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107 Cards in this Set
- Front
- Back
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What does monoecious mean? |
Both male and female reproductive structures in the same organism |
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What are hermaphrodites? |
Organisms that have both male and female reproductive structures (most plants, some animals e.g earthworms) |
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What does dioecious mean? |
Individuals possessing only male or female reproductive structures (most animals, some plants) |
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What does intersex mean? |
A term usually reserved for individuals of an intermediate sexual condition ( most often sterile) N.B sterile = not able to produce children |
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In a plant, where can you find the male structures that make the pollen? |
The stamen |
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In a plant, where can you find the female structures that make the eggs? |
In the stigma and pistil |
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How are male gametes produced in the stamen? |
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How is the production of male gametes in plants different from that in humans? |
Each pollen grain contains two haploid nucleii In sperm, there is one haploid nucleii |
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What is the first stage in the production of female gametes in the pistil of plants? |
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What is the second stage in the production of female gametes in the pistil of plants after this stage? |
N.B the same thing happens in gamete formation in females |
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What happens to most of the cytoplasm from the megaspore? |
It ends up in the megagametophyte |
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What happens after this stage of female gamete production? |
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What is the endosperm nucleii? |
Nutritional part of seed |
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What is the oocyte nucleus? |
Goes on to contribute to new plant |
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How does pollination and double fertilisation take place in plants? |
N.B between stage 2 & 3 the pollen tube invades the embryo sac |
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One sperm nucleus unites with the two endosperm nucleii- what does this form? |
A triploid endosperm nucleus |
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One sperm nucleus invites with haploid oocyte nucleus. What do this form? |
A diploid zygote nucleus |
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In total, how many of the embryo nuclei are used? |
3 |
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How many antipodal nucleii are the in an embryo sac? |
3 |
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How many endosperm nucleii are there in the embryo sac? |
2 |
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How many synergies are there in the embryo sac? |
2 |
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How many oocyte nucleii are there in the embryo sac? |
1 |
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What does the triploid endosperm nucleus become? |
The endosperm which provides nutrition to the embryo |
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What does the diploid zygote nucleus become? |
The embryo |
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What is germination |
A seed/kernel grows into a new plant |
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What are the sex chromosomes in birds? |
ZW/ZZ |
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Why are human females homogametic? |
They only produce one type of gamete-carrying a single X chromosome |
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Why are human males heterogametic? |
They produce two types of gamete, carrying an X or Y chromosome |
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Two X chromosomes cause femaleness and one causes maleness (no role for Y) OR The Y chromosome determines maleness Which is true? |
The Y chromosome determines maleness |
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What is Klinefelter syndrome? |
Where males have an extra X chromosome XXY (Therefore must be presence of Y in this case that determines sex) |
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What are some features of Klinefelter syndrome? |
Genitalia and internal ducts are male Testes are small These individuals are sterile, Limited development of secondary sexual characteristics |
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What is Turner syndrome? |
Females only have one X chromosomes (don't need two X's to be female...one will do |
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What are some features of Turner syndrome? |
Short height Amenorrhoea (lack of menstrual cycle) No adolescent growth spurt Ova degenerate in utero (infertile) Limited development of secondary sexual characteristics |
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Is someone who is XYY male or female? What are their symptoms? |
Male Asymptomatic Increased growth velocity, above average height |
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What causes aneuploidies? |
Non-disjunction : the failure of homologous chromosomes to separate properly during meiosis |
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Meiosis produces gametes. How many round of DNA replication are there in meiosis and how many rounds of cell division are there? How would you describe the gametes produced? |
One round of DNA replication (46 ---> 92 chromosomes) Two rounds of cell division Four haploid gametes produced from one diploid cell Gametes have 23 chromosomes |
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Non disjunction is the failure of homologous chromosomes to separate properly during meiosis. What happens to them instead? |
Homologous chromosomes travel together to the same pole (instead of segregating to opposite poles) All four gametes are aneuploid |
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What is aneuploidy? |
The presence of an abnormal number of chromosomes |
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What would happen if non disjunction occurred at the X chromosome during meiosis? |
