Human Genetics in Biopsychology: Genes, Evolution, and Behavior

the topic of this lecture is human genetics so when we talk about the idea of

biopsychology what it's doing is it's exploring the biological mechanisms that underlie our mental processes and

behavior so among the many things that it studies these things include genetics which will

be the topic of this particular lecture the reason why we talk about genetics is because it focuses on how our inherited

genes can affect not just the physiological but also the psychological traits that a person possesses

biopsychology also looks the structure and function of the nervous system and those will be topics of upcoming

lectures and it also looks at how the nervous system interacts with the endocrine system which will be the topic

of another lecture for this chapter so let's start by talking about human genetics

so studying human genetics can help researchers understand the biological basis underlying the different behaviors

thoughts and reactions of humans this can answer questions such as why do two people who are infected by the same

disease have different outcomes also this leads to things or helps address issues such as are there genetic

components to psychological disorders such as depression for example things like depression there tends to be an

inherited component where people who remembers of the same family for example may be more likely to experience

depression than other people who are unrelated to them we're also interested in questions such

as how genetic diseases are passed through family lines and all of these will be topics that we'll touch on

during this particular lecture so in order to really talk about genetics it's important for us to talk a

little bit about Evolution we've talked a bit about evolutionary theory in the past but it's important for us to

revisit some of these issues so Charles Darwin for example explored the concept of inheritance of Trace

throughout Generations in this theory of evolution through natural selection basic idea is that organisms of the

organisms that are better suited for their environment will survive and reproduce whereas those that are more

poorly suited for their environment tend to die off and not pass on their genes to subsequent Generations

when we're thinking about this idea of evolution it's important for us think about the characteristics and behaviors

that impact survival and reproduction these are characteristics for example that would help protect us against

predators those characteristics that would help us gain access to food and those that would help our Offspring to

survive also things like the sorts of characteristics would help us actually produce offspring are important as well

one of the quotes from Darwin about this sort of issue is it's not the strongest of the species that survives nor the

most intelligent that survives rather it is the one that is most adaptable to change and this will be an

issue that will come back to as we talk about human genetics so following up with Darwin in 1859 he

proposed his theory of evolution by natural selection in his book called The On the Origin of Species and here we can

see a a image of Darwin the book On the Origin of Species contains just one diagram and

it's going to be this diagram here that shows how species evolve over time through the process of natural selection

for example organisms that survive and reproduce tend to then go on to produce offspring of their own to the extent

that they're successful this lineage follows over the course of generations one of the questions that people often

have when talking about this idea of evolution is why is it that certain genetic diseases that cause people to

Die Why Haven't those become less common over time and one example of this is sickle cell

anemia so sickle cell anemia is a genetic condition in which red blood cells take on a crescent-like shape

that's why they're called Sickle cells and these the the change in the shape of these red blood cells affects how they

function one of the consequences of sickle cell anemia is that oftentimes it may cause

individuals to die at an earlier age however this this disorder is still very common among individuals of African

descent if individuals carry only one copy of the Sickle Cell Gene they're thought to

be immune from malaria which is a disease that's really deadly in parts of Africa and so in this example what

happens is that Sickle Cell Anemia right carrying the gene for sickle cell anemia may actually make a person better suited

for their environment right it may make them more resistant to things like malaria however having two copies of

this and actually manifesting the disorder can be problematic itself and we'll talk about other sorts of issues

related to this as we go through the rest of the lecture one of the issues that's important for

us to think about is the issue of genetic variation so genetic variation refers to the genetic differences that

exist between individuals this variation is going to contribute to the ability of a species to adapt to its environment so

for example as environmental conditions change if there's a great deal of variation the idea is that some members

of that species will be better suited to to deal with these change in environmental circumstances

this sort of genetic variation begins when an egg which contains 23 chromosomes in humans is fertilized by a

sperm which also contains 23 chromosomes a chromosome is a long strand of genetic information known as DNA

DNA stands for or is an abbreviation for deoxyribonucleic nucleic acid this is a helix shaped molecule made of nucleotide

base pairs in each chromosome sequences of DNA make up our actual genes and a gene is going to refer to a sequence of

