Monday, January 24, 2022

Human DNA Analysis

Biology Index

Where are we going with this? The information on this page should increase understanding related to this standard:  Identify patterns of inheritance to predict genotype/phenotype and solve punnett square problems.

Article includes ideas, images, and content from Troy Smigielski (2022-01)

Human DNA Analysis
(Sort of digging in deep, eh?)

Using DNA technology and a genome database, scientists can detect specific sequences in DNA that are linked to known genetics or genetic disorders.

They could also be the first to link a sequence to a trait.

Lots of words… wow!

A genome is a complete set of genes in an organism.

Since we are talking about DNA, it is probably worth a few words to review how DNA forms.

Chargaff’s Rules

In nucleic acids…
…a purine will ALWAYS bond with a pyrimidine.
…the A pairs with T or U.
…the C pairs with G.

…the number of A and T is always the same.

…the number of C and G is always the same.

In each nucleotide, you have a sugar, a phosphate, and a nitrogen base.

The nitrogen base will be A, G, C, or T (in DNA).

If the base is A, then there will be a T on the other side of it.

Likewise for C and G

DNA analysis looks at the sequences of the pairs, and from that, can learn things about the genetic structure of an organism.

Why would prospective parents decide to have genetic testing?

Prospective parents are often sequenced to test for the presence of genetic disorders.

So how do you do that?

You might be surprised to know that the DNA between any two humans is exactly the same.

DNA fingerprinting is a technique that identifies unique patterns in a person's DNA. On average, about 99.9% of DNA is the same between two humans. The remaining 0.1% is what is targeted in DNA fingerprinting. 

Sounds like there's not much to go on! This 0.1% is still 3 million base pairs.

How could this be useful in real life?

DNA fingerprinting can be especially helpful in solving crimes.

Forensic scientists can sequence DNA left behind at a crime scene and try to match it to a suspect.

What if you find a suspect with an identical twin? 

That's not always a problem! Mutations often arise that can distinguish between the two twins.

Several things can be used to collect a DNA sample. A few are:
  • Blood
  • Sperm
  • Hair with tissue
  • Saliva
  • Any body tissue that is not degraded

What do lab scientists do with one of these samples?

Today, scientists use a method called polymerase chain reaction. (PCR)

PCR uses technology to produce many copies of a small amount of DNA. It amplifies DNA.

Once PCR is done and several copies are made, DNA is separated based on length using gel electrophoresis.

Gel Electrophoresis Examples

The Human Genome Project

The Human Genome Project is a research program aimed at mapping all of the genes in the human body. One goal of this is to identify functions of all genes and proteins so that we can understand them.

If this project is successful, it could greatly impact the medical field and biotechnology companies. There are many implications for the findings of this research.

Gene Therapy

Gene therapy is a process that identifies the problematic gene(s), targets them and changes it. Viruses are often used to carry the normal genes into cells.

This is because they hijack your cells and insert their DNA.

The goal is to repair the DNA in a non-functioning cell so that future mitosis does not repeat the irregularity.

Genetically Modified Organisms: GMOs

Genetically modified organisms can provide alternatives that have the potential to increase productivity, making good cheaper and more readily available. GMOs, however, are the focus of much controversy and concern.

Pedigrees: Tools to study inheritance

Biology Index

Where are we going with this? The information on this page should increase understanding related to this standard:  Identify patterns of inheritance to predict genotype/phenotype and solve punnett square problems.

Article includes ideas, images, and content from Troy Smigielski (2022-01)

Pedigrees: Tools to study inheritance
(Like the thing with dogs to prove they are a purebred?)

Source, 2022

In human genetics, a pedigree is a diagram that shows family history. It is "a diagram of family history that uses [somewhat] standardized symbols. A pedigree shows relationships between family members and indicates which individuals have certain genetic pathogenic variants, traits, and diseases within a family as well as vital status. A pedigree can be used to determine disease inheritance patterns within a family" (Source, 2022).

Biologists use pedigrees to help track family genetics.

A pedigree is a diagram that tracks a certain trait through a family.

It also shows biological relationships between an organism and its family.

Example of a pedigree diagram…

  • A male is a square.
  • A female is a circle.
  • If a shape is colored in, that person has the trait.
  • If a shape is half-colored in, that person is a carrier for the trait.
  • If a shape is not colored in, that person does not have the trait.

