Genetics Chapter 9: Extranuclear Inheritance

Define Extranuclear Inheritance

transmission of genetic information to offspring through cytoplasm and not nucleus usually from one parent

Define organelle heredity

DNA contained in Mitochondria or Chloroplasts determines certain characteristics of the offspring

example of organelle heredity

uniparental transmission of these organelles from the female parent through the egg to the offspring

Define infectious heredity

symbiotic or parasitic association with a microorganism

Example of infectious heredity

an inherited phenotype is affected by the presence of the microorganism in the cytoplasm of the host cells

Define Maternal effect

Nuclear gene products are stored in the egg and then transmitted through the OOPLASM to offspring

Example of maternal effect

Gene products are distributed to the cells of the developing embryo and influence its phenotype

what 2 reasons are why organelle heredity pattern is difficult to analyze?

1. the function of mitochondria and chloroplasts are dependent on gene products from nuclear and organelle DNA; difficulty distinguishing genetic mutation origin

2. Large # of mitochondria and chloroplasts contributed to each offspring cell following cell division

Define Heteroplasmy

Mutation in one or a few will be diluted out by many mitochondria that lack mutation and function normally

What inheritance pattern is the 4 o'clock plant an example of?

- uniparental inheritance

- inheritance transmitted through the cytoplasm of the maternal parent because the pollen, contributed little to no cytoplasm to the zygote

What inheritance pattern is the chloroplast mutation of the Chlamydomonas?

- uniparental inheritance

- reciprocal crosses results dependent on genotype of the mt+ which is expressed in all offsprings

What inheritance pattern is the cytoplasm mutation of the Chlamydomonas?

- uniparental inheritance

- passed through through female parent

- differences in reciprocal crosses with the susceptible strains

What inheritance pattern is Mitochondrial mutation in Neurospoora and yeast?

- mutations transmitted through the cytoplasm

- Uniparental inheritance (from male parent)

How does the mitochondrial mutation appear in the bread mold?

- slow growing mutant strain

- due to absence of several cytochrome proteins needed for electron transport

- Poky x wild-type = Poky

- Reciprocal cross = all wild-type colonies

How does mitochondrial mutation appear in Yeast?

- Mutations petite in size of colonie

- Deficiency in cellular respiration

- mitochondria performs abnormal electron transport

Define segregational petite mutation

- small percent of mutations are result of nuclear mutations in genes whose products are transported to and function in Mitochondria

- produce some petite and some wild-type offsprings

Define Neutral petite mutation

- cytoplasmic transmission

- lack mtDNA or lack a portion of it

- mitochondria inherited by both parents

- produces all wild-type offsprings

define suppressive petite mutation

- mutant and wild type cross gives DIPLOID zygotes

- expresses petite phenotypes

- dominant-negative mutation

What is dominant-negative mutation

The defective gene of the heterozygote prevents the proper expression of the normal gene's product

What is the endosymbiotic theory?

theory that eukaryotic organelles such as mitochondria and chloroplasts arose from ancient free living prokaryotes invaded primitive eukaryotic cells

what are the main points of endosymbiotic theory?

- bacteria engulfed by larger eukaryotic cells

- beneficial symbiotic relationship developed

-bacterial lost ability to function autonomously

-eukaryotic cells gained oxidative respiration and photosynthesis

describe Mitochondrial DNA

- circular and double stranded DNA

- smaller than DNA on chloroplasts

describe chloroplast DNA

- circular and double stranded

- genes encode products involved in photosynthesis and translation

what is the size of Human mtDNA?

16.6 kb

what is the size of mustard plant mtDNA

367kb

cytoplasm ribosomal variation

uniformly 80S

mitochondria ribosomal variation

55S to 80S

chloroplast ribosomal variation

16S to 23S

What are the proteins for mitochondrial function that are encoded by nuclear genes?

- DNA and RNA polymerase

- initiation and elongation

- ribosomal proteins

- aminoacyl tRNA synthetases

what are synthetase enzymes essential for?

charging mitochondrial tRNA molecules

how many base pairs of mtDNA do humans contain?

16,569

how many proteins are coded that is required for aerobic cellular respiration?

13

How many essential genes does human mtDNA have?

