Are there also genetic disorders that are Y-linked?

Yes there are genetic disorders that are Y-linked. Y-linked genetic disorder means the the disorder of gene of the Y chromosome. As males have only Y chromosomes. Genetic disorders are likely to pass from the father to son.(so all girls....you guys are safe)

Hi! If the color of the flower correlates to the seed coat and the axil color, then How do we know that gene coding for seed cover nor axil color are pleiotropic? I mean, can't one argue that the gene coding for the axil color is what affects the flower color?

The control of purple color in flowers, axils, and seed covers is all from the same gene – the most noticeable phenotype is the flower color, so that is how people generally talk about the gene. However, the gene is actually what is known as a transcription factor and is needed for expression of proteins that make a purple pigment (anthocyanin). https://www.sciencelearn.org.nz/resources/2001-identifying-mendel-s-pea-genes Naming of genes is actually quite chaotic and sometimes very confusing - for example a gene that does the same thing in different organisms will often have a different name.

Does it means that dominant lethal alleles are more harmful than recessive lethal alleles?

Yeah, if you have recesive lethal allele, you can live a happy life as long as you are heterozygous (= you have good dominant allele) , but if you have dominant lethal allele, you will die (no matter what other alleles are). Dominant alleles are rare tho, since carriers often die before they can pass it to next generation.

what is achondroplasia?

Achondroplasia is a genetic disorder with an autosomal dominant pattern of inheritance whose primary feature is dwarfism. In those with the condition, the arms and legs are short, while the torso is typically of normal length. Those affected have an average adult height of 131 centimetres (4 ft 4 in) for males and 123 centimetres (4 ft) for females. Other features can include an enlarged head and prominent forehead. Complications can include sleep apnea or recurrent ear infections. Achondroplasia includes short-limb skeletal dysplasia with severe combined immunodeficiency. Achondroplasia is caused by a mutation in the fibroblast growth factor receptor 3 (FGFR3) gene that results in its protein being overactive. Achondroplasia results in impaired endochondral bone growth (bone growth within cartilage). The disorder has an autosomal dominant mode of inheritance, meaning only one mutated copy of the gene is required for the condition to occur. About 80% of cases occur in children of parents of average stature and result from a new mutation, which most commonly originates as a spontaneous change during spermatogenesis. The rest are inherited from a parent with the condition. The risk of a new mutation increases with the age of the father. In families with two affected parents, children who inherit both affected genes typically die before birth or in early infancy from breathing difficulties.The condition is generally diagnosed based on the clinical features but may be confirmed by genetic testing. Treatments may include support groups and growth hormone therapy. Efforts to treat or prevent complications such as obesity, hydrocephalus, obstructive sleep apnea, middle ear infections or spinal stenosis may be required. Achondroplasia is the most common cause of dwarfism and affects about 1 in 27,500 people.

Is there such a thing as codominance or incomplete dominance in lethal alleles?

https://biology.stackexchange.com/q/107991/67251 These phenotypic dominance terms you learn in school - autosomal recessive/dominant, co-dominance, incomplete dominance... these are all just descriptive terms based on phenotype that become somewhat irrelevant and outdated once you have a better molecular understanding of what exactly goes on with different alleles of a gene. If none of them apply well, that's fine, because the real world doesn't follow these basic rules.

can the alleles that cause sickle cell be seen as lethal alleles in this case.

Yes, sickle cell is when a mutation happens in red blood cells where the amino acid glutamic acid is misplaced by the amino acid valine. This prevents the hemoglobin to form correctly: form crescent instead of the normal disc-shaped. We know that shape determines function, so without having the correct shape, hemoglobin can no longer function. Homozygous recessive will be lethal. However, in some areas where malaria is common, heterozygous will benefit because it helps resist malaria. If you want to dive deeper, use this link: https://www.sciencedirect.com/topics/medicine-and-dentistry/heterozygote-advantage

Still didn't get the names. Recessive lethality is when homozygous dominant dies. why is it called recessive then?