Most pedigrees do not use the half-shaded shapes to denote a heterozygote.

The main purpose of a pedigree is to look at the presence of the traits and "reverse engineer" the genotypes of the people depicted.
In this Punnett Square, two
heterozygous parents are crossed
to produce offspring.

Whereas with a Punnett Square, the genotypes are used as a way to predict the possible phenotypes of the offspring, a pedigree is pretty much the opposite!

A pedigree attempts to determine the genotypes of the individuals involved by looking at the observable phenotypes.

It is very important to remember that the shaded in shapes are the ones that represent people who HAVE the trait. Shaded or unshaded do not directly relate to being dominant or recessive. They show IF a trait is present. The same people coded for different traits will be shaded differently.

The very fancy image above shows the same seven people. On the left, they are shaded in to show who has blue eyes. On the right, they are shaded in to show who has brown eyes. The result is that the two pedigrees, since tracking different traits, are shaded in differently. Also, the shading will usually not be color-synced to the trait.

Working from the pedigree diagram of traits (phenotypes), it is possible to conclude certain things about the genotypes of the individuals represented.

It is a bit of a game, albeit perhaps not a fun game. Not in the sense of, say Candy Crush is fun (if you think that game is fun). Probably, the better way to describe it is to say it is like solving a puzzle.

In genetics, there are rules about dominant and recessive traits that set up strict possible outcomes (recall Punnett Squares.) Using these rules, the puzzle of the pedigree can sometimes be solved fairly easily.

Depending on what traits are passed from the parents to the children, geneticists can make decisions regarding if a trait is dominant or recessive.

In many, many, cases, the key to "cracking the code" is to find in the pedigree a case where parents that are the same (both have a trait, or both don't have the trait) have a child that is their opposite. (See below).

Of the six possible Punnett squares, there is only ONE case where that happens!

The only case where
parents have the same phenotype AND the child has a different phenotype
is in the case of Aa x Aa (Top row, center).

Think about it…

If the parents are the same and the child is different, then one of two things occurs, and—here's the good news—it occurs because the parents are heterozygous AND the child is homozygous recessive.

So… Say a trait (let's use B for dominant and b for recessive) is dominant and both parents have it. In the pedigree, their boxes would be filled in (left image below). For a child to NOT have it, both parents would have to provide the "b" version of the gene (the recessive). So, in the image on the left, the parents are Bb and the child is bb.

Because the trait is dominant, when the child gets the bb genotype, the trait is not expressed. The shape is filled in.

NOW, suppose the trait is recessive and NEITHER parent is showing it. BUT! A child has it. This can only happen if the parents are heterozygous and if they both provide the "b" version of the gene. In this case, the shaded boxes are showing a recessive trait.

Because the trait is recessive, when the child gets the bb genotype, the trait is expressed. The shape is filled in. 

Solving the puzzle of the pedigree begins, however, with the shaded boxes and circles. Based on how they are arranged, we reverse-think the genotypes.

The key, to repeat, is to find same parents with a different child. If you do that, you KNOW that the parents are heterozygous.

  • If both parents have the trait, but one of their children does not, then the trait is dominant.
  • If neither parent has the trait, but one of their children does, then the trait is recessive.

(Let's use B for dominant and b for recessive again.)

1. Find like parents with a different child. 
THIS ASSURES you have heterozygous parents ( Bb ) AND a homozygous recessive ( bb ) child. Let's call this the different child the First-Found. 

2. Do the parents or child have the trait?

3. IF the parents have the trait, it is dominant. IF the child has the trait, it is recessive. 

4. If the First-Found is shaded, then ALL of the shaded boxes are homozygous recessiveIf the First-Found is NOT shaded, then ALL of the NOT shaded boxes are homozygous recessive.  Whatever the First-Found is, everything with that shading is homozygous recessive ( bb ). 

5. Now, for all of the boxes that have shading that is opposite the First-Found, you can put at least ONE of the dominant genes in the shape ( B_ ).

6. You cannot prove that something is homozygous dominant. Some shapes will have just the one gene shone  ( B_ ).

7. Considering that the bb shapes can ONLY provide a b, figuring out the genotype of the rest of the shapes is fairly obvious. Any parent of a bb child must have at least one b!

