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CELLULAR BASIS OF MEDICINE > SEX DETERMINATION > Flashcards

SEX DETERMINATION Flashcards

1
Q

WHICH 3 FACTORS DETERMINE SEX?

A

1: sex chromosomes
2: gonads
3: psychological / environmental differentiation

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2
Q

DOES THE MOTHER OR THE FATHER DETERMINE THE SEX OF THEIR CHILD?

A

father - has X and Y gene

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3
Q

EXPLAIN THE DROSOPHILA SYSTEM

A

two different gonosomes - X and Y
-XX = female
-XY = male
EG: mammals, most amphibians, most insects, some plants and fish

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4
Q

DISCUSS THE PROTENOR SYSTEM

A

only one gonosome - X
-XX = Female
-X = Male
EG: grasshoppers / crickets / cockroaches

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5
Q

DISCUSS THE ABRAXAS SYSTEM

A

2 gonosomes - Z and W
-ZW = male
-ZZ = female
EG: birds / some fish / some insects

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6
Q

DISCUSS THE HAPLOID-DIPLOID SYSTEM

A

-diploid = female
-haploid = male
EG: bees and ants

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7
Q

EXPLAIN EMBRYOGENESIS

A

-paired indifferent gonad developed in week 4-5
-until week 6 gender is unrecognizable
-in week 6, primordial germ cells (up to 2000) migrate from wall of yolk sac to occupy the gonadal ridges
-genital ridge converted into bipotential gonad (SF1, WT1, LHX9 genes)
-cells in ridges induced to form primitive sex cords (MALE = SRY & SOX9 (autosomal) genes) (FEMALE = WNT4 & DAX1 genes)
-Wolffian (mesonephric)(male genetilia) and Mullerian (paramesonephric)(female genetilia) ducts formed

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8
Q

WHICH GENE DETERMINES THE FEMALE GENDER?

A

DAX gene
-DSS-AHS dosage sensitive reversal adrenal hypoplasia on the X chromosome
-DAX1 acts as an anti-testis protein by antagonizing testis determining factor (TDF), the product of SRY gene
-Duplication of the gene for DAX1 on the active X chromosome, even in presence of the SRY gene, causes female development (46,XY with female phenotype)
-DAX1 inhibits the effect of SF1 and WT1 causing inhibition of anti-mullerian (AMH=MIF) hormone production -> no regression of the Müllerian duct
-Individual with XY has 2 DAX genes on X chromosome will be female
-Mutations in the gene for DAX1 cause X-linked congenital adrenal hypoplasia and hypogonadotropic hypogonadism
-NR0B1 gene for DAX1 is located on chromosome Xp21.3

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9
Q

WHICH GENE DETERMINES THE MALE GENDER?

A

SRY gene
-resides on the short arm of Y chromosome
-SRY product -> testis determining factor is a transcription factor which contains HMG box DNA binding domain
-SOX9 codes for HMG box which is required for differentiation and for chondrogenesis and collagen production
-mutations in HMG box (SOX9 gene) cause sex reversals (46,XY with female phenotype) (AD = dwarfism syndrome / camtomelic dysplasia)
-if the SRY gene is present from week 7 within developing testes - 3 main cell types differentiate and proliferate

1: SPERMATOGONIA

2: LEYDIG CELLS - secrete testosterone which cause conversion of Wolffs canals into Vas deferens and epididymis

3: SERTOLI CELLS - secrete SF-1 and mullers duct inhibiting hormone, which causes apoptosis of mullers duct

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10
Q

WHICH HORMONES INDUCE PUBERTY?

A

FSH and LH which are both secreted by the pituitary gland

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11
Q

WHAT ARE THE EFFECTS OF ESTROGENS?

A

growth of mammary gland
pelvic enlargement
fat storage
uterine maturation
menstruation
-> secreted by the ovaries

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12
Q

WHAT ARE THE EFFECTS OF ANDROGENS?

A

growth of pubic hair and auxillary hair
-> secreted by adrenal glands

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13
Q

WHAT ARE THE EFFECTS OF TESTOSTERONE?

A

growth of penis
testicular larynx
spermatogenesis
muscle growth
skeletal changes

-> 5-alpha-reductase converts testosterone into dihydrotestosterone (DHT) (more active and needed for male gender) which causes the penis, scrotum, skin and beard to form and grow

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14
Q

WHAT CODES FOR INTERNAL SEX DETERMINATION?

A

wolffman and mullerian ducts

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15
Q

WHAT CODES FOR EXTERNAL SEX DETERMINATION?

A

Testes and ovaries

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16
Q

WHAT ARE SEX LIMITED TRAITS?

A

expressed only in one sex
-secondary sexual characteristics
-encoded by autosomal genes

17
Q

WHAT ARE SEX INFLUENCED TRAITS?

