What Is The Source Of Genetic Makeup For The Human Body? Psychology

iii.ane Man Genetics

Learning Objectives

By the end of this section, you volition be able to:

Explicate the basic principles of the theory of evolution by natural choice
Describe the differences betwixt genotype and phenotype
Discuss how gene-environment interactions are critical for expression of physical and psychological characteristics

Psychological researchers study genetics in order to better empathise the biological ground that contributes to sure behaviors. While all humans share certain biological mechanisms, we are each unique. And while our bodies have many of the aforementioned parts—brains and hormones and cells with genetic codes—these are expressed in a wide variety of behaviors, thoughts, and reactions.

Why exercise two people infected by the same illness have different outcomes: one surviving and one succumbing to the ailment? How are genetic diseases passed through family lines? Are there genetic components to psychological disorders, such as depression or schizophrenia? To what extent might there be a psychological basis to health atmospheric condition such as childhood obesity?

To explore these questions, let's start by focusing on a specific affliction,sickle-cell anemia, and how it might affect two infected sisters. Sickle-jail cell anemia is a genetic condition in which ruby-red blood cells, which are normally round, accept on a crescent-like shape. The changed shape of these cells affects how they function: sickle-shaped cells can clog claret vessels and block blood flow, leading to loftier fever, severe hurting, swelling, and tissue damage.

An illustration shows round and sickle-shaped blood cells.

Normal claret cells travel freely through the blood vessels, while sickle-shaped cells grade blockages preventing blood menstruation.

Many people with sickle-jail cell anemia—and the detail genetic mutation that causes information technology—die at an early on historic period. While the notion of "survival of the fittest" may suggest that people suffering from this disease have a low survival rate and therefore the disease volition go less common, this is not the case. Despite the negative evolutionary furnishings associated with this genetic mutation, the sickle-cell cistron remains relatively common amongst people of African descent. Why is this? The explanation is illustrated with the following scenario.

Imagine two young women—Luwi and Sena—sisters in rural Zambia, Africa. Luwi carries the gene for sickle-cell anemia; Sena does not conduct the gene. Sickle-jail cell carriers have one copy of the sickle-cell factor merely do not have full-diddled sickle-cell anemia. They experience symptoms only if they are severely dehydrated or are deprived of oxygen (as in mountain climbing). Carriers are idea to be immune from malaria (an ofttimes mortiferous disease that is widespread in tropical climates) because changes in their claret chemistry and immune functioning preclude the malaria parasite from having its furnishings (Gong, Parikh, Rosenthal, & Greenhouse, 2013). Still, full-blown sickle-jail cell anemia, with two copies of the sickle-cell gene, does not provide immunity to malaria.

While walking home from schoolhouse, both sisters are bitten by mosquitos carrying the malaria parasite. Luwi does not get malaria considering she carries the sickle-cell mutation. Sena, on the other hand, develops malaria and dies only 2 weeks later. Luwi survives and eventually has children, to whom she may pass on the sickle-cell mutation.

Visit this website to learn more nearly how a mutation in Dna leads to sickle-cell anemia.

Malaria is rare in the United States, and so the sickle-cell factor benefits nobody: the cistron manifests primarily in health problems—minor in carriers, astringent in the full-diddled disease—with no health benefits for carriers. Still, the situation is quite unlike in other parts of the world. In parts of Africa where malaria is prevalent, having the sickle-cell mutation does provide health benefits for carriers (protection from malaria).

This is precisely the situation that CharlesDarwin describes in the theory of evolution past natural selection. In simple terms, the theory states that organisms that are better suited for their environment will survive and reproduce, while those that are poorly suited for their environment volition dice off. In our instance, we tin can see that every bit a carrier, Luwi'south mutation is highly adaptive in her African homeland; however, if she resided in the Usa (where malaria is much less common), her mutation could prove plush—with a high probability of the affliction in her descendants and pocket-sized health problems of her own.

(a) In 1859, Charles Darwin proposed his theory of evolution past natural selection in his book,On the Origin of Species. (b) The book contains only 1 illustration: this diagram that shows how species evolve over time through natural pick.

TWO PERSPECTIVES ON GENETICS AND Behavior

It's easy to get confused about two fields that report the interaction of genes and the environment, such as the fields ofevolutionary psychology andbehavioral genetics. How can we tell them autonomously?

In both fields, it is understood that genes not simply code for particular traits, but also contribute to certain patterns of knowledge and behavior. Evolutionary psychology focuses on how universal patterns of beliefs and cognitive processes accept evolved over time. Therefore, variations in noesis and behavior would make individuals more or less successful in reproducing and passing those genes to their offspring. Evolutionary psychologists study a variety of psychological phenomena that may take evolved as adaptations, including fearfulness response, food preferences, mate selection, and cooperative behaviors (Confer et al., 2010).

