Bio 203 Unit 2

Extranuclear inheritance (non-mendelian)

genes are not in the nucleus, exist in the mitochondria and chloroplasts

• extranuclear chromosomes are similar to bacterial chromosomes, circular

Epigenetic Inheritance and Imprinting (non-mendelian)

genes are altered in the offspring

• ex: methylation

Maternal effect (non-mendelian)

gene expression in the mother determines traits of offspring

Endosymbiotic Theory

mitochondria and chloroplasts originated from bacteria that took up residence within a primordial eukaryotic cell

Where the chloroplasts originated from

Cyanobacterium

Where mitochondria originated from

Gram-negative nonsulfur purple bacteria

Where modern organelles evolved from

Intracellular bacterial cells evolution

What contains chloroplasts and mitochondria?

Plants and algae

What contains only mitochondria?

Animals and fungi

Supporting theories for endosymbiotic theory

• organelles have circular chromosomes (like bacteria)

  • organelle genes are more similar to bacterial genes than those found within the nucleus

Which parent provides extranuclear genes?

Mother

• maternal inheritance

• sperm, small and only pass on only the nucleus

• egg, large pass on the nucleus and cytoplasm

  • this includes organelles like mitochondria

Chloroplasts

• location of photosynthesis

• their DNA contains genes for rRNA and tRNA

  • needed to make their proteins

• randomly distributed to daughter cells

Chloroplasts Inheritance type

Maternal inheritance

If a plant develops from a zygote with both mutant and wild-type chloroplasts then… one cell with all wild-type chloroplasts would be what color?

Green

If a plant develops from a zygote with both mutant and wild-type chloroplasts then… some cells get all mutant chloroplasts would be what color?

White

If a plant develops from a zygote with both mutant and wild-type chloroplasts then… one cell with a mix of while and mutant chloroplasts would be what color?

Green

Where does oxidative phosphorylation occur?

Mitochondria

• makes ATP

Mitochondrial DNA

• contains rRNA and tRNA genes

• oxidative phosphorylation genes

mtDNA

the genetic material in mitochondria

Where are most mitochondrial proteins encoded?

The nucleus

• proteins are made in the cytoplasm but have a signal to direct them to mitochondria

Human mtDNA

• 17,000 bp - relatively few genes

• rRNA and tRNA genes

• 13 genes encode polypeptides that function in oxidative phosphorylation

2 Mechanisms of mitochondrial disease (200+ discovered dieases)

1. Transmitted from mom to kids via egg

   • string maternal inheritance pattern

2. Mutations can occur in somatic cells during aging

   • mitochondria are very susceptible to DNA damage from free radicals

What cells to mitochondrial diseases typically affect?

usually are chronic degenerative disorders cells needing high levels of ATP

• nerve and muscle cells

How much faster do mitochondrial genomes mutations accumulate than the nuclear genome?

10x faster, good for studying evolutionary biology, increases the risk of deleterious mutations

Epigenetic Inheritance

modification to a gene that changes gene expression but is not permanent over the course of generations

• can permanently affect the life of an individual

• not change in DNA sequence itself,

• may or may not follow Mendelian inheritance

Genomic imprinting

modification occurs to a nuclear gene that alters gene expression, but is not permanent over many generations

• expression of a gene depends on whether its inherited from mom or dad

• several mammalian genes are imprinted

Mice’s growth hormone

lgf2, normal body size

lgf2-, dwarfism

Imprinted genes

not expressed

What type of inheritance do mice have?

maternal alleles are imprinted, paternal alleles expressed (slide 23 note #6)

What type of genes do not follow independent assortment and do not follow Mendel’s law of Assortment

Genes that are physically associated

The further apart genes get from each other on the chromosome…

the less linked the alleles become

What is the expected ratio of the F2 generation of true breeding of a dominant x recessive in a dihybrid cross

9:3:3:1

If genes are linked…

• parental alleles are inherited together

• no independent assortment

• linked genes form linkage groups

If the genes on a chromosome are far apart and have independent assortment then…

the rate of independent assortment is proportional to their distance apart

Recombination (crossing over)

• during prophase 1 of meiosis

• homologs pair up

• non-sister chromatids switch DNA

Why is the crossing over not between sister chromatids?

They are from homologs and not identical to each other

Parentals

non-recombinants

Recombinants

nonparental

Where was the first direct evidence of direct linkage

Thomas Hunt Morgan, demonstrated linkage x-linked genes in Drosophila melanogaster

3 Traits Thomas Hunt Morgan demonstrated of x-linked genes in flies

• Body Color: gray (y+) or yellow (y)

• Eye Color: red (w+) or white (w)

• Wing Length: long (m+) or miniature (m)

  ** + means wild type

When parental traits are the most common what does that indicate?

Linked assortment

What did Thomas Hunt Morgan find?

3 genes:

• all on x-chromosome

• homologous crossing over

• recombination rate depends on gene distance

Is it more common for recombinants if they’re closer together or further apart on a chromosome?

Further apart