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Gametes - Sex Determination Flashcards

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1
Q

3 levels of sexual development

A

1. Chromosomal sex

XY or XX

2. Gonadal sex

Development of gonads

genetically determined

3. Phenotypic sex

internal and external structures

determined by gonadal hormonal secretion

2 distinct systems - internal ducts and external genitalia

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2
Q

period all embryos go through

A

hermaphroditic period

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3
Q

what happens @ 5th week of gestation

A

Gonadal primordia arise

Primordial germ cells become cortex/inner medulla

Cortex → develops into ovary

Medulla → develops into testis

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4
Q

what happens @ 7th week of gestation

A

If XY chromosomes are present, medulla → testis

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5
Q

cortex (of primordial germ cells) becomes

A

ovary

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6
Q

medulla (of primordial germ cells) becomes

A

testis

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7
Q

what happens at conception

A

chromosomal sex is determined

XX or XY

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8
Q

what happens at week 9

A

cortex develops into ovary in females

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9
Q

describe the 7th week embryo

A

undifferentiated gonads can develop into phenotypic male or female gonads

⇒ sexually bi-potential

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10
Q

where is the gene for the differentiation of testis from the bipotential gonad

A

on the Y chromosome

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11
Q

XX and XY - passing on to offspring

A
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12
Q

Karyotyping

A

analysis of chromosomes

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13
Q

karyotype

A

a pictorial display of metaphase chromosomes from a mitotic cell

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14
Q

cytogenetics

A

the study of chromosome

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15
Q

what tissues are appropriate for chromosome study (preparing a karyotype)

A

cells that can be stimulated to undergo cell division in vitro

chromosome only visible with light microscope during mitosis

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16
Q

how is the karyotype then prepared

A
  1. treated with colchicine which arrests the cells in metaphase (no longer need cells to be in metaphase)
  2. stain to observe the chromosomes - Giemsa Stains (bound to certain parts of the chromosomes)
  3. photograph or visualise using a computer
  4. analysis of chromosomes

