Chapter 9: Extranuclear Inheritance Wheeler High School The Center for Advanced Studies in Science, Math & Technology Chapter 9: Extranuclear Inheritance Post-AP DNA/Genetics – Ms. Hager

Extranuclear Inheritance You are accustomed to discussing inheritance as being transferred from the nuclear genes located on chromosomes from your parents. This is not always the case…

Several Varieties of Extranuclear Inheritance Organelle heredity – DNA contained from mitochondria or chloroplasts determines phenotype of offspring Infectious heredity – comes about from the symbiotic (parasitic) relationship associated with a microorganism; inherited phenotype is affected by the presence of the microorganism living in the cell’s cytoplasm Maternal effect – nuclear gene products are stored in the egg and then transmitted through the ooplasm to the offspring

Organelle Heredity – Chloroplast & Mitochondria Analysis of organelle DNA is much more complex than nuclear DNA WHY? Function of organelle dependent of gene products of nuclear DNA and organelle DNA Figuring out where mutations occur is difficult. Lots of organelles in the cell and only one or two may have mutation Therefore the mutant phenotype will not be seen.

Chloroplasts: Variegation in Four O’Clock Plants Mirabilis jalapa Some of the plant’s branches have white leaves, others have green leaves and some are variegated. White leaves lack chlorophyll. Therefore one can conclude that these leaves do not contain chloroplasts.

Chloroplasts: Variegation in Four O’Clock Plants How is this trait inherited? Inheritance is determined based on the location of the ovule, regardless of the phenotype of the source of pollen.

Chloroplasts: Variegation in Four O’Clock Plants What conclusions can be drawn from this observation? Inheritance in the 4 O’Clock must transmitted through the cytoplasm of the maternal parent because the pollen, which contributes little or no cytoplasm to the zygote, had no apparent influence on the progeny phenotypes.

Chloroplast Mutations in Chlamydomonas Chlamydomonas is an excellent model system for studying organelle heredity because it has a single large chloroplast that exhibits a uniparental inheritance pattern. *Circular dsDNA

Figure 9-2 Copyright © 2006 Pearson Prentice Hall, Inc. Chlamydomonas The strR phenotype is transmitted only through the mt+ parent. After the zygote has gone through meiosis and haploid cells are produced, it is clear that the genetic information in the chloroplast of progeny cells is derived only from the mt+ parent. Figure 9-2 The results of reciprocal crosses between streptomycin-resistant and streptomycin-sensitive strains in the green alga Chlamydomonas (shown in the photograph). Figure 9-2 Copyright © 2006 Pearson Prentice Hall, Inc.

Mitochondrial Mutations Mitochondria, like chloroplasts, also have a distinct genes. Also like chloroplasts, mitochondrial mutations are transmitted through the cytoplasm.

Mitochondrial Mutations: The Case of poky (mi-1) in Neurospora 1952 Mitchell and Mitchell studied pink bread mold. Discovered a slow-growing strain & named it poky. Slow growth is associated with impaired mitochondrial function. absence proteins needed for e- transport; therefore aerobic respiration is very slow

Notice that chloroplast DNA is circular. What does this suggest? Chloroplast DNA ranges from 100 to 225 kb in length, and the genes carried on the DNA encode products involved in photosynthesis and translation. Notice that chloroplast DNA is circular. What does this suggest?

Mutations in mtDNA Cause Human Disorders Heteroplasmy is the condition in which a deleterious mutation arises in an organelle, such that an adult will have cells with a variable mixture of normal and abnormal organelles. For a human disorder to be attributed to mitochondrial DNA, the inheritance must exhibit a maternal inheritance pattern, the disorder must reflect a deficiency in the bioenergetic function of the organelle, and there must be a specific mutation in a mitochondrial gene.

Mutations in mtDNA Cause Human Disorders Human mitochondria contains 16,569 bp Produces 13 proteins required for cellular respiration Deletions can cause misfolded proteins which can, in turn, can cause ATP issues No histone proteins, therefore no structural protection from mutations Lots of free radicals (the ‘left-overs’ of cellular respiration) accumulate and can cause mutations

Mutations in mtDNA Cause Human Disorders mtDNA is materially inherited Why do you think that is? There are lots of mtDNA in human cells, therefore the impact of a mutation can be ‘diluted’ Variation in genetic content of organelles is called heteroplasmy!

