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Inheritance of partly genetic conditions

Inheritance of partly genetic conditions


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Suppose Anne has a condition like OCD, that has a significant genetic component. Neither of Anne's parents have OCD, though. Does this mean that each of Anne's OCD genes were carried by at least one of her parents?


Many things are possible theoretically. Consider the following hypothetical example for illustration. Imagine, if you had two genetic variants A and B affecting a trait with the following probabilities

AA: 5% chance of having OCD

AB: 10% chance of having OCD

BB: 20% chance of having OCD

In this case, clearly having OCD has a genetic component, and yet no matter which genes a person has (and its parents had), it is possible for that person to get OCD. Probabilistically, however, they have increased risk if they inherit certain genetic variants over others.

In practice, most common psychatric disorders tend to be highly polygenic. I have answered a similar question (Q: Bipolar disorder genetics) of yours which may be relevant again.


Autism spectrum disorders and autistic traits share genetics and biology

Autism spectrum disorders (ASDs) and autistic traits in the general population may share genetic susceptibility factors. In this study, we investigated such potential overlap based on common genetic variants. We developed and validated a self-report questionnaire of autistic traits in adults. We then conducted genome-wide association studies (GWASs) of six trait scores derived from the questionnaire through exploratory factor analysis in 1981 adults from the general population. Using the results from the Psychiatric Genomics Consortium GWAS of ASDs, we observed genetic sharing between ASDs and the autistic traits 'childhood behavior', 'rigidity' and 'attention to detail'. Gene-set analysis subsequently identified 'rigidity' to be significantly associated with a network of ASD gene-encoded proteins that regulates neurite outgrowth. Gene-wide association with the well-established ASD gene MET reached significance. Taken together, our findings provide evidence for an overlapping genetic and biological etiology underlying ASDs and autistic population traits, which suggests that genetic studies in the general population may yield novel ASD genes.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Validation of the novel questionnaire…

Validation of the novel questionnaire of autistic traits in adults. ( a )…

Bar plots from PRSice showing…

Bar plots from PRSice showing results at seven broad P -value thresholds (…


Symptoms Symptoms

Signs and symptoms of Guillain-Barré syndrome (GBS) include muscle weakness, muscle pain, numbness, and tingling sensations. GBS can affect people of any age. The first symptoms of GBS typically begin in the lower legs. The symptoms can then spread to the muscles of the upper body. Typically, the symptoms continue to worsen over the first 2-3 weeks after they first begin. In some cases, the symptoms of GBS can increase in intensity until the muscles cannot be used at all (paralysis). [1]

Other symptoms of GBS can include difficulty with bladder control or bowel function, difficulty breathing, blood pressure, and heart rate. Some people with GBS have facial droop, double vision, difficulty speaking or swallowing, and changes in eye movements. As the disease progresses, the muscle weakness may worsen to affect the muscles that are important for breathing. [3] [4]

This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.


Research Research

Research helps us better understand diseases and can lead to advances in diagnosis and treatment. This section provides resources to help you learn about medical research and ways to get involved.

Clinical Research Resources

  • ClinicalTrials.gov lists trials that are related to Trisomy 18. Click on the link to go to ClinicalTrials.gov to read descriptions of these studies.

Patient Registry

  • A registry supports research by collecting of information about patients that share something in common, such as being diagnosed with Trisomy 18. The type of data collected can vary from registry to registry and is based on the goals and purpose of that registry. Some registries collect contact information while others collect more detailed medical information. Learn more about registries.


The heart of the law

Criminal responsibility is the conceptual core of criminal laws: it allows us to hold a person accountable for his or her conduct, and justifies punishment if they’re convicted.

Criminal responsibility is different to criminal liability, which concerns the outcome of a trial. Rather, it relates to whether a person is properly recognised as a subject of the law, or put another way, whether it’s appropriate that he or she is held to the moral standard of behaviour criminal laws encode.

Our notion of criminal responsibility centres on a person’s mental state – what the accused knew, thought or perceived. We construct the defendant as an abstract, rational entity – made up of a set of capacities or exercising a set of choices – and abstracted from his or her social and political context.

Genetic science is threatening ideas about criminal responsibility. Esther Dyson/Flickr, CC BY-NC

This approach reflects the influence of psychology on the historical development of the principles and practices of criminal law.

Now, genetic science – in this context, the influence of genes on human behaviour – is threatening or promising (depending on your perspective) to render criminal responsibility – and the ideas about blameworthiness or culpability at its heart – null and void.