Whereas evolutionary psychologists focus on universal patterns that evolved over millions of years, behavioral geneticists report how individual differences arise, in the present, through the interaction of genes and the environs. When studying homo behavior, behavioral geneticists often employ twin and adoption studies to research questions of interest. Twin studies compare the rates that a given behavioral trait is shared among identical and fraternal twins; adoption studies compare those rates among biologically related relatives and adopted relatives. Both approaches provide some insight into the relative importance of genes and environment for the expression of a given trait.

Lookout man this interview with renownedevolutionary psychologist David Osculation for an explanation of how a psychologist approaches development and how this approach fits within the field of social science.

<br />

Genetic Variation

Genetic variation, the genetic difference between individuals, is what contributes to a species' accommodation to its environment. In humans, genetic variation begins with an egg, about 100 meg sperm, and fertilization. Fertile women ovulate roughly once per month, releasing an egg from follicles in the ovary. During the egg'south journey from the ovary through the fallopian tubes, to the uterus, a sperm may fertilize an egg.

The egg and the sperm each contain 23 chromosomes. Chromosomes are long strings of genetic material known every bit deoxyribonucleic acrid (DNA). DNA is a helix-shaped molecule made up of nucleotide base of operations pairs. In each chromosome, sequences of DNA make up genes that control or partially control a number of visible characteristics, known every bit traits, such as eye color, pilus color, and so on. A single gene may have multiple possible variations, or alleles. An allele is a specific version of a factor. So, a given factor may lawmaking for the trait of hair colour, and the dissimilar alleles of that gene impact which pilus colour an individual has.

When a sperm and egg fuse, their 23 chromosomes pair up and create a zygote with 23 pairs of chromosomes. Therefore, each parent contributes half the genetic information carried by the offspring; the resulting physical characteristics of the offspring (called the phenotype) are determined by the interaction of genetic material supplied by the parents (chosen the genotype). A person's genotype is the genetic makeup of that individual. Phenotype, on the other hand, refers to the individual'south inherited physical characteristics, which are a combination of genetic and environmental influences.

Image (a) shows the helical structure of DNA. Image (b) shows a person's face. (a) Genotype refers to the genetic makeup of an individual based on the genetic material (DNA) inherited from one's parents. (b) Phenotype describes an individual's observable characteristics, such as hair color, skin colour, acme, and build. (credit a: modification of work by Caroline Davis; credit b: modification of work by Cory Zanker)

Most traits are controlled by multiple genes, but some traits are controlled by one cistron. A feature likecleft chin, for example, is influenced by a unmarried gene from each parent. In this example, we volition call the gene for cleft chin "B," and the gene for smooth mentum "b." Crack mentum is a ascendant trait, which ways that having the dominant allele either from i parent (Bb) or both parents (BB) will always result in the phenotype associated with the dominant allele. When someone has two copies of the aforementioned allele, they are said to be homozygous for that allele. When someone has a combination of alleles for a given gene, they are said to be heterozygous. For case, smooth chin is a recessive trait, which ways that an individual will merely brandish the smooth chin phenotype if they are homozygous for that recessive allele (bb).

Imagine that a adult female with a crack mentum mates with a man with a smoothen chin. What type of chin will their child accept? The answer to that depends on which alleles each parent carries. If the adult female is homozygous for cleft chin (BB), her offspring will always accept crevice chin. It gets a petty more complicated, withal, if the mother is heterozygous for this factor (Bb). Since the male parent has a smoothen chin—therefore homozygous for the recessive allele (bb)—we can expect the offspring to have a l% take chances of having a cleft chin and a 50% chance of having a polish chin.

(a) APunnett square is a tool used to predict how genes will interact in the production of offspring. The majuscule B represents the dominant allele, and the lowercase b represents the recessive allele. In the example of the scissure chin, where B is cleft chin (dominant allele), wherever a pair contains the dominant allele, B, you lot can expect a crevice chin phenotype. You lot can expect a smooth mentum phenotype only when there are two copies of the recessive allele, bb. (b) A cleft chin, shown here, is an inherited trait.

Sickle-cell anemia is just 1 of many genetic disorders caused by the pairing of 2 recessive genes. For example,phenylketonuria (PKU) is a condition in which individuals lack an enzyme that normally converts harmful amino acids into harmless byproducts. If someone with this condition goes untreated, he or she will experience significant deficits in cognitive function, seizures, and increased hazard of various psychiatric disorders. Because PKU is a recessive trait, each parent must have at least one copy of the recessive allele in society to produce a child with the condition.

So far, we take discussed traits that involve only one gene, but few human characteristics are controlled by a single gene. Most traits are polygenic: controlled by more than than ane gene. Top is one example of a polygenic trait, as are skin color and weight.

