L4: Sex Determinatino Flashcards
What is monoecious?
Both male & female reproductive structures in the same organisms
What is dioecious?
Individuals possessing only male/female reproductive structures
What determines sex in dioecious organisms?
Genetic or environmental factors
Define intersex
Individuals of an intermediate sexual condition (infertile)
What is the female reproductive structures in a plant made up of?
Stigma + pistil
What is the male reproductive structure in the plant?
Stamen
Production of female gametes in the pistil
- Diploid megaspore mother cell undergoes meiosis to produce megaspores (4 haploid nuclei’s)
- 3 of the 4 nuclei degrade, left with a megagametophyte (1 haploid nucleus)
- it undergoes 3 rounds of mitosis to produce an embryo sac of 8 haploid nuclei
Where are male gametes (pollen) formed from?
Diploid microspore mother cells via meiosis
Where are female gametes formed from?
Megaspores
- Only 1 of 4 haploid survives
What are the different nucleii’s in the embryo sac in the pistil?
3- antipodal nucleii
2- endosperm nucleii
2- synergids
1- oocyte nucleus
Which nucleus contributes DNA to the next plant?
Oocyte nucleus
Describe the events of pollination & double fertilisation
1) Pollen transfer from stamen (male) to stigma (women)
2) Pollen tube grows towards embryo sac
3) 2 sperm nuclei enter embryo sac
What do the sperm nucleus unites with in the embryo sac?
1 sperm nucleus unites with 2 endosperm nucleii
1 sperm nucleus unites with haploid oocyte nucleus
Scientific term for 1 sperm nucleus unites with 2 endosperm nucleii
Triploid endosperm nucleus
Scientific term for 1 sperm nucleus unites with haploid oocyte nucleus
Diploid zygote nucleus
Define homogametic
Only produce 1 type of gametes, carrying a single X chromosome (XX)
Define heterogametic
Produce 2 types of gametes, X & Y chromosome
What is aneuploidies?
Caused by non-disjunction
Failure of homologous chromosomes to separate properly during meiosis
Is the 47, XXY (Klinefelter Syndrome) male or female?
Is the 45, X (Turner Syndrome) male or female?
1) Male, but sterile
2) Female, but infertile
What does the SRY gene (sex-determing region of Y) encode for?
Testis Determing Factor (TDF)
Features of the SRY
Only part of Y chromsome required for male development
- Initiates testis development at week 6 of embryogenesis
NO SRY- female development
What region determines male development?
SRY
When does the differentiation of male & female start happening in embyrogenesis?
6th week
What gene does SRY activate for testis development?
Sox9
What 2 hormones does the developing testes produce, and what are their functions?
1) Testosterone -> promotes development of Wolffian duct into male reproductive structures
2) anti-Mullerian Hormone (AMH) -> causes Mullerian ducts to degenerate
What reproductive structures does the Wolffian duct develop into?
1) Epididymis: sperm maturation
2) Vas deferens (transport)
3) Seminal vesicle (storage of seminal fluid)
What happens to gonads if SRY is absent?
Gonadal structures develop into ovaries
- Wolffian duct degenerates
- Mullerian duct gives rise to oviduct, uterus, and upper part of vagina
D
Difference between primary vs secondary sexual differentiation
Primary: Determined by SRY
e.g presence; testes
absence: ovaries
Secondary: Controlled by sex hormones
e.g testosterone
oestrogen
Does the sperm/egg determine sex of offspring in birds?
Egg
Chromosomes in birds
Females: ZW
Males: ZZ
How is dosage compensation achieved?
Females have 2 X chromosomes, could lead to double gene expression
SO
1 X chromosome is randomly inactivated early in development
How is the X chromosome inactivated?
Xic contains the Xist gene on chromosome, leading to it producing a long RNA that silences 1 X chromosome
What is a Barr body?
Inactivate X chromsome found in female mammals
What is Lyonization and who is it named after?
A process of X chromosome inactivation in female mammals, named after Mary Lyon
What is the difference between the ZZ/ZW system and the XX/XY system of sex determination?
The XX/XY system has homogametic females, while the ZZ/ZW system has homogametic males