37

what happens to mitochondrial genes with mutations

disruption causes severe impacts on the organism

How is mtDNA susceptible to mutations?

- no structural protection from histone proteins present in nuclear DNA

- DNA repair mechanism is limited

- high concentrations of Reactive oxygen species generated by cell respiration

What does ROS do to mtDNA?

- it is toxic

- damages organelle contents such as lipids, proteins, and mtDNA

- increases the frequency of point mutations and deletions in the mitochondria

- mtDNA rate 10-fold higher than nuclear DNA

How do zygotes receive large numbers of organelles?

through the egg

what is the criteria for human disorders to be attributed to mtDNA?

- inheritance must exhibit maternal inheritance pattern

- disorder must reflect bioenergetic function of organelle

- must have mutation in one or more mitochondria gene

what are the three human disorders arising from mtDNA?

- myoclonic epilepsy and ragged-red fiber disease (MERRF)

- LEber's heredity optic neuropathy (LHON)

- Kearns-sayre syndrome (KSS)

What are the effects of MERRF?

- lack of muscular coordination

- ragged-red skeletal muscle fibers

- deafness

- dementia

- epileptic seizures

- neurologic symptoms

How is MERRF inherited?

- maternal mitochondrial transmission

- only the offspring of affected mothers inherit the disorder

- offsprings of affected fathers are normal

what is happening on a cellular level with MERRF?

- mutation in 1 of 22 mitochondrial genes encoding a transfer of RNA

- Gene encoding tRNA^Lys contains A & G within sequence

- alteration interferes with the capacity for translation within the organelle

- various manifestations of the disorder

True or False: affected individuals of MERRF exhibit heteroplasmy?

true

What are the effects of Lebers hereditary optic neuropathy?

sudden bilateral blindness that average loss at age 27

how is LHON inherited?

- maternal mitochondrial inheritance

- transmitted to ALL offsprings

what happens on a cellular level of LHON

- 4 mutations disrupt normal oxidative phosphorylation, the final pathway of respiration of cells

- mutation at specific position in mitochondria encoding a subunit of NADH dehydrogenase

what is special about the inheritance of LHON?

- no family history

- significant number of cases are sporadic and newly arisen mutations occur

what are the effects of Kearns-Sayre syndrome?

- loss of vision

- hearing loss

- heart conditions

- symptom free as children but display progressive symptoms as adults

what happens on a celluar level of KSS?

- deletion at various positions within mtDNA

- proportion of mtDNA = deletion mutations increase as symptom severity increases

what human diseases is mitochondrial dysfunction commonly seen in?

- anemia

- blindness

- type 2 diabetes

- autism

- infertility

-neurodegenerative diseases (parkinson and alzheimer)

- cancers

what is the purpose for mitochondrial replacement therapy (MRT)?

may offer option for preventing mtDNA disease transmission in families with known Hx of mtDNA disorders

How does MRT work?

- transplanting the nuclear genome from an egg of one mother to an enucleated recipient egg of another female with a normal content of mitochondria

- reconstructed eggs fertilized with sperm and implanted in the uterus of the original mother

- result production of a 3-parent offspring containing nuclear DNA from the transplanted maternal genome of one female, mitochondria from the recipient egg of another female, and a paternal genome from the sperm donor

Describe the Maternal influence (maternal effect)

- offsprings phenotype is under the control of the nuclear gene products present in the egg

- nuclear genes of female gamete transcribed and genetic products accumulate in egg's cytoplasm

- products distributed among newly formed cells influencing patterns/traits established early in development

describe Biparental inheritance

BOTH parents transmit information on genes in the nucleus that determines the offsprings phenotype

How does maternal effect impact shell coiling pattern in Lymnaea snails?

- offspring shell coil pattern determined by genotype of parent producing egg regardless of the phenotype of parent

How does maternal effect impact phenotype in Drosophila?

- protein products of genes function to activate other genes (cascade effect)

- gene products synthesized by developing egg and stored in oocyte

- upon fertilization, products specify molecular gradients for organization in zygote

true or false: the genotype of the embryo determines the phenotype of the offspring?

- False

- the genotype of the FEMALE PARENT determines the phenotype of the offspring