In thisPunnett square, N represents the normal allele, and p represents the recessive allele that is associated with PKU. If 2 individuals mate who are both heterozygous for the allele associated with PKU, their offspring have a 25% chance of expressing the PKU phenotype.

Where do harmful genes that contribute to diseases similar PKU come up from? Gene mutations provide one source of harmful genes. A mutation is a sudden, permanent change in a gene. While many mutations can be harmful or lethal, once in a while, a mutation benefits an individual by giving that person an advantage over those who do not have the mutation. Recall that the theory of evolution asserts that individuals best adapted to their particular environments are more than likely to reproduce and pass on their genes to futurity generations. In guild for this process to occur, at that place must be competition—more technically, at that place must exist variability in genes (and resultant traits) that allow for variation in adaptability to the surroundings. If a population consisted of identical individuals, then any dramatic changes in the surroundings would affect anybody in the same manner, and there would be no variation in selection. In contrast, diversity in genes and associated traits allows some individuals to perform slightly better than others when faced with environmental modify. This creates a distinct advantage for individuals all-time suited for their environments in terms of successful reproduction and genetic transmission.

Gene-Environment Interactions

Genes exercise not exist in a vacuum. Although we are all biological organisms, nosotros also exist in an environment that is incredibly important in determining non only when and how our genes express themselves, but too in what combination. Each of united states represents a unique interaction between our genetic makeup and our environment; range of reaction is one way to describe this interaction. Range of reaction asserts that our genes set the boundaries inside which we can operate, and our environment interacts with the genes to determine where in that range nosotros will fall. For example, if an private's genetic makeup predisposes her to loftier levels of intellectual potential and she is reared in a rich, stimulating environment, and so she will be more likely to achieve her full potential than if she were raised under conditions of significant impecuniousness. Co-ordinate to the concept of range of reaction, genes set definite limits on potential, and environment determines how much of that potential is accomplished. Some disagree with this theory and argue that genes do not prepare a limit on a person's potential.

Some other perspective on the interaction between genes and the surround is the concept of genetic environmental correlation. Stated but, our genes influence our environment, and our surround influences the expression of our genes. Not merely exercise our genes and environment collaborate, as in range of reaction, but they also influence i another bidirectionally. For instance, the kid of an NBA actor would probably be exposed to basketball from an early historic period. Such exposure might let the child to realize his or her full genetic, athletic potential. Thus, the parents' genes, which the child shares, influence the child'southward environs, and that environment, in turn, is well suited to support the child's genetic potential.

Nature and nurture work together like complex pieces of a human puzzle. The interaction of our surround and genes makes us the individuals nosotros are. (credit "puzzle": modification of work by Cory Zanker; credit "houses": modification of work by Ben Salter; credit "Dna": modification of piece of work by NHGRI)

In another arroyo to gene-surroundings interactions, the field of epigenetics looks beyond the genotype itself and studies how the same genotype can be expressed in different means. In other words, researchers study how the same genotype can lead to very different phenotypes. As mentioned earlier, gene expression is often influenced past environmental context in ways that are non entirely obvious. For instance, identical twins share the same genetic information (identical twins develop from a single fertilized egg that split, so the genetic fabric is exactly the aforementioned in each; in contrast, fraternal twins develop from two different eggs fertilized by different sperm, so the genetic fabric varies equally with non-twin siblings). But even with identical genes, in that location remains an incredible amount of variability in how gene expression can unfold over the class of each twin's life. Sometimes, ane twin will develop a disease and the other volition not. In one example, Tiffany, an identical twin, died from cancer at age 7, just her twin, at present 19 years sometime, has never had cancer. Although these individuals share an identical genotype, their phenotypes differ as a consequence of how that genetic information is expressed over time. The epigenetic perspective is very different from range of reaction, because here the genotype is not fixed and limited.

Visit this site for an engaging video primer on theepigenetics of twin studies.

Genes affect more than than our physical characteristics. Indeed, scientists have plant genetic linkages to a number of behavioral characteristics, ranging from basic personality traits to sexual orientation to spirituality (for examples, come across Mustanski et al., 2005; Comings, Gonzales, Saucier, Johnson, & MacMurray, 2000). Genes are also associated with temperament and a number of psychological disorders, such as depression and schizophrenia. Then while it is truthful that genes provide the biological blueprints for our cells, tissues, organs, and trunk, they besides take meaning impact on our experiences and our behaviors.

Let's look at the following findings regarding schizophrenia in light of our three views of gene-environment interactions. Which view do you remember all-time explains this evidence?

