Genetics Lecture 10 Flashcards
Define the process of crossing over.
Regions of DNA between homologous chromosomes are exchanged during meiosis.
Are the X and Y chromosomes considered homologous?
Yes, but only a the pseudoautosomal regions, found at the tips of the arms.
What is essential for X-Y chromosome pairing during meiosis in males?
Pseudoautosomal regions.
Do all organisms have sex chromosomes to determine their gender?
No, some fungi, plants, and protozoa no difference in chromosomes between males and females.
Name 2 significant sex determining regions (male). If females are mutated to have these genes, what happens?
SRY gene
SOX9 gene
Mutants to these genes will develop testes.
Is sex always determined by genetics?
No, some organisms have their gender determined fully or in part by the temperature during embryonic development.
Define a Barr body, and why they are significant, and why they are thought to form.
In females, one random copy of the X chromosome becomes condensed into a facultative heterochromatin.
Occurs to equalise the number of active X linked genes between males and females.
What kind of structure is a Barr body?
Facultative heterochromatin.
Does the entire X chromosome become silenced?
No, a small block on the short arm escapes inactivation.
Define sex chromosome nondisjunction, and when it occurs.
A sex chromosome fails to be isolated into its own gamete. Will therefore result in one of four gametes having no sex chromosomes, and one gamete having two copies.
If this gamete is fertilised, will result in additional or absent sex chromosomes.
Define the sex chromosomes of klinefelters syndrome, and whether they are sterile.
XXY - sterile
Define the sex chromosomes of turners syndrome, and whether they are sterile.
XO - sterile
Define triplo-X syndrome, and their phenotype compared to normal XX.
Trisomy of the X chromosome.
Individuals are phenotypically normal, but tend to have lower IQ than XX.
Explain the phenotype and mental development of individuals with more than 3 X chromosomes.
Normal sex development.
Severely retarded, with many physical abnormalities.
Define XYY, its cause, and phenotype.
Caused by Y chromosome disjunction.
Males tend to be tall, slightly impaired mental function.
