Child Development From Infancy to Adolescence. Laura E. Levine
active, and evocative way at different ages.
Conclusion
All human beings begin with the combination of the genes of their two parents. However, we are then born into an environment that shapes the way those genes will be expressed. As we have seen, our genetic inheritance also shapes the environment we will experience. We are a long way from understanding all the complex interactions between genetic inheritance and environmental experiences. As we continue our study of child development, we examine the way development is shaped both by our genetic inheritance and by the environmental context of children’s lives.
Chapter Summary
3.1 How has the study of genetic inheritance changed in the last century?
In the 19th century, Mendel studied the transmission of genetic information from one generation to the next, but genes and their structure were not discovered until the 1950s by Watson and Crick. In 2003, the Human Genome Project mapped all the genes that make up a human being. Genome-wide association tests can now provide information on all the genes in an individual’s genome.
3.2 How do genes and chromosomes function?
Chromosomes are made of chains of genes, which consist of chains of the nucleotide bases guanine, adenine, thymine, and cytosine. The order of these bases gives a cell the instructions for producing different proteins. Genes are generally paired up, with half of each pair coming from each parent. A genotype is the genes a person has for a particular characteristic and the phenotype is the characteristics that are expressed in that person. Dominant genes are expressed in the phenotype regardless of the gene they are paired with, but recessive genes are expressed only if they are paired with another recessive gene, or if they are carried on the X chromosome of a male child with no matching gene on the Y chromosome. Each trait or behavior can be produced by the interaction of many genes, a process called polygenic inheritance. In addition, any one gene may have many different influences, called pleiotropic effects.
3.3 How do genetic disorders develop, and what role do genetic testing and counseling play in identifying, preventing, and treating these disorders?
Single-gene disorders, such as sickle-cell disease and Tay-Sachs disease, result when an individual inherits a pair of recessive genes that carry that disorder. A recessive gene can also appear in the phenotype if it is carried on the X chromosome of a male child and there is no partner for it on the smaller Y chromosome. Disorders such as cystic fibrosis can also result when mutations occur in a gene. Chromosome disorders such as Down syndrome occur when a child receives the wrong number of chromosomes or when there is a change in the structure of the chromosome caused by breakage. Multifactorial inheritance disorders, such as depression and alcoholism, result from the action of many genes that also interact with environmental influences. Genetic counseling helps parents assess the risk that their child might have for certain conditions. During pregnancy, genetic screening tests of the mother’s blood, amniocentesis, and chorionic villus sampling can assess genetic defects. Parents are also offered genetic screening for their newborn, and under certain circumstances older children may receive genetic testing. Important ethical considerations include the privacy of the reports and, when possible, informed consent of the child. Gene therapy is a promising new approach to treating genetic disorders, and some disorders can be treated with environmental interventions.
3.4 How do researchers study the relationship between genetic inheritance and individual traits and behavior?
Studies of concordance rates between adopted children and their birth parents and their adoptive parents, twin studies comparing the concordance rate between monozygotic and dizygotic twins, and studies of identical twins reared apart have examined the relative contributions of genes and environment on children’s behavior. Genome-wide association studies can now link personality characteristics and other traits and behaviors with specific areas of the genome and combinations of genes.
3.5 How do genes and the environment interact?
Canalization is the degree to which genes are affected by environmental variations. Behavioral epigenetics is a system through which chemical tags activate or silence gene activity in response to events or circumstances in the individual’s environment. Genes can also affect the nature of an individual’s environment. In a passive gene-environment interaction, children are born into a family that shares and promotes their own genetically determined abilities and interests. In an active gene-environment interaction, children seek out experiences on their own that fit their genetic endowments. In an evocative gene-environment interaction, children act in a way that draws out or evokes certain responses from those around them.
Key Terms
Active gene-environment interaction 96
Allele 95
Amniocentesis 84
Behavioral epigenetics 94
Canalization 93
Chorionic villus sampling (CVS) 84
Chromosome disorders 81
Chromosomes 72
Concordance rate 88
Dizygotic (DZ) twins 88
Dominant genes 76
Evocative gene-environment interaction 97
Fertilization 72
Gene 73
Gene therapy 86
Generalist genes 79
Genome 73
Genome-wide association 72
Genotype 76
Heritability 87
Molecular genetics 72
Monozygotic (MZ) twins 89
Multifactorial inheritance disorders 81
Mutations 75
Nucleotide 75
Passive gene-environment interaction 96
Phenotype 76
Pleiotropic effects 79
Polygenic inheritance 79
Recessive genes 76
Single-gene disorders 80
Zygote 72
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The genetic transmission of eye