HONR 1034 Chapter Notes - Chapter 9: Carl Correns, Chloroplast Dna, Nuclear Dna
Chapter 9: Extranuclear Inheritance
I. Terms
A. Organelle heredity: in this type of extranuclear inheritance, DNA contained in the mitochondria
or chloroplasts determines certain phenotypic characteristics of the offspring
B. Infectious heredity: results from a symbiotic (both the host and the microorganism benefit) or
parasitic (only the microorganism benefits by using all of the hosts resources, usually killing it
at the end) association with a microorganism → inherited phenotype is affected by the
presence of the microorganism in the cytoplasm of the host cells
C. Maternal effects: nuclear gene products are stored in the egg then transmitted through the
ooplasm to offspring
D. The ooplasm is the cytoplasm of the egg
E. The common element is the transmission of genetic information to offspring through the cytoplasm
rather than through the nucleus
II. Organelle heredity
A. Analysis of inheritance patterns resulting from mutant alleles in chloroplasts and mitochondria has
been difficult for two reasons
1. The function of these organelles is dependent on gene products from both nuclear
and organelle DNA → hard to find the mutations
2. Many of the organelles are contributed to each progeny cell after cell division → if
only one or two of the organelles get a new mutation it may not appear in the
phenotype
a) The phenotype may be diluted and unobservable
b) Before cell divides in two, everything must grow to be partitioned
3. Heteroplasmy: variation in the genetic content of organelles
B. Chloroplasts: variegation in Four O’Clock Plants
1. Carl Correns discovered the variant plant with some white and some green branches
a) Completely white areas lack chlorophyll and provides green color → caused
by a mutation
b) Chlorophyll: light-absorbing pigment made within chloroplasts
2. Inheritance in all possible combinations determined the phenotype
3. Concluded that inheritance is transmitted through the cytoplasm of the maternal plant
because the pollen (which contributes little to the cytoplasm) had no apparent influence
on the progeny type; source of pollen doesn’t matter
C. Chloroplast mutations in chlamydomonas
1. Is a unicellular green alga, haploid eukaryotic organism with a single large chloroplast
containing about 75 copies of circular double-stranded DNA molecule
2. Ruth Sager’s discoveries
a) Knew that plant has two mating types: mt+ and mt-
b) Appear to make equal cytoplasmic contributions to the zygote
c) She determined that the strR phenotype is only transmitted through mt+
parent
(1) strR mt+ x strS mt-
(2) R = the algae is resistant to antibiotics
(3) S = sensitive so it will grow
d) Reciprocal crosses between sensitive and resistant strains show different results
depending on the mt+ parent → expressed in all offspring
e) ½ offspring mt+ and ½ mt- → demonstrates that the mating type is controlled
by a nuclear gene that segregates in a Mendelian fashion
f) If you cross them, you get half + and half - but all strR → proved with a
reciprocal test
g) The mutation is what gives the resistance to antibiotics
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