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Understanding Extranuclear Genes & Maternal Effects: Anticipation & Cytoplasmic Inheritanc, Study notes of Genetics

Colorado State University (CSU)Genetics
Prof. Sarah M. Ward

Genetic anticipation, a phenomenon where inherited genetic disorders show earlier and more severe symptoms in each succeeding generation. The text also delves into cytoplasmic inheritance, a type of extranuclear inheritance where traits are coded for by genes located in mitochondria or chloroplasts. Topics include huntington’s disease, fragile x syndrome, variegated leaves in four o’clock plants, and maternal effect. Real-life examples of maternally inherited mitochondrial diseases are discussed, such as myoclonic epilepsy, retinitis pigmentosa, and various neuropathies.

Typology: Study notes

2010/2011

Uploaded on 11/15/2011

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19 September
Genetic Anticipation
Inherited genetic disorder shows symptoms earlier and with increased severity in each
succeeding generation
Huntington’s disease, fragile X syndrome
Caused by meiotic slippage increasing number of abnormal trinucleotide repeats each
generation
Cytoplasmic Inheritance
Also known as extranuclear inheritance or maternal inheritance
Trait coded for by genes located in DNA of mitochondria or chloroplast
Cytoplasmic organelles in most organisms have high levels of uniparental inheritance, usually
maternal
Cytoplasm of ovum or ovule contains multiple mitochondria and/or chloroplasts with copies of
maternal organelle DNA
Inheritance of Variegated Leaves in Four O’Clock Plants
First described by Correns in 1908
Reciprocal crosses do not give same F1 phenotypes
Maternal but not paternal extranuclear genotype inherited by F1 offspring
Trait transmitted via cytoplasm
Ovules from variegated maternal parent may contain:
All white chloroplasts → white F1 (dies)
All green chloroplasts → green F1
Mixture of white and green chloroplasts → white, green, and variegated F1
Maternally Inherited Mitochondrial Diseases
Increasing number of human diseases recognized as caused by maternally inherited
mitochondrial defects
pf2

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19 September Genetic Anticipation Inherited genetic disorder shows symptoms earlier and with increased severity in each succeeding generation Huntington’s disease, fragile X syndrome Caused by meiotic slippage increasing number of abnormal trinucleotide repeats each generation Cytoplasmic Inheritance Also known as extranuclear inheritance or maternal inheritance Trait coded for by genes located in DNA of mitochondria or chloroplast Cytoplasmic organelles in most organisms have high levels of uniparental inheritance, usually maternal Cytoplasm of ovum or ovule contains multiple mitochondria and/or chloroplasts with copies of maternal organelle DNA Inheritance of Variegated Leaves in Four O’Clock Plants First described by Correns in 1908 Reciprocal crosses do not give same F1 phenotypes Maternal but not paternal extranuclear genotype inherited by F1 offspring Trait transmitted via cytoplasm Ovules from variegated maternal parent may contain: All white chloroplasts → white F1 (dies) All green chloroplasts → green F Mixture of white and green chloroplasts → white, green, and variegated F Maternally Inherited Mitochondrial Diseases Increasing number of human diseases recognized as caused by maternally inherited mitochondrial defects

Examples: Myclonal epilepsy Retinitis pigmentosa Various neuropathies including Leber’s optic neuropathy Maternal Effect Maternal genotype influences offspring phenotype independently of inheritance of maternal genes Some mothers (cows, horses, humans…) produce bigger babies because mother’s genotype creates favorable uterine environment Some mothers (cows, horses, humans…) are genetically good milk producers – creates environmental effect on offspring phenotype Some plant genotypes create more favorable environment for growth on maternal parent Maternal Effect in Limnaea Peregra Shell coils right (dextral) or left (sinistral) Due to autosomal allele (D = dextral, d = sinistral) Maternal genotype dictates coiling of developing offspring Snail’s own D or d alleles do not affect its own shell coiling but will affect coiling of progeny