Mutations in mtDNA Cause Human Disorders Criteria For mtDNA Mutation Diagnosis Inheritance pattern must be maternal rather than Mendelian Disorder must reflect deficiency in the bioenergetic function of organelle Must be a mutation in 1 or more of the mt genes

Mutations in mtDNA Cause Human Disorders Three disorders arising from mtDNA are: 1) myoclonic epilepsy and ragged red fiber disease (MERRF) 2) Leber’s hereditary optic neuropathy (LHON) 3) Kearns– Sayre syndrome (KSS).

MERRF Myoclonic Epilepsy Only offspring of affected mothers inherit this Symptoms: Ataxia (lack of muscle coordination) Deafness Dementia Epileptic seizures “ragged-red” because there are blotchy red patches due to proliferation of mitochondria Neurological symptoms (since the brain has a high energy demand)

Figure 9-9a Copyright © 2006 Pearson Prentice Hall, Inc. Figure 9-9a Ragged red fibers in skeletal muscle cells from patients with a mitochondrial disease. (a) The muscle fiber has mild proliferation. (See red rim and speckled cytoplasm.) (b) Marked proliferation where mitochondria have replaced most cellular structures. Figure 9-9a Copyright © 2006 Pearson Prentice Hall, Inc.

LHON Leber’s hereditary optic neuropathy Maternal inheritance mtDNA lesions Blindness by age of 27 Abnormal oxidative phosphorylation (final pathway in cell respiration) Point mutations in gene that codes for NADH dehydrognease Many cases are sporadic Includes a lack of muscular control

KSS Kearns– Sayre syndrome Loss of vision Hearing loss Heart conditions Deletions in mtDNA Deletions increase as severity of symptoms increase Usually symptom-free as children

The Maternal Effect In maternal effect, an offspring’s phenotype for a specific trait is under the control of nuclear gene products present in the egg. Classic Example: Shell coiling in snails dd = sinistral (left-handed) Dd & DD = dextral (right-handed)

Figure 9-13 Copyright © 2006 Pearson Prentice Hall, Inc. A maternal effect is evident in generations II and III, where the genotype of the maternal parent, rather than the offspring’s own genotype, controls the phenotype of the offspring. The photograph illustrates a mixture of right- vs. left-handed coiled snails. Figure 9-13 Inheritance of coiling in the snail Limnaea peregra. Coiling is either dextral (right handed) or sinistral (left handed). A maternal effect is evident in generations II and III, where the genotype of the maternal parent, rather than the offspring’s own genotype, controls the phenotype of the offspring. The photograph illustrates a mixture of right- vs. left-handed coiled snails. Figure 9-13 Copyright © 2006 Pearson Prentice Hall, Inc.

Any Questions?

Figure 9-13-01 Copyright © 2006 Pearson Prentice Hall, Inc. Figure 9-13-01 Inheritance of coiling in the snail Limnaea peregra. Coiling is either dextral (right handed) or sinistral (left handed). A maternal effect is evident in generations II and III, where the genotype of the maternal parent, rather than the offspring’s own genotype, controls the phenotype of the offspring. The photograph illustrates a mixture of right- vs. left-handed coiled snails. Figure 9-13-01 Copyright © 2006 Pearson Prentice Hall, Inc.

Figure 9-13-02 Copyright © 2006 Pearson Prentice Hall, Inc. Figure 9-13-02 Inheritance of coiling in the snail Limnaea peregra. Coiling is either dextral (right handed) or sinistral (left handed). A maternal effect is evident in generations II and III, where the genotype of the maternal parent, rather than the offspring’s own genotype, controls the phenotype of the offspring. The photograph illustrates a mixture of right- vs. left-handed coiled snails. Figure 9-13-02 Copyright © 2006 Pearson Prentice Hall, Inc.