Determination of Sex Flashcards Preview

ESA 4 - Reproductive System > Determination of Sex > Flashcards

Flashcards in Determination of Sex Deck (155):
1

What is a germ cell? 

​A biological cell that gives rise to the gametes of an organism to reproduce sexually

2

What is a gamete? 

A mature haploid male or female germ cell, which is able to unite with another of the opposite sex in sexual reproduction to form a zygote

3

What does the female gamete always contain? 

X chromosome

4

What does the male gamete contain? 

Either X or Y chromosome

5

What is the result of the male gamete containing either an X or Y chromosome? 

Sperm decides the sex of offspring

6

What is found on the Y chromosome? 

A gene known as SRY gene 

7

What does the SRY gene code for? 

Transcription factors that are members of the SOX family

8

What do the SOX transcription factors do? 

Induces expression of another family of transcription factors

9

What does the action of male derived transcription factors do? 

Determines that the gonad that develops will be a testis 

10

What are primordial germ cells? 

A special population that are the 'seed' for the next generation

11

When are the primordial germ cells allocated? 

Shortly after gastrulation

12

What is the significance of the primordial germ cells being allocated shortly after initiation of the current generation? 

They are recruited and specialise very early 

13

Where do primordial germ cells arise? 

In the yolk sac, near a structure called the allantois 

14

What happens to the primordial germ cells once they have arisen? 

They migrate 

15

What course to the primordial germ cells take during migration? 

They migrate into the retroperitoneum, in through the umbilicus, move up through the dorsal mesentery, and populate the gonads 

16

What is the problem with the migration of primordial germ cells? 

They have to migrate widely along the posterior abdominal wall, which may cause them to get lost or die 

17

What can sometimes occur due to errors in primordial germ cell migration? 

Get germ cell tumours along pathway of migration 

18

What is true of the gonad at the point of migration of primordial germ cells? 

It is indistinguishable between male and female 

19

Where do male germ cells (XY) colonise the gonad? 

The medulla 

20

Where do female germ cells (XX) colonise the gonad? 

The cortex

21

What is the 'default' position of the gonad? 

Female 

22

What happens to germ cells after they have colonised the gonad? 

  • Proliferate by mitosis
  • Reshuffle genetically and reduce to haploid
  • Cytodifferentiate into mature gametes 

23

How do germ cells reshuffle genetically and reduce to haploid once they have colonised the gonad? 

By meiosis 

24

What are the functions of meiosis in the gonad? 

  • Reduces the chromosome number in the gamete to 23, giving a haploid gamete 
  • Ensures every gamete is genetically unique 

 

25

When is meiosis used? 

Only in the production of sperm and eggs 

26

What happens in meiosis? 

There are two successive divisions, meiosis 1 and 2 

27

What do the divisions in meiosis 1 and 2 produce?

4 daughter cells 

28

What happens to the daughter cells from meiosis in the females? 

Only one develops into mature oocyte, others from polar bodies 

29

What does genetic variation arise from in meisois? 

  • Crossing over
  • Random segregation
  • Independant assortment 

 

30

What happens in crossing over? 

Exchange of regions of DNA between 2 homologous chromosomes 

31

When does crossing over occur? 

Prophase 1 of meiosis 1 

32

When is crossing over visible? 

Not until metaphase 1

33

What happens in random segregation? 

Distribution of chromosomes among four gametes 

34

What happens in independent assortment? 

Two homologous chromosomes of a pair must go into seperate gametes 

35

How does cytodifferentiation into mature gametes differ between the sexes? 

Timing and scale varies 

36

What produces the ovum? 

Oogenesis 

37

What produces the sperm? 

Spermatogenesis 

38

How do oogenesis and spermatogenesis differ? 

  • In oogenesis, there are very few gametes. In spermatogenesis, there are a huge number of gametes 
  • In oogenesis there is intermittent production. In spermatogenesis, production is constant 

 

39

How many gametes are produced from oogenesis? 

About 400 in a lifetime 

40

What does each ovum have? 

1/400 of the potential to pass on gene to next generation 

41

What is the result of each ovum having 1/400 of the potential to pass on genes to next generation? 

