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Biomedical Genetics > Sex Determination & Sex Chromosomes > Flashcards

Sex Determination & Sex Chromosomes Flashcards

1
Q

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

A

Asexual and Sexual

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2
Q

What are the pros and cons of asexual reproduction?

A

pros: rapid increase in population size
cons: no variation

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3
Q

What are the pros in sexual reproduction?

A

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

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4
Q

What are the cons of sexual reproduction?

A

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

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5
Q

What is isogamy?

A

similar gametes

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6
Q

What is anisogamy?

A

different gametes

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7
Q

What are the different types of sex determinators?

A

environmental sex determination and genetic sex determination

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8
Q

What are the different factor in genetic sex determination?

A

autosomal factors and sex chromosomes

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9
Q

What are isogametes?

A

morphologically identical but chemically different

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10
Q

Sex chromosomes are…

A
  1. characteristic to one sex or another
  2. heteromorphic
  3. different in gene content
  4. Do NOT recombine during meiosis in the heterogametic gender
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11
Q

What is heteromorphic?

A

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

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12
Q

What are the principle sex chromosome systems?

A

XY and ZW

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13
Q

Which gender is heterogametic in a XY system?

A

Males

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14
Q

Which gender is heterogametic in a ZW system?

A

Females

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15
Q

What type of sex chromosomes do plants have?

A

Majority have no sex chromosomes; there are a few exceptions

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16
Q

What type of sex chromosome system are roundworms?

A

XX/X system
Males: X
Hermaphrodite: XX

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17
Q

What type of sex chromosome system are insects?

A
  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.
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18
Q

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

A

Males: haploid
Females: diploid

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19
Q

What type of sex system are reptiles?

A
  1. XY
  2. ZW
  3. Environmental
  4. combination of genotypic and environmental
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20
Q

What type of sex system are birds?

A

ZW system
males: ZZ
females: ZW

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21
Q

What type of sex system do mammals have?

A

XY

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22
Q

What are the characteristics of the conservative X in mammals?

A

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

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23
Q

What are the characteristics of the inventive Y in mammals?

A

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

24
Q

What type of sex system are mammals (eutherians)?

A

XX/XY

25
Q

What type of sex system are mammals (marsupials)?

A

XX/XY

26
Q

How are marsupial sex chromosomes different from eutherians?

A

Marsupials have XAR and XCR regions on their chromosomes

27
Q

What is the XAR

A

X added region autosomal in marsupials

28
Q

What is the XCR?

A

X conserved region shared between marsupials and eutherians

29
Q

What type of sex system are monotremes?

A

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

30
Q

Are sex chromosomes paired in marsupials?

A

No

31
Q

Are sex chromosomes paired in monotremes?

A

Males: No
Females: Yes

32
Q

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

A

suppressed recombination

33
Q

What are the characteristics of human sex chromosomes?

A

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

34
Q

What is the PAR?

A

the Pseudoautosomal Region

35
Q

Why is the PAR important?

A

XY pairing and segregation in male meiosis

36
Q

What are the characteristics of the human X chromosome?

A

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

37
Q

What are the purpose of the X chromosomes?

A

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

38
Q

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

A

females have 2x more than males

39
Q

What is a Barr Body?

A

genetic mechanism to compensate X chromosome dosage between males and females

40
Q

What are facultatively heterochromatic X chromosomes?

A

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

41
Q

What is the rule of Barr bodies?

A

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

42
Q

When does inactivation occur?

A

later in embryonic development, blastocyst stage after sex determination

43
Q

What are XCI escape genes?

A

PARs and X-Y gametologs

44
Q

XCI important facts

A
  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
45
Q

How is XCI different in somatic cell nuclear cloning?

A

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

46
Q

What are the molecular features of XCI?

A

~6 genes, dominated by noncoding RNA genes

47
Q

What are XIST?

A

long noncoding RNA which coats the X with active XIST gene

48
Q

What is XIST expression?

A

triggers suppressive chromatin modifications

49
Q

Is XCI reversible?

A

Yes, X is reactivated in oocytes before meiosis

50
Q

What is the structure of the Y chromosome?

A

palindromic sequences

51
Q

What the classes of Y chromosomes?

A

X-degenerate or X-Y ancestral genes
Ampliconic

52
Q

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

A

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

53
Q

What are ampliconic?

A

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

54
Q

What are the functions of the Y chromosome?

A

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

55
Q

What are some specific features of the Y chromosome?

A

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

56
Q

What is a haplotype?

A

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

Biomedical Genetics (6 decks)

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