Genes L11 Notes Flashcards by Jade Benita McLaughlin

Give an example of interactions between genes

Coat colour -> mammals

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

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

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

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

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

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

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

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

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

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What is epistasis?

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

Recessive -> 9:4:3

Dominant -> 12:3:1

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Describe how recessive epistasis occurs using an example

• 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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Describe how dominant epistasis occurs using an example

• 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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Describe the characteristics of the albino allele of coat colour

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

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

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Describe dominant white / white spotting

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

 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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Describe the characteristics of ww melanoctytes

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

-> Proliferation & migration

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Describe the characteristics of Ww melanoctytes

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

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What is phenotypic variation?

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

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What is penetrance? Give an example

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

What is expressivity? Give an example.

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

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

• 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 &amp; variable expressivity

Describe modifier genes & their consequences using examples

• 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)

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

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

What is the 2nd hit hypothesis regrading modifier genes?

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

 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)

What is epigenetics?

• Epigenetics: |  Inherited changes in gene function -> not caused by mutation

Describe epigenetic regulation of gene expression

• 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.

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

> Green gene -> transient (a) | -> not expressed -> daughter cells

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

> Red gene -> persistant (b) - > expressed along multiple cell divisions / generations - >>Epigenetic effect.

What are epigenetic tags?

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

What is genomic imprinting? | Describe both paternal and maternal genomic imprinting.

• 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

Describe paternal genomic imprinting

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

Describe maternal genomic imprinting

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

Give an example of genomic imprinting & describe

``` 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

Describe maternal genomic imprinting using an example.

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

Describe paternal genomic imprinting using an example.

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

What is the parent of origin effect? Give an example

• 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

Describe the affect of genomic imprinting on growth

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

Describe the effect of paternally expressed genomic imprinted genes on growth

Paternally expressed genes -> promote growth

Describe the effect of maternally expressed genomic imprinted genes on growth

Maternally expressed genes -> suppress growth

Describe the parental conflict / kinship theory

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

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

>> Mother -> equally related to all offspring | >Wants to divide resources equally

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

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

What is the parental conflict/kinship theory?

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