Only the best cells are selected to survive 

42

How often are ovums produced? 

˜1 per month

43

How many sperm are produced per day? 

˜200million 

44

Where does spermatogenesis occur? 

In seminiferous tubules 

45

What happens once spermatogenesis has occured in the seminiferous tubules? 

They coalesece in the rete testis 

46

What happens to sperm in the rete testis? 

They are concentrated 

47

When does the initial development of gonads occur? 

In the indifferent stage

48

What causes development of a male or female gonad following the indifferent stage? 

Y influence, or lack of it 

49

What happens to the indifferent gonad in males? 

  • Medually cords develop 
  • No corticol cords
  • Thick outer covering, called the tunica albuginea 

 

50

What does the tunica albuginea do? 

Encloses the gonad quite tightly 

51

What happens to the indifferent gonad in females? 

  • Medually cords don't develop 
  • Corticol cords develop
  • No tunica albuginea 

 

52

Why is there no tunica albuginea in females? 

Facilitates ovulation 

53

What is the urogenital ridge? 

A region of intermediate mesoderm 

54

What does the urogenital ridge give rise to? 

Both embyonic kidney and gonad 

55

What is the gonad derived from? 

Both intermediate mesoderm and primordial germ cells (extragonadal) 

56

What is meant by the primordial germ cells being extragonadal? 

They have to move into supporting tissues 

57

What does the gonad start off as? 

An indifferent stage gonad 

58

What is the indifferent stage gonad? 

Just supporting tissue 

59

What is the purpose of the indifferent stage gonad? 

Provides environment for gametogenesis to occur 

60

What embryonic tissues does the vagina have contributions from? 

The endoderm and mesoderm 

61

What does the internal genitalia of the male consist of? 

  • Testis
  • Duct system 
  • Seminal vesicles 
  • Prostate gland 
  • Bulbo-urethral glands 

 

62

What does the duct system consist of in the male? 

  • Epididymis 
  • Vas deferens
  • Urethra 

 

63

What is the purpose of the epididymis? 

Main storage of sperm 

64

What does the external genitalia of the male consist of? 

  • Penis 
  • Scrotum 

 

65

What does the internal genitalia of the female consist of? 

  • Ovaries
  • Duct system 

 

66

What does the duct system of the female consist of? 

  • Fallopian tube
  • Uterus
  • Cervix
  • Vagina

 

67

What does the external genitalia of the female consist of? 

  • Vagina
  • Vestibule 
  • Labia minora
  • Labia majora
  • Clitoris 

 

68

Why is development of the reproductive tracts complex? 

Because at some point, you have to choose a path 

69

What is the path chosen by development of the reproductive tract regulated by? 

The karyotype of embyro (XX or XY) 

70

What does the karyotype of the embryo (XX or XY) do? 

Sets chain of events that leads to development of specific genitalia

 

71

What does the indifferent stage of the gonad encompass? 

Development of the gonad and duct system 

72

Where does structural development of the reproductive system occur? 

In utero 

73

What does functional develoment and maturation of the reproductive system occur? 

After birth 

74

Describe the reproductive system in babies and childhood

  • Human babies are born physically immature 
  • Childhood is a period of complete immaturity, with no sexual reproduction possible 

 

75

When does sexual maturation and puberty occur? 

In adolesence 

76

What develops in sexual maturation and puberty? 

Systems are activated that cause secondary sexual characteristics to develop 

77

What is the purpose of secondary sexual characteristics? 

  • Allows function of system 
  • Behavioural characteristics 

 

78

What are the male sexual secondary characteristics? 

  • Larger body size
  • Body composition and fat distribution 
  • Hair and skin 
  • Facial hair, male pattern baldness
  • Central nervous effects
  • Skin 

 

79

What are the female sexual secondary characteristics? 

  • Smaller body size
  • Subcutaneous fat distribution 
  • Hair and skin 
  • Breast development
  • Central nervous effects

 

80

What does the secondary sexual characteristic of subcutaneous fat distribution relate to? 

