Ch 4 Part 5: modifications of mendelian ratios (SEPT 24th)

Endosymbiotic, origins of eukaryotes

Eukaryotic cells evolved from a symbiotic relationship where a larger host cell engulfed smaller prokaryotic cells,

which then developed into mitochondria and chloroplast

(Extranuclear) Endosymbiotic inheritance…

-what type of fission & chromosomes

-what is relocated to the nucleus

-what sort of parental inheritance

-what is it inherited as

-prokaryotic fission & circular, compact chromosomes

-regulatory genes relocated to nucleus

-uniparental inheritance

-inherited as haplotype

what does carl corrnes discover

define veriagation

-he discovers that patterns of chloroplast inheritance are not explainable by mendelian genetics

-variegation: explained by inheritance of two different kinds of chloroplasts

Define heteroplasmy

the phenomenon in which plastids or mitochondria with different genes are inherited

Mitochondrial mutations context of DNA 

what was discovered in

1952,1953, 1963

1952: DNA is identified as hereditary material

1953: structure of DNA is explained

1963: DNA is discovered in mitochondria

Mitochondrial Mutation, reciprocal crosses in Neurospora crassa (1952)

what was observed and what was the hypothesis

-poky phenotype is transmitted by one parent to all offspring; never appears to be heterozyous

-hypothesis: something in the cytoplasm of the recipient

Mitochondrial Mutation, reciprocal crosses in Saccharomyces cervesiae (1956)

what was observed

-petite mutation in yeast shows similar pattern as poky

-slow growth of petite associated with known mitochondrial function

Mitochondrial mutations in humans…

what about the human mitogenome

how many protein, tRNA and rRNA

how do mutations affect humans and how many mt disease are known

The human mitogenome is highly reduced

-13 proteins, 22 tRNA, 2 rRNA

-because every gene is essential, mutations tend to be harmful. there are 150 known mitochondrial diseases

why are mtDNA mutations rarely passed in generations

-because egg-cell has many mitochondria at time of fertilization.

-Mitochondrial DNA encodes mostly proteins essential for cellular respiration, so most mutations would be selected against the cell.

-Only mother can pass on mitochondrial mutations, so only half of mitochondrial mutations that take place are heritable.

Describe Myoclinin Epilepsy and Ragged-red Fiber disease MERRF (mt mutation in humans):

what does tRNA mutation casue

what could it be lethal without

what is most strongly impacted

how is the ragged red appearance caused

-tRNA mutation results in inefficient protein assembly and ultimately inefficient respiration

-would be lethal without heteroplasmy

-because brain uses so much energy, it is most strongly impacted

-ragged red appearance caused by aggregatoin of mutant mitochondria at the plasma membrane

MERRF symptoms

ataxia

deafness/blindness

epilepsy

dementia

muscle weakness

How do maternal effects alter phenotypic expectations?

what is already present at fertilization

-phenotype of the offspring depends on genotype of the mother

-on fertilization regulatory proteins already present in egg cell guide development

Describe the maternal effects in bicoid gene, what happens?

bicoid: accumulation in Drosophila egg cell determines embryonic anterior-posterior axis

bc-: recessive allele that prevents embryogenesis (formation and development of embryo)

bicoid gene, bc-/bc- in mother results in what?

failure of embryogenesis (formation and development of embryo)

How is the inheritance of mitochondrial and chloroplast encoded traits different from nuclear inheritance?

Mitochondrial and chloroplast inheritance: It is extranuclear (patterns of chloroplast inheritance does not follow mendelian genetics), uniparental (from the mother), undergoes prokaryotic fission, and inherited as haplotype, circular chromosomes

Nuclear inheritance: Inherited biparental (from both parents), and follows mendelian patterns (linear chromosomes undergo meiosis and separate into haploid gametes, offspring inherit one chromosome from each parent).