Sex Determination

Front 1

Sex is defined by...

Back 1

Which gametes are produced, the smaller of the gametes refers to the male sex.

Front 2

What is the purpose of sex?

Back 2

Sex is a means of increasing genetic diversity, also sexual selection can result in higher genetic fitness for a species.

Front 3

What does it mean when an organism is monoecious?

Back 3

The male and female reproductive organs are produced on the same organism, and the games are genetically identical (homogametic).

Front 4

What does it mean when an organism is dioecious?

Back 4

Male and female organism are found on different individuals, the gametes produced are not genetically identical. (Heterogametic)

Front 5

What is the haplodiploidy system?

Back 5

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.

Front 6

What is the XX-XO sex determination system?

Back 6

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.

Front 7

What is the lygaeus system?

Back 7

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.

Front 8

What is genic sex determination?

Back 8

Genic sex determination relies on specific genes to determine sex without the presence of a specific sex chromosome.

Front 9

How does sex determination in fruit flies work?

Back 9

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.

Front 10

What is Turner syndrome caused by?

Back 10

Turner syndrome is caused by a missing X chromosomes in females. This will result in an individual who is phenotypically female, but sterile.

Front 11

What is Klinefelter syndrome caused by?

Back 11

Klinefelter syndrome is caused by an excess of X chromosomes. This typically occurs in phenotypic males and results in sterility.

Front 12

What causes Klinefelter and Turner syndrome to alter chromosome number?

Back 12

Typically these syndromes are caused by non-disjunction, that is a failure to separate during division.

Front 13

At what stage of growth is sex determined in humans?

Back 13

Sex is determined approximately 5 weeks after fertilization when the gonadal primordial forms in the zygote.

Front 14

What protein is responsible for stimulating the formation of testis?

Back 14

Testis determining factor or TDF

Front 15

What role does the Y chromosome play in determining sex?

Back 15

The Y chromosome carries genes that produce TDF, without TDF humans will naturally develop into females.

Front 16

How is the X chromosome able to pair with the Y chromosome?

Back 16

Certain homologous regions enable the X and Y chromosomes to pair.

Front 17

What does SRY refer to?

Back 17

SRY refers to the sex determining region of the Y chromosome.

Front 18

What has been discovered in sex reversal studies of phenotypic males with XX genotype?

Back 18

It was discovered that a fragment of the Y chromosome had attached to one of the X chromosomes

Front 19

Why might an individual with XY genotype be phenotypically female?

Back 19

Y chromosome is mutant and does not contain SRY

Front 20

Why are male offspring slightly more likely than female offspring in humans?

Back 20

The Y chromosome carrying sperm travel slightly faster than X chromosome carrying sperm.

Front 21

What is Lyon's hypothesis?

Back 21

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.

Front 22

What evidence is there for Lyon's hypothesis?

Back 22

The coat colors of calico cats is an example of the single X activation hypothesized by Lyon.

Front 23

What gene is responsible for X inactivation?

Back 23

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.