What Is The Genetic Makeup Of An Individual

iii.1 Human Genetics

Learning Objectives

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

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

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

Why do two people infected by the same illness accept different outcomes: one surviving and one succumbing to the ailment? How are genetic diseases passed through family lines? Are in that location genetic components to psychological disorders, such as low or schizophrenia? To what extent might there be a psychological basis to health conditions such as childhood obesity?

To explore these questions, let'due south start by focusing on a specific disease,sickle-cell anemia, and how it might touch two infected sisters. Sickle-cell anemia is a genetic status in which cherry blood cells, which are normally round, take on a crescent-like shape. The changed shape of these cells affects how they function: sickle-shaped cells can clog claret vessels and cake blood flow, leading to high fever, severe pain, swelling, and tissue damage.

An illustration shows round and sickle-shaped blood cells.

Normal blood cells travel freely through the blood vessels, while sickle-shaped cells form blockages preventing blood flow.

Many people with sickle-cell anemia—and the particular genetic mutation that causes it—dice at an early age. While the notion of "survival of the fittest" may propose that people suffering from this disease take a depression survival rate and therefore the disease will become less common, this is non the case. Despite the negative evolutionary effects associated with this genetic mutation, the sickle-prison cell gene remains relatively mutual among 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 carry the factor. Sickle-cell carriers have 1 copy of the sickle-cell gene but practice not take full-diddled sickle-cell anemia. They feel symptoms only if they are severely dehydrated or are deprived of oxygen (as in mountain climbing). Carriers are thought to be immune from malaria (an often deadly affliction that is widespread in tropical climates) because changes in their claret chemistry and immune performance prevent the malaria parasite from having its effects (Gong, Parikh, Rosenthal, & Greenhouse, 2013). However, full-blown sickle-cell anemia, with ii copies of the sickle-prison 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 non get malaria considering she carries the sickle-cell mutation. Sena, on the other manus, develops malaria and dies just 2 weeks afterward. Luwi survives and eventually has children, to whom she may pass on the sickle-prison cell mutation.

Visit this website to learn more virtually how a mutation in Deoxyribonucleic acid leads to sickle-cell anemia.

Malaria is rare in the U.s.a., and then the sickle-cell gene benefits nobody: the gene manifests primarily in health problems—minor in carriers, severe in the full-blown illness—with no health benefits for carriers. All the same, the situation is quite different 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 state of affairs that CharlesDarwin describes in the theory of evolution by natural option. In simple terms, the theory states that organisms that are amend suited for their environment will survive and reproduce, while those that are poorly suited for their surroundings volition die off. In our case, nosotros tin can see that every bit a carrier, Luwi's mutation is highly adaptive in her African homeland; however, if she resided in the Us (where malaria is much less common), her mutation could bear witness costly—with a loftier probability of the disease in her descendants and pocket-size wellness bug of her ain.

(a) In 1859, Charles Darwin proposed his theory of development by natural option in his book,On the Origin of Species. (b) The book contains but one illustration: this diagram that shows how species evolve over time through natural selection.

Two PERSPECTIVES ON GENETICS AND Behavior

It's easy to go confused virtually ii fields that study the interaction of genes and the environs, such as the fields ofevolutionary psychology andbehavioral genetics. How tin can nosotros tell them autonomously?

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

Whereas evolutionary psychologists focus on universal patterns that evolved over millions of years, behavioral geneticists study how individual differences arise, in the nowadays, through the interaction of genes and the environment. When studying human being behavior, behavioral geneticists oftentimes employ twin and adoption studies to research questions of involvement. Twin studies compare the rates that a given behavioral trait is shared amongst 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.

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

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Genetic Variation

Genetic variation, the genetic difference between individuals, is what contributes to a species' adaptation to its surroundings. In humans, genetic variation begins with an egg, most 100 million sperm, and fertilization. Fertile women ovulate roughly in one case per calendar month, releasing an egg from follicles in the ovary. During the egg's 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 as deoxyribonucleic acrid (Dna). DNA is a helix-shaped molecule fabricated up of nucleotide base pairs. In each chromosome, sequences of Deoxyribonucleic acid make up genes that command or partially control a number of visible characteristics, known equally traits, such equally middle color, hair colour, and so on. A single gene may accept multiple possible variations, or alleles. An allele is a specific version of a cistron. So, a given gene may lawmaking for the trait of hair color, and the unlike alleles of that gene bear on which hair color an individual has.

