Sex Determination & Sex Chromosomes

Question 1

What are the two types of reproduction modes found in nature?

Answer 1

Asexual and Sexual

Question 2

What are the pros and cons of asexual reproduction?

Answer 2

pros: rapid increase in population size
cons: no variation

Question 3

What are the pros in sexual reproduction?

Answer 3

creates variation, increases resistance to parasites, removes deleterious traits, increase fitness, promotes evolution

Question 4

What are the cons of sexual reproduction?

Answer 4

slow increase in numbers, sexual differentiation, search for mates, sexual selection

Question 5

What is isogamy?

Answer 5

similar gametes

Question 6

What is anisogamy?

Answer 6

different gametes

Question 7

What are the different types of sex determinators?

Answer 7

environmental sex determination and genetic sex determination

Question 8

What are the different factor in genetic sex determination?

Answer 8

autosomal factors and sex chromosomes

Question 9

What are isogametes?

Answer 9

morphologically identical but chemically different

Question 10

Sex chromosomes are…

Answer 10

1. characteristic to one sex or another
2. heteromorphic
3. different in gene content
4. Do NOT recombine during meiosis in the heterogametic gender

Question 11

What is heteromorphic?

Answer 11

(dissimilar) different size and shape- distinguishable from autosomes and from each other

Question 12

What are the principle sex chromosome systems?

Answer 12

XY and ZW

Question 13

Which gender is heterogametic in a XY system?

Answer 13

Males

Question 14

Which gender is heterogametic in a ZW system?

Answer 14

Females

Question 15

What type of sex chromosomes do plants have?

Answer 15

Majority have no sex chromosomes; there are a few exceptions

Question 16

What type of sex chromosome system are roundworms?

Answer 16

XX/X system
Males: X
Hermaphrodite: XX

Question 17

What type of sex chromosome system are insects?

Answer 17

1. plant bugs/fruit flies: XX/XY
2. Moths/butterflies: ZZ/ZW
3. Bees/Wasps: Haploidy/diploidy: No sex chrom.
4. Genomics imprinting: No sex chromosomes
5. Environmental: depends on temp.

Question 18

Bees and wasps have a haploid/diploid sex system. Which gender is haploid and which is diploid?

Answer 18

Males: haploid
Females: diploid

Question 19

What type of sex system are reptiles?

Answer 19

1. XY
2. ZW
3. Environmental
4. combination of genotypic and environmental

Question 20

What type of sex system are birds?

Answer 20

ZW system
males: ZZ
females: ZW

Question 21

What type of sex system do mammals have?

Answer 21

XY

Question 22

What are the characteristics of the conservative X in mammals?

Answer 22

ancestral gene content and order
cytogenetically similar between species
~5% of the genome

Question 23

What are the characteristics of the inventive Y in mammals?

Answer 23

unique gene content
cytogenetically/genetically different between species
<2% of the genome

Question 24

What type of sex system are mammals (eutherians)?

Answer 24

XX/XY

Question 25

What type of sex system are mammals (marsupials)?

Answer 25

XX/XY

Question 26

How are marsupial sex chromosomes different from eutherians?

Answer 26

Marsupials have XAR and XCR regions on their chromosomes

Question 27

What is the XAR

Answer 27

X added region autosomal in marsupials

Question 28

What is the XCR?

Answer 28

X conserved region shared between marsupials and eutherians

Question 29

What type of sex system are monotremes?

Answer 29

X1-5X1-5/X1-5Y1-5

Question 30

Are sex chromosomes paired in marsupials?

Answer 30

No

Question 31

Are sex chromosomes paired in monotremes?

Answer 31

Males: No Females: Yes

Question 32

What is the driving force for the evolution of sex chromosomes?

Answer 32

suppressed recombination

Question 33

What are the characteristics of human sex chromosomes?

Answer 33

pseudoautosomal region 1 (top) pseudoautosomal region 2 (bottom) X larger than Y

Question 34

What is the PAR?

Answer 34

the Pseudoautosomal Region

Question 35

Why is the PAR important?

Answer 35

XY pairing and segregation in male meiosis

Question 36

What are the characteristics of the human X chromosome?

Answer 36

5% genome >800 protein coding genes ~156 mega-base pairs

Question 37

What are the purpose of the X chromosomes?

Answer 37

Sex and reproduction genes brain and mental functioning genes muscle genes X inactivation

Question 38

What is the dosage of X chromosomes between males and females?

Answer 38

females have 2x more than males

Question 39

What is a Barr Body?

Answer 39

genetic mechanism to compensate X chromosome dosage between males and females

Question 40

What are facultatively heterochromatic X chromosomes?

Answer 40

condensed, late replicating, histones are deacetylated, DNA is methylated

Question 41

What is the rule of Barr bodies?

Answer 41

inactivation of all but one X chromosome total number of X chromosomes= N Number of Barr bodies= N-1

Question 42

When does inactivation occur?

Answer 42

later in embryonic development, blastocyst stage after sex determination

Question 43

What are XCI escape genes?

Answer 43

PARs and X-Y gametologs

Question 44

XCI important facts

Answer 44

1. XCI occurs during embryonic development 2. XCI in female somatic cells is random 3. XCI is clonal: all descendants of that cell have the same parental X inactivated 4. All mammalian females are mosaics for maternal (Xm) and paternal (Xp) X-linked alleles

Question 45

How is XCI different in somatic cell nuclear cloning?

Answer 45

XCI in clones is altered: X reactivation in cloned blastocysts is heterogeneous, X inactivation is later inconsistent across cells

Question 46

What are the molecular features of XCI?

Answer 46

~6 genes, dominated by noncoding RNA genes

Question 47

What are XIST?

Answer 47

long noncoding RNA which coats the X with active XIST gene

Question 48

What is XIST expression?

Answer 48

triggers suppressive chromatin modifications

Question 49

Is XCI reversible?

Answer 49

Yes, X is reactivated in oocytes before meiosis

Question 50

What is the structure of the Y chromosome?

Answer 50

palindromic sequences

Question 51

What the classes of Y chromosomes?

Answer 51

X-degenerate or X-Y ancestral genes Ampliconic

Question 52

What are X-degenerate/X-Y ancestral genes?

Answer 52

ancestral homologs between X and Y usually single copy and broad expression/cellular function

Question 53

What are ampliconic?

Answer 53

often novel and Y born often species specific testes limited expression function in male fertility

Question 54

What are the functions of the Y chromosome?

Answer 54

Male sex determination (SRY) spermatogenesis, male fertility Predicted genes for male characteristics

Question 55

What are some specific features of the Y chromosome?

Answer 55

haploid male specific inherited exclusively through patrilinies no pairing/recombination with a homolog haplotype

Question 56

What is a haplotype?

Answer 56

combination of alleles at adjacent locations on the chromosome that are transmitted together