Two of the gametes are XX (instead of single X) |
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How much of the Y chromosome confers maleness? |
A small region at the the end of the short arm of the Y is all that is needed to confer maleness |
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Some human males are 46, XX. Why is this? |
Attached to one of the X chromosomes is a short region from the p end of the Y |
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Some human females are 46, XY. How can this be? |
A small region near the long end of the Y chromosome is missing |
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This is a Y chromosome. What is the PAR? (psedoautosomal region) |
Homologous in sequences to parts of the X chromosome This is what allows X and Y to pair up during meiosis |
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What is the MSY region of the Y chromosome? |
Male specific region (does not synapse with X-i.e you never see these regions in the X chromosomes) |
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What is the SRY part of the Y chromosome? |
The sex determining region SRY is a gene that encodes a protein that acts as a testis determining factor (TDF). SRY is the only region of the Y required for male development. |
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In what instance would an X chromosome that carries the SRY gene (X*) be generated? What would happen if X* fertilises an egg? |
Abnormal recombination in the father of XX males If X* fertilises an egg, then an XX* male results-presences of the SRY gene, even in the absence of a Y chromosome, initiates male sex determination |
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Until the 6th week of development, how would you describe embryos? |
Gonadally identical, regardless of the sex chromosomes |
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What happens at the 6th week of development? |
If SRY present, genes are activated in the gonad that lead to development of testes and degeneration of female duct |
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What are each of these features? |
Bipotential gonad-yet to differentiate into testes or ovary Female duct-gives rise to female related structures Male duct- gives rise to male related structures |
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In the absence of anything else, what sex is development skewed towards? |
Female, by default, unless there is Y chromosome with SRY gene |
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Which two hormones do the tests produce? |
Anti-Mullerian hormone Testosterone (which means male structures like vas deferens and seminal vesicle develop) |
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What does the anti-Mullerian hormone result in? |
Mullerian Duct degeneration |
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What is a consequence of testosterone? |
Wolffian duct develops into epididymis (where sperm mature) , vas deferens (transport) and seminal vesicle (storage of seminal fluid) |
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What happens in the seminal vesicle? |
Storage of seminal fluid |
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What does the vas deferens do? |
Transports sperm from testes into urethra |
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If SRY is absent in XX individuals, what is the default pathway? |
Indifferent gonadal structures develop into ovaries Wolffian ducts degenerates Mullerian duct gives rise to oviduct ( connects ovary to uterus), the uterus and upper portion of vagina |
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Once the embryonic gonads develop as either testes or ovaries, all subsequent steps of sexual reproduction are controlled by what? |
Sex hormones |
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What controls primary sexual differentiation? |
Controlled by SRY in mammals. Expression of SRY leads to development of testes, lack of SRY leads to ovaries. |
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What does secondary sexual differentiation refer to? |
All sex development controlled by hormones, including characteristics such as external genitalia, appearance of mammary tissue, body build etc |
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Why was cytological identification of sex chromosomes in chickens not achieved until 1961? |
Owing to the large number of chromosomes (78) Difficult to locate sex chromosomes |
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In birds, what kind of gametes does: a) the male produce? b) the female produce? Therefore what determines the sex in birds? |
a) Z gametes b) Z and W gametes Therefore the ovum determines the sex in birds |
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As well as birds, the ZZ/ZW mode of sex determination is found in what other things? |
Reptiles Some insects (moths, butterflies) |
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Why do birds lack SRY? |
ZW/ZZ are unrelated to XX/XY, having evolved from a different pair of chromosomes |
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In the fruit fly, what determines sex? |
The ratio of X chromosomes to the number of haploid sets of autosomes |
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What is the sex chromosome composition in Drosophila? |
The same as in mammals, XX in females and XY in males. But....the Y chromosomes is not involved in sex determination in this case. |
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In drosophila, Y does not cause maleness. A ratio number of X : number of autosomes of haploid set that is >0.5, leads to development of males or females? |
Females |
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What is the ratio of X chromosomes to autosomes here? Therefore what is the sex? |
2 : 2n (1) Female |
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What is the ratio of X chromosomes to autosomes here? Therefore what is the sex? |
1 : 2n (0.5) Male |
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What is the ratio of X chromosomes to autosomes here? Therefore what is the sex? |
1:2n (0.5) Male |
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What is the ratio of X chromosomes to autosomes here? Therefore what is the sex? |
2 : 2n (1) Female |
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What is the ratio of X chromosomes to autosomes here?