It is so called because the lethality caused by that gene is recessive as we can see that a heterozygote survived. Recessive lethality whether it be a dominant or recessive gene it causes lethality only in homozygous condition.

What does it mean to breed true, as mentioned in the yellow mice section?

it means it would be homozygous for the yellow allele.

what if the mouse caring both trait of AA will it have a birth defect?

It will die as an embryo. So technically no, the mouse caring AA will not have a chance to survive to actually carry a birth defect, since, in order to have birth defects, one must be birth first, right? :D

Main content

Course: Biology library > Unit 16

Lesson 2: Variations on Mendelian genetics

Pleiotropy and lethal alleles

Google Classroom

Pleiotropy: where one gene affects multiple characteristics. Lethal alleles: alleles that prevent survival when homozygous or heterozygous.

Introduction

From Mendel’s experiments, you might imagine that all genes control a single characteristic and affect some harmless aspect of an organism’s appearance (such as color, height, or shape). Those predictions are true for some genes, but definitely not all of them! For example:

A human genetic disorder called Marfan syndrome is caused by a mutation in one gene, yet it affects many aspects of growth and development, including height, vision, and heart function. This is an example of pleiotropy, or one gene affecting multiple characteristics.
A cross between two heterozygous yellow mice produces yellow and brown mice in a ratio of $2 : 1$ ‍, not $3 : 1$ ‍. This is an example of lethality, in which a particular genotype makes an organism unable to survive.

In this article, we’ll take a closer look at pleiotropic genes and lethal alleles, seeing how these variations on Mendel's rules fit into our modern understanding of inheritance.

Pleiotropy

When we mentioned Mendel’s experiments with purple-flowered and white-flowered plants, we didn’t discuss any other phenotypes associated with the two flower colors. However, Mendel noticed that the flower colors were always correlated with two other features: the color of the seed coat (covering of the seed) and the color of the axils (junctions where the leaves met the stem)

^{1, 2}

In plants with white flowers, the seed coats and axils were colorless. In plants with purple flowers, on the other hand, the seed coats were brown-gray and the axils were reddish. Thus, rather than affecting just one characteristic, the flower color gene actually affected three.

Genes like this, which control multiple, seemingly unrelated features, are said to be pleiotropic (pleio- = many, -tropic = effects)

^{1}

. We now know that Mendel’s flower color gene specifies a protein that causes colored particles, or pigments, to be made

^{2}

. This protein works in several different parts of the pea plant (flowers, seed coat, and leaf axils). In this way, the seemingly unrelated phenotypes can be traced back to a defect in one gene with several jobs.

Importantly, alleles of pleiotropic genes are transmitted in the same way as alleles of genes that affect single traits. Although the phenotype has multiple elements, these elements are specified as a package, and the dominant and recessive versions of the package would appear in the offspring of two heterozygotes in a ratio of

3 : 1

Pleiotropy in human genetic disorders

Genes affected in human genetic disorders are often pleiotropic. For example, people with a hereditary disorder called Marfan syndrome may have a set of seemingly unrelated symptoms, including the following

^{1, 3}

Unusually tall height
Thin fingers and toes
Dislocation of the lens of the eye
Heart problems (in which the aorta, the large blood vessel carrying blood away from the heart, bulges or ruptures).

These symptoms don’t seem directly related, but as it turns out, they can all be traced back to the mutation of a single gene. This gene encodes a protein that assembles into chains, making elastic fibrils that give strength and flexibility to the body’s connective tissues

^{4}

. Mutations that cause Marfan syndrome reduce the amount of functional protein made by the body, resulting in fewer fibrils.

