Chapter 13: Extensions of and Deviations from Mendelian Genetic Principles Flashcards Preview

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Flashcards in Chapter 13: Extensions of and Deviations from Mendelian Genetic Principles Deck (35):

Multiple alleles?

- in a population of individuals a given gene can have multiple alleles (usually one wild type and the rest mutant) not just two as previously we've been studying.


Wild type allele?

- most common in the population


Multiple allele example?

- blood types


Multiple alleles:

- Blood Types

L> two possible antigens?

L> four possible blood groups ?

L> rules for each blood group?

L> A and B

L> AB, A, B, O (phenotypes)

L> do not have antibodies against self antigens - do not have antibodies against non self antigens


What are the genotypes of O, A, B and AB?

- ii 

-  IAIA or IAI




For the blood genotypes what kind of expression goes on?

IA and IB are dominant to i (no surface antigens)

IA and IB are codominant with each other! 


IA and IB code for what?

- glycosyl transferase...each enzyme modifies the H structure on the red blood cell surface in a different way. 


Since IA and IB are codominant what does this mean for their structure?

- Both H structure mods are present on the RBC 


In RBC the i allele produces what kind of enzyme?

- nonfunctional 


Multiple Alleles.....Codominance example with Drosophila! 

- X-linked eye colour gene: 

W+= red eye colour

W= white eye colour 

We= eosin eye colour


W+ is dominant to We and W 

We is dominant to W  

(see slides for run through example of this)


Incomlete dominance? 

- when one allele  of a gene is not completely dominant to another allele of the same gene....the phenotype of a heterozygote lies within the range of the phenotypes of the homozygotous parents....this phenotype is called an intermediate 


Incomplete dominance? 

- this is called ___ dominance 

- Heterozygous pheno is an ____ with repsect to the phenotype of the homozygous for either allele. 

- An F2 ratio of _:_:_ from mating of heterozygous F1's. 

- intermediate 

-  1:2:1 



- the heterozygote exhibits phenotypes of both homozygotes

Ex: blood type IAIB 


Complete dominance? 

- this is called a ___ condition. Meaning?

- heterozygous condition

- Haplosufficient: 1/2 production sufficient for normal cell phenotype; dominant phenotype

- dominant allele is transcribed twice as frequently to result in an increase of protein production  

(involves one gene)


Incomplete dominance? 

- _____ condition 



- heterozygous condition 

- haploinsufficient: 1/2 product is insufficent for normal cell phenotype; resulting in an intermediate phenotype 

- gene product from one allele results in a mixed intermediate. 


Gene interaction? 

- interaction between genes that control the same character..... two genes, four alleles. 

- interactions of different genes in which an allele of one gene masks the expression of alleles of another gene


Example of phenotypes of combs in chickens for gene interaction...

- rose, pea, walnut, single 

- cross rose with single 

L> F1? F2? 

- cross pea with single 

L> F1? F2?  

- cross pea with rose?

- rose 

L> 3 rose: 1 single

- all pea

L> 3 pea: 1 single 

- all walnut  


Parents: R/R p/p (rose) and r/r P/P (pea)

F1: R/r P/p via 


Rp        R/r P/p

** Rp= gamete of one parent ....rP=gamete of another parent

F2 geneotypes: 

R/-,P/- = walnut dom for R and P

R/-, p/p = R dominant allele=rose 

r/r,P/- = P dominant allele= pea 


Explain the chicken comb question for gene interaction ....for recessive, dominant alleles! 

Recessive:  no influence on the basic phenotype of single comb 

dominant R allele: may produce gene product that  interacts with  product of genes controlloing single comb to get rose comb 

- Dominant P allele: acts like R to get Pea comb 

- Dominant R and P alleles:  may produce gene products that interact to produce  the comb variation of walnut.



- form of gene interaction 

- one gene masks the phenotypic epression of another 




epistatic gene?

hyostatic gene?

-gene that does the masking 

- gene that has its phenotypic expressionmasked 


Recessive Epistasis?