DNA that controls or at least partially controls physical characteristics so for example things like our eye color and

our hair color would be relatively simple the illustrations of that a gene may have multiple possible

variations also known as alleles right this is a specific version of the gene a specific Gene May code for hair color

and the different alleles of that Gene affect what the person's actual hair color will actually be

it's also important for us to discuss the the differences between genotype and phenotype so genotype refers to the

genetic makeup of an individual based on the genetic material the DNA that they've inherited from their parents

in contrast a phenotype describes an individual's observable characteristics such as their hair color skin color

height and build so it's possible that two people may for example have the same phenotype right but may have different

underlying genotypes and so we'll talk about the similarities and differences of genotype versus phenotype as we move

forward it's also important for us to be familiar with the idea of dominant

versus recessive alleles so a majority of inheritable traits are controlled by more than just one Gene

and these are referred to as polygenic traits some traits however are controlled by

only one gene but we'll talk about some of those in these cases alleles can be dominant

or recessive in the example shown up here what we can see is that a is going to be the dominant allele for flower

color this is going to be purple capital A is the dominant and a lowercase a is recessive allele for flower color and

that's going to be white possession of a dominant allele will always result in the expression of that

particular phenotype right so this could be inherited from one parent an a a sort of combination or from both parents a A

or both are capital A's the phenotype of a recessive allele will only be physically expressed in the

phenotype if the person is homozygous for that allele meaning they inherited a recessive allele from both parents so in

this case you would have to have two lowercase a alleles zygous means consisting of two different

alleles so a capital A and a lowercase a homozygous means consisting of two identical alleles so for example two

Capital A's or two lower cases Punnett squares can be a helpful tool for helping us predict how genes will

interact in the production of Offspring basically what will exit what will the phenotype be from these different

genotypes capital B is going to represent the dominant allele and the lowercase BL the lowercase b is going to

represent the recessive allele in this particular Punnett Square so in the example of the cleft chin

which you can see an image of over here so the cleft chin is this little indentation in the example of the cleft

chin where B is a cleft chinless is going to be the dominant allele wherever a pair contains the dominant allele B

you can expect to see a cleft chin phenotype however in cases where there where you would actually see a smooth

chin phenotype right not a cleft chin you'd only see that in in places where there were two copies of the recessive

allele the lowercase B's so for example father if he has uh two of the recessive mother has a dominant anorecessive If

the child inherits uh the dominant from the mother they'll Express the dominance if the if the kid here is going to

inherit the dominant from the mother they would Express dominant in these cases if the if the child is inheriting

the recessives from both the mother and the father they would Express the recessive right the smooth chin

phenotype here's another example of the Punnett Square in this Punnett Square the

capital N represents the dominant allele and lowercase p represents the recessive allele that's associated with the

disorder called PKU if two individuals mate who are heterozygous NP for the allele

associated with PKU their offspring then have a 25 chance of experience of expressing this particular PKU phenotype

right so for example both Mom and Dad both have uh they're both heterozygous for the PKU allele and in this case what

we could see is we get two of the dominant we get a dominant recessive dominant recessive two recessives right

so in this case what we would see is that the only uh individual could be expressing right the uh the PKU the

recessive trait is going to be these individuals here who inherit both recessive alleles from their parents

so where do harmful genes like a PKU come from well many of these are results of mutations mutations are going to be

sudden permanent changes in a gene they occur throughout the process of development

many mutations are harmful but some of these can actually be beneficial so some of the variation that we see among

organisms come through mutations over time we also want to address Gene environment

interactions so nature and nature and nurture are going to work together like complex pieces of a human puzzle

the interaction of our environment and genes makes us who the individuals that we actually are right so again this idea

of nature versus nurture probably is not the right way to think about these sorts of issues in the vast majority of cases

rather it's the interaction of Nature and nurture that make us the people that we are

there are many different ways to consider the interaction between our genes and our environment one is the

idea of the range of reaction so the basic idea here is that genes are going to set the boundaries within which we

can operate and our environment then interacts with the genes to determine where we fall within that range this

idea is going to be a very powerful one that will have a lot of implications for many of the sorts of qualities we'll be

talking about we can also look at genetic environmental correlations this is the

view of Gene environment interaction that asserts that our genes affect our environment and our environment also

influences the expression of our genes there's also the idea of epigenetics this is the study of Gene environment

interactions such as how the same genotype may lead to the expression of different phenotypes