Ability to support pregnancy 

81

What is the purpose of the secondary sexual characteristic of breast development? 

For lactation

82

What must be true for a genetic male to be created? 

The male gamete (from the father) must carry the Y chromosome, therefore an XY male conceptus, thus primordial germ cells carry Y chromosomes 

83

What genes drive the development of a genetic male? 

SRY genes

84

What does the gonad become in the male? 

Testis

85

What does the internal genitalia develop into in the male? 

The male duct system

86

What is the develoment of the external genitalia of the male under the influence of? 

Testistoride hormones 

87

What must happen for a genetic female to be produced? 

The male gamete (father) must carry the X chromosome, therefore XX female conceptus, therefore primordial germ cells do not carry the Y chromosome

88

What leads to the development of a female? 

Absence of SRY chromsomes (and other factors)

89

What is the gonad in the female? 

The ovary 

90

What does the internal genitalia develop into in the female? 

The female duct system, including uterine tubes and uterus 

91

In what gender do the mesonephric ducts and paramesonephric ducts develop in? 

Both male and female

92

What are the mesonephric ducts? 

The ducts of the embryonic kidney 

93

Where do the mesonephric and paramesonephric ducts end? 

At the cloaca

94

What is the cloaca?

A single structure that the GI, urinary, and reproductive tract end at early in development 

95

How do paramesonephric ducts appear? 

As invaginations of the epithelium of the urogenital ridge

96

What do the paramesonephric ducts do caudally? 

Make contact with the cloaca

97

What do the paramesonephric ducts do cranially? 

Opens into abdominal cavity

98

What do the paramesonephric ducts do in the abdominal cavity

Grow into the abdominal cavity, try to meet each other in the midline

99

What happens when the paramesonephric ducts try to meet in the midline of the abdominal cavity? 

To start with, there is a septum, but this disappears and ducts fuse

100

What ultimately happens to the mesonephric and paramesonephric ducts?

What happens to them depends on the effect of the gondal hormones

101

What effect to the gondal hormones from the testis have on the mesonephric and paramesonephric ducts? 

  • Androgen secretion supports mesonephric duct 
    • This is a positive act to maintain the duct
  • Testis secrete Mullerian Inhibiting Substance, which causes the degeneration of the paramesonephric duct 

102

What can be said of androgen secretion maintaining the mesonephric duct? 

It is a positive act to maintain the duct 

103

What does the mesonephric duct develop into? 

  • Vas deferens
  • Epididymis 
  • Seminal vesicles 

 

104

Why does the testis need to secrete Mullerian Inhibiting Substance? 

Because you need to actively suppress the paramesonephric ducts, as its natural program is to develop 

105

What is Mullerian Inhibiting Substance secreted from? 

Sertioli cells 

106

What happens to the mesonephric and paramesonephric ducts in the female? 

  • No androgen means mesonephric duct degenerates 
  • No testis derived Mullerian Inhibitng Substance means paramesonephric duct develops 

 

107

What does the paramesonephric duct develop into? 

  • Fallopian tubes
  • Cervix
  • Uterus
  • Upper 1/3 of vagina

 

108

When are the basic components of the external genitalia derived? 

In the indifferent stage 

109

What are the basic components of the external genitalia? 

  • Genital tubercle 
  • Genital folds
  • Genital swellings

 

110

What do the genital folds surround? 

The urogenital sinus 

111

What do the genital folds become in males? 

The urogenital sinus 

112

What do the genital folds become in females? 

Labia minora 

113

What do the genital swellings become in males? 

Scrotum 

114

What do the genital swellings become in females?

Labia majora 

115

What happens to the genital tubercle in males? 

The GT elongates and genital folds fuse to form spongy urethra 

116

What is the elongation of the genital folds in the male under the influence of? 

Testis-derived androgen hormones, including dihydrotestosterone 

117

What must be true for the genital tubercles to respond to dihydrotestosterone? 

They must have working receptors 

118

What happens to the genital tubercle in the female? 

No fusion occurs, and the urethra opens into the vestible 

119

Where do the testis arise in males? 

In the upper lumbar region

120

How are the testis secured in the upper lumbar regions? 