Research suggests genetic as well as shared environmental influences are important factors in persistent antisocial behaviour. On the face of it, such research appears incompatible with beliefs about individual choice on which criminal law rests.

Genetic science does indeed pose a challenge for criminal law. It’s not possible or desirable to ignore developments in scientific knowledge, for the legitimacy of criminal law practices if nothing else. But genetic science isn’t yet living up to its promise – or threat – to overwhelm current practices.

Evidence from the United States, where the effect of genetics on crime has been hotly debated, indicates limited use. In particular, “gene evidence” appears to be brought into the courtroom by defence counsel, rather than prosecution, and to be used for mitigation at sentencing, rather than at the point of conviction.

As this suggests, the impact of this evidence is modest, and it’s being integrated into existing criminal practices.


Problem 3

Flower position, stem length, and seed shape were three characters that Mendel studied. Each is controlled by an independently assorting gene and has dominant and recessive expression as follows:

Character Dominant Recessive
Flower position Axial (A ) Terminal (a )
Stem length Tall (T ) Dwarf (t )
Seed shape Round (R ) Wrinkled (r)

If a plant that is heterozygous for all three characters were allowed to self-fertilize, what proportion of the offspring would be expected to be as follows: (Note – use the rules of probability (and show your work) instead of huge Punnett squares)

a) homozygous for the three dominant traits

AATTRR = 1/4 x 1/4 x 1/4 = 1/64

b) homozygous for the three recessive traits

aattrr = 1/4 x 1/4 x 1/4 = 1/64

c) heterozygous (assumed for each trait)

AaTtRr = 1/2 x 1/2 x 1/2 = 1/8

d) homozygous for axial and tall, heterozygous for seed shape

AATTRr = 1/4 x 1/4 x 1/2 = 1/32

Problem 4 A black guinea pig crossed with an albino guinea pig produced 12 black offspring. When the albino was crossed with a second one, 7 blacks and 5 albinos were obtained.

What is the best explanation for this genetic situation?

Black is dominant over white

Write genotypes for the parents, gametes, and offspring.

Parent’s genotypes = BB (black) x bb (white)
gametes = B b
F1 offspring = all Bb

Parent’s genotypes = Bb (black) x bb (white)
gametes = B or b b
F1 offspring = Bb or bb

There should be 50% black to 50% white offspring in this cross.

Problem 5 In sesame plants, the one-pod condition (P ) is dominant to the three-pod condition (p ), and normal leaf (L ) is dominant to wrinkled leaf (l) . Pod type and leaf type are inherited independently. Determinine the genotypes for the two parents for all possible matings producing the following offspring:

a. 318 one-pod normal, 98 one-pod wrinkled

Parental genotypes: PPLl x PPLl or PpLl x PPLl

b. 323 three-pod normal, 106 three-pod wrinkled

Parental genotypes: ppLl x ppLl

Parental genotypes: PPLL x PpLL or PPLl x PPLL or PPLL x PpLl etc (nine possible genotypes).

d. 150 one-pod normal, 147 one-pod wrinkled, 51 three-pod normal, 48 three-pod wrinkled. (a 3: 3: 1: 1 ratio)

Parental genotypes: PpLl x Ppll (see below for details)

3 One-pod wrinkled (PPll , Ppll , Ppll)

1 Three-pod normal (ppLl)

1 Three-pod wrinked (ppll)

e. 223 one-pod normal, 72 one-pod wrinkled, 76 three-pod normal, 27 three-pod wrinkled (a 9: 3: 3: 1 ratio)

Parental genotypes: PpLl x PpLl

Problem 6 A man with group A blood marries a woman with group B blood. Their child has group O blood. What are the genotypes of these individuals?

First Child = OO (or ii)

What other genotypes and in what frequencies, would you expect in offspring from this marriage?

Examine the Punnett square to determine the other genotypes possible.

Problem 7 Color pattern in a species of duck is determined by one gene with three alleles. Alleles H and I are codominant, and allele i is recessive to both. Note: this situation is similar to the ABO blood system.

How many phenotypes are possible in a flock of ducks that contains all the possible combinations of these three alleles?

As in the ABO blood system 4 phenotypes are possible in this case:

Genotype Phenotype
HH, Hi (H)
II, Ii (I)
HI (HI)
ii (i)

Problem 8 Phenylketonuria (PKU) is an inherited disease caused by a recessive allele. If a woman and her husband are both carriers, what is the probability of each of the following?

