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Genes Evo & Dev Y1 > Genes L11 Notes > Flashcards

Genes L11 Notes Flashcards

1
Q

Give an example of interactions between genes

A

Coat colour -> mammals

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2
Q

List the Genes controlling coat colour in mammals & what they control

A 
	A gene:
>> Distribution of pigment -> hair strands
	B gene:
>>Colour of pigment
	C gene:
>>Colour expression
	W gene:
>> Distribution of pigment -> overall coat
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3
Q

Describe what the A gene involved in controlling coat colour is in charge of & describe it’s different alleles.

A 
	A gene:
>> Distribution of pigment -> hair strands
	Allele (A):
Agouti -> Lighter hair in middle
	Allele (a):
Solid black
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4
Q

Describe what the B gene involved in controlling coat colour is in charge of & describe it’s different alleles.

A 
	B gene:
>>Colour of pigment
	Allele (B):
Black 
	Allele (b):
Cinnamon
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5
Q

Describe what the C gene involved in controlling coat colour is in charge of & describe it’s different alleles.

A 
	C gene:
>>Colour expression
	Allele (C):
Colour expressed
	Allele (c):
Albino -> colour not expressed.
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6
Q

Describe what the W gene involved in controlling coat colour is in charge of & describe it’s different alleles.

A 
	W gene:
>> Distribution of pigment -> overall coat
	Allele (W):
Dominant white / white spotting
	Allele (w):
Even distribution
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7
Q

What is epistasis?

A

• Epistasis:
 Interaction between 2 or more genes controlling a single genotype.
Allele of one gene masks phenotypic effect of allele of another gene
Used to dissect biochemical & developmental pathways.

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8
Q

Name the two types of epistasis & their associated phenotypic ratios.

A

Recessive -> 9:4:3

Dominant -> 12:3:1

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9
Q

Describe how recessive epistasis occurs using an example

A

• Recessive epistasis:
 9:4:3 phenotypic ratio
Eg. Parental Phenotypes: Cinnamon x Albino
Genotypes: bb CC x BB cc
 100% Agouti offspring (WT)

    Offspring F1 Phenotypes:  Agouti x Agouti
                         Genotypes:    Bb Cc x Bb Cc
                                          9 Agouti              -> B_C_
                                          3 Albino              -> B_cc
                                          3 Cinnamon        -> bbC_
                                          1 Albino               -> bbcc
                           Phenotypes: 9:4:3 
                                           9 Agouti : 4 Albino : 3 Cinnamon 
                                             Instead of normal 9:3:3:1 ratio.
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10
Q

Describe how dominant epistasis occurs using an example

A

• Dominant Epistasis:
 12:3:1 Phenotypic Ratio
Eg. Parental Phenotypes: White x Cinnamon
Genotypes: WW BB x ww bb
 100% White offspring (Ww Bb)

    Offspring F1 Phenotypes:  White x White
                         Genotypes:    Ww Bb x Ww Bb
                                          9 White              -> W_B_
                                          3 White              -> W_bb
                                          3 Agouti             -> wwB_
                                          1 Cinnamon       -> wwbb
                           Phenotypes: 12:3:1 
                                           12 White : 3 Agouti : 1 Cinnamon 
                                             Instead of normal 9:3:3:1 ratio.
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11
Q

Describe the characteristics of the albino allele of coat colour

A 
•	Albino allele:
	Epistatic -> all coat colour genes
	Mutation
 Recessive 
 Loss of function
 Enzyme tyrosinase -> melanin synthesis -> melanocytes
>	Tyrosine -> Tyrosinase 
>>Eumelanin (Black)
>>Pheomelanin (Yellow)
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12
Q

Name the two types of melanin / melanocytes of coat colour produced by tyrosinase

A

> 

Tyrosine -> Tyrosinase  >Eumelanin (Black) >Pheomelanin (Yellow)
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13
Q

Describe dominant white / white spotting

A

• Dominant White / White Spotting
 Epistatic -> all coat colour genes (except albino)
 Mutation
 Dominant
 Loss of function
 Transmembrane growth factor receptor (c-kit) -> proliferation (division) &
migration -> melanocytes
&raquo_space; ww melanocytes -> Active growth factor receptor (dimer)
-> Proliferation & migration
&raquo_space; Ww melanocytes -> Inactive growth factor receptor (dimer)
-> No proliferation & migration.

