Genetic and Environmental Foundations of Child Development
Nature and Nurture: Genetic and Environmental Foundations of Child Development
Child development is impacted by both genetic or inherited factors and environmental factors. Genetic factors are inherited from both parents at the time of conception, but can be the result of different types of gene interactions. Environmental factors impact different ways families function and children develop. Environmental factors include the ecological systems that may alter family function, socio-economic status and cultural values and public policy.
TOPICS COVERED WILL INCLUDE:
· Family functioning from an ecological systems perspective
· The impact of socioeconomic status
· Cultural values and public policies
The Influence of Alleles
In the argument over nature versus nurture in child development, nature is determined by genes passed down from parent to child during conception. Both parents pass genetic traits to their offspring, but different offspring may acquire different traits from each parent. Why do some children in one family have similar characteristics or appearances and yet other children in the same family look very different? The answer lies in the interaction of genes inherited from the mother and father.
Genes and alleles influence the inheritance of traits, through dominant–recessive inheritance, incomplete dominance, X-linked inheritance, genomic imprinting, mutation, and polygenic inheritance. In order to understand genetic inheritance, you need to understand the basics of how genes work, and how they work together with one another.
Understanding the basic structures and elements of genetics is essential to recognize how various traits are inherited, from appearance to intelligence.
The basic building block of the study of genetics is the gene; a gene is a single unit of genetic information.
A chromosome is a threadlike strand of DNA encoded with a large number of genes. Humans receive 23 chromosomes from each parent, for a total of 46 chromosomes.
An allele is one of a pair of genes that appear at a particular location on a particular chromosome and control the same characteristics in the individual. Humans have two alleles, one from each parent, at each genetic locus, or position, on a chromosome.
The entire genetic makeup of an individual is called the genotype. The genotype can refer to the genetic makeup of an organism with reference to a single trait, set of traits, or an entire complex of traits. It can also refer to the sum total of genes transmitted from parent to offspring.
The phenotype is the appearance of an individual resulting from the interaction of the genotype and the environment, or the expression of the individual’s genes. You can see the phenotype when you look at someone–the phenotype includes expressed and observed traits. The genotype can include a range of traits that are not expressed or observable.The phenotype is determined by the a variety of factors, including how genes relate to one another in the individual, and how environmental factors impact the expression of various genes.
Patterns of Gene-Gene Interactions
Blue eyes are an example of a recessive trait
Genes interact with one another in a variety of different ways to produce genetic traits, ranging from eye color or height to a variety of genetic diseases. Genetic expression and inheritance is not simple. In this lesson, you will learn about some of the ways genes interact with one another and how their interactions define and change the expression of genetic traits.
The expression of many genes is defined by whether or not a gene is dominant or recessive. These terms describe how likely or unlikely it is for the offspring to express this gene, or for the genetic phenotype to appear in the offspring. Differences in the alleles can lead to different visible traits in the individual.
· The differences in the alleles can cause variations in the protein that’s produced by the gene, or they can change protein expression, including when, where, and how much protein is made. Proteins affect the expression of different traits, so variations in protein activity or expression can produce different phenotypes.
Incomplete Dominance Pattern
· Alleles are defined as dominant or recessive. If a dominant allele is present, that allele will be expressed. If a recessive allele is present, it will not be expressed if there is a dominant allele. Dominant and recessive genes were first identified by Gregor Mendel in the 19th century. While studying pea plants, Mendel recognized that the color of the flowers was determined by a dominant or a recessive gene.
The second allele in the pair of genes may be dominant as well, if two of the dominant genes are inherited, or it can be recessive. Think about eye color–while this is a simplified example, many people are familiar with it and it’s a relatively easy one to understand.