Under these circumstances assume the following Punnett square to be true.

a. all three of their children will be of normal phenotype

b. one or more of the three children will have the disease (x)

All three have x 2 out of 3 has x 1 out of 3 has x
+ + =
x x o o o x
3 Combinations x o x o x o
o x x x o o
+ 3(3/4 x 1/4 x 1/4) + 3(3/4 x 3/4 x 1/4) =

Note: the probability of the disease (x) = 1/4 & the probability of being normal (o) = 3/4

c. all three children will have the disease

d. at least one child out of three will be phenotypically normal

(Note: Remember that the probabilities of all possible outcomes always add up to 1)

Problem 9 The genotype of F1 individuals in a tetrahybrid cross is AaBbCcDd. Assuming independent assortment of these four genes, what are the probabilities that F2 offspring would have the following genotypes?

a. aabbccdd = x x x = 1/256

b. AaBbCcDd = x x x = 1/16

c. AABBCCDD = x x x = 1/256

d. AaBBccDd = x x x = 1/64

e. AaBBCCdd = x x x = 1/128

Just remember that the probability of a heterozygote (Xx) = 2/4 or 1/2 and the probability of a homozygote XX or xx = 1/4

Problem 10 In 1981, a stray black cat with unusual rounded curled-back ears was adopted by a family in California. Hundreds of descendants of the cat have since been born, and cat fanciers hope to develop the “curl” cat into a show breed. Suppose you owned the first curl cat and wanted to develop a true breeding variety.

How would you determine whether the curl allele is dominant or recessive?

Mate the stray to a non-curl cat. If any offspring have the “curl” trait it is likely to be dominant. If the mutation is recessive, then on ly non-curl offspring will result.

How would you select for true-breeding cats?

You know that cats are true-breeding when curl crossed with curl matings produce only curl offspring.

How would you know they are true-breeding?

A pure-bred “curl cat” is homozygous.

  1. If the trait is recessive any inividual with the “curl” condition is homozygous recessive.
  2. If the trait is dominant you can determine if the individual in question is true breeding (CC) or heterozygous (Cc) with a test cross (to a homozygous recessive individual).

Problem 11 What is the probability that each of the following pairs of parents will produce the indicated offspring (assume independent assortment of all gene pairs?

a. AABBCC x aabbcc —-> AaBbCc

b. AABbCc x AaBbCc —–> AAbbCC

c. AaBbCc x AaBbCc —–> AaBbCc

d. aaBbCC x AABbcc —-> AaBbCc

Problem 12 Karen and Steve each have a sibling with sickle-cell disease. Neither Karen, Steve, nor any of their parents has the disease, and none of them has been tested to reveal sickle-cell trait. Based on this incomplete information, calculate the probability that if this couple should have another child, the child will have sickle-cell anemia.


Inheritance of partly genetic conditions - Biology

Deoxyribonucleic Acid (DNA) And Chromosomes:

  • In a cell, the &ldquoinstructions&rdquo come in the form of DNA.
  • DNA stands for deoxyribonucleic acid.
  • DNA is present in almost every human cell. It provides the blueprint or recipe for how our bodies grow, develop, and function.
  • DNA is a double helix (imagine a twisted ladder) that is made of two sugar and phosphate backbones and four different nitrogenous bases: adenine, thymine, guanine, and cytosine (A, T, G, and C).
  • DNA is packaged onto proteins called histones to form chromosomes.
  • Humans have 23 pairs of chromosomes, including the X and Y chromosomes. X and Y are the sex chromosomes that determine whether someone is male (XY) or female (XX).
  • The other 22 chromosome pairs are called the autosomes.

Each chromosome contains thousands of genes. A gene is a portion of DNA that codes for a protein.

  • Each gene is made up of billions of letters, which our body reads in three-letter units called codons.
  • Each three-letter codon determines a specific amino acid.
  • The amino acids are strung together to make proteins, such as hormones, enzymes, and antibodies.
  • The many genes that provide the instructions for the proteins in our bodies determine a wide range of features, including outwardly appearing physical traits such as height, eye color and hair color, to inner functioning, such as how each organ system works.
  • There are over 20,000 genes in the human genome! We are only beginning to understand how many of them might work.

Although genes and chromosomes are mostly similar from person to person, there is variation among people. Most of the time, this variation does not impact health or development. Genetic variation explains some of the wonderful differences that we see among humans.

&ldquoJournal of Genetics and Genomes&rdquo publishes peer-reviewed research work on the discoveries and current developments in the field of Genetics relating to all the domains of life, from humans to plants to livestock and other model organisms, headed by pre-eminent Editorial Board to ensure article quality and to provide unbiased and efficient publishing process.