As an example, here is a pedigree with the parents and three generations of offspring:

It could be a pedigree for any trait. We'll call it the "B" trait (B for dominant and b for recessive). 

Using this pedigree, it is possible to deduce both genotypes and whether or not the trait is dominant or recessive.

Let's just pick out some things this pedigree shows…

There are 10 males in this family line.

Three (3) of them are affected by the trait.

Since the trait appears in the offspring of non-affected parents, it must be recessive. Hence the genotype of everyone in shaded boxes is bb.

Therefore, the non-affected parents must both pass the recessive trait to the child and, thus, must be heterozygous (e.g. Bb).

Looking at the II generation, the female #1 (who is not a descendent of the parents) crosses with a double recessive (homozygous recessive, bb) male. Since the produce three affected offspring, then it can be concluded that Gen II Female 1 is heterozygous (Bb) for the trait.

Looking at the II generation, male #2 must be double recessive (homozygous recessive, bb), since the recessive trait appears (when crossed with heterozygous, Bb female #2).

If a trait appears in individuals of both typical sexes (XX, XY), then the trait is autosomal and not a sex-linked trait. 

In the pedigree below , for a recessive trait, any individual showing the trait (colored boxes) must have the double recessive (homozygous recessive, bb) genotype.

Similarly, any individual NOT showing the trait must have at least one B in their genotype.

Pedigree of a autosomal recessive trait.

The "puzzle buster" is found in the children of parents 8 and 9. 

Since child 17 shows the trait that the parents (8 and 9) don't show, then the trait MUST be recessive AND the parents MUST be heterozygous.

17 is bb.

8 and 9 are Bb.

Then, ALL of the shaded boxes are bb

Then, ALL of the unshaded boxes have at least 1 dominant gene ( B_ ).

Then, any parent of a bb child has at least 1 b.

Let's have a look at another pedigree and think about a few more things…

Both 1 and 2 have the trait. Of their children, one of them has a different trait. Since 7 has a different trait from the parents…

1. The parents gave a gene to the child different from the one they are expressing, and that trait showed up. Therefore the trait the parents are showing is dominant.

2. Since 7 shows the other trait (which must be recessive) they must have received the recessive trait from both parents.

3. Therefore the parents are heterozygous (Bb) and 7 is homozygous recessive (double recessive, bb).

4. Since both 7 and 8 are expressing the recessive trait, they both must be homozygous recessive (bb).

5. Since 5, 6, and 9 have the trait and include both male and female individuals, the trait must NOT be sex-linked which makes it autosomal dominant.

In a dominant trait, the shaded in individuals must have at least one “B” while the unshaded individuals must be “bb”.

Here is a pedigree showing a sex linked trait:

Whereas neither Generation I, 1 nor 2 show the trait, but it appears in generation II means that it is recessive. That it appears only in males suggests that it is sex-linked. Thus, females I-2, II-1, II-5, and III-2 must carry the trait.

When determining whether the trait is autosomal or sex-linked, look at the gender of those affected. As a general trend, males are more commonly affected by sex-linked genetic traits than females.

Another way to know it is sex-linked is if the mother has the trait and so do all of her sons.

However, just because a trait is sex-linked does not mean that females can never get it too.

Wednesday, January 19, 2022

Introducing Human Genetics

Biology Index

Where are we going with this? The information on this page should increase understanding related to this standard:  Identify patterns of inheritance to predict genotype/phenotype and solve punnett square problems.

Article includes ideas, images, and content from Troy Smigielski (2022-01)

Introducing Human Genetics:
Sex-linked Inheritance
(Pleased to meet you! See what I did, there?)

In previous articles, we have looked closely at genetics. In this and a few more that will follow, we will apply those to humans as a specific case of some additional general genetics principles.

Recall that…

  • Genetic information is carried by DNA.

  • DNA is organized into structures called chromosomes.

  • Chromosomes carry information for specific traits in sections called genes.

  • Genes having different versions or variations of a trait are alleles.

  • Some traits are dominant, some are recessive, some are incompletely dominant, and some are codominant.

  • Some traits require information from more than one gene; these are polygenic.

  • Humans have 46 chromosomes organized into 23 pairs; one chromosome from each pair comes from the mother and the other one comes from the father.
We should probably repeat some of that, but with pictures!

Humans have 23 pairs of each chromosome. That is to say, there are two each of the 23 different chromosomes that are paired up. That makes 46; 23 come from the mother and 23 come from the father.