- epistasis due to presence of homozygous  alleles of one gene pair 


Recessive epistasis ex:  

Coat colour in mice 

-Explanation first:

- Agouti: normal "wild type coat" A/-

- Black coat : recessive.... a/a 

- at a second locus "c" permits coat colour when it is dominant..C/ is not permitted when it is in the form c/c

Q. Double homozygous Agouti parent  is crossed Albino Parent (that is homozygote for Black coat)

P1:            AACC            x     aacc

                  agouti                     albino(but should be brown) 

F1: all AaCc (100% agouti) 

F2:       AaCc            x              AaCc 


               3/4 C-             9/16 A-C- agouti 

3/4 A-       1/4 cc            3/16  A-cc albino 


1/4 aa       3/4 C-               3/16 aaC- black 

                 1/4 cc               1/16 aacc    albino 


9    :       3                :      4 

agouti; black; white 


Lethal allele?

L> essential gene?

- an allele that results in the death of an organism  

L> genes that when mutated can result in a lethal phenotype... 


Dominant lethal allele?

- mutation of an essential gene is caused by a dominant lethal allele...both homozygous and heterozygotes for that allele show the lethal phenotype


Recessive lethal allele?

- if the mutation in the essential gene is caused by a recessive allele, only homozygotes for that allele have the lethal phenotype. 


What does one mean by essential genes exactly?

- the gene product is essential for normal functioning of the organism 


Example of an Essential gene question: 

  1. Mice coat colour

yellow variety never breed true (essential gene) 

Cross two Yellow coated mice. 

AY/A    x AY

gametes:                       AY and A                                    AY and A 

                                 AY                                     A

AY                      AYA                                  AYA


A                   AY A                                    AA 


dies:  1/4 AYAY  

1/2 AYA = yello 

1/4 A/A = nonyellow 



Example of an Essential gene question: 

1.Mice coat colour

yellow variety never breed true (essential gene) 

Cross Yellow coated mouse with a non-yellow coated mouse! 

L> cross the F1's?

AY/AY     x  A/A

Gametes:        Aand A                                           A   and A 

                        A                              A

AY                AYA                            AY



A             AA                            AA 

two yellow, two non yellow.....results are similar to a test cross for the F1 generation!  1:1  


2.     Cross F1's                      AYA      x     AA  

2:1 ratio?


Explain the logic behind the yellow mice coat corsses

yellow allele is dom wrt coat colour 

when heterozygotes are crossed, a 2:1 ratio is indicative of a recessive lethal allele 

L> lethality? only homozygotes die ie AYAY

- raly gene is deleted and its promoter is next to the agouti -yellow allele controlling tis expression


Gene manifestation

L> Penetrance??

- % of individuals that show at least some degree of expression of the mutant genotype/ Not all genotypes penetrate the phenotype..complete or incomplete 

**basically what you see in phenotype wrt genotype in a pop 


Gene manifestations: 


- range of expression of the mutant phenotype

- due to other genes modifying the phenotype 

- due to environmental factors 

ex: retina blastoma 90% penetrance 

** generally lethal alleles are not common in a pop unless via mutation or if its dom past reproduction stage. 


Temperature effects?

L> Conditional?(breaks down into two)

- mutations affected by temp

L> functional at one temp = permissive 

L> non functional at different temp = restrictive  for the enzyme because its not working 


Temperature effects?


-Protein denaturaiton occurs?

- dark patches due to temperature sensitive alleles  --> tyrosinase gene: permits melanin synthesis 

-active at lower temps  >30 C - leaving a white/creame coloured fur 

- inactive at higher temps  <25 C 



- non-hereditary phenotype modification 

- mimics a similar phenotype caaused by a gene mutation

L> copy of a phenotype with no genetic basis..only mimics showing phenotypically but not genotypically 


Examples of phenocopy?

- Rickets (Vit D deficiency)

L> due to malnutrition or x-linked alleles 


L> due to thalidamide or recessive alleles 

L> causes suppression of long bone development....