How does the identity of this gene explain the range of symptoms? Our eyes and the aortas normally contain many fibrils that help maintain structure, which is why these two organs are affected in Marfan syndrome

^{5}

. In addition, the fibrils serve as “storage shelves” for growth factors. When there are fewer of them in Marfan syndrome, the growth factors cannot be shelved and thus cause excess growth (leading to the characteristic tall, thin Marfan build)

^{4}

Lethality

For the alleles that Mendel studied, it was equally possible to get homozygous dominant, homozygous recessive, and heterozygous genotypes. That is, none of these genotypes affected the survival of the pea plants. However, this is not the case for all genes and all alleles.

Many genes in an organism’s genome are needed for survival. If an allele makes one of these genes nonfunctional, or causes it to take on an abnormal, harmful activity, it may be impossible to get a living organism with a homozygous (or, in some cases, even a heterozygous) genotype.

Example: The yellow mouse

A classic example of an allele that affects survival is the lethal yellow allele, a spontaneous mutation in mice that makes their coats yellow. This allele was discovered around the turn of the 20th century by the French geneticist Lucien Cuenót, who noticed that it was inherited in an unusual pattern

^{6, 7}

When yellow mice were crossed with normal agouti (brown) mice, they produced half yellow and half brown offspring. This suggested that the yellow mice were heterozygous, and that the yellow allele,

A^{Y}

, was dominant to the agouti allele,

A

. But when two yellow mice were crossed with each other, they produced yellow and brown offspring in a ratio of

2 : 1

, and the yellow offspring did not breed true (were heterozygous). Why was this the case?

Two yellow mice (

A^{Y} A

genotype) are crossed to one another. The Punnett square for the cross is:

		$A^{Y}$ ‍	$A$ ‍
$A^{Y}$ ‍		$A^{Y}$ ‍ $A^{Y}$ ‍ (dies as embryo)	$A^{Y}$ ‍ $A$ ‍ (yellow)
$A$ ‍		$A^{Y}$ ‍ $A$ ‍ (yellow)	$A$ ‍ $A$ ‍ (agouti/brown)

There is a phenotypic ratio of 2:1 yellow:brown among the mice that survive to birth.

As it turned out, this unusual ratio reflected that some of the mouse embryos (homozygous

A^{Y} A^{Y}

genotype) died very early in development, long before birth. In other words, at the level of eggs, sperm, and fertilization, the color gene segregated normally, resulting in embryos with a

1 : 2 : 1

ratio of

A^{Y} A^{Y}

A^{Y} A

, and

A A

genotypes. However, the

A^{Y} A^{Y}

mice died as tiny embryos, leaving a

2 : 1

genotype and phenotype ratio among the surviving mice

^{7, 8}

Alleles like

A^{Y}

, which are lethal when they're homozygous but not when they're heterozygous, are called recessive lethal alleles.

The lethal recessive

A^{Y}

allele also happens to give a dominant, non-lethal phenotype in the heterozygote (yellow coloration, along with health problems such as obesity, diabetes, and tumor formation). The trick is that the lethality is recessive, even though the color phenotype is dominant.

The color of the yellow mouse heterozygote is helpful because it lets us keep track of genotypes, but in many other cases, recessive lethal genes don’t have a dominant phenotype in the heterozygote. Instead, they are purely recessive to the normal allele, resulting in a normal phenotype for the heterozygote and an embryonic lethal phenotype for the homozygote.

Lethal alleles and human genetic disorders

Some alleles associated with human genetic disorders are recessive lethal. For example, this is true of the allele that causes achondroplasia, a form of dwarfism. A person heterozygous for this allele will have shortened limbs and short stature (achondroplasia), a condition that is not lethal. However, homozygosity for the same allele causes death during embryonic development or the first months of life, an example of recessive lethality

^{7, 9}

Some human disorders are also caused by dominant lethal alleles. These are alleles that cause death when they are present in just a single copy. If an allele leads to death of heterozygotes before birth, we’ll never see that allele in the living human population (but rather, as an implantation failure or miscarriage). However, if a dominant lethal allele allows heterozygotes to survive past birth, it can be seen in the population as a genetic disorder.

