BGM1004/L10 Sex in Genetics Flashcards
Give 2 advantages to asexual reproduction.
Fast cycle
Less energy required than sexual reproduction
Give an advantage to sexual reproduction.
Gives new gene combinations
Give 2 disadvantages to sexual reproduction.
Time & energy to find a mate
Potential of breaking apart favourable gene combinations
What kind of reproduction drives natural selection?
Sexual reproduction
What kind of reproduction gives an advantage in harsh environments?
Sexual reproduction
What are the products of spermatogenesis according to the Protenor mode of sex determination?
7 chromosomes with 1X
6 chromosomes without X
What is another name for the Protenor mode of sex determination?
XX/X0
What are the products of spermatogenesis according to the Lygaeus mode of sex determination?
6 autosomes + X OR
6 autosomes + Y
What is another name for the Lygaeus mode of sex determination?
XX/XY
What is the term for the sex that produces unlike gametes? (In humans = male sex)
Heterogametic
Give 2 species in which the female is the heterogametic sex.
Moths
Butterflies
Some fish
Most birds
What nomenclature is commonly used to describe a heterogametic female?
ZW
What nomenclature is commonly used to describe a homogametic male?
ZZ
What was the outcome of the Tijo experiment (1956)?
Improved method of preparing human metaphase chromosomes (karyotyping)
What results in variation in numbers of X chromosomes?
Nondisjunction (failure of X chromosomes to separate properly during meiosis)
What genotypes result in Klinefelter syndrome?
47,XXY, 48,XXXY, 48,XXYY, 49,XXXXY and 49,XXXYY
What genotypes result in Turner syndrome?
45,X0
Give 3 symptoms of Klinefelter syndrome.
Tall stature
Slightly feminised physique
Tendency to lose chest hair
Breast development
Testicular atrophy
Female-type public hair pattern
Give 3 symptoms of Turner syndrome.
Short stature
Small fingernails
Shortened metacarpal IV
No menstruation
Poor breast development
Rudimentary ovaries
How did X and Y chromosomes likely begin their existence?
Ordinary autosomes
How many proteins are encoded by the Y chromosome for male fertility?
At least 26
What are PARs (pseudoautosomal regions)?
Regions that share homology with X chromosome
What is MSY?
Male-specific region of Y that does not synapse with X chromosome
What is SRY?
Sex-determining region Y, producing testis determining factor (TDF)
In what species is sex determined by incubation temperature?
All crocodile
Most turtles
Some fish
How does temperature determine sex in some species?
Activity of enzymes and inhibitors control production of steroid hormones such as oestrogen
What is dosage compensation?
Mechanism to keep X-linked gene doses similar between males and females
How is dosage compensation achieved?
X chromosome inactivation
How many X chromosomes are active in a given organism?
All but 1
What is the number of Barr Bodies in a given organism?
X(n-1)
What is a Barr Body?
Condensed X chromosome with RNA attached
What is the Lyon Hypothesis (1961)?
Inactivation is random at an early point in development
Once inactivated, all progeny cells have the same X chromosome inactivated
What is anhidrotic ectodermal dysplasia?
X-linked mutation causing absence of sweat glands
How does anhidrotic ectodermal dysplasia present in men?
Men carrying dominant allele (D) have no sweat glands
How does anhidrotic ectodermal dysplasia present in heterozygous females?
Mosaic of D and d sectors across the body
Where is X chromosome inactivation initiated?
XIC (X-inactivation centre)
What are the key products from the XIC? (2)
Xist
Tsix
What is the function of Xist?
Progressive coating of one X chromosome spreading outwards from XIC
What does the coating of an X chromosome lead to?
Packaging into heterochromatin
Approximately what percentage of genes escape inactivation?
15%
