Sex determination Flashcards
(17 cards)
Heterogametic sex (digametic sex)
- refers to the sex of a species in which the sex chromosomes are not the same
- e.g. in humans, males, with an X and a Y sex chromosome, would be referred to as the heterogametic sex
Homogametic sex
- refers to the sex of a species in which the sex chromosomes are the same
- e.g. in humans, females are XX
Monoecious
this is a system where there are two sexes present in one individual (in plants it is called monoecious = one house containing the two things)
Hermaphrodite
- when we talk about animals
- when you are actually a male and a female at the same time in that you produce both male and female gametes
Haplodiploid
- similar to XO but not just haploid in sex chromosomes, males end up haploid in all chromosomes (males are truly haploid in their genome)
Pseudoautosomal region
- homologous sequences of nucleotides on the X and Y chromosomes
- these regions match between the two chromosomes and allow for pairing in meiosis
SRY gene
- a gene on the Y chromosome that is a primary determinant of sex in humans
- provides instructions for making a protein called the sex-determining region Y protein
- this protein is involved in male sexual development
What are some examples of chromosomal sex determination systems
- X-Y system
- Z-W system
- X-O system
- haplodiploid system
- monoecious/hermaphrodite system
- temperature-gated system
- social determination
What is the example used for social sex determination
- individuals have the potential to be male or female but what they become is socially determined (based on the other members of the groups, socially)
- clownfish; largest individual in the group becomes a female and the rest become males
What is the example used for temerature-gated sex determination
- turtles and alligators and other reptiles
- no chromosome determines sex, it is environmental
- you have genes that are involved in sex-determination cascades, which get turned on or off depending on temperature that the embryos are incubated
What is the mechanism of gene regulation underlying temperature-gated sex determination in red-eared slider turtles?
- at 26*C
- histones are demethylated
- triggers male development
- at 31*C
- the histones are methylated
- represses male development
What are the example of organisms with mutiple sex chromosomes?
- duck-billed platypus (females have five pairs of X chromosomes and males have five pairs of XY)
- leptodactylus pentadactylus (12 total -> 6X and 6Y)
What is the mechanism and outcome underlying XY females and XX males in humans?
- SRY can translocate so we get
- female-like but it’s XY
- male-like but it’s XX
- some phenotypically males may have intersex phenotypes
- sterile
- rare
- not enough data to asses rates of heterosexuality and gender identity
Mechanism of epigenetic gene regulation
- many different types
- activated by binding estrogen, testosterone, coritsol, etc.
- recruit molecules that acetylate or methylate
- can use epigenetics to turn off or on genes throughout life and may be heritable
- also are transcription factors that affects transcription directly
Tale of alternative splicing in female Drosophila
- the Sex-lethal gene is functional and is producing the Sex-lethal protein
- the transformer gene is function by masking the intron consensus sequence by the Sex-lethal protein
- produce the transformer protein
- fruitless has an early stop codon and is nonfuncitonal
- this triggers female behaviour
Tale of alternative splicing in male Drosophila
- Sex-lethal has an early stop codon: nonfunctional protein
- transformer has an early stop codon: nonfunctional protein
- fruitless makes a functional protein which triggers male behaviour
Sex determination in Drosophila
- the initiation of sex is determined by the ratio of how many X chromosomes you have to autosomes
- still considered an XY system because males that don’t have a Y chromosome, although they appear to have developed as males on the outside, are considered sterile
- need genes on the Y chromosomes for fertility reasons
- even though what sex you really turn into is determined by how many X chromosomes you actually have in the end
