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23 Cards in this Set
- Front
- Back
Sex is defined by... |
Which gametes are produced, the smaller of the gametes refers to the male sex. |
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What is the purpose of sex? |
Sex is a means of increasing genetic diversity, also sexual selection can result in higher genetic fitness for a species. |
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What does it mean when an organism is monoecious? |
The male and female reproductive organs are produced on the same organism, and the games are genetically identical (homogametic). |
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What does it mean when an organism is dioecious? |
Male and female organism are found on different individuals, the gametes produced are not genetically identical. (Heterogametic) |
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What is the haplodiploidy system? |
The haplodiploidy system involves females that carry 2n chromosomes and males that carry N number chromosomes. Fertilization of an egg by the male will result in 2n female, conversely the female may produce males from unfertilized eggs via meiosis. |
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What is the XX-XO sex determination system? |
XX-XO sex determination relies on the ratio of # of X chromosomes to # of sets of autosomes. In this system females are XX with a 1:1 ratio, males are XO with a 1:2 ratio. |
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What is the lygaeus system? |
Sex determination where one sex is homogametic and the other is heterogametic. XX-XY system of mammals is an example of this, where males are typically the heterogeneous sex. |
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What is genic sex determination? |
Genic sex determination relies on specific genes to determine sex without the presence of a specific sex chromosome. |
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How does sex determination in fruit flies work? |
Similar to XX-XO system, fruit fly sex determination relies on the ratio of X to Autosomal chromosomes. Fruit flies differ in that they can have many multiples of X or A chromosomes. |
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What is Turner syndrome caused by? |
Turner syndrome is caused by a missing X chromosomes in females. This will result in an individual who is phenotypically female, but sterile. |
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What is Klinefelter syndrome caused by? |
Klinefelter syndrome is caused by an excess of X chromosomes. This typically occurs in phenotypic males and results in sterility. |
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What causes Klinefelter and Turner syndrome to alter chromosome number? |
Typically these syndromes are caused by non-disjunction, that is a failure to separate during division. |
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At what stage of growth is sex determined in humans? |
Sex is determined approximately 5 weeks after fertilization when the gonadal primordial forms in the zygote. |
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What protein is responsible for stimulating the formation of testis? |
Testis determining factor or TDF |
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What role does the Y chromosome play in determining sex? |
The Y chromosome carries genes that produce TDF, without TDF humans will naturally develop into females. |
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How is the X chromosome able to pair with the Y chromosome? |
Certain homologous regions enable the X and Y chromosomes to pair. |
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What does SRY refer to? |
SRY refers to the sex determining region of the Y chromosome. |
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What has been discovered in sex reversal studies of phenotypic males with XX genotype? |
It was discovered that a fragment of the Y chromosome had attached to one of the X chromosomes |
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Why might an individual with XY genotype be phenotypically female? |
Y chromosome is mutant and does not contain SRY |
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Why are male offspring slightly more likely than female offspring in humans? |
The Y chromosome carrying sperm travel slightly faster than X chromosome carrying sperm.
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What is Lyon's hypothesis? |
Lyon's hypothesis is known as the single active X principle. Basically it states that only one X chromosome is transcriptionally active, the other inactive chromosome becomes a barr body. |
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What evidence is there for Lyon's hypothesis? |
The coat colors of calico cats is an example of the single X activation hypothesized by Lyon. |
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What gene is responsible for X inactivation? |
X inactive specific transcript (XIST) is the gene responsible for X inactivation. The region on the X chromosome responsible for this is the proximal p arm. |