In fact, if a dominant lethal allele lets a person survive to reproductive age, it may even be passed on to children. This is the case in Huntington’s disease, a fatal genetic disorder affecting the nervous system. People with a Huntington allele inevitably develop the disease, but they may not show any symptoms until age 40 and can unknowingly pass the allele on to their children.

Attribution:

This article is a modified derivative of “Characteristics and traits,” by OpenStax College, Biology (CC BY 3.0). Download the original article for free at http://cnx.org/contents/185cbf87-c72e-48f5-b51e-f14f21b5eabd@9.85.

The modified article is licensed under a CC BY-NC-SA 4.0 license.

Works cited:

Lobo, I. (2008). Pleiotropy: One gene can affect multiple traits. Nature Education, 1(1), 10. Retrieved from www.nature.com/scitable/topicpage/pleiotropy-one-gene-can-affect-multiple-traits-569.
Reid, J. B. and Ross, J. J. (2011). Mendel's genes: Towards a full molecular characterization. Genetics 189(1), 3-10. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3176118/#s4title.
Marfan syndrome. (2012). In Genetics home reference. Retrieved from http://ghr.nlm.nih.gov/condition/marfan-syndrome.
FBN1. (2015). In Genetics home reference. Retrieved from http://ghr.nlm.nih.gov/gene/FBN1.
Marfan syndrome. (2015, November 3). Retrieved November 21, 2015 from Wikipedia: https://en.wikipedia.org/wiki/Marfan_syndrome.
Lethal allele. (2016, July 13). Retrieved July 26, 2016 from Wikipedia: https://en.wikipedia.org/wiki/Lethal_allele#History.
Lobo, I. (2008). Mendelian ratios and lethal genes. Nature Education, 1(1), 138. Retrieved from http://www.nature.com/scitable/topicpage/mendelian-ratios-and-lethal-genes-557.
Griffiths, A. J. F., Gelbart, W. M., Miller, J. H., and Lewontin, R. C. (1999). Interactions between alleles of one gene. In Modern Genetic Analysis. New York, NY: W. H. Freeman. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK21226/#_A824_.
Achrondroplasia. (2015, September 12). Retrieved November 21, 2015 from WIkipedia: https://en.wikipedia.org/wiki/Achondroplasia.

Additional references:

Achrondroplasia. (2015, September 12). Retrieved November 21, 2015 from WIkipedia: https://en.wikipedia.org/wiki/Achondroplasia.

Bergmann, D. C. (2011). Genetics lecture notes. Biosci 41, Stanford.

FBN1. (2015). In Genetics home reference. Retrieved from http://ghr.nlm.nih.gov/gene/FBN1.

Griffiths, A. J. F., Gelbart, W. M., Miller, J. H., and Lewontin, R. C. (1999). Interactions between alleles of one gene. In Modern Genetic Analysis. New York, NY: W. H. Freeman. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK21226.

Lethal allele. (2015). In The free dictionary. Retrieved from http://medical-dictionary.thefreedictionary.com/lethal+allele.

Lethal allele. (2016, July 13). Retrieved July 26, 2016 from Wikipedia: https://en.wikipedia.org/wiki/Lethal_allele.

Lobo, I. (2008). Mendelian ratios and lethal genes. Nature Education, 1(1), 138. Retrieved from http://www.nature.com/scitable/topicpage/mendelian-ratios-and-lethal-genes-557.

Lobo, I. (2008). Pleiotropy: One gene can affect multiple traits. Nature Education, 1(1), 10. Retrieved from www.nature.com/scitable/topicpage/pleiotropy-one-gene-can-affect-multiple-traits-569.

Lucien Cuénot. (2016, February 13). Retrieved July 26, 2016 from Wikipedia: https://en.wikipedia.org/wiki/Lucien_Cuénot.

Marfan syndrome. (2012). In Genetics home reference. Retrieved from http://ghr.nlm.nih.gov/condition/marfan-syndrome.

Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., and Jackson, R. B. (2011). Mendel and the gene idea. In Campbell biology (10th ed., pp. 267-291). San Francisco, CA: Pearson.

Reid, J. B. and Ross, J. J. (2011). Mendel's genes: Towards a full molecular characterization. Genetics 189(1), 3-10. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3176118/

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Mary Straka
Posted 8 years ago. Direct link to Mary Straka's post “Are there also genetic di...”
Are there also genetic disorders that are Y-linked?
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(8 votes)
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- Princè Àyàn Ðàs
  Posted 7 years ago. Direct link to Princè Àyàn Ðàs's post “Yes there are genetic dis...”
  Yes there are genetic disorders that are Y-linked. Y-linked genetic disorder means the the disorder of gene of the Y chromosome. As males have only Y chromosomes. Genetic disorders are likely to pass from the father to son.(so all girls....you guys are safe)
  Comment on Princè Àyàn Ðàs's post “Yes there are genetic dis...”
  (22 votes)
Eponine Everdeen-Ramirez-Arellano
Posted 6 years ago. Direct link to Eponine Everdeen-Ramirez-Arellano's post “I am a 13-year-old with a...”
I am a 13-year-old with achondroplasia. Does that mean I am heterozygous for the trait, since obviously I've survived this long?
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Yuya Fujikawa
Posted 7 years ago. Direct link to Yuya Fujikawa's post “Hi! If the color of the f...”
Hi! If the color of the flower correlates to the seed coat and the axil color, then How do we know that gene coding for seed cover nor axil color are pleiotropic? I mean, can't one argue that the gene coding for the axil color is what affects the flower color?
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(7 votes)
Answer
- tyersome
  Posted 6 years ago. Direct link to tyersome's post “The control of purple col...”
  The control of purple color in flowers, axils, and seed covers is all from the same gene – the most noticeable phenotype is the flower color, so that is how people generally talk about the gene. However, the gene is actually what is known as a transcription factor and is needed for expression of proteins that make a purple pigment (anthocyanin).
  https://www.sciencelearn.org.nz/resources/2001-identifying-mendel-s-pea-genes
  
  Naming of genes is actually quite chaotic and sometimes very confusing - for example a gene that does the same thing in different organisms will often have a different name.
  Comment on tyersome's post “The control of purple col...”
  (7 votes)
Swaiya Rehman
Posted 8 years ago. Direct link to Swaiya Rehman's post “Does it means that domina...”
Does it means that dominant lethal alleles are more harmful than recessive lethal alleles?
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- Daltara Darana
  Posted 8 years ago. Direct link to Daltara Darana's post “Yeah, if you have recesiv...”
  Yeah, if you have recesive lethal allele, you can live a happy life as long as you are heterozygous (= you have good dominant allele) , but if you have dominant lethal allele, you will die (no matter what other alleles are). Dominant alleles are rare tho, since carriers often die before they can pass it to next generation.
  Comment on Daltara Darana's post “Yeah, if you have recesiv...”
  (7 votes)
Hannah West
Posted 4 years ago. Direct link to Hannah West's post “what is achondroplasia?”
what is achondroplasia?
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- zidanehamid
  Posted a year ago. Direct link to zidanehamid's post “Achondroplasia is a genet...”
  Achondroplasia is a genetic disorder with an autosomal dominant pattern of inheritance whose primary feature is dwarfism. In those with the condition, the arms and legs are short, while the torso is typically of normal length. Those affected have an average adult height of 131 centimetres (4 ft 4 in) for males and 123 centimetres (4 ft) for females. Other features can include an enlarged head and prominent forehead. Complications can include sleep apnea or recurrent ear infections. Achondroplasia includes short-limb skeletal dysplasia with severe combined immunodeficiency.
  
