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Sex Determination & Sex Chromosomes Flashcards

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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?

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A

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

24
Q

What type of sex system are mammals (eutherians)?

25
What type of sex system are mammals (marsupials)?
XX/XY
26
How are marsupial sex chromosomes different from eutherians?
Marsupials have XAR and XCR regions on their chromosomes
27
What is the XAR
X added region autosomal in marsupials
28
What is the XCR?
X conserved region shared between marsupials and eutherians
29
What type of sex system are monotremes?
X1-5X1-5/X1-5Y1-5
30
Are sex chromosomes paired in marsupials?
No
31
Are sex chromosomes paired in monotremes?
Males: No Females: Yes
32
What is the driving force for the evolution of sex chromosomes?
suppressed recombination
33
What are the characteristics of human sex chromosomes?
pseudoautosomal region 1 (top) pseudoautosomal region 2 (bottom) X larger than Y
34
What is the PAR?
the Pseudoautosomal Region
35
Why is the PAR important?
XY pairing and segregation in male meiosis
36
What are the characteristics of the human X chromosome?
5% genome >800 protein coding genes ~156 mega-base pairs
37
What are the purpose of the X chromosomes?
Sex and reproduction genes brain and mental functioning genes muscle genes X inactivation
38
What is the dosage of X chromosomes between males and females?
females have 2x more than males
39
What is a Barr Body?
genetic mechanism to compensate X chromosome dosage between males and females
40
What are facultatively heterochromatic X chromosomes?
condensed, late replicating, histones are deacetylated, DNA is methylated
41
What is the rule of Barr bodies?
inactivation of all but one X chromosome total number of X chromosomes= N Number of Barr bodies= N-1
42
When does inactivation occur?
later in embryonic development, blastocyst stage after sex determination
43
What are XCI escape genes?
PARs and X-Y gametologs
44
XCI important facts
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
How is XCI different in somatic cell nuclear cloning?
XCI in clones is altered: X reactivation in cloned blastocysts is heterogeneous, X inactivation is later inconsistent across cells
46
What are the molecular features of XCI?
~6 genes, dominated by noncoding RNA genes
47
What are XIST?
long noncoding RNA which coats the X with active XIST gene
48
What is XIST expression?
triggers suppressive chromatin modifications
49
Is XCI reversible?
Yes, X is reactivated in oocytes before meiosis
50
What is the structure of the Y chromosome?
palindromic sequences
51
What the classes of Y chromosomes?
X-degenerate or X-Y ancestral genes Ampliconic
52
What are X-degenerate/X-Y ancestral genes?
ancestral homologs between X and Y usually single copy and broad expression/cellular function
53
What are ampliconic?
often novel and Y born often species specific testes limited expression function in male fertility
54
What are the functions of the Y chromosome?
Male sex determination (SRY) spermatogenesis, male fertility Predicted genes for male characteristics
55
What are some specific features of the Y chromosome?
haploid male specific inherited exclusively through patrilinies no pairing/recombination with a homolog haplotype
56
What is a haplotype?
combination of alleles at adjacent locations on the chromosome that are transmitted together

Biomedical Genetics (6 decks)

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