L10 Sex from a Genetic Perspective Flashcards
Sexual reproduction is common in ( eukaryotic / prokaryotic ) organisms
Eukaryotic
Asexual reproduction is theoretically twice as fast, so what is the advantage of sexual reproduction?
Creates genetic variation which enables a population to better respond to changes in the environment
Two main modes of sex determination are (2)…
- Protenor Mode ( XX / XO )
2. Lygaeus Mode ( XX / XY )
In the Protenor mode sex is determined by the…
Presence or absence of the X chromosome in the male gametes
The homogametic sex produces…
Only one kind of gamete (e.g. XX)
The heterogametic sex produces…
Varying gametes (e.g. XX or XY)
In moths, butterflies and most birds (such as chickens) males are the…
Homogametic sex
In species where the female is the heterogametic sex the notation…
ZZ (male) and ZW (female) is used
The diploid number of chromosomes in human cells is…
46!
In Klinefelter and Turner syndromes the non-disjunction of sex chromosomes results in…
Aneuploidy
Klinefelter syndrome is commonly designated
47, XXY
Turner syndrome involves a missing ? and is designated…
Sex chromosome, 45 XO
The human Y chromosome contains ( the same / far fewer / far more ) genes than the X
Far fewer
Key features of the human Y chromosome are (3):
• PAR Pseudo-autosomal region (homologous with the X chromosome)
• MSY Male-specific region (doesn’t synapse with X)
- SRY Sex-determining region Y produces Testis Determining Factor (TDF)
Sex determination in some organisms is governed by temperature during incubation. Temperature affects…
Enzymes and enzyme inhibitors relating to steroid hormones (e.g. oestrogen)
X-Inactivation (lyonization)
One x chromosome is always turned off, forming a Barr Body
X-Inactivation prevents female cells from producing twice as much product from X-linked genes. This is known as…
Dosage compensation
X-Inactivation (lyonization) occurs…
Randomly to one of the X chromosomes in a cell. After this occurs ALL progeny cells maintain the same pattern of inactivation!
The random nature of X-inactivation can be observed in the disease…
Anhidrotic Ectodermal Displasia (men have no sweat glands, whereas women have sweat glands in certain regions depending on which X is active)
Mechanism of X-Inactivation (4)
- X-Inactivation centre (XIC)
- Xist gene expressed in inactive X
- XIST coats the inactivated X chromosome
- This X is packed into dense heterochromatin
What does ZZ and ZW notation refer to?
Females and males (respectively) in species where the female is the heterogametic sex
Name 3 X-linked syndromes in humans…
- Anhydrotic ectodermal displasia
- Haemophilia B
- Red-green colour blindness
What is the process by which X-linked gene expression is kept similar between males and females?
Dosage compensation