  Achondroplasia is caused by a mutation in the fibroblast growth factor receptor 3 (FGFR3) gene that results in its protein being overactive. Achondroplasia results in impaired endochondral bone growth (bone growth within cartilage). The disorder has an autosomal dominant mode of inheritance, meaning only one mutated copy of the gene is required for the condition to occur. About 80% of cases occur in children of parents of average stature and result from a new mutation, which most commonly originates as a spontaneous change during spermatogenesis. The rest are inherited from a parent with the condition. The risk of a new mutation increases with the age of the father. In families with two affected parents, children who inherit both affected genes typically die before birth or in early infancy from breathing difficulties.The condition is generally diagnosed based on the clinical features but may be confirmed by genetic testing.
  
  Treatments may include support groups and growth hormone therapy. Efforts to treat or prevent complications such as obesity, hydrocephalus, obstructive sleep apnea, middle ear infections or spinal stenosis may be required. Achondroplasia is the most common cause of dwarfism and affects about 1 in 27,500 people.
  Button navigates to signup page
  (6 votes)
cozymonster
Posted 6 years ago. Direct link to cozymonster's post “Is there such a thing as ...”
Is there such a thing as codominance or incomplete dominance in lethal alleles?
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- robinsonbiologyofficialchannel
  Posted 2 years ago. Direct link to robinsonbiologyofficialchannel's post “https://biology.stackexch...”
  https://biology.stackexchange.com/q/107991/67251 These phenotypic dominance terms you learn in school - autosomal recessive/dominant, co-dominance, incomplete dominance... these are all just descriptive terms based on phenotype that become somewhat irrelevant and outdated once you have a better molecular understanding of what exactly goes on with different alleles of a gene. If none of them apply well, that's fine, because the real world doesn't follow these basic rules.
  Button navigates to signup page
  (2 votes)
Chukwuma Anayo- Ezikeoha
Posted 4 years ago. Direct link to Chukwuma Anayo- Ezikeoha's post “can the alleles that caus...”
can the alleles that cause sickle cell be seen as lethal alleles in this case.
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(3 votes)
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- Han G. Tran
  Posted 4 years ago. Direct link to Han G. Tran's post “Yes, sickle cell is when ...”
  Yes, sickle cell is when a mutation happens in red blood cells where the amino acid glutamic acid is misplaced by the amino acid valine. This prevents the hemoglobin to form correctly: form crescent instead of the normal disc-shaped. We know that shape determines function, so without having the correct shape, hemoglobin can no longer function. Homozygous recessive will be lethal. However, in some areas where malaria is common, heterozygous will benefit because it helps resist malaria.
  If you want to dive deeper, use this link: https://www.sciencedirect.com/topics/medicine-and-dentistry/heterozygote-advantage
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  (2 votes)
kmcneil2023
Posted 4 years ago. Direct link to kmcneil2023's post “what if the mouse caring ...”
what if the mouse caring both trait of AA will it have a birth defect?
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(1 vote)
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- Han G. Tran
  Posted 4 years ago. Direct link to Han G. Tran's post “It will die as an embryo....”
  It will die as an embryo. So technically no, the mouse caring AA will not have a chance to survive to actually carry a birth defect, since, in order to have birth defects, one must be birth first, right? :D
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  (5 votes)
Lesia_Lark
Posted 3 years ago. Direct link to Lesia_Lark's post “Still didn't get the name...”
Still didn't get the names.
Recessive lethality is when homozygous dominant dies. why is it called recessive then?
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- p k021
  Posted 3 years ago. Direct link to p k021's post “It is so called because t...”
  It is so called because the lethality caused by that gene is recessive as we can see that a heterozygote survived.
  Recessive lethality whether it be a dominant or recessive gene it causes lethality only in homozygous condition.
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layaz7717
Posted 4 years ago. Direct link to layaz7717's post “What does it mean to bree...”
What does it mean to breed true, as mentioned in the yellow mice section?
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- 25henry.deanashcraft
  Posted 3 years ago. Direct link to 25henry.deanashcraft's post “it means it would be homo...”
  it means it would be homozygous for the yellow allele.
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