Sex Chromosome and Determination

Question 1

The process in which two gametes fuse with each other to begin the life of a new individual

Answer 1

Sexual Reproduction

Question 2

The underlying mechanism by which an individual develops into a female or a male

Answer 2

Sexual Determination

Question 3

A theory stating that chromosomes carry the genes that determine an organism’s traits

Answer 3

Chromosome Theory of Inheritance

Question 4

Who suggested that male and female sexes are due to the inheritance of particular chromosomes?

Answer 4

Clarence McClung (1901)

Question 5

System that operates in mammals wherein one sex is heterogametic while the other is homogametic

Answer 5

X-Y System

Question 6

Term used for when one gamete carries the X chromosome while another carries the Y

Answer 6

Heterogametic

Question 7

Term used for when all gametes carry a single chromosome

Answer 7

Homogametic

Question 8

The presence of a gene on the Y chromosome called the […] causes maleness

Answer 8

SRY gene

Question 9

System that operates in many insects wherein the male has only one sex chromosome whereas the female has a pair

Answer 9

X-0 System

Question 10

System that operates in birds and some fish wherein the male is homogametic while the female is heterogametic

Answer 10

Z-W System

Question 11

System that operates in bees, wasps, and ants wherein the male is produced from an unfertilized haploid egg

Answer 11

Haplodiploid System

Question 12

How many chromosomes in a set do male honeybees have?

Answer 12

16 chromosomes

Question 13

A reptile whose sex is controlled by temperature

Answer 13

American Alligator
Alligator mississippiensis

= 33C (100% male)
< 33C (100% female)
> 33C (95% female)

Question 14

A fish whose sex is determined by behavior, wherein when the female dies, the male changes sex to become a female

Answer 14

Clownfish
Amphiprion

Question 15

Term used for organisms that can switch from male to female

Answer 15

Protandrous Hermaphrodites

Question 16

A harem of clownfish consists of […]

Answer 16

• A large female
• A medium-sized reproductive male
• Small nonreproductive juveniles

Question 17

The hormones that control the expression of particular genes in clownfish

Answer 17

• Testosterone (androgen)
• Estradiol (estrogen)

Question 18

Plants that produce only male or female gametophytes

Answer 18

Dioecious

Question 19

Examples of dioecious plants

Answer 19

• Hollies
• Willows
• Ginkgos
• White campion, Silene latifolia

Question 20

The phenomenon in which the level of expression of many genes on the sex chromosomes is similar in both sexes, even though males and females have a different complement of sex chromosomes

Answer 20

Dosage Compensation

Question 21

Dosage Compensation

Female mammals equalize the expression of genes on the X chromosome by turning off one of their two X chromosomes

Answer 21

X-chromosome inactivation (XCI)

Question 22

Proposed that dosage compensation in mammals occurs by the inactivation of a single X chromosome in females

Answer 22

Mary Lyon (1961)

Question 23

Identified a highly condensed structure in the interphase nuclei of some somatic cells in female cats that was not found in male cats

Answer 23

Murray Barr
Ewart Bertram
(1949)

Question 24

Correctly proposed that the Barr body is a highly condensed X chromosome

Answer 24

Susumu Ohno
(1960)

Question 25

A female cat that is heterozygous for a gene on the X chromosome that can occur as an orange or a black allele

Answer 25

Calico Cat

Question 26

Identified the XIC from its key role in XCI

Answer 26

Eeva Therman Klaus Patau

Question 27

Plays a critical role in X-chromosome inactivation

Answer 27

X-inactivation center (XIC)

Question 28

An X-inactive specific transcript gene discovered in 1991

Answer 28

Xist gene

Question 29

The 3 phases of XCI

Answer 29

- Initiation - Spreading - Maintenance

Question 30

**Phase of XCI** Occurs during embryonic development wherein one of the X chromosomes remains active while the other is chosen for inactivation

Answer 30

Initiation

Question 31

**Phase of XCI** Occurs during embryonic development wherein the chosen X chromosome is inactivated

Answer 31

Spreading

Question 32

**Phase of XCI** Occurs from embryonic development onwards wherein the inactivated X chromosome is maintained as a Barr body during future cell divisions

Answer 32

Maintenance

Question 33

Differences between the X and Y chromosomes

Answer 33

- The X chromosome is typically larger - The X chromosome carries ~800 genes while the Y has ~50

Question 34

Genes found only on the X chromosome

Answer 34

X-linked genes

Question 35

Genes found only on the Y chromosome

Answer 35

Y-linked genes (holandric genes)

Question 36

Genes found on both the X and Y chromosomes

Answer 36

Pseudoautosomal genes

Question 37

The inheritance pattern of the gene is the same as the inheritance pattern of a gene located on an autosome even though the gene is actually located on the sex chromosomes

Answer 37

Pseudoautosomal

Question 38

Carried out the first study that confirmed the location of a gene on a particular chromosome

Answer 38

Thomas Hunt Morgan

Question 39

A gene affecting eye color in fruit flies is located on which chromosome?

Answer 39

X chromosome

Question 40

Occurs when an individual with a dominant phenotype and unknown genotype is crossed to an individual with a recessive phenotype

Answer 40

Testcross

Question 41

A condition that causes signs of muscle weakness as early as age 3

Answer 41

Duchenne Muscular Dystrophy (DMD) (Guillaume Duchenne)

Question 42

The gene for DMD, found on the X chromosome, encodes a protein called [...] that is required inside muscle cells for structural support

Answer 42

dystrophin

Question 43

A protein that strengthen muscle cells by anchoring elements of the internal cytoskeleton to the plasma membrane

Answer 43

Dystrophin

Question 44

A second cross in which the sexes and phenotypes are reversed

Answer 44

Reciprocal Cross

Question 45

Occurs when the allele causing the disease is recessive and located on the X chromosome

Answer 45

X-linked recessive