Therefore what is the sex? |
3 : 2n ( 1.5) Female |
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What is the ratio of X chromosomes to autosomes here? Therefore what is the sex? |
1 : 3n (0.33) Male |
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Another method of sex determination is the haplodiploid system. What things does this happen in? |
Bees, ants, wasps. |
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Describe the haplodiploid system in bees/ants/wasps. |
Male bee ( drone) is produced from unfertilised haploid eggs (16 chromosomes) Female honeybees ( workers and queens), are produced from fertilised eggs and are diploid (32 chromosomes) |
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Only males are produced by sexual reproduction in bees. True or false. |
False. Only females are produced by sexual reproduction in bees. |
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The human chromosome has ca. 1,500 genes. Females have twice as many X genes in comparison to males-but twice the amount of transcription is not observed. i.e females should have 2x the amount of X associated protein as males but they actually have the same amount of X associated protein as males. What does this suggest? |
Such a situation would be lethal |
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How is it resolved that the males only have half an man X genes as female? |
Dosage compensation is achieved because one of the X chromosomes in females is transcriptionally silent |
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One of the X chromosomes in females is transcriptionally silent. By what mechanism does it become transcriptionally silent? |
Xic contains the Xist gene which is transcribed to a 25kb non-coding RNA. |
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Xic contains the Xist gene which is transcribed to a 25kb non-coding RNA. What happens as a result of this RNA being present? |
RNA persuades supercoiling of the rest of the chromosomes-this forms heterochromatin The condensed DNA cannot be transcribed ( so condensed that promotors cannot bind to it) N.B this only happens to one of the X's |
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What is this showing? |
The inactivated X becomes highly condensed and is visible by light microscopy of interphase cells (Barr body) |
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What is the condensation process also referred to as? |
Lyonization |
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At any given point in a female cell, you want one X chromosomes switched on, irrespective of how many X chromosomes you have. How does the number of Barr bodies relate to the number of X chromosomes? |
The number of Barr bodies is always one less than the number of X chromosomes |
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When does X inactivation occur? |
In embryogenesis |
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The choice of which X to inactivate ( maternal or paternal) is random or pre-determined? |
Random |
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Once inactivation of an X chromosome has occurred, all cells descended from the initial cell in which inactivation took place will exhibit inactivation of the same chromosome (inhibited somatically). True or false. |
True Therefore, all females are mosaics for all X-linked alleles. |
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In calico (tortoise shell) cats, the gene for brown or orange is on the X chromosome. All cells in an organ patched are descended from one cell in the early embryo in which the X bearing gene for the black pigment was __________. |
Inactivated |
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Is this cat heterozygous or homozygous? |
Heterozygous |
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An example of an X-linked recessive disorder that reveals inactivation in humans is Anhidrotic ectodermal dysplasia (defective sweat glands). What is this and who does it occur in? |
Heterozygous females have random patterns of tissue with and without sweat glands |
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Red-green colour blindness is an example of an X-linked recessive disorder that reveals X inactivation in humans. Males are fully colour blind if they carry _________ |
the mutant allele
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In females, if X chromosome carrying the dominant gene is switched on, heterozygous females have mosaic retinas with patches of defective colour perception. True or false. |
False. In females, if X chromosome carrying the dominant gene is switched off, heterozygous females have mosaic retinas with patches of defective colour perception. |
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In mammals, how is dosage compensation achieved? In fruit flies, how is dosage compensation achieved? |
By switching off X chromosome By superactivating ( the level of expression of genes on the X chromosome in males is increased 2-fold) |
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How is dose compensation achieved in marsupial mammals? |
The paternally derived X chromosome is inactivated in the somatic cells of females |
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If you cloned this calico cat, would the clone look the same? Why? |
No X inactivation happens at random during embryogenesis |
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Could a male calico cat exist? Why? |
Yes- You could have a male with 2 X chromosomes ( Klinefelter syndrome) |
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What is meant by bilateral gynandromorphs? |
Male on one side, female on the other. Mistakes occur in the earliest cell divisions after an egg is fertilised |
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What causes bilateral gynandromorphs? |
An X chromosome may be lost during the 1st mitotic division of an XX zygote. One daughter cell ends up female, the other mitotic product has one X, so develops as male. |
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What are two things that can determine non-genetic sex determination? |
Environmental Factors Social Factors |
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What are some environmental factors that determine sex? |
Temperature Crocodiles, most turtles, and certain lizards are achieved according to incubation temperature of egg. In both patterns, certain temperatures result in both males and females (Tp) i.e 50% hatch as males, 50% hatch as females. The pivotal temperature (Tp) is narrow |
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What does a harem of clownfish consist of? |
A large female A medium sized reproductive male Small reproductive juveniles (not sexually developed) |
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What happens when the large female dies? |
Reproductive male changes sex to become a female, and the largest of the juveniles matures into a reproductive male. |
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Why is there only one female is a harem of clownfish? |
Female is aggressively dominant and her behaviour suppresses an area in the brain of other clownfish that is responsible for triggering synthesis of female hormones |
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If a female dies, why does a male clownfish develop into a female? |
The lack of aggression towards other clownfish means that this suppression no longer occurs |
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If a clownfish is left by itself in an aquarium, what will happen? |
It will automatically develop into a female |
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What is a harem? |
A social group where there is a dominant member of one sex, and everything else is the other sex |
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Label this Y chromosome |
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What is the genetic composition of these syndromes: Klinefelter Turner |
XXY X |
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The ratio of X chromosomes to autosome sets determines sex in which organisms? |
Nematode worms and Drosophila |
