Exam 4 Chapter 19

What is organelle inheritance?

The transmission of genes on mitochondrial and chloroplast chromosomes

What is uniparental origin (usually maternal)

many eukaryotic species, mitochondria and chloroplasts come from the egg

What is biparental origin?

cytoplasmic organelles are contributed to the zygote by both parents

How many chromosomes do mitochondria and chloroplast contain of their own?

multiple copies

What also can influence traits controlled by cytoplasmic inheritance?

nuclear genes

How much can the number of organelles per cell vary?

one to hundreds

How much can the number of copes of the organelle genome per organelle vary?

one to many

What does it mean to be homoplasmic?

a cell or organism in which all copies of an organelle gene are the same

What does it mean to be heteroplasmic?

a cell or organism in which not all copies of an organelle gene are the same

In maternal inheritance, phenotype of progeny depends on what?

only on the genotype of the maternal parent

What is a nucleoid?

area where the organelle’s DNA is packaged into the protein-DNA complexes

What does each nucleoid contain?

multiple copies of the organelle genome

How is the coupling of replication of the organelle genome packed?

not tightly coupled to the cell cycle

What three factors does organelle transmission genetics depend on?

• The growth, division, and segregation of the organelles themselves

• the division and segregation of the nucleoids in the organelle

• the replication of the individual organelle genomes

What does the variation in numbers of organelles and their genomes influence?

The phenotypic effects of mutant alleles of organelle genes

What can heteroplasmic cells produce?

heteroplasmic and homoplasmic descendants

If a mutation arises in a chloroplast genome, what can chloroplasts do?

arise in which all copies of the genome harbor the mutation and homoplasmic descendants can occur by chance

What is replicative segregation?

random segregation of organelles during replication

What does replicative segregation affect?

the proportion of mutant organelle genomes in a cell

What does replicative segregation lead to?

genetically mosaic organisms with some mutant cells and some wild type cells

In heteroplasmic individuals. what does penetrance and expressivity depend on?

The ratio of mutant to wild-type alleles

What makes heteroplasmic individuals appear to be wild type?

when wild-type alleles complement mutant alleles

What can influence the ratio of mutant to wild-type organelles in gametes?

The number of chloroplasts or mitochondrial genomes present in germ cells

What are the two mechanisms that inheritance of organelle genomes occur through?

• Inheritance can be based on biparental or uniparental transmission

• Inheritance is genetically determined

What are the three consequences of maternal inheritance of the mitochondrial genomes?

• Predication of phenotype can be based on mothers phenotype

• maternal lineage of organisms can be examined

• maternal history of species can be interpreted

What do mothers and children share?

identical mitochondrial DNA

What are mitochondrias?

strictly maternally inherited in mammals, no recombination of alleles

What happens when the mitochondrial mutation occurs in the germ cell of a female?

the mutation is transmitted to ALL of her offspring

• this means that is can be traced back in time and can allow identification of a common ancestor

What is the mitochondrial Eve?

the carrier of the ancestral mtDNA

What can mutations in the mitochondria result in?

human genetic diseases

• pleiotropic

What matters in mitochondrial transmission in mammals?

the number of mitochondria present in the egg cell

How many mitochondrial genomes are in an egg cell?

2000

What makes disease symptoms develop?

if the tissues that are vulnerable to the disorder contain a high proportion of mutant mitochondria

What is endosymbiosis?

mutually beneficial relationship in which one organism inhabits the body of another

What is the endosymbiosis theory?

the invaders establish endosymbiotic relationships with their hosts and evolved along with the hosts to produce the organelles

Where have the “lost” genes from chloroplast and mitochondrial genomes been relocated?

nuclear genome

What do genes found in mitochondria of some species but not others suggest?

Nuclear transfer occurred in the latter case

What is the criteria of functionality of transferred genes?

• must acquire sequences to allow their correct expression in nuclei

• must be transferred back to the organelle in which they function

• amino terminal signal sequence for transport, DNA seq must also be acquired by the organelle gene in the nucleus