If only males are affected in a pedigree chart...?
Well it's definitely a sex-linked trait, but while X-linked traits are more common than Y-linked traits because males only have one copy of the X, and therefore don't get a second chance to get a normal copy, I am going to interpret this question literally to mean that ONLY males are affected in the pedigree chart and that females are NEVER affected, and if that's the case, then the inheritance pattern is not an X-linked trait, but rather a Y-linked one.
Find the gentype and modes of inheritance?
Norsi, I’ll assume that square is male, circle is female, and coloured shapes are the ones affected. That’s the usual standard, but if my assumption isn’t correct, my answers won’t be either. A) Autosomal recessive: No, can’t be excluded. The condition is clearly a recessive trait, and although statistically it is improbable that 15 males and only one female would be affected, it is not impossible. Autosomal dominant: Yes, can be excluded. The acrophobia was not present in I-1 or I-2, and yet turned up in one of their children (II-2), and dominant traits must be present in at least one parent if they are present in the child. X-linked recessive: No, can’t be excluded. In X-recessive all sons of an affected mother would be affected themselves, and this is demonstrated by IV-9’s children. Also, the condition did not express itself in a female until IV-9, and those siblings were the first instance where both parents had evidence of the condition in their family. X-linked dominant: Yes, can be excluded. III-7 did not pass the condition on to all of his female children. He did pass his one and only X-chromosome on to all of them. Y-linked recessive: No, because the condition is present in both males and females. B) X-linked recessive, because only one in 16 of the affected individuals on this chart was female. This uneven gender distribution is unlikely in an autosomal disease. C) The symbols I used are XA for normal X chromosome, Xa for affected X chromosome, and Y for a Y chromosome. III-5 = XA, Y III-6 = XA, Xa IV-9 = Xa, Xa IV-11 = Xa, Y V-9 = XA, Xa D) If V-1 (genotype XA, Xa) marries V-4 (genotype Xa, Y), the probability of an affected first child is 50%. This is the same regardless of gender, because there is a 50% chance that any child would receive V-1’s healthy XA chromosome, which would prevent the recessive condition from expressing itself. If the child received V-1’s Xa chromosome instead, the genotype would be either (Xa, Xa) or (Xa, Y). Either one would express the condition in their phenotype. Good luck with the rest of your biology homework!
Why are pedigree charts used to determine mode of inheritance in humans, but not with other organisms?
I don't know who you heard this from, but Pedigree charts can be used with other animals, specifically dogs, cats, horses and some other livestock animals. They are used to trace lineage and traits of ancestors to try and determine the health of offspring according to the health of parents.
How do I determine if a pedigree is X-Linked or Autosomal?
To expand with some specific rules, consider these (consider confirming with a Punnett square if that helps you to think about them).For an X-linked recessive trait…A healthy father cannot have affected daughters. Since he is healthy, his (only) X must have a healthy version of the allele… and since he passes that single X to every one of his daughters, they MUST be healthy (if the trait is recessive, it doesn’t matter what the mother gives since the father is giving the dominant, healthy allele).An affected mother MUST have affected sons. Since it is a recessive trait, the mother must be homozygous recessive to manifest the trait. Since son’s receive their ONLY copy of the gene involved from their mother (the Y generally doesn’t have the genes that are represented on the X) then the son must receive the defective allele from the mother and express it.Pedigrees are sort of like Sudoku—after you solve several, you start to recognize certain ‘points of vulnerability’ where you can quickly make progress. As alluded in another answer, one example is in dominant traits—an individual with a dominant trait must have at least one copy of the dominant allele, and must therefore have gotten it from one of their parents… who must in turn have the disease, since the trait is dominant and a single defective allele is sufficient.Edit: I’ve got the first release of a “Pedigree deduction” browser app going; you can find it here:PediDucer_Opts
Why is Pedigree important for dog breeds?
In short: It’s the dogs documentation of who it is and what it is. But it has many purposes as can be seen below.It’s a tool for breeders to keep track of lines. Breeding dogs the right way include more than just health testing of every dog, test the mentality, show results and other titles of the dogs that should be breed.Look at the German Shepherd Dog. The breed is (not officially but kind of any way) divided into show lines and working lines. It’s still the same breed but breeders usually never breed show lines to working lines and vise verse. Dogs from show lines and dogs from working lines usually look slightly different from each other but if there was no way of telling, then the pedigree would.The pedigree is a dog’s identification papers. A person can adopt a dog that looks like a pure breed Labrador retriever. And will most likely call it a pure breed Labrador retriever. Even if it may not have 1% of Labrador retriever in it. The pedigree tell you what breed you have and you can prove it if you ever had to show documentation of the dog’s breed (for example if you live in an area that have banned some breeds, and you dog look like one of those even if it’s for sure not one of them).Sometimes only dogs with a pedigree are allowed to compete in some dog shows. So the person with the “Labrador retriever” from the shelter in the example above may not be able to show what it can do in an official competition just because it doesn’t have any papers. Silly reason you may think, but for people who has dog training and showing as their passion in life, getting a dog that could not be used for that purpose would be like throwing money, time and effort in the ocean. (Also the competitions are usually linked to the main kennel club of the country, so they gain from only letting pure breeds with pedigrees compete in their competitions).
