Genetic Influences on Development Flashcards
What is the “heritability index”?
A statistic used to estimate the degree to which a particular characteristic can be attributed to genetic factors.
What have studies on the heritability index of intelligence shown?
Range from .30 to .70 with average being about .50 meaning that about 50% of individual differences in IQ scores can be explained by genetic factors.
22 of the 23 pairs of human chromosomes are ___________ meaning that they are exact duplicates of each other. They are known as ___________.
Homologous; autosomes
23rd pair of chromosomes are made up of the _____ chromosomes. In females the pair is ___________ and called the ____ chromosome pair; in males, the pair is ___________ and called the ____ chromosome.
Sex chromosomes; homologous; XX; not homologous; XY
What are some examples of dominant characteristics and recessive characteristics?
Dominant = dark hair, immunity to poison ivy, normal hearing, and type B blood
Recessive = red hair, susceptibility to poison ivy, congenital deafness, and type O blood
What is one example of a sex-linked characteristic?
Red-green color blindness which is carried on the X chromosome and is twice as common in males than in females.
Give a few examples of disorders due to presence of 2 recessive gene.
PKU = lacking enzyme to break down amino acid (phenylalanine) which in undigested form is a toxic agent in brain and causes severe MR. MR preventable by diet low in phenylalanine in first 6-9 years of life (avoid foods like milk, eggs, fish, bread). Tay-Sachs, sickle-cell, cystic fibrosis are other recessive gene examples.
Give an example of a disorder due to the presence of a single dominant gene.
Huntington’s Chorea is an example of an autosomal dominant gene disorder. Child of affected parent has a 50% chance of inheriting this disorder.
How many babies born with chromosomal abnormalities?
Approximately 1 in 200
Chromosomal abnormalities can be caused by:
Extra chromosome, missing chromosome, chromosome translocation (when section of chromosome is attached to another chromosome), or chromosomal deletion (which occurs when part of a chromosome is missing like in Prader-Willi characterized by MR and extreme obesity).
What is the most common chromosomal abnormality?
Down Syndrome (trisomy 21); occurs in about 1 of every 800 live births with frequency rising dramatically with increasing maternal age; 1 in 1,900 ages 20-24; 1 in 30 for mothers over 45
Characteristics of Down Syndrome
Moderate to profound MR, short, stocky build, flattened face, protruding tongue, almond-shaped eyes; often have heart abnormalities, thyroid dysfunction, malformations of intestinal tract, susceptibility to respiratory infections
Sex-linked chromosomal abnormalities include
Klinefelter’s Syndrome and Turner’s Syndrome
Klinefelter’s Syndrome
Affects males and caused by extra X chromosome, i.e., XXY; have typical masculine interests and develop normal male identity but show incomplete development of secondary sex characteristics and are often sterile
Turner’s Syndrome
Occurs in females when all or part of second X chromosome is missing; they don’t develop secondary sex characteristics, are sterile, and tend to have short stature, stubby fingers, and webbed neck.
Fragile X Syndrome
Due to weak site on X chromosome and can occur in both males and females though more evident effects are seen in males who lack influence of normal/2nd X chromosome; constellation of physical, intellectual, and behavioral deficits including mod to severe MR, facial deformities, and rapid, staccato speech rhythm
The effects of exposure to teratogens depend on what kinds of factors (name 3)
- Amount of exposure
- Length of exposure
- Period of development when exposure occurs
Over what period of time does the germinal period last? What can effects of teratogens over this time be?
Lasts from conception to implantation, occurring 8-10 days later; may only damage a few cells having little to no effect on development OR may affect many cells and cause organism’s death
Over what period of time does the embryonic period last? What can effects of teratogens over this time be?
From end of 2nd week after conception to end of 8th week; developing organs are MOST susceptible to major defects, with time of greatest susceptibility depending on particular organ system; i.e., CNS from beginning of 3rd week to beginning of 6th week and heart from middle of 3rd week to middle of 6th week
Over what period of time does the fetal period last? What can effects of teratogens over this time be?
Beginning of 9th week to birth; organ systems less affected, but exposure can still cause less severe defects, especially to external genitalia and brain; prolonged exposure tends to cause retarded growth and lowered IQ
Most common teratogens include
Alcohol, drugs (illegal, prescription, OTC), smoking, maternal disease
Alcohol as a teratogen info
Heavy consumption can lead to severe and largely irreversible abnormalities to child including FAS;
FAS
FAS sxs vary depending on amount consumed and can include retarded growth, facial deformities, microcephaly (small, underdeveloped brain), irritability, hyperactivity, variety of neurological abnormalities; most children mentally retarded w/IQs between 65-70; it’s the leading cause of MR in US; can be born w/o full syndrome present and w/1 or more sxs, i.e., lowered IQ, irritability; as many as 1 in every 100 births shows FAS or FAE
Heroin or methadone
Increases risk for prematurity, low birth weight, physical malformations, respiratory disease, mortality at birth; born physically addicted to drug and show w/d sxs at birth; may show similar sxs as maternal marijuana use
Marijuana
Associated with low birth weight, muscle tremors, increased startle response and visual problems; may show similar sxs as maternal heroin use
Cocaine use
Retard fetal growth, can cause preterm birth and malformations of brain, intestinal and genital-urinary tract; Babies may be born w/hemorrhages, lesions and swelling in brain, small head circumference, heart defects, brain seizures, abnormal motor development
Cocaine-exposed infants tend to show more…
Irritability, rigidity, muscle tremors, difficulty self-soothing, difficulty being consoled, excessively reactive to environmental stimuli; often impaired sensory fx, decreased visual attention, difficulty regulating own state of arousal (asleep, awake, attentive); in school, concentration/memory problems, learning disabilities, & social problems
OTC & Prescription Drugs (benzos)
Benzos associated w/prenatal syndrome including feeding problems, hypothermia, deficiency in baby’s muscle tone
Mood stabilizers
Known teratogens; Lithium in 1st trimester increases risk for Ebstein’s Anomaly (heart defect) by 10x & valproic acid increases risk for fetal malformation; lithium around time of birth associated with perinatal syndrome including bluish discoloration of skin and decreased muscle tone
Smoking
At risk for spontaneous abortion, prematurity, low birth weight, death during period surrounding birth; less responsive to environment more irritable as compared to infants of nonsmokers; prenatal nicotine exposure linked to increased hyperactivity, short attention span, reduced school achievement in reading, math, spelling
Most maternal diseases that cause prenatal defects are viral or bacterial?
