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Enviromental Influences, Expressivity,Penetrance, Nongenetic Factors that affect Genotype

by: Chinade Notetaker

Enviromental Influences, Expressivity,Penetrance, Nongenetic Factors that affect Genotype BIOL 3900

Marketplace > Georgia State University > Biology > BIOL 3900 > Enviromental Influences Expressivity Penetrance Nongenetic Factors that affect Genotype
Chinade Notetaker
Principles of Genetics

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About this Document

This document has another example of environmental influences. There is also an example of how to do the math when penetrance is involved. Nongenetic Factors that change phenotype shown is also di...
Principles of Genetics
Class Notes
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This 3 page Class Notes was uploaded by Chinade Notetaker on Thursday October 8, 2015. The Class Notes belongs to BIOL 3900 at Georgia State University taught by Dr.Oommen in Fall 2015. Since its upload, it has received 19 views. For similar materials see Principles of Genetics in Biology at Georgia State University.


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Date Created: 10/08/15
Environmental In uences Continued Penetrance Example Problem 1 Polydactyly in Humans BPolydactyly bnormal Expected Genotype BB polydactyly 100 polydactyly Bb polydactyly 80 polydactyly 20 normal bb normal 100 normal Question 1 Is the genotype BB completely or incompletely penetrant Answer This genotype is completely penetrant because all of the individuals quotshowquot the expected phenotype for this particular genotype Question 2 Is the genotype Bb completely or incompletely penetrant Answer This genotype is incompletely penetrant because all of the individuals do not quotshowquot the expected genotype As you can see above in red under the expected genotype section 20 of the individuals that have the Bb genotype come out normal even though we expected them to have polydactyly Question 3 Is the genotype bb completely or incompletely genotype Answer This genotype is completely penetrant because all of individuals quotshowedquot the expected genotype Question 4 Does polydactyly have invariable or variable expressivity Answer lnvariable expressivity This is because all hands look the same and show polydactyly in the same way Expressivity lnvariable Expressivity Show the same degree of the phenotype In these cases all of the individuals will show a severe case of something moderate case of something etc Variable Expressivity Show a range in phenotypes In these cases you will see individuals with different degrees of severity An example would be balding Some people might have a receding hair line some will bald in the middle of the head some will lose all their hair etc Example Problem 2 Two parents want to know the chances of their children having polydactyly Their genotypes are Tt x tt Individuals that are heterozygous have an 80 chance of showing poydactyy and a 20 chance of being normal Step 1 Complete the Punnett Square A a a Aa aa a Aa aa After completing the Punnett Square we recognize that there is a 50 chance of their children having a Aa phenotype and there is also a 50 chance their children will have the aa phenotype Step 2 Deal with the incomplete penetrance of poydactyy 12 Aa 80 of Aa individuals will be polydactyly and 20 will be normal 0 Math 5008 40 chance of Aa child will show poydactyy Math 5002 10 chance of Aa child will be normal 12 aa All aa children will be normal because it is completely penetrant Step 3 Sum up the percentages There is a 60 chance that the children will be normal You add the 10 chance that Aa children will be normal with the 50 chance that they could have children that are aa Since aa is completely penetrant there was no additional math for that part There for there is 60 chance that they will have normal child This is not Mendelian because Mendelian expectations would be that there would be a 50 chance that the children would show poydactyy and there would also be a 50 chance that the children would be normal 0 The chance of the child being poydactyy is simply 40 which was calculated in Step 2 after apply incomplete penetrance Nongenetic Factors That Can Affect Phenotype A Age 0 Sometimes you have to wait to an quotappropriatequot age in order to observe a certain phenotype of a person Sometimes assigning a certain phenotype to a person too early and too late may be incorrect Example Balding You have to wait to certain age before being able to state that a person inherited the balding trait You can determine by looking at a baby that they inherited balding For the most part most babies are come into this world bald so that does not mean that for the rest of their life they are going to be bald You cannot observe a 90 year old man and say that he has also inherited balding At that age the balding could be due to old age so that does not necessarily mean that he is balding due to inherited traits Sex Genotypes may not appear the same in males and females due to their chemistry makeup and other reasons The three ways this can happen is sexlinked trait sexlimited trait and sex in uenced trait These different traits have different de nitions from each other 1 Sexlinked trait trait is decided by a gene is located on a sex chromosome either on the X chromosome 0 Y chromosome Example color blindness This trait appears on the X chromosome and is a recessive trait 2 Sex Limited Trait this is decided by a autosomal gene there are 22 of them Autosomes can be found in males and females Males can have the same genotype as females but the trait is observed in one sex but not the other sex Example Feathering in chickens differ between the sexes Let s assign letters for the alleles Cock feathers are recessive to hen feathers So H hen feathers and hcock feathers When a chicken genotype is HH both male and female chickens have hen feathers When a chicken has a Hh genotype both male and female chickens also show hen feathers However when a chicken has a genotype hh the female shows hen feathers BUT the male shows cock feathers Even though the female is homozygous recessive for the trait she will still show hen feathers because she does not have the proper chemistry in order to produce cock feathers like the male 3 Sexin uenced Trait These are also decided by autosomal genes The trait is observed in both sexes but the modes of inheritance are different Example Baldness Baldness is recessive in females but is dominant in males Lets assign alleles for baldness R hair and r bald Female Male RR Hair Hair Rr Hair Bald rr Bald Bald As you can see in the table Men only need to inherit one quotrquot in order to become bald which is why the balding gene is dominant in males However females have to be quotrrquot in order to become bald and that is because the quotrquot gene is recessive in females


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