When a sperm and egg fuse, their 23 chromosomes pair upward 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 (called the genotype). A person'south genotype is the genetic makeup of that individual. Phenotype, on the other manus, 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 (Deoxyribonucleic acid) inherited from one'south parents. (b) Phenotype describes an individual's observable characteristics, such as hair colour, skin color, superlative, and build. (credit a: modification of work by Caroline Davis; credit b: modification of work by Cory Zanker)

Well-nigh traits are controlled past multiple genes, just some traits are controlled past one gene. A characteristic likecleft chin, for example, is influenced past a single gene from each parent. In this example, we will call the gene for scissure mentum "B," and the factor for polish chin "b." Fissure chin is a dominant trait, which means that having the dominant allele either from i parent (Bb) or both parents (BB) will always consequence in the phenotype associated with the ascendant 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 cistron, they are said to be heterozygous. For example, smooth chin is a recessive trait, which means that an individual will only display the smooth mentum phenotype if they are homozygous for that recessive allele (bb).

Imagine that a woman with a crack mentum mates with a human being with a shine chin. What type of chin will their child have? The respond to that depends on which alleles each parent carries. If the adult female is homozygous for fissure chin (BB), her offspring will ever have crack mentum. It gets a niggling more complicated, however, if the female parent is heterozygous for this gene (Bb). Since the father has a smooth chin—therefore homozygous for the recessive allele (bb)—nosotros tin expect the offspring to have a 50% chance of having a cleft chin and a fifty% chance of having a smoothen mentum.

(a) APunnett foursquare is a tool used to predict how genes volition interact in the product of offspring. The capital letter B represents the dominant allele, and the lowercase b represents the recessive allele. In the example of the crack chin, where B is cleft mentum (dominant allele), wherever a pair contains the dominant allele, B, y'all can expect a fissure chin phenotype. You can expect a smooth chin phenotype simply when at that place are 2 copies of the recessive allele, bb. (b) A crevice chin, shown here, is an inherited trait.

Sickle-cell anemia is but one of many genetic disorders caused by the pairing of two recessive genes. For instance,phenylketonuria (PKU) is a condition in which individuals lack an enzyme that commonly converts harmful amino acids into harmless byproducts. If someone with this condition goes untreated, he or she will feel pregnant deficits in cognitive function, seizures, and increased risk of various psychiatric disorders. Considering PKU is a recessive trait, each parent must take at to the lowest degree one copy of the recessive allele in gild to produce a kid with the condition.

So far, we take discussed traits that involve just one gene, merely few human characteristics are controlled by a single gene. Most traits are polygenic: controlled by more one gene. Height 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 two 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 like PKU come 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 private by giving that person an reward over those who exercise not have the mutation. Think that the theory of development asserts that individuals all-time adapted to their particular environments are more than likely to reproduce and laissez passer on their genes to future generations. In club for this process to occur, there must be contest—more technically, at that place must be variability in genes (and resultant traits) that allow for variation in adaptability to the environment. If a population consisted of identical individuals, then whatsoever dramatic changes in the environment would affect anybody in the aforementioned manner, and there would be no variation in selection. In contrast, diversity in genes and associated traits allows some individuals to perform slightly amend than others when faced with environmental change. This creates a distinct reward for individuals all-time suited for their environments in terms of successful reproduction and genetic transmission.

Factor-Environment Interactions

Genes do non exist in a vacuum. Although nosotros are all biological organisms, we also be in an environs that is incredibly important in determining not only when and how our genes limited themselves, only too in what combination. Each of united states of america represents a unique interaction between our genetic makeup and our environment; range of reaction is one way to draw this interaction. Range of reaction asserts that our genes prepare the boundaries within which we can operate, and our environment interacts with the genes to determine where in that range we will fall. For example, if an individual'southward genetic makeup predisposes her to loftier levels of intellectual potential and she is reared in a rich, stimulating environment, then she will be more likely to attain her full potential than if she were raised under conditions of significant impecuniousness. According to the concept of range of reaction, genes set definite limits on potential, and surround determines how much of that potential is achieved. Some disagree with this theory and argue that genes practise not set a limit on a person'due south potential.