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14
Q

Name the two types of melanocytes involved in transmembrane growth factor receptors & describe their characteristics

A

 Transmembrane growth factor receptor (c-kit) -> proliferation (division) &
migration -> melanocytes
&raquo_space; ww melanocytes -> Active growth factor receptor (dimer)
-> Proliferation & migration
&raquo_space; Ww melanocytes -> Inactive growth factor receptor (dimer)
-> No proliferation & migration.

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15
Q

Describe the characteristics of ww melanoctytes

A

> > ww melanocytes -> Active growth factor receptor (dimer)

-> Proliferation & migration

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16
Q

Describe the characteristics of Ww melanoctytes

A

> > Ww melanocytes -> Inactive growth factor receptor (dimer)
-> No proliferation & migration.

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17
Q

What is phenotypic variation?

A

Phenotypic variation -> Individuals w/ same phenotype but different alleles/genetic seq.

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18
Q

What is penetrance? Give an example

A

• Penetrance:
 Measures % of individuals with a given phenotype -> express expected phenotype
Incomplete penetrance
Eg. Breast cancer susceptibility (BRCA genes)

19
Q

What is expressivity? Give an example.

A

• Expressivity:
 Measures extent of expression -> given genotype at phenotypic level.
Variable expressivity
Eg. Agouti viable yellow
–> Insertion -> transposable element -> promoter region of agouti gene

20
Q

Name & describe the measures of phenotypic variation, including examples.

A

• Penetrance:
 Measures % of individuals with a given phenotype -> express expected phenotype

• Expressivity:
 Measures extent of expression -> given genotype at phenotypic level.

       Incomplete penetrance 
        Eg. Breast cancer susceptibility (BRCA genes)
       Variable expressivity 
        Eg. Agouti viable yellow
               --> Insertion -> transposable element -> promoter region of agouti gene
       Incomplete penetrance & variable expressivity
21
Q

Describe modifier genes & their consequences using examples

A

• Modifier genes:
Genetic interactions
Eg. Retinitis pigmentosa
Double heterozygosity -> mutations in PRPH2 & ROM1 genes
&raquo_space; +/PRPH2- -> No phenotype
&raquo_space; +/ROM1- -> No phenotype
Digenic inheritance
&raquo_space; +/PRPH2- & +/ROM1- -> Retinitis pigmentosa
 2nd Hit required:
&raquo_space; 2 hit hypothesis -> familial cancer syndromes -> tumour suppressor genes
>Both alleles of tumour suppressor gene
-> must be inactivated for tumour formation (loss -> heterozygosity)
Eg.
&raquo_space; Neurofibromatosis Type 1 (peripheral nervous system)
- Dominant familial cancer syndrome
- 1/3500
- Benign neurofibromas under skin & ‘Café au lait’ spotting -> skin
- Very varied severity
Pearson Twins -> Facial tissue cells -> Adam -> homozygous -> NF1 mutation
-> Neil -> heterozygous
Loss of heterozygosity -> Adam -> during foetal dev. -> Cell
lineage forming face.
CT scans -> tumors -> Neils abdomen -> asymptomatic.

> > Retinoblastoma (Retina)
BRCA1/2 (breast & ovary)

22
Q

Give an example of genetic interactions as a result of modifier genes

A 
•	Modifier genes:
Genetic interactions
Eg. Retinitis pigmentosa 
       Double heterozygosity -> mutations in PRPH2 & ROM1 genes
        >> +/PRPH2- -> No phenotype
        >> +/ROM1-   -> No phenotype 
Digenic inheritance 
        >> +/PRPH2- & +/ROM1- -> Retinitis pigmentosa
23
Q

What is the 2nd hit hypothesis regrading modifier genes?

A

 2nd Hit required:
&raquo_space; 2 hit hypothesis -> familial cancer syndromes -> tumour suppressor genes
>Both alleles of tumour suppressor gene
-> must be inactivated for tumour formation (loss -> heterozygosity)

24
Q

Explain/describe the 2 hit hypothesis of modifier genes using examples

A

 2nd Hit required:
&raquo_space; 2 hit hypothesis -> familial cancer syndromes -> tumour suppressor genes
>Both alleles of tumour suppressor gene
-> must be inactivated for tumour formation (loss -> heterozygosity)
Eg.
&raquo_space; Neurofibromatosis Type 1 (peripheral nervous system)
- Dominant familial cancer syndrome
- 1/3500
- Benign neurofibromas under skin & ‘Café au lait’ spotting -> skin
- Very varied severity
Pearson Twins -> Facial tissue cells -> Adam -> homozygous -> NF1 mutation
-> Neil -> heterozygous
Loss of heterozygosity -> Adam -> during foetal dev. -> Cell
lineage forming face.
CT scans -> tumors -> Neils abdomen -> asymptomatic.