In a study of people who were given upward for adoption, adoptees whose biological mothers had schizophrenia (i.eastward. genetic risk present)and who had been raised in a 'dysfunctional' family unit, (i.e. ecology hazard present), environment were much more probable to developschizophrenia or some other psychotic disorder than were whatever of the other groups in the study:

Of adoptees whose biological mothers had schizophrenia (loftier genetic adventure) and who were raised in a dysfunctional family environments, 36.8% were likely to develop schizophrenia.
Of adoptees whose biological mothers had schizophrenia (high genetic risk) and who were raised in healthy family environments, 5.8% were likely to develop schizophrenia.
Of adoptees with a depression genetic risk (whose mothers did not have schizophrenia) and who were raised in a dysfunctional family environments, v.3% were likely to develop schizophrenia.
Of adoptees with a low genetic take chances (whose mothers did non have schizophrenia) and who were raised in healthy family unit environments, iv.8% were probable to develop schizophrenia (Tienari et al., 2004).

The study shows that adoptees with loftier genetic adventure were especially likely to develop schizophrenia only if they were raised in a dysfunctional home environments. This enquiry lends brownie to the notion that both genetic vulnerability and ecology stress are necessary for schizophrenia to develop, and that genes alone practise not tell the full tale.

SUMMARY

Genes are sequences of Deoxyribonucleic acid that code for a particular trait. Different versions of a gene are chosen alleles—sometimes alleles tin exist classified as dominant or recessive. A dominant allele always results in the ascendant phenotype. In lodge to exhibit a recessive phenotype, an private must be homozygous for the recessive allele. Genes affect both physical and psychological characteristics. Ultimately, how and when a cistron is expressed, and what the outcome volition be—in terms of both physical and psychological characteristics—is a function of the interaction between our genes and our environments.

References:

Openstax Psychology text past Kathryn Dumper, William Jenkins, Arlene Lacombe, Marilyn Lovett and Marion Perlmutter licensed under CC Past v4.0. https://openstax.org/details/books/psychology

Exercises

Review Questions:

1. A(n) ________ is a sudden, permanent change in a sequence of DNA.

a. allele

b. chromosome

c. epigenetic

d. mutation

2. ________ refers to a person's genetic makeup, while ________ refers to a person's physical characteristics.

a. Phenotype; genotype

b. Genotype; phenotype

c. Deoxyribonucleic acid; cistron

d. Factor; Deoxyribonucleic acid

3. ________ is the field of study that focuses on genes and their expression.

a. Social psychology

b. Evolutionary psychology

c. Epigenetics

d. Behavioral neuroscience

4. Humans accept ________ pairs of chromosomes.

a. fifteen

b. 23

c. 46

d. 78

Disquisitional Thinking Questions:

1. The theory of evolution by natural selection requires variability of a given trait. Why is variability necessary and where does information technology come from?

Personal Application Questions:

i. You share half of your genetic makeup with each of your parents, simply you lot are no dubiousness very different from both of them. Spend a few minutes jotting downwards the similarities and differences between you and your parents. How do you recall your unique environment and experiences have contributed to some of the differences you see?

Glossary:

allele

chromosome

deoxyribonucleic acid (DNA)

dominant allele

epigenetics

congenial twins

gene

genetic environmental correlation

genotype

heterozygous

homozygous

identical twins

mutation

phenotype

polygenic

range of reaction

recessive allele

Answers to Exercises

Review Questions:

1. D

two. B

iii. C

4. B

Critical Thinking Questions:

one. Variability is essential for natural selection to piece of work. If all individuals are the same on a given trait, there will exist no relative divergence in their reproductive success because everyone will be every bit adapted to their environments on that trait. Mutations are one source of variability, simply sexual reproduction is some other important source of variation given that individuals inherit half of their genetic makeup from each of their parents

Glossary:

allele:specific version of a cistron

chromosome:long strand of genetic information

deoxyribonucleic acid (Deoxyribonucleic acid): helix-shaped molecule made of nucleotide base of operations pairs

dominant allele: allele whose phenotype volition be expressed in an individual that possesses that allele

epigenetics:study of factor-environment interactions, such as how the same genotype leads to different phenotypes

fraternal twins:twins who develop from two different eggs fertilized by different sperm, then their genetic material varies the aforementioned every bit in non-twin siblings

cistron:sequence of Dna that controls or partially controls physical characteristics

genetic environmental correlation: view of gene-environment interaction that asserts our genes affect our environment, and our environment influences the expression of our genes

genotype:genetic makeup of an individual

heterozygous:consisting of two dissimilar alleles

homozygous:consisting of two identical alleles

identical twins: twins that develop from the aforementioned sperm and egg

mutation:sudden, permanent alter in a factor

phenotype: individual's inheritable concrete characteristics

polygenic:multiple genes affecting a given trait
range of reaction: asserts our genes fix the boundaries within which we tin operate, and our environs interacts with the genes to determine where in that range we will fall

recessive allele:allele whose phenotype will exist expressed only if an individual is homozygous for that allele
theory of evolution by natural pick: states that organisms that are better suited for their environments will survive and reproduce compared to those that are poorly suited for their environments