Ch. 5 Slides (Exam 2) - Sex Determination and Sex Chromosomes

Question 1

Successful fertilization depends on ____
____ in reproductive organisms.

Answer 1

Sexual differentiation

Question 2

In complex life forms, differentiation of sexes is more evident as ____ ____ of males and females.

Answer 2

Phenotypic dimorphism

Question 3

____ chromosomes (XY in mammals) characterize one sex or the other in a wide range of species:
– Labeled as ____ chromosomes.
– ____, not chromosomes, ultimately serve as basis for ____ ____.

Answer 3

Heteromorphic; Sex chromosomes; Genes; Sex determination

Question 4

Nuclear structure in sperm of insect discovered in 1891—
labeled ____-____.

Answer 4

X-body

Question 5

In butterfly (Protenor):
▪ Female somatic cells have ____ chromosomes, including ____ X chromosome(s).
▪ Male somatic cells have ____ chromosomes with ____ X chromosome(s).

Answer 5

14; 2; 13; 1

Question 6

Protenor and Lygaeus insects:
- Males produce unlike gametes (____ sex).
Their gametes determine the sex of ____.
- Female produce like gametes (____ sex) -
uniform gametes.

Answer 6

Heterogametic; Progeny; Homogametic

Question 7

In some organisms, females produce ____ gametes:
- Protenor ____/____or Lygaeus ____/____ mode of sex determination.

Answer 7

Unlike; XX/XO; XX/XY

Question 8

____: Failure of sex chromosomes to segregate during meiosis.

Answer 8

Nondisjunction

Question 9

Turner syndrome has karyotypes other than ____,____.

Answer 9

45, X

Question 10

____: Somatic cells display two different genetic cell lines with different karyotypes.

Answer 10

Mosaics

Question 11

Presence of additional Y chromosome is only deviation from ____.

Answer 11

Diploidy

Question 12

Y chromosome houses ____ information for maleness—gene provides “____.”

Answer 12

Genetic; Signal

Question 13

In humans: By 5th week, gonadal ridges form either ovaries or testes (____ ____).

Answer 13

Bipotential gonads

Question 14

In early embryonic development human embryo ____—gonadal phenotype sexually
indifferent.

Answer 14

Hermaphroditic

Question 15

If cell of ridge has XY constitution, ____
develops into testes.

Answer 15

Medulla

Question 16

Absence of Y chromosome:
▪ ____ of ____ forms ovarian tissue.
▪ ____ ____ forms oviducts (Fallopian tubes),
uterus, cervix, and portions of vagina.

Answer 16

Cortex of ridge; Mullerian duct

Question 17

____ regions (PARs):
– Present on both ends of ____ chromosome—share homology with regions on ____ chromosome.
– Synapse and recombine with ____ chromosome during meiosis.

Answer 17

Pseudoautosomal; Y; X; X

Question 18

____ region critical for segregation of X and Y chromosomes during male gametogenesis.

Answer 18

Pairing

Question 19

____: Male-specific region of Y:
– ____% of Y chromosome which does not recombine with X chromosome.
– Some portions share ____ with genes on X chromosome.

Answer 19

MSY; 95; Homology

Question 20

____: Sex-determining region Y:
▪ Critical gene controlling sexual development.
▪ Gene becomes active in XY embryos at ____–____ weeks of development.

Answer 20

SRY; 6-8

Question 21

SRY gene encodes protein ____:
Present in all ____- Causes undifferentiated gonadal tissue of embryo to form ____.

Answer 21

TDF; Mammals; Testes

Question 22

Females with one X chromosome and one Y chromosome are missing ____ gene.

Answer 22

SRY

Question 23

TDF believed to be ____ factor: Behaves as ____ switch controlling genes involved in sexual differentiation.

Answer 23

Transcription; Master switch

Question 24

____ sex ratio: Reflects proportion of males to females conceived in population.

Answer 24

Primary

Question 25

____ sex ratio: Reflects proportion of each sex born / Does not account for fetal mortality.

Answer 25

Secondary

Question 26

Why are more males born than females?

Answer 26

Likelihood is a 50/50 chance, so this question is “still under investigation.”

Question 27

____ ____: Inactivation of X chromosome is random; all descendant cells have same inactivation.

Answer 27

Lyon Hypothesis