Viral
Maternal Rubella virus (German measles)
heart defects, eye cataracts, deafness, gastrointestinal anomalies, MR; 20% die shortly after birth; most severe damage during 4th-8th week of pregnancy
Maternal Herpes simplex virus (HSV)
3x increased risk of miscarriage if contracted in early pregnancy; babies usually contract it through delivery rather than prenatal development; baby typically delivered via cesarean to prevent exposure; exposed babies have high risk for death, brain damage, or blindness; use of antiviral meds helps about 1/2 infected prevent permanent damage (e.g., serious neurological damage, MR, or even death)
Cytomegalovirus (CMV)
Another type of herpes virus that is very dangerous to fetuses; infection during embryonic stage (weeks 2-8) usually results in death of embryo; later infection baby at risk for retarded growth, blindness, deafness, MR, microencephaly (small head circumference associated w/delayed motor, speech, and mental development), and cerebral palsy
Syphilis
Baby at risk for birth defects like deafness, facial deformities, malformations of teeth and bones, excess fluid in brain and MR; Tx of mother can protect baby from effects of syphilis
HIV virus
Transmission from mother to child during pregnancy, labor, and delivery or breast-feeding called perinatal transmission; in US, w/o antiretroviral therapy approx 25% pregnant women infected will transmit virus to child; however, w/therapy, rate can be decreased to 2% or less; risk reduced w/AZT given to mom during last 2 trimesters of pregnancy and to infant during 1st 6 weeks of life; so far no adverse effects of AZT found
HIV Newborns
Higher-than-average rates of prematurity and small for gestational age; during 1st year of life, most develop early sxs of virus including increased susceptibility to other infections, failure to thrive, swollen lymph nodes, and developmental delays
Development of HIV
About 25% HIV-infected infants develop AIDS & 15% die during 1st year of life though reports of children living into late adolescence w/current txs of AZT & antibiotics; High risk for infections and immunological abnormalities & CNS dysfunctions including loss of developmental milestones, attention/concentration problems, & declining IQ scores
Name 3 other maternal conditions that affect development
Prenatal nutrition, emotional stress, & maternal age
Prenatal nutrition
Depends when it occurs and severity; 1st trimester = spontaneous abortion or congenital malformations; 3rd trimester = low birth weight and low brain weight d/t fewer neurons, less dendrite branching, and reduced mylenization; behavioral consequences can include apathy, unresponsive to environmental stimuli, irritability, abnormally high-pitched cry, intellectual deficits, & lags in motor development
Emotional stress
Chronic, severe anxiety or stress = more medical complications and infants w/greater number of abnormalities than women who are relatively anxiety-free; stress associated with spontaneous abortion, premature delivery, more difficult labor; high risk for low birth weight, respiratory problems, irritability & hyperactivity, bowel irregularities, sleep & eating problems; high stress during pregnancy doesn’t always lead to negative outcomes and problems associated w/stress greatly reduced w/supportive social relationships
Maternal age
Majority of women have healthy births regardless of age; percentage of babies w/low birth weight greatest for moms under 15 y.o. and over 45; over 35, slightly higher risk for complications like miscarriage, placenta previa, high BP, diabetes, & cesarean birth; egg & sperm quality decline w/age; increased risk of congenital defects like Down’s Syndrome in older mothers, especially first time moms in 40s
Other complications of pregnancy or delivery =
Premature infants, small-for-gestational age (SGA), and fetal distress
Premature infants
Infant born before 37 weeks considered premature; risks linked to lack of prenatal care, malnutrition, maternal age (esp < 15 y.o.), drug use, low SES, multiple gestations; many premature now survive however; w/appropriate medical attention & supportive environment, premature infants w/o significant abnormalities often catch up to peers in terms of cognitive language and social skills by 2-3 y.o.
Small-for-gestational age (SGA)
Newborn or birth weight below 10th percentile for expected weight; higher risk for respiratory disease, hypoglycemia, & asphyxia during birth
Fetal distress
Condition during birth process that indicates fetus is at risk d/t change in heart rate, respiration, or anoxia; prolonged anoxia may result in delayed cognitive and motor development, MR, & cerebral palsy