What's the difference between sex-linked and autosomal, dominant and recessive, in a pedigree?
A dominant allele will show the corresponding phenotype if the individual only has one copy of the allele, whereas a recessive allele will show the phenotype only if the individual has the recessive allele on both chromosomes (one from each parent). If you are looking at a pedigree chain you can usually determine if a gene is dominant or recessive by looking to see if the trait skips a generation. If an individual and their grandparent have the trait but the parent does not, then it is recessive, because if it were dominant, all three would have it. Sex linked means that the allele is located on one of the sex chromosomes, either X or Y, whereas autosomal means that it is on one of the non-sex related chromosomes that everyone has. Figuring out sex linkage from a pedigree can be a little tricky. Look to see if the trait is evenly distributed between sexes or if it is seen more often in men or women. Men are more affected by X linked recessive traits because they only have one copy of the X chromosome. If you have a situation where a man and woman without the trait have children with only males showing the trait, it is likely sex linked and X-linked recessive. Hope this helps!
How is the inheritance of traits traced by geneticists?
Traits that are inherited in a mendelian fashion can be easily traced using information obtained through pedigree diagrams, which are visual representations of disease transmission within in family.There are 5 archetypal Mendelian inheritance patterns:Autosomal(non-sex linked) DominantAutosomal RecessiveX - Linked DominantX - Linked RecessiveY - LinkedLet’s consider the simplest example, autosomal dominant.How can we determine that the inheritance pattern is autosomal dominant? We can establish dominance because every affected individual has at least one affected parent, if the trait was recessive then an affected individual could be produced by the mating of two unaffected carries. Another way to view it is the trait is dominant because no unaffected parents produce an affected offspring. Now for the “autosomal” part, if the trait was Y-linked it would only be transmitted from fathers to sons, since it is the father who provides the Y chromosome and since only males are XY. If the trait was X-linked we would see a greater proportion of affected males, since they only have one X chromosome they are more likely to express the disease compared to a female who have two copies (kind of like having a back up).Most human diseases, however, are not inherited in an typical Mendelian fashion, but rather exhibit a “complex” patterns of inheritance. Complex disease theory states that it is not the genotype at a single locus that determines disease status, but rather a combination of multiple alleles and environmental factors which determine the disease outcome. A threshold model is used to describe an individual’s susceptibility to disease.The above distribution shows that only when a certain accumulation/combination of genetic and environmental factors are present will the disease phenotype manifest itself.
What is the difference between hereditary and familial disorder?
Both these terms are confusing and have often been used interchangeably.Let me try to explain the difference using cancer as an example.Hereditary:You can inherit a gene mutation from your parents. You can pass it on to your child. The genetic mutations are present in the cells of the ovaries and the testes, which produce the eggs and the sperm.Every cell in the body will have the mutation. If you are born with the mutation, you are more likely to develop cancer than somebody who doesn't have it. The disease is also more likely to happen to you at a young age.An example of a hereditary cancer syndrome is Li-Fraumeni. If you have Li-Fraumeni syndrome, the mutation occurred in the p53 gene.Different kinds of hereditary cancers are:breastovary andcolon.Familial:This involves having one or more cases of the disease in a person's family. If you have family members with a history of cancer, you have a slightly higher risk of developing it.In the familial kinds of cancer, abnormal cells are caused by a combination of germline and somatic mutations. Inheriting the mutations poses only a slight risk of developing the disease.The genes that influence familial cancer are still unknown and the effects of these mutated genes are still not fully understood. The germline mutations are also present in every cell of a person's body.
How do you know if a pedigree is dominant or recessive?
You can't exactly be 100% sure all the time, but there are some tips that could tell you whether it's recessive or dominant. Let's say that A is dominant and a is recessive. First, if there are two parents without the trait, but their children have it, then the gene must be recessive, because if it were dominant, and the two parents both are homozygous recessive, then there is no why their children could have the trait. Their genotype must both be Aa, so that there is a possibility that one child could have the trait. Note: if, in the second generation, there is an offspring that does not have the trait, and married someone who also doesn't have the trait and have kids that don't have it either, you still cannot be sure that the offspring is homozygous dominant, because there is a chance that they could be Aa. If you have one parent that doesn't have the trait and one who does, and most or all of their children have the trait, then the gene must be dominant. If most of the offspring have the trait and some don't, then it is still possible that the gene could be recessive, but because MOST have it, it is more likely that it is dominant. If you have both parents that have the trait, and their children either have the trait or not, then it is most definitely dominant. If it were recessive, then those parents could only ever have children who have the gene. And if they had children who don't have the gene as well, then both parents genotype must be Aa, and the normal children's genotype is aa.