In other words, humans have two copies of each chromosome. This makes us diploid organisms.

Wooo, that's a cool picture! What's it called?

Biologists use diagrams called karyotypes to map out chromosomes of an organism. For example, there is not a human.

To create a karyotype, biologists take pictures of cells in stages of mitosis. Then, they organize the chromosomes by size and shape. Something like the following…

So, in other words, it's magic?

A karyotype can give you three major pieces of information:

  1. How many chromosomes an organism has
  2. Sex of the organism
  3. Presence of a chromosomal disorder
How can that bunch of dark splotches tell what the sex of an organism is?

Sex/gender is all about the 23rd pair of chromosomes.

The 23rd chromosome pair of a male is XY.
The 23rd chromosome pair of a female is XX.

To indicate an organism biologically, scientists use the number of chromosomes followed by XX or XY for sex. For example, a human male would be 46,XY and a human female would be 46,XX.

The X and Y chromosomes are called sex chromosomes because they determine sex. In humans, these are found on the 23rd pair.

All chromosomes that do not determine sex are called autosomes. In humans, these are the first 22 pairs. Most genes are located somewhere on an autosome.

Determining The Sex of Offspring

So, genetics… all that… genes… chromosomes… all of this must let us figure things out. For instance, what is the probability that a baby will be a male? A female?


How do we know that? 

What two sex chromosomes does mom have? X and X…

What two sex chromosomes does dad have? X and Y…

We can find probabilities of the offspring being a certain sex through Punnett squares. Males will either pass on an X or a Y chromosome. Females will pass on an X chromosome no matter what.

Looking at the Punnett square, two of the boxes have XX and two have XY. Hence, half will be mail and half will be female.

Since only the male can pass the Y, then ultimately, the father ultimately the sex of the child.

Somebody should have told Henry XIII… Just saying…

Sex-linked Traits and Disorders

Although most traits are carried on the autosomes, some traits and disorders are carried on the sex chromosomes. These are called sex-linked traits.

Sex-linked traits: traits that are carried on the sex chromosomes.

Other traits that are carried on Chromosomes #1-22 are called autosomal traits. Sex-linked traits and disorders are typically carried on the X chromosome because it is larger and has more space to carry genes. The Y chromosome is shorter and does not carry as many genes. Most sex-linked traits are recessive.

So… Think… If the recessive trait is on the X chromosome, since the male has only one of them, it will be expressed; there's no "competing trait" on the Y chromosome. In the female, there is a chance that the other X chromosome will carry the dominant trait, so the recessive trait won't be expressed.

Let's look at this idea with another image…
Source, 2022-01-21

In the image above, the Y chromosome does not have the genes labeled A, B, and C. (This is an example and does not necessarily model real genes exactly.) Therefore, whatever traits are controlled by those genes will come through in the child. The Y chromosome has no alternative to offer; the gene of the X chromosome will be expressed.

Example: Color Blindness

Many people can think of someone who is color blind. If you can, are they male or female? You probably answered that they were male. Why?

Sex-linked traits and disorders are more common in males. Why is that?

Since men only have one X chromosome, whatever is on it will be expressed. Since women have two X chromosomes, they get “two chances”.

Example: Hemophilia

Hemophilia is a recessive, sex-linked disorder. Both males and females can have it.

In the image to the right, the father has the recessive trait on the X chromosome. He has no allele for that trait on the Y chromosome. The female has one X with, and one X without the trait. 

Therefore, the presence of hemophilia is determined by which of th X chromosomes the female passes.

The four possible outcomes are shown in among the daughters and sons.

There are numerous sex-linked disorders that come from X chromosome. Thus, these disorders can only be passed on from the mother. Three of them are shown in the image below.

Some Examples of Sex-linked Traits:

  • Red-green colorblindness
  • Male Pattern Baldness
  • Hemophilia
  • Duchenne Muscular Dystrophy

Predicting The Inheritance of Sex-linked Traits

We can do Punnett squares to determine the likelihood that offspring will inherit a sex-linked trait.

Below, the gene H is indicated as being part of the X chromosome. The H is the dominant, "unaffected" trait and the h is the recessive "affected" trait.

If we were to cross a normal male with a colorblind female, the results would be predictable using a Punnett square. It would show both the chances for sons and daughters to have the condition. 

