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

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

1
Q

Multiple alleles?

A
  • 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.
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2
Q

Wild type allele?

A
  • most common in the population
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3
Q

Multiple allele example?

A
  • blood types
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4
Q

Multiple alleles:

  • Blood Types

L> two possible antigens?

L> four possible blood groups ?

L> rules for each blood group?

A

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

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5
Q

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

A
  • ii
  • IAIA or IAI
  • IBIB or IBI
  • IAIB
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6
Q

For the blood genotypes what kind of expression goes on?

A

IA andIB are dominant to i (no surface antigens)

IA and IB are codominant with each other!

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7
Q

IA and IB code for what?

A
  • glycosyl transferase…each enzyme modifies the H structure on the red blood cell surface in a different way.
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8
Q

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

A
  • Both H structure mods are present on the RBC
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9
Q

In RBC the i allele produces what kind of enzyme?

A
  • nonfunctional
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10
Q

Multiple Alleles…..Codominance example with Drosophila!

  • X-linked eye colour gene:

W+= red eye colour

W= white eye colour

We= eosin eye colour

ranking?

A

W+ is dominant to We and W

We is dominant to W

(see slides for run through example of this)

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11
Q

Incomlete dominance?

A
  • 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
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12
Q

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.
A
  • intermediate
  • 1:2:1
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13
Q

Codominance?

A
  • the heterozygote exhibits phenotypes of both homozygotes

Ex: blood type IAIB

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14
Q

Complete dominance?

  • this is called a ___ condition. Meaning?
A
  • 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)

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15
Q

Incomplete dominance?

  • _____ condition
  • called?

L>meaning?

A
  • 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.
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16
Q

Gene interaction?

A
  • 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
17
Q

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?
A
  • 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

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

18
Q

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

A

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.
19
Q

Epistasis??

A
  • form of gene interaction
  • one gene masks the phenotypic epression of another
  • NO NEW PHENOS ARE PRODUCED
20
Q

epistatic gene?

hyostatic gene?

A
  • gene that does the masking
  • gene that has its phenotypic expressionmasked
21
Q

Recessive Epistasis?

A
  • epistasis due to presence of homozygous alleles of one gene pair
22
Q

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/-….it 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)

A

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

23
Q

Lethal allele?

L> essential gene?

A
  • an allele that results in the death of an organism

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

24
Q

Dominant lethal allele?

A
  • mutation of an essential gene is caused by a dominant lethal allele…both homozygous and heterozygotes for that allele show the lethal phenotype
25
Q

Recessive lethal allele?

A
  • if the mutation in the essential gene is caused by a recessive allele, only homozygotes for that allele have the lethal phenotype.
26
Q

What does one mean by essential genes exactly?

A
  • the gene product is essential for normal functioning of the organism
27
Q

Example of an Essential gene question:

  1. Mice coat colour

yellow variety never breed true (essential gene)

Cross two Yellow coated mice.

A

AY/A x AYA

gametes: AY and A AY and A

                             A<sup>Y</sup>                                     A

AY AYAY AYA

A AY A AA

F1

dies: 1/4 AYAY

1/2 AYA = yello

1/4 A/A = nonyellow

28
Q

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?

A

AY/AY x A/A

Gametes: AYand A A and A

                    A                              A

AY AYA AYA

A AA AA

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

  1. Cross F1’s AYA x AA
    2: 1 ratio?
29
Q

Explain the logic behind the yellow mice coat corsses

A

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
30
Q

Gene manifestation

L> Penetrance??

A
  • % 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

31
Q

Gene manifestations:

Expressivity??

A
  • 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.

32
Q

Temperature effects?

L> Conditional?(breaks down into two)

A
  • mutations affected by temp

L> functional at one temp = permissive

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

33
Q

Temperature effects?

-Protein denaturaiton occurs?

A
  • 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
34
Q

Phenocopy??

A
  • 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

35
Q

Examples of phenocopy?

A
  • Rickets (Vit D deficiency)

L> due to malnutrition or x-linked alleles

-Phocomelia

L> due to thalidamide or recessive alleles

L> causes suppression of long bone development….

Genetics (14 decks)

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