A

level of their expression is different in each gender
-encoded by autosomal genes
EG: early baldness is dominant in males, recessive in females

18
Q

WHAT IS HERMAPHRODITISM?

A

presence of both ovarian and testicular tissue -> genetilia are ambiguous

19
Q

WHAT IS PSEUDOHERMAPHRODITISM?

A

presence of gonadal tissue of only one gender but with ambiguous or opposite external genetilia

MALE - 46,XY (female pheno) ~> normal testes, but outer female genetilia and secondary sexual characteristics, incompletely developed vagina and uterus, no menstruation
-5alpha reductase deficiency (AR) results in impaired conversion of testosterone to dihydrotestosterone (DHT)
-androgen insensitivity syndrome = X linked recessive - unresponsive to androgens caused by mutation in androgen receptor gene in Xq chromosome

FEMALE - 46,XX (male pheno) ~> normal ovaries, external male genetilia and secondary characteristics
-congenital adrenal hyperplasia (AR) caused by the regulatory feedback mechanism causing overstimulation of the adrenal cortex -> increase in ACTH
-most common cause is 21-hydroxylase deficiency = cortisol and aldosterone decrease while androgens increase
-other causes include 17alpha-hydroxylase deficiency, 3beta-dehydrogenase deficiency and 11beta-hydroxylase deficiency

20
Q

NAME AND DISCUSS A DISEASE RELATED TO ABNORMAL LOCALIZATIKN OF SRY GENE

A

EG: DE LA CHAPELLE SYNDROME
-male phenotype with karyotyoe 46,XX with Azoospermia
-normal male phenotype, sterility, no uterus or adnexa
-SRY gene on X chromosome (SRY positive)
-exchange occurs as random event during formation of sperm cells in affected persons father
-SRY gene is located onto autosome by translocation
-azoospermia factor a, b, c are missing

21
Q

GIVE EXAMPLES OF DISORDERS OF SEXUAL DEVELOPMENT IN BOTH GENDERS

A

-one cause is due to nondisjunction of gonosomes in meiosis

Turner Syndrome: 45,X (60%)
-mosaics =. some cells have 1 X chromosomes while others have 2 or more X chromosomes (40%)
-symptoms = short stature, low hairline, widely spaced nipples, no menstruation, poor breast development, rudimentary ovaries, small finger nails, neck fold of skin, characteristic facial features
-also called monosomy X
-98-99% of the embryos are miscarriages
-affects women only

Klinefelters syndrome: 47,XXY
-can be 48,XXXY / 49,XXXXY / 50,XXXXXY
-trisomic
-symptoms include infertility, tall stature, small penis, osteoperosis, female type pubic hair pattern, breast development, poor beard growth, long legs, short torso, psychological or behavioural issues
-affects men

22
Q

WHAT ARE CHROMOSOMAL MOSAICISMS?

A

different cells in the same individual have different numbers of arrangements of chromosomes

23
Q

EXPLAIN XYY SYNDROME

A

extra copy of Y chromosome
-47,XYY
-many males are tall and hyperactive
-most males have normal testosterone production and usually fertile

24
Q

EXPLAIN XXX SYNDROME

A

additional X chromosome
-47,XXX
-females are tall, small head, poor muscle tone
-most females have normal sexual development and are fertile and able to conceive

25
Q

WHAT COMMON PRECURSOR DO THE TESTES AND OVARIES DIVERGE FROM?

A

Bipotential gonad

26
Q

HOW CAN MALE PHENOTYPE WITH GENOTYPE 46,XX BE FORMED?

A

abnormal crossing over (gene STY translocated to X)
translocation (SRY gene translocated into autosome)

27
Q

HOW CAN FEMALE PHENOTYPE WITH GENOTYPE 46,XY BE FORMED?

A

deletion or mutation of SRY gene

28
Q

WHAT RATIO DO ALL SEX DETERMINING GENES PROVIDE?

A

1:1 in progeny

29
Q

WHAT CELLS OF THE OVARY ARE CAPABLE OF SYNTHESIZING ESTROGEN?

A

thecal and granulosa cells

30
Q

WHY DO MALES NEED ESTROGENS?

A

in order to be fertile

31
Q

EXPLAIN DIFFERENT TYPES OF SEX REVERSAL

A

46,XY -> X(duplicated DAX1) = FEMALE
46,XY -> mutated SRY gene = FEMALE

46,XX -> duplicated SOX9 gene = MALE
46,XX -> SRY positive gene = MALE (infertile as person does not have Y chromosome)

32
Q

WHAT ARE THE PSEUDOAUTOSOMAL REGIONS?

A

one at end of p arm
one at end of q arm
homologous to X chromosome and crossing over occurs here

CELLULAR BASIS OF MEDICINE (32 decks)

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