This is the Punnett square for the above cross:

Note that the female carries the recessive c gene for color blindness on each of the X chromosomes. The male does not have gene for color blindness at all on the Y chromosome and has the dominant gene (not color blind) on his X chromosome.

Hence, the daughters will always get the "not color blind" X chromosome from the father (and the recessive c "color blind" gene from the mother. So, 0% of the daughters will be color blind.

The sons will get the Y chromosome from the father which does not have a gene for color blindness at all. Thus, the Xc chromosome from the mother (she has 2) will always be expressed. Therefore, 100% of the sons will be color blind.

Origins of Sex-linked Trait Understanding

The classic example of X-linked inheritance is eye color of fruit flies (Drosophila melanogaster).

Thomas Hunt Morgan was working with fruit flies when he noticed that most of the flies that had white eyes were males. (Fruit flies can have either red or white eyes.) 

This told him that eye color must be carried on the X chromosome because one is much more common in males. This also told him that red eyes are dominant to white eyes.

Red eyes are the wild type which means they are normal and more common. White eyes are the mutant type which means they are abnormal and less common.

Using Punnett squares, different combinations of different crosses can be examined. Where R is the dominant (red) trait and r is the recessive (white) trait, we get this:

Female Key:
XRXR = red eyes
XRXr = red eyes
XrXr = white eyes

Male Key:
XRY = red eyes
XrY = white eyes

Crossing a heterozygous female with a white-eyed male would result in:

50% of females have red eyes.

50% of males have red eyes.

This process can be repeated, of course, for any variation of the cross.

Non-typical Genetic Outcomes

There are occasions when the normal process does not take pace just right. Normally, the process of meiosis results in four haploid gametes.

Sometimes, the separating process does not go as expected. When chromosomes separate incorrectly during Meiosis, it is called non-disjunction.

That might look something like this (instead of the illustration above).

This leads to aneuploidy which is when one of the gametes has the incorrect number of chromosomes.

Aneuploidy can occur in both the autosomes and in the sex chromosomes. There are a numerous kinds of aneuploidy caused by nondisjunction. A few of them are illustrated below:

is when the offspring only received one copy of a chromosome.
Trisomy is when the offspring received three copies of a chromosome.

Down syndrome is when an individual received three copies of chromosome #21. This is also known as Trisomy 21.

Klinefelter’s syndrome is when an individual receives XXY chromosomes; this results in the male phenotype with enlarged breasts.

Turner's syndrome is when an individual receives one X chromosome; this results in the female phenotype with underdeveloped breasts and degenerated ovaries.

Interactions Of Chromosomes

The human body only needs one X chromosome. Women have 2 X chromosomes, so they inactivate one of them. The inactivated chromosome is called a Barr body.

The presence or absence of the disorder is determined as soon as you are created. X-inactivation happens after zygote formation, and some scientists think that a type of decision making process may occur at the cellular level.

A cat with different colors is very likely a female. This is because the fur color gene is on the X chromosome. At different places on the cat’s body, different X chromosomes are inactivated. Therefore, there are different colors in different spots. 

For a male to have different colors, he would have to have XXY.

Wednesday, January 12, 2022

Law of Independent Assortment and Non-Mendelian Genetics

Biology Index

Where are we going with this? The information on this page should increase understanding related to this standard:  Identify patterns of inheritance to predict genotype/phenotype and solve punnett square problems.

Article includes ideas, images, and content from Troy Smigielski (2022-01)

Law of Independent Assortment
and Non-Mendelian Genetics
(Onward and upward?)

So in previous articles, we explored genetics, many concepts of which grew out of Gregor Mendel's research.

Beyond the importance of how traits pass, he discovered something else.

Gregor Mendel also found out that genes are distributed to gametes independently from one another. He called this Law of Independent Assortment. This means that the version passed on of Gene A has no effect on the probability of getting either version of Gene B.

For example, just because a person has brown hair does not mean he or she will definitely have green eyes. Nor does it mean that the eye color will definately be green. Hair color does not determine eye color.

This is because the hair color gene is distributed (assorted) independently from the eye color gene. The gene for any one trait can be passed on with any combination of genes for other traits.

The  Law of Independent Assortment greatly increases genetic variation because it allows for any possible combination of available genes. Combined with the crossover process in meiosis, independent assortment results in the vast range of trait variations genetic diversity that can be observed.