size, position of centromere, banding and staining regions determined

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17
Q

22 pairs of autosomes + female sex chromosomes

A
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18
Q

22 pairs of autosomes + male sex chromosomes

A
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19
Q

Turner’s Syndrome

A
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20
Q

Kleinefelter Syndrome

A
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21
Q

Jacob’s Syndrome

A
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22
Q

what does the use of fluorescent dyes as a new karyotyping method allow for

A

dye can bind to specific regions of chromosomes

variations in colour can be detected, resulting in a digital image

pairing of chromosomes becomes easier - homologous pairs show identical colours

aberrations and crossovers are easily recognised

detect translocations not previously recognisable

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23
Q

karyotypes may be prepared using

A

lymphocytes

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24
Q

metaphase - FISH

A

housekeeping genes - ones we know will be expressed

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25
interphase FISH
⇒ don't have to induce metaphase
26
Smith Magenis Syndrome
microdeletion green control probe is present in both paternal and maternal Chr 17 red SMS probe only fluoresces on a single chromosome
27
how to identify all chromosomes at once
use probes of different colours
28
describe the genome of cancer cells
cancer cells are characterised by aberrations in chromosome size, number, banding patterns chaotic genome
29
genetic content of X vs Y chromosome
Y chromosome contains far fewer genes than the X chromosome
30
size difference between X and Y chromosome
Y is much smaller than X even though it's thought to have originated from a common progenitor
31
structure of Y chromosome
32
PseudoAutosomal Region (PAR) function
necessary for tetrad formation so there is crossover during meiosis - synapses and recombines with X chromosome during meiosis region on Y that shares homology with regions on X **presence of such a pairing region is critical to segregation of X and Y chromosomes during male gametogenesis**
33
role of SRY in XY female
deletion on Y chromosome mapped deletion - SRY gene (sex determining region of Y chromosome)
34
role of SRY in XX males
translocation of SRY region of Y → X chromosome
35
SRY gene in mice studies
converts chromosomal female mouse to phenotypically male
36
mutant mouse lacking SRY
XY female
37
expression of SRY is seen when and where
sertoli cells at time of testis development - SRY upregulated at this time transcripts in hypothalamus, midbrain of adult male mice - male specific neural properties
38
transgenic SRY experiment
nuclei of fertilised XX eggs were injected with SRY gene, then the eggs were transplanted to surrogate mothers SRY genes then randomly incorporated into a chromosome and was inherited in subsequent cell divisions animals were karyotyped after development to adult of 3 XX transgenic mice that were born, 2 were female and 1 was a sex reversed male
39
genes involved in male testis determination pathway
SRY Sox9 Amh Fgf9 Dmrt1
40
SRY what is it associated syndromes
transcription factor Turner's Syndrome Kleinefelter Syndrome XY sex reversal - loss of function (LOF) XX sex reversal - gain of function (GOF)
41
Amh what is it associated syndromes
hormone XY sex reversal (LOF) codes for Anti-Mullerian Hormone - responsible for regression of female ductal system
42
Sox9 what is it associated syndromes
transcription factor campomelic dysplasia XY sex reversal (LOF) abnormal sertoli cell differentiation XY sex reversal (LOF) XX sex reversal (GOF)
43
Fgf9 what is it associated syndromes
growth factor XY sex reversal (LOF)
44
Dmrt1 what is it associated syndromes
transcription factor XY gonadal dysgenesis XY sex reversal (LOF) post-natal feminisation in XY mice, defective seminiferous tubule (LOF)
45
Sox9 and sertoli cells
Sox9 is upregulated in sertoli cells just after SRY expression phenotypically female with XY genotypes altered expression/coding of Sox9
46
genes involved in the initial development of the bipotential gonad
Emx2 Gata4 Wt1 Lhx9 Sf1
47
Emx2 protein function mouse models
aberrant tight junction assembly failure in genital ridge formation (LOF)
48
Gata4 protein function human syndrome mouse models
* transcription factor * ambiguous external genitalia, congenital heart disease (LOF) * failure in thickening of coelomic epithelium, defective initial formation of genital ridge (LOF)
49
Wt1 protein function human syndrome mouse models
* transcription factor * Denys-Drash, Frasier syndrome (LOF) * disruption of seminiferous tubule and somatic cell apoptosis, XY sex reversal (LOF)
50
Lhx9 protein function mouse models
transcription factor failure in genital ridge formation (LOF) - no gonads forming at all
51
Sf1 protein function human syndrome mouse models
* **_nuclear receptor_** * embryonic testicular regression syndrome, gonadal dysgenesis * delayed organisation of male testis cord, failure in genital ridge formation (LOF) initially expressed in genital ridges of both sexes but remains solely in developing testes
52
what allows for the expression of Sox9
SF1
53
emerging genetic pathways involved in initial expression and maintenance of Sox9 in sertoli cells
54
absence of gonads
can have individuals without gonads so female not default state
55
what is on the Y chromosome of XY females
XY females with Sry - extra region on Y chromosome - includes region for DAX1 gene
56
gene needed for female gonadal formation
DAX gene
57
other evidence for role of DAX1 (over-riden SRY in this case)
expressed in developing gonads at critical time - repressed by SRY
58
balance between male and female sex-determining pathways
59
dosage compensation
female (XX) should have a genetic dosage problem for all X linked genes potential for females to produce twice as much X linked gene products
60
X chromosome dosage compensation?
inactivation of 1 X chromosome
61
what is present in females only
female cats - single condensed body (black dot) sex chromatin - **inactive X chromosome** **⇒ Barr body** (happens at day 12)
62
what does the Barr body represent
inactivated X chromosome
63
what is present in XXY males
Barr body
64
when does inactivation of X chromosome (Barr body) occur
outside of ovary at day 12 in utero (happens outside of ovary because both X chromosomes are required for the initial oogonia - without 2 X chromosomes there would be rudimentary oogonia development)
65
what would be absent in Turner's Syndrome
Barr body
66
X-inactive Specific Transcript (XIST)
* product of an X-linked gene * initially XIST is transcribed from both X chromosomes * when transcribed the mRNA binds to the X chromosome * coats the 2nd X chromosome - condensation * X inactivation centre (Xic) is active on the inactive X * only 1 X will continue to produce XIST - inactive (X inactivated centre is only active in X chromosome that is about to be inactivated)
67
inactive X - what does it look like
highly condensed can be observed in stained interphase cells BARR BODIES
68
overview of X inactivation
69
anhidrotic ectodermal dysplasia
heterozygous for the X-linked condition depiction of the absence of sweat glands (shaded regions) in a female locations vary from female to female based on the random pattern of X chromosome inactivation during early development, resulting in unique mosaic distributions of sweat glands in heterozygotes
70
androgen insensitivity syndrome what does it confirm how is it caused
confirms importance of sex hormones in sex differentiation caused by a mutation in the gene encoding the androgen receptor → coded for on X chromosome gene
71
symptoms of males who inherit this condition
produce testosterone and DHT are unable to respond to either hormone **hence they develop as phenotypically females but have normal male chromosomes** the low levels of oestrogen that is produced by adrenal glands is enough to stimulate female secondary characteristics
72
how do individuals with androgen insensitivity syndrome develop female secondary sex characteristics
low levels of oestrogen produced by adrenal glands

GGE (33 decks)

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