The Impact of Genetics on Child Development

While there are many nuances to the nature vs. nurture debate surrounding child development and the human experience in general – like we talked about in this article – it’s no doubt that genes form the basis of just about everything.

To briefly touch on the nurture side of the conversation, our environment – i.e., how and where we are raised, the beliefs of the community and family that raised us, and every other variable associated with our early childhood surroundings – helps determine which genes are “turned on” throughout our lifetime. So, in spite of our desire to turn the nature vs. nurture conversation into a debate to be won or lost, these two phenomena collaborate with one another, creating unique human beings like you and me.

As we all know, genes from our parents influence everything from height, weight, eye color, and other physical characteristics, to behavioral patterns in achievement, intelligence and motivation. A child’s biology can have major implications on their development, so the more we, as parents and teachers, can understand the science behind our children’s bodies and minds, the better we’re able to nurture them to their full potential and healthiest, happiest selves.

Let’s start from the very beginning: conception. When a male’s sperm cell combines with a female’s ovum cell, they each contribute half of the DNA necessary to create an embryo.

Typically, this means that the resulting embryo contains 46 chromosomes, which are the DNA molecules that house genetic information. However, genetic abnormalities are not so “abnormal” after all, and DNA doesn’t always divide into chromosomes evenly. These instances can lead to babies born with disabilities and conditions such as Down syndrome, characterized by an extra 21 st chromosome, or trisomy 21.

For children and students with Down syndrome, the effects on learning can vary widely and specialized education techniques are often necessary. Whether you’re a trained special educator or not, it’s important to every student’s success to know how to best interact with students of different needs and learning abilities. For easy access to resources on teaching students with genetic disorders and special needs, check out our specially curated list of Twitter feeds.

In addition to Down syndrome, there are many other genetic disorders with their own set of nuanced symptoms, neurological effects, physical characteristics and potential learning hurdles. Though rare in comparison to Down syndrome, some of these other genetic disorders include, Edwards syndrome, Patau syndrome and Warkany syndrome, among others.

Many scholars have put considerable time and effort into researching the interplay of genes and childhood development, largely to unravel the misconception that genes are set in stone at birth like we once thought. As mentioned above, genes and our environment interact to form the whole picture of every child, and certain genes – like CHRM2, which was pinpointed by researchers at Virginia Commonwealth University – predict a child’s resiliency to early life traumas and parental neglect.

Findings like these and their implications for education have helped develop the new field of “educational genomics,” which could enable to academia to create curricula tailored to a student’s DNA profile. Although much headway has yet to be made in this field before developing into a viable option, the rise in research and funding on this subject makes it a legitimate option for future generations of teachers and learners.


AP Genetics Problems

1. A rooster with gray feathers is mated with a hen of the same phenotype. Among their offspring, 15 chicks are gray, 6 are black, and 8 are white.

  • What is the simplest explanation for the inheritance of these colors in chickens?
  • What offspring would you predict from the mating of a gray rooster and a black hen?

2. In some plants, a true-breeding, red-flowered strain gives all pink flowers when crossed with a white-flowered strain: RR (red) x rr (white) —> Rr (pink). If flower position (axial or terminal) is inherited as it is in peas what will be the ratios of genotypes and phenotypes of the generation resulting from the following cross: axial-red (true-breeding) x terminal-white? What will be the ratios in the F2 generation?

3. Flower position, stem length, and seed shape were three characters that Mendel studied. Each is controlled by an independently assorting gene and has dominant and recessive expression as follows:

Character Dominant Recessive
Flower position Axial (A ) Terminal (a )
Stem length Tall (T ) Dwarf (t )
Seed shape Round (R ) Wrinkled (r)

If a plant that is heterozygous for all three characters were allowed to self-fertilize, what proportion of the offspring would be expected to be as follows: (Note – use the rules of probability (and show your work) instead of huge Punnett squares)

  1. homozygous for the three dominant traits
  2. homozygous for the three recessive traits
  3. heterozygous
  4. homozygous for axial and tall, heterozygous for seed shape

4. A black guinea pig crossed with an albino guinea pig produced 12 black offspring. When the albino was crossed with a second one, 7 blacks and 5 albinos were obtained.

  • What is the best explanation for this genetic situation?
  • Write genotypes for the parents, gametes, and offspring.

