BIOL 265 Lecture 8: BIOL 265 Lecture : Extensions and Modifications of Mendelian Principles of Inhertiance (Part 2)
15 Apr 2019
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BIOL 265 Genetics
Thursday January 24th 2019
Lecture 8
Extension and Modifications of Mendelian Principles of Inheritance (Part 3)
1. Cytoplasmic Inheritance
• Chloroplasts and mitochondria contain DNA
• Zygote inherits cytoplasmic organelles (and cytoplasmic genes) usually from egg
(maternal)
o Genes encoding cytoplasmically-inherited characteristics usually inherited from the
mother
o Cytoplasmically-inherited characteristics show extensive phenotypic variation
o Chloroplast and mitochondria randomly partitioned between daughter cells during
mitosis/meiosis
o Reciprocal crosses can give different results
• Variegated Four o’clock plants (eg: of inheritance of chloroplast gene)
o Some branches have all green leaves, some all white, others variegated (green and
white splotches)
o White splotches: Mutation in a chloroplast gene that inhibits chlorophyll
production→ “white chloroplasts”
o Egg cells from flowers on variegated branches have either white, green or a mixture
of green and white chloroplasts.
o Chloroplast genes only inherited from egg
BIOL 265 Genetics
Thursday January 24th 2019
Lecture 8
2. Genetic Maternal Effect
• Genes for a particular characteristic inherited from both parents but phenotype of
offspring not determined by its own genotype but determined by genotype of mother
(Maternal effect is different from cytoplasmic inheritance)
• Substances in cytoplasm of mother’s egg (encoded by nuclear genes) passed on to
offspring
• Ex. shell coiling in snails:
o Allele for dextral/right handed coiling: s+ (dominant)
o Allele for sinistral/left handed coiling: s (recessive)
