Lecture 4 Flashcards
(24 cards)
What does monoecious mean?
Organisms with both male and female reproductive structures
What does dioecious mean?
Organisms with either male OR female reproductive structures
What are the stigma and pistil?
The ‘female’ reproductive structures in plants that emulate the egg cell
What is the stamen?
The pollen found in plants that makes up the ‘male’ reproductive structure
What happens in the stamen leading up to fertilisation?
Diploid mother cell in stamen undergoes meiosis to form 4 haploid microspores
Each haploid cell undergoes mitosis to produce one pollen grain with 2 haploid nuclei (one contributes to genetic material)
What happens in the pistil leading up to fertilisation?
Diploid cell in the pistil undergoes meiosis to form 4 haploid nuclei (encased in megaspore), 3 of the nuclei degrade and 1 is left
Haploid nucleus undergoes 3 rounds of mitosis to produce 8 nuclei (2 are endosperm nuclei which makes material to help the seed germinate and stay alive, 1 is the oocyte nucleus and contributes DNA to the next plant)
What is the endosperm nuclei?
Created from a pistil haploid nucleus after mitosis and makes material to help the seed germinate and stay alive
What is the oocyte nucleus?
Created from a pistil haploid nucleus after mitosis and contributed DNA to the next plant
How does fertilisation occur in plants?
Self fertilisation, the pollen grain grows towards the embryo sac (product of the meiosis of the megaspore mother cell)
Two sperm nuclei (produced in pollen grains) enter the embryo sac and one sperm nucleus unites with two endosperm nuclei to form a triploid endosperm nucleus
The other sperm unites with oocyte nucleus to form a diploid zygote nucleus
What is the microspore?
Immature male spores that develop into pollen grains which then produce sperm cells
What is the sex determination in other organisms?
ZZ (males) and ZW (females) in birds
Other organisms have a different mode of sex determination, the ratio of X to Y chromosomes
The number of autosome sets
What is homogametic?
This means being able to produce one type of gamete (eg: female human can only produce the X chromosome)
What is heterogametic?
Being able to produce 2 types of gametes (eg: human males can produce X and Y chromosomes)
What is evidence for the Y chromosome determining maleness?
Some individuals may have certain chromosomes that don’t align with their sex, eg: someone male have two X chromosomes and be male, in this case, one of their chromosomes may be longer than the other, the longer fragment coming from the Y chromosome, this means only a certain gene of the Y chromosome is required for maleness
This idea is further demonstrated in females with XY chromosomes, they have a missing fragment in their Y chromosome
What is SRY?
Sex determining region of Y
This is the gene that is speculated to determine ‘maleness’
What happens if SRY is present?
During embryonic development, the gonads could either develop into ovaries or testes, at 6 WEEKS, if SRY is present, testes are produced
These testes produce an ANTI-MULLERIAN HORMONE which prevents the development of any sexual structures as the Mullerian duct degrades
Testosterone is produced and allows the formation of the epididymis, vas deferens and seminal vesicle
What happens if SRY is not present?
The gonads develop into ovaries and the Mullerian duct gives rise to the oviduct, uterus and upper portion of the vagina
Secondary sex determination is determined by hormones after testes or ovaries are formed
What determines sex in birds?
Ovum
How is sex determined in Drosophila?
The ratio of X chromosomes to the number of haploid sets of autosomes
In genetic disorders in flies, a single X chromosome causes maleness
What is evidence for the ratio of X chromosomes to the number of haploids sets in autosomes controlling sex in fruit flies?
Fruit flies with XXY and 2n autosomes have a ratio of 2:2n are female
Fruit flies with XXX and 2n autosomes have a ratio of 3:2n are female
Fruit flies with XY and 3n autosomes have a ratio of 1:3n are male
This means that if the ratio is less than 0.5 leads to maleness and above 0.5 leads to femaleness
How is sex determined in bees, wasps and ants?
The type of egg: unfertilised haploid eggs become male whereas fertilised diploid eggs become female
What are Barr bodies?
A condensed inactive X chromosome found in the somatic cells of female mammals, the decision of which X chromosome is inactive is random and due to embryogenesis
The number of Barr bodies is always 1 less than the X chromosomes
Why is only one X chromosome active in cells during transcription?
The X chromosome contains an X inactivation centre, containing ‘X-ist gene’
Transcribing this gene leads to heterochromatin formation and the condensation of the X
What is Bilateral gynandromorphs?
Organisms that can be female on one side and male on the other
This can be seen in organisms with certain characteristics that are controlled by sex chromosomes (such as butterflies, they can have male and female wing patterns)
