collagen makes bones flexible
- Osteoids – pre-calcified bone cells
- Needs calcium and minerals (from old bone and obtained in diet), vitamin D
- Osteoblasts – form new bone by secreting collagen and calcium salts
- Osteocytes – bone cells that are calcified from osteoblasts; maintain the bone matrix
- Osteoclasts – resorb bone; old/injured bone is broken down
- Osteoblasts are continually creating new bone while osteoclasts are continually breaking down old bone; continuously reshapes bone
Bone
- Bone is a dynamic tissue that changes with growth and environmental stressors
- Muscle use
- Weight
- External stress
- Haversian system – tubes and tunnels in bone that house nerve fibers and blood vessels; transports osteocytes
- Spongy (trabecular) bone (20%)
- Interior of bones
- No Haversian system
- Contains red marrow
- Compact/cortical bone (80%)
- Haversian system
- Solid, dense bone
Bone Growth
- Neoteny – retention of juvenile characteristics into adulthood
- Large head to body ratio
- Lots of fat
- Less pronounced bony features
- Allows for prolonged brain growth and lots of plasticity
- Intramembranous ossification
- How compact and spongy bone develops in the face, cranial bones, and clavicles during growth
- Immature bone cells (osteoids) become calcified, turning into osteoblasts
- Osteoblasts become osteocytes
- Cartilage – more water, no calcium salts (more flexible)
- Endochondral ossification – process where bone replaces cartilage during growth
- Occurs in long bones and bones at base of the skull
- Cartilage doesn’t turn into bone but is more of a “template” that gets replaced by bone
- By the time the skeleton is fully developed, cartilage only remains in joints and at the growth plate (epiphyseal plate) in long bones
- Bones continue to grow until adulthood
- Hormones control the rate of bone growth
- Bone remodeling – old or damaged bone is resorbed and new bone replaces it
- Not the same as repair
- Remodeling to increase strength in highest stress areas
- Bumps and ridges enlarge when muscles are used heavily
- Weaken with inactivity
Calcium and Vitamin D
- The body cannot create calcium, and it loses calcium through skin, nails, hair, sweat, and waste
- Calcium cannot be absorbed in small intestine without vitamin D
- Vitamin D is manufactured in the skin after absorbing sunlight; also ingested through food and supplements
- Vitamin D deficiencies:
- Darker skin complexion – may need supplements
- Areas in northern latitudes where sun rays are not as strong
- Pollution
- Lack of sunlight
- Sunblock can affect vitamin D absorption – skin cancer is still a concern, so some may be prescribed supplements
Childhood Bone Health
- Growth is affected by genetics and environment
- Stunted growth – environment detracts from “genetic potential”; malnutrition and/or stress leads to periods of time where growth stops
- Harris lines (growth arrest lines) – indicate growth was halted and restarted; can be seen in X-rays
- Zebra lines – rapid bone growth due to medicines used to stimulate growth
- Cribra orbitalia and porotic hyperostosis can occur with anemia and iron deficiencies
- Red blood cells can affect spongy bone
- Rickets – vitamin D deficiency in children; lack of calcification causing bones to bend
Hormones
- Maintain homeostasis by altering cell activity
- Circulate in blood and contact cells; only cause effects in cells with receptors
- Calcitriol – vitamin D hormone produced by kidneys that stimulates the absorption of calcium in small intestine
- Amenorrhea – lack of menstruation
- Can occur with low body mass index, excessive exercise, malnutrition
- Increases osteoporosis risk
- Puberty
- Estrogen increases calcium absorption and retention
- Progesterone increases osteoblast activity
- Estrogen and progesterone fluctuate during monthly bleeding, pregnancy, and/or lactation
- Lactation
- Driven by estrogen and can cause amenorrhea
- Lowers bone mineral density, but it returns after lactation ends
Adult Bone Health
- Influenced by childhood health
- Aging also affects bone health (osteoarthritis)
- Osteomalacia – like Rickets; vitamin D deficiency in adults; bone is formed incorrectly (osteoids don’t become calcified)
- Influenced by climate, culture, diet
- Osteopenia and osteoporosis
- Smoking affects bone mineral density
Osteoporosis
- Rate of bone resorption exceeds rate of bone formation
- Loss in bone density
- Osteopenia – before fracture
- Osteoporosis – involves fracturing
- Affected by menopause – ceases production of estrogen (which affects maintenance of bone matrix)
- Prevention – maximize bone mass
- Vitamin D and calcium
- Weight-bearing exercise