Single Parent Genetics

Question 1

Define parthenogenesis

Answer 1

Reproduction from a female ovum with no male involvement

Eg, bananas, potatoes, stick insects

Question 2

Define anisogamy

Answer 2

Union of two gametes that differ in size. Generally males produce many smaller and females fewer larger

Question 3

Describe the Y chromosome

Answer 3

• ~200 genes, many redundancies and repeats and mostly housekeeping genes
• Splits from X in mammalian lineage ~300mya

• Structure
-Differential regions- pseudoautosomal- recombine with X (tips of Y)
-Heterochromatin= large portion
-X-degenerate=once X, now redundant
-X-transposed= more recently came from X
• 50.4% from segmental duplication-> palindromic regions can bind and form a hairpin- recombine with itself

Question 4

Outline SRY

Answer 4

Sex-determining region Y
• Short arm of Y chromosome
• Codes for TDF (testis-determining factor) binds to DNA, leads to male development
• Discovered after male XX mouse found to have SRY transposed from Y
• Many animals no SRY
-Birds have ZW- monotreme system suggested to be similar in platypus paper (evo. origins)- defo no SRY
(Veyrunes et al., 2008)
-Reptiles temp determined sex
-Particular amphipod day-length, males produced early in mating season, females later (adaptation as male fitness improves more than female with increased size- longer growing season)

Question 5

Give human examples of patrilineal inheritance

Answer 5

• Many surnames share a Y chromosome- eg. Attenborough
• One very common chromosome type in Asia which shows highest incidence within the boundaries of the Mongol Empire
• More paternal white chromosomes in black Americans than there are maternal white mitochondria

-> reveal information about ancestral inheritance

Question 6

Give non-human examples of matrilineal inheritance

Answer 6

Mirabilis (four o’clock plant)
• Main shoot variegated, some branches green some white
• Gene passed down in chloroplasts (in cytoplasm)- some able to make chlorophyll, some not-> green/white/variegated offspring dependant on which chloroplasts received

Neurospora fungi
• Slow growth mutants- poky mutant
• 4bp deletion
• Mitochondrial inheritance- cytoplasm
• Microinjection of cytoplasm transfers the phenotype

Chlamydomonas- green algae with flagella
• Shows cytoplasmic mutants
• Order of genes changes with three point cross- circular chloroplast genetic material- same in mitochondria
-> proved by electron microscopes

Question 7

Outline the Endosymbiotic Theory

Answer 7

Eukaryotes evolved from different types of free-living prokaryotes becoming engulfed in larger prokaryotes.
Chloroplasts and mitochondria

Question 8

Outline the evidence for the Endosymbiotic Theory

Answer 8

• Wolbachia live inside host cells, passed on through female cytoplasm
• Not passed on through males so can stop their development, make them infertile, feminise males or instruct females to kill and eat them
• Nematode now rely on Wolbachia to survive so can be killed by antibiotics

Question 9

Outline with examples the inheritance of mitochondrial diseases

Answer 9

Mitochondria have no introns- allows for faster genetic replication
• Diseases generally deletions- shorter mitochondrial DNA- faster replication
• -> Accumulate with age and phenotype can start to show later as overtake healthy mitochondria (Leigh)
• Cytoplasmic segregation means some children inherit, some don’t.
• Treatment- mitochondrial replacement therapy

Leigh syndrome
• Usually begins late first year of life
• Seizures, dementia, ventilatory failure

Leber’s hereditary optic neuropathy (LHON)
• Degeneration of retinal cells leads to vision loss

Red Ragged fibres
• muscle weakness