What happens when our recipes combine with our partner’s recipes?
What happens when our recipes combine with our partner’s recipes?
Well, each member of the couple, irrespectively of what their personal combination might be, will find that the other partner may express any of the previously mentioned combinations for any given recipe. Based on these recipes, at the time of fertilisation, the different combinations, giving the different probabilities of presenting some trait or hereditary disorder, will be appear.
As stated previously, in order for the number of chromosomes to remain constant and for germinal cells to be able to fertilise, a reductional division or meiosis has to occur. To explain the risk percentages in the different types of heredity, we will focus on the type of cells that are produced immediately after reductional division has taken place, as these are the only possible resulting combinations.
Under normal conditions in a woman, one of these cells is lost. Since we do not know which one of them will be lost, and one cell complements the other, both will be studied. These are the only two possible combinations and any of the two can occur.
From now on we will only refer to one single character encoded by the same chromosomal set, which will be represented as follows:
Given that each of us has two chromosomes from each set, our resulting gametes will be these.
And our partner’s gamete will be these.
We will always be talking about the same recipe within the same chromosomal set, for both members of the couple.
And now let me give you a graphic representation of the different combinations that can result in reproduction.
If we pay close attention we will see that we are all a mixture of all the characters that run in our family. Our hair can be the same colour as that of our maternal grandfather and our eyes can be the same colour as our paternal grandfather’s, the hands may resemble our maternal grandmother’s and the teeth can be exactly like our father’s.
For sure, you will ask yourselves: How is this mixture possible?
Well, it is extremely easy. Chromosomes of a same set exchange information between them before they undergo reductional division or meiosis. That is, recipe number 4 from chromosome number 1 is exchanged for recipe number 4 from the other chromosome number 1, and this same process is repeated in many other recipes.
In the end, the resulting chromosomes are a mixture of all the recipes or characters from our ancestors.
And it is thanks to this exchange that the variability of the species prevails, making each of us different from the other, unique and unrepeatable.
But, for every thing to come out right, each chromosome of the same set must contain the same recipes at the end of this process, irrespectively of whether they have been exchanged or not, so that each chromosome has all the recipes it needs, without a single one missing or in excess.
And, which different combinations can result when we reproduce?
You have different options:
Read through all the combinations, which will provide you with a global view. We recommend this option as it will enhance your overall understanding as to how we fight disorders today.
Read through only a few pages starting at the beginning, so that you become familiar with how these combinations give rise to disorders.
And if you are at specific risk, because you fall into any of the situations described, I suggest that you first read everything and then come back to the section that concerns your particular case.
As you can see, it is very easy.
Sex linked disorders (X-chromosomes disorders)
In this group, there can be two possible scenarios: that the pathological “X”-chromosome is carried by the female or the male, and that, in turn, this X-chromosome-linked character is expressed in a dominant or recessive way.
To identify the “X” -chromosomes that are contained in the incorrect recipe, this symbol will be used:
Please do not forget that we are always referring to the same character or allele located in the X -chromosome, both in the man and in the woman alike.
“That is, we are always referring to the same recipe in both genders”.
PLEASE REMEMBER that in this case, the X chromosome with the wrong recipe, in the presence of another X chromosome with the right recipe, will express because it is dominant, IN OTHER WORDS, IT DOMINATES THE SITUATION.
Healthy woman who reproduces with an affected male
The expected offspring will be as follows:
50% affected women
50% healthy men
In this case, all the male children will be healthy because they inherit the father’s Y – chromosome, while all the daughters will be affected because they receive the father’s X- chromosome, which in this case is pathological.
The fact that all the daughters of an affected male are affected and all the sons are healthy, allows us too distinguish between a family with an autosomal dominant disorder and another with a X-linked dominant disorder. In dominant autosomal disorders, the affected male transmits the pathological gene to both males and females, as it is not gender-dependent.
In synthesis, if we focus on males only, we can see that each male has a 50% chance of being healthy and a 50% chance of being affected. And the same thing happens if we focus on women only, each woman has a 50% chance of being healthy and a 50% chance of being affected.
REMEMBER that dominant characters, even if they are present in one single dose, are always expressed. Thus, in this particular case, and despite the fact that we are looking at sex chromosomes, if a woman has a X chromosome with the incorrect ” X ” recipe, and the other chromosome contains the correct recipe, she will express the disorder, given that the same concept as for autosomal dominant disorders applies because two X chromosomes are shared and one of them is incorrect.
As regards the male, it will depend on which of the two X chromosomes he has inherited, the “good one” or the “bad” one.
25% have one correct recipe and one incorrect recipe
25% in whom both recipes are incorrect
25% of healthy males
25% of affected males
That is, if we take males only, we can see that each male has a 50% chance of being healthy and a 50% chance of being affected, whereas if we take women only, they will always be affected because they inherited their father’s X-chromosome (and in this case, it is pathological).
Healthy female carrier who reproduces with a healthy male
If the female is the carrier, she does not express the disorder, but during meiosis or reductional division, two types of gametes will be produced, one that has a normal X chromosome and one that has a mutated X chromosome, therefore, according to the sex that this child has after the paternal contribution, the probabilities are as follows.
25% are healthy non carriers
25% are healthy but carriers
25% healthy males
25% affected males
Therefore, if we just focus on males only, each male has a 50% probability of being healthy and a 50% probability of being affected. Whereas if we focus on females only, they will always be healthy, although a 50% of them will be carriers.
25% affected females because both recipes are wrong
25% healthy males
25% affected males
Therefore, each male has a 50% probability of being healthy and 50% probability of being affected, whereas each female has a 50% probability of being healthy but a carrier and a 50% probability of being affected.