Mendel came to the understanding of independent assortment while doing his famous experiment with pea plants.

In additions to the color of the flower bloom, pea plants exhibit many other traits (including those pictured above). The dominant variations of the trait are at the top.

So, crossing the purebred (homozygous) varieties resulted in heterozygous plants in the F1 generation. When Mendel crossed those heterozygous plants, he ended up with a lot of variations in the F2 generation.

If he looked at any one trait, in the F2 generation, the predicted 1:2:1 genotype and 3:1 phenotype was observed. But many of the other traits would be mixed in.

This is because genes for the various traits are inherited separately from each other (Law of Independent Assortment).

So, would it be possible for a cross between AaYy (axial; yellow) x AaYy (axial; yellow) to produce an axial, green-seed plant?

In order to have an axial plant, there must be at least one dominant "A" gene (AA or Aa). To have green seeds, requires that both of the genes be recessive (yy).

Can that happen?

REMINDER: Each parent will contribute one allele for each gene.

Yes; it is possible because you could inherit an “A” from either parent resulting in the genotype “AA” (axial). 

You could also inherit a “y” from both parents resulting in the genotype “yy” (green). 

This is possible because these genes are inherited separately from each other (Law of Independent Assortment).

We can visualize that with two punnett squares. Because the genes assort independently, you can do two independent Punnett squares to find out if this is possible.

What if you wanted to examine two traits at the same time using a single Punnett square? Is that possible? 

Dihybrid Cross Punnett Squares

It is possible to set up two or more traits in one Punnett square. There's a process…

Recall that to look at one trait, the genotype of each parent is written, one at the top horizontally and one at the side vertically. (See above examples.)

When looking at more than one trait, the genotype will take on a form like…




Now, the same process is used… but with an added level of complexity.

To set up the square, write out the genotype for both, one at the top and one along the side.

In the above illustration, we have two homozygous parents:


Number the genes 1 to 4…

1  2  3  4
A a  Y  y

Going along the top, you will put in the genes in this order:

1 and 3

1 and 4

2 and 3

2 and 4

Do the same thing down the side to get what is shown in the image above.

Then, you fill in each box much like with a one trait Punnett square. Take the genes from the top and side and order them into the boxes. You would end up with this:

A dihybrid Punnett square is an effective way to examine the offspring with consideration to two trait at the same time.

Law of Independent Assortment Recap

The Law of Segregation states that alleles separate independently during gamete formation.

Law of Independent Assortment states that genes separate independently during gamete formation.

Non-Mendelian Inheritance

Not all patterns of inheritance follow Mendelian Laws of dominance. There are other other systems by which traits can be passed from the parents to the offspring.

Incomplete dominance is where one allele does not show complete dominance over the other; they meet in the middle. Instead, of seeing the dominant trait, the traits of each allele can be thought to blend.

The most common example of this if crossing a red flower with a white flower and all offspring have pink flowers.

Though the homozygous parents are red and white, the heterozygous offspring are neither. They are a blend of the two.

Codominance is where both alleles appear in the phenotype; they are both expressed. A common example of this is blood type. 
If blood type can be homozygous A or homozygous B, the heterozygous version of this is AB. Both traits are present.

You can think of incomplete dominance as blending of one version of the trait with the other. Red wasn't quite dominant enough to fully show up… it partly showed up as a blend. Dominance was incomplete.

For codominance, think of a team with co-captains or a club with co-presidents. You would say Bob and Mary are the co-chairs of our club. Codominance means that both of the versions of the trait show up. The flower is red and white, both. Co = and.

Polygenic traits are traits (physical appearance) that are affected by more than one gene. In actuality, most traits are polygenic. Common examples include height, skin color, eye color, and hair color.

To explain a little more, a trait like height might be made up of… let's say four genes. Each gene would appear as two alleles (versions) of the trait. Height would be the result of all of the genes combined.

Suppose someone's genotype for height looked like…


Those four genes would work together to establish the genetic potential for height. Of course, environmental factors such as nutrition would further influence height.

Someone with AAbbCcdd would have a different genetic potential for height.
Someone with aaBbccDD would also have a different genetic potential for height.

In polygenic traits (remember, most traits are polygenic), several genes mutually have a say in the ultimate phenotype that is produced.