> > Retinoblastoma (Retina)
BRCA1/2 (breast & ovary)

25
Q

What is epigenetics?

A

• Epigenetics:

 Inherited changes in gene function -> not caused by mutation

26
Q

Describe epigenetic regulation of gene expression

A

• Epigenetic regulation -> Gene expression
 Environmental factor -> switches on expression -> red & green genes
-»Expression
> Green gene -> transient (a)
-> not expressed -> daughter cells
> Red gene -> persistant (b)
-> expressed along multiple cell divisions / generations
-»Epigenetic effect.

27
Q

Describe the role of the green gene in epigenetic regulation of gene expression

A

> Green gene -> transient (a)

-> not expressed -> daughter cells

28
Q

Describe the role of the red gene in epigenetic regulation of gene expression

A

> Red gene -> persistant (b)

                        - > expressed along multiple cell divisions / generations
                              - >>Epigenetic effect.
29
Q

What are epigenetic tags?

A

• Epigenetic tags:
DNA methylation & histone modifications
>Alter chromatin structure
–>passed to daughter cells.

30
Q

What is genomic imprinting?

Describe both paternal and maternal genomic imprinting.

A

• Genomic imprinting:
- Paternal:
 Paternal allele imprinted & silenced ->By epigenetic tags
 Maternal allele preferentially expressed -> embryo
- Maternal:
 Maternal allele imprinted & silenced ->By epigenetic tags
 Paternal allele preferentially expressed -> embryo

31
Q

Describe paternal genomic imprinting

A
  • Paternal:
     Paternal allele imprinted & silenced ->***By epigenetic tags
     Maternal allele preferentially expressed -> embryo
32
Q

Describe maternal genomic imprinting

A
  • Maternal:
     Maternal allele imprinted & silenced ->***By epigenetic tags
     Paternal allele preferentially expressed -> embryo
33
Q

Give an example of genomic imprinting & describe

A 
Eg. lgf2 gene:
	Insulin-growth-like-factor 2 
>>Required -> normal growth 
>>Only paternal copy of gene expressed
>>Maternal copy of gene silenced & imprinted
             Both mice heterozygous for recessive lgf2 mutant allele
                >Mouse -> Mutant allele inherited -> mother -> Normal size
                                   Maternal genomic imprinting 
                >Mouse ->  Mutant allele inherited -> father -> Dwarf size
                                    Paternal genomic imprinting
              >>Parent of origin effect
34
Q

Describe maternal genomic imprinting using an example.

A

Both mice heterozygous for recessive lgf2 mutant allele
>Mouse -> Mutant allele inherited -> mother -> Normal size
Maternal genomic imprinting

35
Q

Describe paternal genomic imprinting using an example.

A

Both mice heterozygous for recessive lgf2 mutant allele
>Mouse -> Mutant allele inherited -> father -> Dwarf size
Paternal genomic imprinting

36
Q

What is the parent of origin effect? Give an example

A

• Parent of origin effect:
 When the phenotypic effect of an allele depends on whether it is inherited from the mother or father.
Eg. Igf2 gene

37
Q

Describe the affect of genomic imprinting on growth

A

 Affects limited no. genes (100 -> mouse)
 Many imprinted genes -> involved -> foetal growth
Paternally expressed genes -> promote growth
Maternally expressed genes -> suppress growth

38
Q

Describe the effect of paternally expressed genomic imprinted genes on growth

A

Paternally expressed genes -> promote growth

39
Q

Describe the effect of maternally expressed genomic imprinted genes on growth

A

Maternally expressed genes -> suppress growth

40
Q

Describe the parental conflict / kinship theory

A

***–»> Kinship / Parental conflict theory:
Conflict between sexual / reproductive interests -> maternal &
paternal genes in foetus.
&raquo_space; Mother -> equally related to all offspring
>Wants to divide resources equally
&raquo_space; Father -> likely related to subset of foetuses
>Wants to incr. survival chances of his offspring -> promoting
their growth.

41
Q

Describe the mother’s stance in the kinship/parental conflict theory

A

> > Mother -> equally related to all offspring

>Wants to divide resources equally

42
Q

Describe the father’s stance in the kinship/parental conflict theory

A

> > Father -> likely related to subset of foetuses
>Wants to incr. survival chances of his offspring -> promoting
their growth.

43
Q

What is the parental conflict/kinship theory?

A

***–»> Kinship / Parental conflict theory:
Conflict between sexual / reproductive interests -> maternal &
paternal genes in foetus.

Genes Evo & Dev Y1 (23 decks)

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