5. In sesame plants, the one-pod condition (P ) is dominant to the three-pod condition (p ), and normal leaf (L ) is dominant to wrinkled leaf (l) . Pod type and leaf type are inherited independently. Determine the genotypes for the two parents for all possible matings producing the following offspring:

  1. 318 one-pod normal, 98 one-pod wrinkled
  2. 323 three-pod normal, 106 three-pod wrinkled
  3. 401 one-pod normal
  4. 150 one-pod normal, 147 one-pod wrinkled, 51 three-pod normal, 48 three-pod wrinkled
  5. 223 one-pod normal, 72 one-pod wrinkled, 76 three-pod normal, 27 three-pod wrinkled

6. A man with group A blood marries a woman with group B blood. Their child has group O blood.

  • What are the genotypes of these individuals?
  • What other genotypes and in what frequencies, would you expect in offspring from this marriage?

7. Color pattern in a species of duck is determined by one gene with three alleles. Alleles H and I are codominant, and allele i is recessive to both. How many phenotypes are possible in a flock of ducks that contains all the possible combinations of these three alleles?

8. Phenylketonuria (PKU) is an inherited disease caused by a recessive allele. If a woman and her husband are both carriers, what is the probability of each of the following?

  1. all three of their children will be of normal phenotype
  2. one or more of the three children will have the disease
  3. all three children will have the disease
  4. at least one child out of three will be phenotypically normal

(Note: Remember that the probabilities of all possible outcomes always add up to 1)

9. The genotype of F1 individuals in a tetrahybrid cross is AaBbCcDd. Assuming independent assortment of these four genes, what are the probabilities that F2 offspring would have the following genotypes?

10. In 1981, a stray black cat with unusual rounded curled-back ears was adopted by a family in California. Hundreds of descendants of the cat have since been born, and cat fanciers hope to develop the “curl” cat into a show breed. Suppose you owned the first curl cat and wanted to develop a true breeding variety.

  • How would you determine whether the curl allele is dominant or recessive?
  • How would you select for true-breeding cats?
  • How would you know they are true-breeding?

11. What is the probability that each of the following pairs of parents will produce the indicated offspring (assume independent assortment of all gene pairs?

  1. AABbCc x aabbcc —-> AaBbCc
  2. AABbCc x AaBbCc —–> AAbbCC
  3. AaBbCc x AaBbCc —–> AaBbCc
  4. aaBbCC x AABbcc —-> AaBbCc

12. Karen and Steve each have a sibling with sickle-cell disease. Neither Karen, Steve, nor any of their parents has the disease, and none of them has been tested to reveal sickle-cell trait. Based on this incomplete information, calculate the probability that if this couple should have another child, the child will have sickle-cell anemia.

13. Imagine that a newly discovered, recessively inherited disease is expressed only in individuals with type O blood, although the disease and blood group are independently inherited. A normal man with type A blood and a normal woman with type B blood have already had one child with the disease. The woman is now pregnant for a second time. What is the probability that the second child will also have the disease? Assume both parents are heterozygous for the “disease” gene.

14. In tigers, a recessive allele causes an absence of fur pigmentation (a “white tiger”) and a cross-eyed condition. If two phenotypically normal tigers that are heterozygous at this locus are mated, what percentage of their offspring will be cross-eyed? What percentage will be white?

15. In corn plants, a dominant allele I inhibits kernel color, while the recessive allele i permits color when homozygous. At a different locus, the dominant gene P causes purple kernel color, while the homozygous recessive genotype pp causes red kernels. If plants heterozygous at both loci are crossed, what will be the phenotypic ratio of the F1 generation?

16. The pedigree below traces the inheritance of alkaptonuria, a biochemical disorder. Affected individuals, indicated here by the filled-in circles and squares, are unable to break down a substance called alkapton, which colors the urine and stains body tissues. Does alkaptonuria appear to be caused by a dominant or recessive allele? Fill in the genotypes of the individuals whose genotypes you know. What genotypes are possible for each of the other individuals?

18. Imagine you are a genetic counselor, and a couple planning to start a family came to you for information. Charles was married once before, and he and his first wife had a child who has cystic fibrosis. The brother of his current wife Elaine died of cystic fibrosis. What is the probability that Charles and Elaine will have a baby with cystic fibrosis? (Neither Charles nor Elaine has the disease)

19. In mice, black color (B ) is dominant to white (b ). At a different locus, a dominant allele (A ) produces a band of yellow just below the tip of each hair in mice with black fur. This gives a frosted appearance known as agouti. Expression of the recessive allele (a ) results in a solid coat color. If mice that are heterozygous at both loci are crossed, what will be the expected phenotypic ratio of their offspring?

20. The pedigree below traces the inheritance of a vary rare biochemical disorder in humans. Affected individuals are indicated by filled-in circles and squares. Is the allele for this disorder dominant or recessive? What genotypes are possible for the individuals marked 1, 2, and 3.


Footnotes

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