Genetics 7

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Genetics 7
2012-07-14 17:42:14
Dr Troy Bray

Genetics lecture exam number 2.
Show Answers:

  1. What is the Maternal effect?
    The Genotype of a mother is expressed in the phenotype of the offspring regardless of the genotype of the father or the offspring themselves.
  2. Who discovered the maternal effect?
  3. How is the maternal effect produced?
    Nurse cells produce gene products (mRNA and proteins) that can be transported into the oocyte(cytoplasmic bridge). This can affect early development stages of the embyro by donating to unequipped oocytes.
  4. What is Epigenetic inheritance?
    A modification occurs to nuclear gene or chromosome (usually in spermo or oogeneisis) that alters gene expression for that individual, but the expression is not permanently changed over the course of many generations.
  5. Why does Epigenetic inheritance not occur over the course of many generations?
    Because the modififcations do not change the actual DNA sequence.
  6. What is Dosage compensation?
    A method used to offset differences in the number of active sex chromosomes. One X chromosome is altered so that there is equal expression of genes in both males and females.
  7. What are the mechanisms of dosage compensation among species?
    • Placental mammals: Random inactivation of one X chromosome.
    • Marsupial mammals: Inactivation of a paternally derived X chromosome.
    • Insects: Level of expression of X chromosomes in males is multiplied by two. 
  8. In placental mamals, how does the X chromosome become inactivated?
    The X chromosome becomes highly condensed in the interphase nuclei of random somatic cells preventing the expression of most genes.
  9. What is a Barr body?
    An inactivated X chromosome.
  10. In placental mammals, is the same X chromosome inactivated after cell division?
  11. What is the Xic locus?
    Short region on the X chromosome that plays a critical role in X inactivation.
  12. What is the Xist (E-inactivated specific transcript)?
    Gene within the Xic region codes for a long RNA molecule that binds to the one of the X chromosomes and promotes its compaction.
  13. What is the Xce (X chromosome controlling element) region  function?
    Affects which X chromosome is inactivated. Genotypes with genes of this particular alleles in this region are more likely to avert compaction & thus remain activated.
  14. What is the TsiX gene's function?
    Encodes an RNA that is complementary to the Xist RNA. It binds to Xist RNA and prevents it from inactivating the X chromosome.
  15. Abnormalitites in the number of sex chromosomes can affect the number of what?
    Barr bodies
  16. Gender testing moved from Barr body analysis to testing for the presence of what?
    SRY gene
  17. What is the SRY gene?
    • Sex determining region Y chromosome.
    • It is loacted on the short p arm outside the pseudoautosomal regions.
  18. Without the SRY gene, the embryo defaults to what?
  19. What is AIS (Androgen Insensitivity Syndrome)?
    Males without the ability to respond to male hormones. Three types dependent upon degree on genital masculinization. (Caster Semenya)
  20. What is Genomic Imprinting?
    A marking process in which DNA is marked but not changed. This affects the pehnotype, but not the genotype. The segmenting is expressed throughout the life of the organism. Usually distinguishes between the materanl and paternal alleles.
  21. What is mono allelic expression and what can this cause?
    The expression of one allele regardless of dominant or recessive alleles. This is do to the genomic imprinting of a gene.
  22. In marsupial mammals, which X chromosome is always inactivated?
  23. What are DMR and where are they normally located?
    • Differentially Methylated regions
    • Located near the imprinted genes. 
  24. How do DMRs silence genes?
    They contain binding sites for one or more proteins that regulate the transcription of nereby genes.
  25. When does demethylation occur? What is the exception?
    • In cells destined to become gammetes.
    • De novo methylation can occur in sperm cells. 
  26. Describe human mtDNA.
    • Codes for relatively few genes.
    • Located in the nucleoid region of the mitochondria.
    • 13 genes encoding proteins that function within the mitochondrian.
    • Also codes for other genes that encode for rRNA and tRNA necessary for the synthesis of proteins. 
  27. Describe cpDNA.
    • Tends to be 10 times larger than mtDNA.
    • 110 different genes ( such as rRNA, tRNA, and photosynthesis proteins) 
  28. What is heteroplasmy?
    Cell containing variation in a particular type of organelle (wild type and mutant)
  29. Can transmission of organelles be both maternal and paternal?
  30. What is paternal leakage?
    In species where maternal inheritance is generally observed, the paternal parent on rare occasions may provide mitochondria via sperm.
  31. What is Endosymbiosis?
    Symbiotic relationship in which two symbionts (smaller of the two species) lives inside the larger of the two species.