In eye color, brown eyes are dominant and blue eyes are recessive. If one parent has two dominant brown genes, represented by BB, all offspring will be brown eyed. If both parents have blue eyes or bb, offspring will be blue eyed. If one parent has brown eyes, but carries a recessive blue eye gene or has the genotype Bb, and the other parent is blue eyed or bb, the parents have a 50 percent chance of having a blue eyed child and a 50 percent chance of having a brown eyed child.
While eye color really doesn’t have a significant impact, other dominant and recessive traits can have a much greater impact on the individual’s life and well being. Some genetic illnesses are typically recessive traits. A healthy individual can carry the recessive gene without expressing signs of the illness. These individuals are called carriers. They do not express the gene, but carry it to the next generation and may pass it to their children. The child is only at risk if each parent carries a recessive gene that codes for the illness. Cystic fibrosis is a common example. If both parents have a recessive gene, the child may be born with cystic fibrosis, even though both parents appear healthy.
In some cases, the genetics associated with an illness of this sort provide other benefits. For instance, sickle cell anemia is a recessive disease that damages red blood cells. For individuals with two recessive sickle cell genes, the illness can be devastating. Individuals with only one copy to the recessive sickle cell gene, however, have a much lower risk of contracting malaria. Being a carrier offers benefits, but having two copies of the recessive gene causes illness.
In these examples, the dominant trait, if present, will be the one expressed. The recessive trait will only be expressed if the individual contains two recessive alleles. While some alleles are dominant and recessive, other alleles show different dominance patterns, including co-dominance and incomplete dominance.
Incomplete Dominance Pattern
· INTERACTIONS BETWEEN ALLELES
· INCOMPLETE DOMINANCE
· RECOGNIZING INCOMPLETE DOMINANCE
While some alleles are dominant and recessive, other alleles interact differently with one another. Where there are several different allele types for a single gene, they may interact differently with one another. They may not be dominant or recessive, but co-dominant.
Alleles that are co-dominant produce a different phenotype than dominant or recessive phenotypes. Blood type presents an effective way to consider co-dominance. You’re probably aware that there are several different blood types: A, B, O and AB. A and B are codominant types, while O is recessive. If you have a type O parent and a type A parent, you will be type A, as O is recessive. If you have a type A and a type B parent, you could end up type AB, if you inherit one type A allele and one type B allele. Co-dominant alleles are alleles that are both expressed in the phenotype-they are neither dominant or recessive.
Incomplete dominance allows aspects of both alleles to be expressed in the phenotype of the individual. For instance, a red flower that cross-breeds with a white flower might produce a white flower, a red flower, or a pink flower. The pink flower would be an example of incomplete dominance. If a black cat and a white cat produced black, white and gray kittens, this would also be an example of incomplete dominance, when the gray kittens show traits of both the black and the white parent.
When incomplete dominance occurs, aspects of both alleles will be expressed. Incomplete dominance may be recognized when the offspring shows a phenotype different from both parents; however, this is not an entirely accurate test for incomplete dominance. The different phenotype must show traits of both parental phenotypes.
X-linked pattern inheritance is another type of genetic inheritance and expression. X-linked traits are found on the X chromosome, one of two sex chromosomes. Females have two X chromosomes, while males have one X chromosome and one Y chromosome. X-linked traits are typically expressed only in males, rather than females.
· In females, the presence of one healthy functional gene and one unhealthy, missing or defective gene on the X chromosomes allow the healthy trait to be expressed or minimize the impact of the unhealthy gene. In a male, the defective x-linked genes are the only ones present, since the Y chromosome is different. In this case, the male may present with the X-linked inheritance.
A number of genetic disorders are x-linked, including hemophilia, a bleeding and clotting disorder, and Fragile-X, a disorder which causes developmental delays. Because of the X-linked inheritance, these disorders are prevalent and more severe in boys than in girls.
We inherit two copies of most genes and both genes are working, functional copies. Epigenetics defines how genes are expressed. In most cases, all epigenetic changes are stripped out of the genes soon after conception; the parental expression of genes does not therefore impact the offspring.