In this case all their children will be healthy because:
the males inherit the Y chromosome from their father, the females will all be healthy, but all of them carriers, because although they inherit the X chromosome from their father which is pathological, it is compensated by the X chromosome they inherit from their mother, which is normal.
Having seen how hereditary diseases are transmited, if you require specific information on a certain disease, the following links can help you.
And please, regardless of all the information you get on the subject of your interest, do not forget that it is only an information service, containing data that must be interpreted by a specialist, so please before you make any decision, have a consultation with a Genetics department, where your individual case will be accurately assessed and where all your questions will be answered.
Well, it is easy, when one of the progenitors is sick, or one or both of them are carriers of the same genetic disorder, they have a risk to produce affected children. The amount of risk and the sex of the affected individual is dependent on the type of inheritance.
For this reason, in case a malformation or a family disorder exists, the first thing to do is to study the family background and see which inheritance pattern runs in the family.
To this end, a genealogical tree is made using an international nomenclature in which all the individuals appear, identifying those who are affected and once these are identified, to determine the degree of severity, because we know that, in some cases, this can vary among the particular individuals.
¡Remember that the final flavour depends on all the ingredients mixed in the pie!
In this case, the degree of severity for each individual depends on how all the recipes are assembled.
In case that the disorder or malformation is not diagnosed, appropriate exams must be performed to try and obtain a diagnosis, and on the basis of this diagnosis, the risk of the particular individual to produce children with the same problem is calculated.
Some of these disorders are very severe, so at the time of deciding on their reproductive future, couple may encounter the following situations:
They ACCEPT the prenatal diagnosis, if available for this particular disorder, regardless of whether they decide to terminate or go ahead with the pregnancy.
Because people that are blood related are more likely to have the same mutations causing different diseases, thus contributing to the emergence of recessive diseases, whether autosomal or linked to sex chromosomes, sex chromosome X.
Because both SHARE THE SAME COMMON ANCESTOR, and if this ancestor had pathological genes, these could have been transmitted from generation to generation.
Because we know that the PROBABILITY of having inherited the same gene is directly proportional to the degree of kinship; in other words, the closer the kinship relationship, the greater the chance of having inherited the gene.
To take an example: let’s go check out the third option of autosomal recessive diseases described above, because it is the most common situation among relatives, reproduction between two healthy individuals who are both carriers of the same pathological hidden recessive gene.
“Healthy individual who is a carrier that reproduces with another healthy individual who also happens to be a carrier “.
We can see that merely because that both progenitors share the same ancestor they have much higher chances, compared to the general population, of both being carrier of the same pathological gene or genes. And this significantly increases the probabilities (by a 25%) that when reproducing, the offspring may inherit the affected gene and manifest the disease because he or she has inherited the same wrong recipe from each of the two progenitors. That is, a baby with both affected genes or wrong recipes (homozygous) for a particular gene.
In contrast, if reproduction takes place with an individual that does not belong to the same blood- related family, these possibilities go down to the risk of the general population; that is, the risk continuous to exist but it is much lower.
And, do you know why there is still a small risk?
Because it has been estimated that each person carries between one and five recessive lethal mutations that would be lethal if the children inherited them in the homozygous state. Therefore, all mankind carries pathological genes. We also know that there are pathological genes that are much more common in certain groups or human populations. Hence, if we belong to any of these population groups, we run a much higher risk to reproduce with a healthy carrier like us, which even if there is no family blood connection, will lead to a higher chance of having a child that has inherited the mutations.
Because both specialists will assess whether there is any risk factor to be correct, prevented, or taken into consideration before conception, and will implement the appropriate measures to ensure that everything goes well.
YES, and it is done by estimating the kinship coefficient.
To estimate the kinship coefficient, you need to have a consultation with a geneticist physician who will assess your familial history and draw your genealogical tree.
The geneticist, apart from assessing the mean genes that the couple may have in common (siblings born to the same parents share 1/2 of DNA sequences, uncles and nephews share ¼ of DNA sequences due to their common ancestors, cousins share 1/8, second cousins share 1/16 and third cousins share 1/32) will also assess the ethnic origin (due to the possibility that this population group may have high incidence specific diseases).
Taking into account all of the above, the geneticist should assess the possibility of requesting some sort of study to rule out if the future couple are or not carriers of any disease in particular, and based on the findings, if positive, decide whether or not it is advisable to do some sort of specific follow-up during the pregnancy to detect specific conditions. The geneticist will also assess the different reproductive options that assisted reproductiontechniques available (from preimplantational diagnosis to gamete donation: ovum or spermatozoon), or even look at the possibility of adoption, in case:
there is no prenatal diagnosis for a specific disease
or, if there is a prenatal diagnosis, the couple might not consider abortion, should the affected offspring have any specific disease.
REMBEMBER: the kinship coefficient must be calculated by a geneticist, specifically for each couple.
It is very important to take into account that many human groups have been isolated by barriers of different types, for instance, geographical barriers, language barriers, as well as social, religious, political barriers, etc. In all these populations there is an increased risk for non-related individuals to be carriers of the same pathology and to reproduce among themselves, thus causing the disease to manifest.
If you belong to this group, it is highly recommended before reproduction attend the consultation of a geneticist physician for assessment and genetic counseling custom , as the risk to have sick children can be as high as in the case of blood relatives.
"Genetics Made Easy" is a non-profit divulgative web site on human genetics, the objective of which is to bring the scientific community closer to the general community in order to disseminate the advances and knowledge that arise in this field and how the general population can benefit from this developments. The language used in the website is simple and the terminology easy to comprehend, with clear and straight forward explanations and user-friendly software.