sex determination & gene interaction (I,II) Flashcards
what is a monoecious organism
male and female reproductive structures in same organism
what is a dioecious organism
either male or female reproductive structures - US
what is an intersex organism
individuals with intermediate sexual condition (sterile)
monoecious plant - stamen is the male/female reproductive structure
-stigma+pistil is the male/female reproductive structure
stamen - male
stigma + pistil - female
production of pollen (male gametes) in stamen
-diploid microspore to 4 haploid microspores by meiosis
-haploid microspore to pollen grain by mitosis
-pollen grain has 2 haploid nuclei
production of female gametes in pistil
-diploid megaspore to megaspore (4 haploid nuclei) by meiosis
- megametophyte (1 haploid nucleus) undergoes 3 rounds of mitosis to form embryo sac with 8 haploid nuclei
–>endosperm nuclei provides growth for new seed to germinate
–>oocyte nucleus contributes DNA to next generation of plants
females XX - how are they homogametic
produce 1 type of gamete carrying a single X chromosome
males XY - how are they heterogametic
produce 2 types of gamete carrying X or Y chromosome
in mammals - sex determination determined by … chromosome - absence of this means you’re a female
Y
how does aneuploidy 47 XXY show that Y chromosome determines maleness
extra sex chromosome
2 X but still male because of Y
how does aneuploidy 45 X show that Y chromosome determines maleness
missing sex chromosome
1 X but female because of no Y
how does aneuploidy 47 XYY show that Y chromosome determines maleness
extra sex chromosome
aneuploidies caused by non-disjunction - non-disjunction - irregular segregation of homologous chromosomes during meiosis
what is non-disjunction
homologous chromosomes fail to separate properly during meiosis
-homologous chromosomes travel to same pole instead of segregating to opposite poles
what region on Y chromosome is needed for male development and what does it code for
SRY gene codes for TDF - testis determining factor
how can SRY gene be present on X chromosome if there’s no Y chromosome
-so XX but a male
abnormal non-homologous recombination event
how SRY leads to development of a male
SRY - means TDF protein is coded for
-anti-mullerian hormone means female duct (mullerian duct) is degraded by apoptosis
-development of testes
-testosterone hormone
how absence of SRY leads to development of a female
gonads become ovaries
-male duct (wolffian duct) degenerates
-female duct (mullerian duct) becomes oviduct - connecting ovaries to uterus, and upper portion of vagina
in birds, female is homogametic/heterogametic
heterogametic
ZW
NO SRY GENE
in fruit flies, X or Y determines sex determination?
ratio of X chromosomes : no. of autosome haploid set
> 0.5 = development of females
- Y has no role in sex determination - NO SRY GENE
in bees - haplodiploid system
- no. of haploid sets present
- sex chromosomes are irrelevant
male produced from unfertilised haploid eggs
female produced from fertilised diploid eggs - only females produced by sexual reproduction
what is dosage compensation
females have 1 switched off X gene (random)
inactivated condensed X chromosome is called
Barr body