They are tethered to the labioscrotal folds (future scrotum) by the gubernaculum 

121

What happens to the testis as the body grows? 

The relative position of the testis becomes more caudal 

122

What happens to the scrotum as it develops? 

A musculo-fasical layer evaginates the scrotum, together with the peritoneal membrane

123

What is formed by the invagination of the scrotum with a musculo-fascial layer and the peritoneal membrane? 

Processus vaginalis 

124

What happens to the testis between 25 and 28 weeks gestation? 

The testis migrate over the pubic bone, behind the processus vaginalis 

125

When do the testis reach the scrotum? 

Between 34-40 weeks

126

What happens above the testis once they have reached the scrotum? 

The fascia and peritoneum become closely apposed 

127

What is the spermatic cord formed by? 

  • Fascial layers 
  • Obliterated stem of processus vaginalis 
  • Vas deferens 
  • Testicular vessels and nerves

 

 

128

Where does the spermatic cord occupy? 

The inguinal canal

129

What is the scrotal ligament? 

The vestigial remnant of gubernaculum in males 

130

Where does the ovary originate? 

On the posterior abdominal wall 

131

What is the ovary attached to? 

The labio-scrotal folds, inferiorly 

132

What attaches the ovary to the labioscorotal folds? 

The gubernaculum 

133

What happens to the ovary after it has originated on the posterior abdominal wall? 

It descends into the pelvis

134

What does the gubernaculum become in females? 

  • Ovarian ligament 
  • Round ligament of uterus 

 

135

What does the ovarian ligament do?

Connects ovary to uterus 

136

Where does the round ligament of the uterus run? 

In the inguinal canal, the only structure occuping the inguinal canal in females

137

What does the round ligament of the uterus do? 

Connects uterus to labia

138

What are the common abnormalities in genital development? 

  • Genotype-phenotype mismatches
  • Structural defects

 

139

What can happen if external genitalia are ambiguous at birth? 

Investigations can be undertaken

140

What investigations can be undertaken if external genitalia are ambigous at birth? 

  • Investigate internal genitalia 
  • Test for sex hormones 
  • Genetic testing using cells from cheek
  • Karyotyping
  • Biopsy of glands 

 

141

How can internal genitalia be investigated? 

  • Endoscopy
  • Abdominal X-ray 
  • Pelvic ultrasound 

 

142

What sex hormones can be tested for? 

  • Androgens 
  • Oestrogens 

 

143

Give 3 genital structural defects? 

  • Clocal partioning defects 
  • Hypospodias 
  • Uterine structural defects 

 

144

What structures produce reproductive hormones? 

  • Hypothalamus 
  • Posterior pituitary 
  • Anterior pituitary 
    Gonads (ovaries and testes)
  • Placenta

 

145

What reproductive hormones does the hypothalamus produce? 

  • Peptides releasing factor
  • GnRH (gonadotrophin releasing hormone)
  • PRH (prolactin releasing hormone) 
  • PIH (prolactin inhibiting hormone) 

 

146

What reproductive hormones does the posterior pituitary release? 

Posterior pituitary hormone 

147

What does posterior pituitary hormone do? 

Produces oxytocin 

148

How does posterior pituitary hormone produce oxytocin? 

Through neural control from hypothalamus 

149

What type of reproductive hormones does the anterior pituitary gland produce? 

Gonadotrophins 

 

150

What gonadotrophins does the anterior pituitary gland produce? 

  • FSH (follicle stimulating hormone) 
  • LH (lutenizing hormone) 

 

151

What reproductive hormones to the gonads produce? 

  • Gondal steroids
  • Inhibin 

 

152

What are the gonadal steriods in the male? 

Testosterone

153

What are the gondal steroids in the female? 

  • Oestrogens 
  • Progesterone 

 

154

What are the different types of oestrogens? 

  • Principally oestradiol 
  • Also oestrone and oestriol 

 

155

What reproductive hormones does the placenta produce? 

  • Human chorionic gonadotrophin (hCG) 
  • Human placental lactogen (hPL)
  • Oestrogens 
  • Progesterone