Genetic Influences on Development Flashcards
(46 cards)
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