Another perspective on the interaction between genes and the environment is the concept of genetic environmental correlation. Stated only, our genes influence our environs, and our environment influences the expression of our genes. Not only exercise our genes and surroundings collaborate, as in range of reaction, just they likewise influence one another bidirectionally. For example, the child of an NBA actor would probably exist exposed to basketball from an early age. Such exposure might permit the child to realize his or her total genetic, able-bodied potential. Thus, the parents' genes, which the child shares, influence the child'south environment, and that surroundings, 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 environment and genes makes us the individuals we are. (credit "puzzle": modification of work past Cory Zanker; credit "houses": modification of work past Ben Salter; credit "Dna": modification of work by NHGRI)

In another arroyo to gene-environment interactions, the field of epigenetics looks across the genotype itself and studies how the same genotype tin can be expressed in different ways. In other words, researchers study how the same genotype tin can lead to very different phenotypes. Every bit mentioned earlier, gene expression is often influenced by 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 material is exactly the same in each; in contrast, fraternal twins develop from 2 dissimilar eggs fertilized by different sperm, so the genetic fabric varies every bit with non-twin siblings). But even with identical genes, in that location remains an incredible amount of variability in how factor expression can unfold over the class of each twin's life. Sometimes, one twin will develop a affliction and the other will non. In 1 example, Tiffany, an identical twin, died from cancer at age 7, just her twin, now nineteen years old, has never had cancer. Although these individuals share an identical genotype, their phenotypes differ as a result of how that genetic information is expressed over time. The epigenetic perspective is very dissimilar from range of reaction, considering here the genotype is not stock-still and limited.

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

Genes bear on more than our physical characteristics. Indeed, scientists accept institute 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. So while it is true that genes provide the biological blueprints for our cells, tissues, organs, and body, they also have significant touch on our experiences and our behaviors.

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

In a study of people who were given upwardly for adoption, adoptees whose biological mothers had schizophrenia (i.e. genetic risk nowadays)and who had been raised in a 'dysfunctional' family, (i.due east. environmental risk present), environment were much more than probable to developschizophrenia or some other psychotic disorder than were any of the other groups in the study:

Of adoptees whose biological mothers had schizophrenia (high genetic risk) and who were raised in a dysfunctional family environments, 36.eight% 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 low genetic risk (whose mothers did not have schizophrenia) and who were raised in a dysfunctional family environments, v.three% were likely to develop schizophrenia.
Of adoptees with a depression genetic risk (whose mothers did non take schizophrenia) and who were raised in good for you family environments, 4.8% were likely to develop schizophrenia (Tienari et al., 2004).

The study shows that adoptees with loftier genetic run a risk were particularly likely to develop schizophrenia only if they were raised in a dysfunctional home environments. This research lends credibility to the notion that both genetic vulnerability and environmental stress are necessary for schizophrenia to develop, and that genes solitary practise non tell the full tale.

SUMMARY

Genes are sequences of DNA that code for a particular trait. Different versions of a factor are called alleles—sometimes alleles can be classified equally dominant or recessive. A ascendant allele always results in the dominant phenotype. In order 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 part of the interaction betwixt our genes and our environments.

References:

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

Exercises

Review Questions:

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

a. allele

b. chromosome

c. epigenetic

d. mutation

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

a. Phenotype; genotype

b. Genotype; phenotype

c. DNA; factor

d. Gene; Dna

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

a. Social psychology

b. Evolutionary psychology

c. Epigenetics

d. Behavioral neuroscience

iv. Humans have ________ pairs of chromosomes.

a. 15

b. 23

c. 46

d. 78

Critical Thinking Questions:

one. 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:

one. You share half of your genetic makeup with each of your parents, but you are no incertitude very different from both of them. Spend a few minutes jotting downward the similarities and differences betwixt y'all and your parents. How do you call back your unique environment and experiences accept contributed to some of the differences you come across?

Glossary:

allele

chromosome

deoxyribonucleic acid (Dna)

dominant allele

epigenetics

fraternal 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

ii. B

3. C

iv. B

Disquisitional Thinking Questions:

1. Variability is essential for natural selection to piece of work. If all individuals are the same on a given trait, at that place will be no relative difference in their reproductive success because everyone volition be as adjusted to their environments on that trait. Mutations are one source of variability, but sexual reproduction is another 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 (Dna): helix-shaped molecule made of nucleotide base pairs

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

epigenetics:written report of cistron-environment interactions, such as how the same genotype leads to different phenotypes

congenial twins:twins who develop from two dissimilar eggs fertilized past dissimilar sperm, and then their genetic material varies the same as in non-twin siblings

cistron:sequence of Deoxyribonucleic acid that controls or partially controls concrete characteristics

genetic ecology correlation: view of factor-environs 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 unlike alleles

homozygous:consisting of ii identical alleles

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

mutation:sudden, permanent alter in a factor

phenotype: individual's inheritable physical characteristics

polygenic:multiple genes affecting a given trait
range of reaction: asserts our genes set the boundaries within which we can operate, and our environment interacts with the genes to determine where in that range we will autumn

recessive allele:allele whose phenotype will be expressed merely if an private is homozygous for that allele
theory of evolution by natural selection: states that organisms that are ameliorate suited for their environments will survive and reproduce compared to those that are poorly suited for their environments