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Chapter 3

PSYC 351 Chapter 3.docx

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PSYC 351
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Chapter 3 1. Mechanism of Inheritance a. Cell Division i. In humans, each cell nucleus contains 23 pairs of chromosomes ii. 22 pairs of autosomes iii. Two types of specialized cells: body cells, germ cells. The difference is based on how they reproduce and their role in hereditary transmission b. Inside the Chromosome c. The Human Genome Project d. Mendel's Studies i. Principles of Genetic Transmission ii. Revision of Mendel's Principles 2. Genetic and Chromosomal Disorders- Mutations are the driving force of evolution. When the errors turn out to be adaptive, they result in improvements in the species. However, most mutations are maladaptive. 90% of all genetic abnormalities result in miscarriage rather than live births. Some genetic disorders are hereditary, while others occur due to errors during cell division meiosis a. Hereditary Disorders- Whether defective genes are expressed in the phenotype depends on whether they are dominant or recessive i. Dominant Traits 1. Dominant traits that cause disorder usually disappear from the species because the affected people usually do not live to reproduce. However, others do get passed to the child, because it simply isn't expressed until late in adulthood (i.e. Huntington's disease) ii. Recessive Traits 1. on average, each of us carries four potentially lethal genes as recessive traits 2. Tay-Sachs disease (infants appear normal at birth and through their first half-year. Then, at about 8 months of age, they usually become extremely listless, blind, die by. No treatment, but carrier screening program dramatically reduced the incidence 3. PKU- body fails to produce an enzyme that breaks down phenylalanine. Thus, abnormal amounts of the substance accumulate in the blood and harm the developing brain cells. Periodic convulsion, seizures, intellectual disability (a disorder characterized by limited intellectual and adaptive functioning) iii. X-linked Traits 1. Y chromosome is much smaller and carries fewer genes (only 307 genes) 2. males are more vulnerable than females to recessive disorders that travel only on the X chromosome 3. hemophilia is an x-linked disorder characterized by serious bleeding disorder caused by low levedls or complete absence of a blood protein essential for clotting 4. Other X-linked diseases are Duchenne muscular dystrophy, red-green colour blindness, and fragile X syndrome b. Structural Defects in the Chromosome- about 1 percent of hyuman babies are born with a chromosomal abnormality. The actual occurrence of chromosomal anomalies may be 25%, but those pregnancies are usually terminated due to miscarriage i. Autosomal Disorders 1. Down syndrome (trisomy-21) - cheerful dispositions and are friendly and outgoing, moderate to severe intellectual disability, poor muscle tone, problems with expressive language, flattened face, folded eyelids 2. likelihood that a couple will produce a child with Down Syndrome increases with the age of the mother 3. <1/1000 babies of mothers under age 30 have down syndrome 4. chance is 70 times higher for mothers between the age of 45-49 5. it's not almost the mother's problem, but sometimes the father who contributes the extra chromosome 6. trisomies may affect other chromosomes as well. However, only those involving the sex chromosomes or the autosomes 13, 18, and 21 result in a viable embryo 7. problem can arise if part of a chromosome is missing 8. a small deletion of genetic material from chromosome 5 produces cri du chat (cat's cry) syndrome (intellectual disability and neuromuscular problems) ii. Disorders of the Sex Chromosome 1. An example: ovum is fertilized by a sperm that carries no sex chromosome at all, or when the sperm provides an X and the ovum has no sex chromosome 2. monosomy of the sex chromosome- an embryo has only an X and is designated 45, XO. 3. Turner's syndrome: 45, XO. Usually, the pregnancy gets terminated before mother even knows about conception. However, those that survive the baby is female in appearance, but the ovaries quickly begin to disappear and do not produce the hormones necessary for the sex differentiation process to continue. The women do not develop breast or menustration , unless they are given hormone therapy. typically short, unusual neck and chest structure, deficiencies in spatial skills, mathematics, attention, and social interaction 4. Trisomny when a male acquires an extra X chromosome. Result: 47 XXY (Klinefelter's syndrome): child is normal male appearance, effect of X may be undectected until puberty: long arms, very little body hair, underdeeveloped penis, overdeveloped breasts, timd, unassertive 5. trisomy: 47: XYY: poor frustration tolerance, increased risk for learning difficulties, poor physical coordination. Current research does not support the contention that most XYY males end up in jail. 3. Studying the Effects of Genes on Behaviour a. Family Studies i. Siblings on average share 50 percent of their genes, Grandchildren with their grandparents/ uncles/ aunts, share 25% ii. Distinguishing between hereditary and environmental influences is a major limitation of the family study method iii. family studies can be of value because they may point have a genetic component and so encourage more definitive research iv. for example, family sudies have shown that a number of traits (i.e. intelligence), do follow the pattern we would expect if genes are imoprant v. family stides have shown that children of mothers who have schizophrenia are about 13 times as likely as children of normal mothers to d
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