Bloodlines

Bloodlines

            Are you good-looking?  Honestly, are you?  Oh, don’t fret.  Beauty or lack of it is not a curse or divine providence.  We are what we are because of the genes passed on to us by our parents.  Sadly, some genes transmit certain conditions which challenge medical doctors and those who carry them.

Doctors or not, we try to find answers to such questions as “Are you good-looking?” especially when at a loss on how to answer them.  Genetics, the science of genes, therefore, plays a role when faced with questions regarding one’s physicality (or lack thereof) and/or medical condition.  Now, I cordially invite you to learn the fundamentals of inheritance a.k.a. genetics.

 The basics

Chromosomes are threadlike structures found in the nucleus (center) of the cell.  Cells resemble fried eggs (sunny side up) under the microscope, and the egg yolk is the nucleus that contains the chromosomes.

Chromosomes contain the genetic material that codes for specific traits or attributes that will make us what we are, i.e., black-haired, dark, tall, etc.  Humans have 46 or 23 pairs of chromosomes: 23 from the mother and 23 from the father.  A pair is called sex chromosomes because they confer one’s biological sex, i.e., XX in females and XY in males.  The other 22 pairs are called autosomes and they determine traits (hair color, height, etc.) other than one’s biological sex.

The genetic material contained in chromosomes is called DNA.  Deoxyribonucleic acid (DNA) is commonly described as the blueprint of life and is organized into units called genes.

Genes are units of heredity.  We, humans and animals, always inherit a pair of genes from our parents because we, as Earth-born beings, have two biological parents.  Each gene codes for a specific attribute or trait and is designated a letter for easier identification.  For example, the “a” gene stands for the black color (if we assign “a” as black) and makes the animal appear black, “d” for opal, etc.

Alleles are alternate forms of genes, i.e., different versions of a given gene.  Therefore, alleles are also genes.  Let us assume that “MS Word” is a gene.  It has alleles (versions) such as 97 and 2000.  While MS Word 2000 is different from 97, both of them are word processing software and, therefore, function the same way, i.e., they make typing much easier.

Locus is a specific site in the chromosome where the genes that code for a trait or attribute are located.  For example, the A locus contains genes/alleles (A, a, etc.) that code for the color black and its gradations.  The “MS Word” locus contains the alleles 2000, 97, etc.

There are three usual modes of inheritance: recessive, dominant, and sex-linked.  Other modes of inheritance are beyond the scope of this article.

Inheritance is recessive if both parents have to contribute the same allele (I will use “gene” and “allele” interchangeably from this point forward) for the trait to manifest.  Let us say that the black color (trait) is recessive and is designated “a.”  For the offspring to appear black, both parents have to contribute “a” so that the child will have “aa” genes: one “a” from the mother and another “a” from the father.  Genotype is the genetic makeup of an individual.  In this instance, the genotype is “aa.”  Phenotype is the appearance or expression of the genotype.  In this instance, the phenotype of “aa” is black.

Recessive inheritance is represented by lowercase letters, e.g., aa, bb, cc, etc.

Inheritance is dominant if only one allele is needed for the trait to manifest.  Let us say that the black color is dominant and is designated “A.”  For the offspring to appear black, only one parent has to contribute “A.”  The offspring will appear black whatever its companion allele is.  “AA” will appear black and so will “Aa.”

Dominant inheritance is represented by uppercase letters, e.g., Aa, AA, Bb, BB, Cc, etc.

Remember that alleles/genes come in pairs because non-magical Earth-born human beings always have two biological parents.

Identical gene pairs are called homozygous, e.g., AA, aa.  “AA” is homozygous dominant (uppercase) and “aa” is homozygous recessive (lowercase).

Non-identical gene pairs are called heterozygous, e.g., Aa.  Heterozygous gene pairs contain both dominant (A) and recessive (a) genes.

Dominant and recessive modes of inheritance are processed through the autosomes.

Autosomal inheritance

Let us assume that ugliness is inherited dominantly and is designated as “U”; “u” therefore is the opposite of ugliness and represents non-ugliness or beauty.

If an ugly man mates with a beautiful woman, what will their children look like?

In predicting inheritance, we create a Punnett square that tabulates possible genotypes and their corresponding phenotypes.  A Punnett square is a table that crosses the genes contributed by each parent, like this:

	u	u
U
u

Uu = ugly male

uu = non-ugly/beautiful female

Males are usually placed vertically, while females are placed horizontally.  Follow whatever is convenient for you.

Match u (first row, second column) with U (first column, second row) to get Uu, and so on.  The initial Punnett square drawn above now looks like this:

	u	u
U	Uu	Uu
u	uu	uu

The Punnett square above shows that two out of four children will have the genotype Uu, while two will have uu.  This means that half of the children will be ugly (Uu), while the other half will be non-ugly (uu). 

Please note that the “u” in Uu signifies that the ugly child carries a gene for beauty.  “Ugly split for beautiful” is the genetic jargon for this.

What if the mating is between ugly “UU” and non-ugly “uu”?

	u	u
U
U

	u	u
U	Uu	Uu
U	Uu	Uu

The Punnett square above shows only one genotype: Uu.  This means that all the children will be ugly.  Again, the “u” in Uu signifies beauty.  Therefore, they also carry genes for beauty but do not manifest the desirable phenotype.

What if ugliness is inherited recessively? 

Let us designate it as “u.”  “UU” and “Uu” represent non-ugliness (or beauty) and are dominant as their capitalization indicates.  “uu” represents ugliness and is recessive as indicated by lowercase letters.

Let us mate a beautiful person (Uu) to an ugly one (uu).

	U	u
u
u

	U	u
u	Uu	uu
u	Uu	uu

The table above shows that half the children will be non-ugly (Uu) and half will be ugly (uu).

What if the non-ugly person has two doses of non-ugly genes, i.e., has the genotype UU and is mated to an ugly person?  The table should look like this:

	U	U
u
u

	U	U
u	Uu	Uu
u	Uu	Uu

The table above shows that all the children will be non-ugly (Uu) no matter how ugly (uu) one of the parents is.  Please note that the “u” in Uu signifies ugliness.  This means that these beautiful children carry genes for ugliness (beautiful split for ugly).

Please note that the above are only examples to illustrate autosomal modes of inheritance.  Beauty or ugliness is multifactorial and is not limited by genes.  Dermatologists and plastic surgeons not only save lives.  They also do wonders on one’s physical assets, augmenting or adding beauty not accorded by genes. 

Sex-linked inheritance

In humans, female sex chromosomes are represented by XX, while male chromosomes are XY.

Sex-linked inheritance means the trait is transmitted via the sex chromosomes.  All (but one) human sex-linked conditions are transmitted via the X chromosome.  That is why sex-linked is called X-linked inheritance in medical literature.  The most well-known X-linked condition is hemophilia A.  Hemophilia A is a condition where one lacks clotting factor VIII, resulting in easy bruising and bleeding. 

Hemophilia A is carried only in the X chromosome.  The Y chromosome does not carry the trait.  There is another catch in hemophilia A and X-linked inheritance in general in humans: males only need one X chromosome to manifest the condition (to become symptomatic).  There is no carrier condition in males.  Females are carriers (have no symptoms) if only one X chromosome is affected.  They only become symptomatic if both their X chromosomes carry the trait.  One rationale for this is that the X chromosome is so large that it can accommodate a whole bunch of genes.  The Y chromosome, on the other hand, is so small that it can only accommodate maleness.

Let us mate a hemophilic man to a non-carrier, non-hemophilic woman.

	Xh	Y
X
X

XX = woman

XhY = man with hemophilia A

Attach any letter of your choice to X to indicate hemophilia.  I just used “h” for simplicity.  Please remember that female humans have XX chromosomes, and male humans have XY chromosomes.

	Xh	Y
X	XXh	XY
X	XXh	XY

The Punnett square above shows that all the daughters will be carriers (no symptoms because only one X is affected), while all the sons (XY) will be hemophilia-free.

What if the woman is a carrier and the man is hemophilia-free?  This seems to be the usual case because either one has no symptoms.

XY = man with no hemophilia

XXh = asymptomatic woman who carries hemophilia A

	X	Y
Xh
X

	X	Y
Xh	XXh	XhY
X	XX	XY

From the Punnett square above, half the daughters (XXh) will be carriers while half (XX) will be free of hemophilia A, and half the sons (XhY) will have symptoms of hemophilia A and half (XY) will be hemophilia-free.

What if a carrier woman mates with a symptomatic man?

XhY = man with hemophilia A

XXh = asymptomatic woman who carries hemophilia A

	Xh	Y
Xh
X

	Xh	Y
Xh	XhXh	XhY
X	XXh	XY

The table shows that half the daughters (XhXh) will be symptomatic while half (XXh) will be carriers, and half the sons (XhY) will be symptomatic while half (XY) will be hemophilia-free.

Lastly, what if a symptomatic woman mates with a hemophilia-free man?

XhXh = symptomatic woman

XY = man with no hemophilia

	X	Y
Xh
Xh

	X	Y
Xh	XXh	XhY
Xh	XXh	XhY

The table above shows that all the daughters will become carriers (XXh), while all the sons (XhY) will have hemophilia A.

The gay gene

            Which would you prefer?  Looks transmitted via autosomal modes (recessive and dominant) or the X chromosome (X-linked)?  Alas, some things are not given to us by choice, like beauty, like homosexuality.  This brings us to the question: Is there a gay gene?  How is it transmitted?

            Some claim the existence of a gay gene, but this remains to be proven beyond the shadow of a doubt. 

Would it be better for us if a gay gene were found?  Such a gene would finally put to rest the argument that homosexuality is “nurtured.”  This, however, would pose another problem: homophobes trying to excise the gay gene.  Scientific research would then focus on ways to counter our precious DNA.  Can you imagine the X-Men taking their last stand?

            Genes are snippets of what makes us tick.  We have no choice on what attribute they accord us.  However, we have a choice whether or not we let their prescription rule our lives.  If you have a gay gene in you, will you embrace or shun it?

Reminder

            While genetics can give us an idea how many of our children will inherit our traits, it does not always reflect the truth.

            In some families, children are of one sex only, either all male or all female, when there should have been females and males in equal distribution.

            Real-life scenarios shy away from genetics.

            Letter symbols used in genetics vary from breed to breed and species to species.  Chromosome number also differs between species.  Humans have 46 chromosomes.  Cats have 38.  The principles of genetics are the same.

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The above article first appeared in L magazine (now defunct) in 2006 in a slightly different form.  L was a beefcake gay magazine in the Philippines.  The prose and poetry were written by the country’s finest like J. Neil Garcia, Danton Remoto, Roel Manipon, et al.  I was the health columnist.