Sex Determination and chromosomes numbers & human genetic traits Flashcards
1
Q
disjunction
A
- term for when chromosomes separate into different cells in division
2
Q
nondisjunction
A
- when some mistake happens in chromosome separation
- particular chromosome has been lost
3
Q
primary nondisjunction
A
- in first meiotic division, one chromosome fails to separate
- end up with both chromosomes in one cell, and 0 chromosomes in the other cell
- then in second division separation is normal–> end up with 2 gametes with 2 copies of chromosomes, and 2 gametes with 0 chromosomes
4
Q
secondary nondisjunction
A
- first meiotic division is normal (chromosomes separate)
- second division–> one of the cells does not separate correctly
- -> end up with 2 normal gametes, 1 gamete with 2 copies of chromosome, and 1 gamete with no chromosome
5
Q
somy
A
- wrong number of chromosomes
6
Q
Trisomic
A
- having triple copies of one chromosome (instead of double)
- Don’t see babies with extra chromosomes on 1 and 2 or 3, since chromosomes are so big–> this would derail development
- the bigger the chromosome, the harder to survive
- see it in chromosomes 21, 13, 18
7
Q
Trisomic 21/down syndrome
A
- Range of effects, mental defects, physical problems, tend to get cancers more frequently
- More likely to live that other somy
- extra chromosome 21
- Phenotypic effect- on palm, line goes straight across in Down, usually doesn’t meet lifeline (simian line)
- Think it is a dose effect- genes on 21 are being overexpressed
- some people have a sever disability, some don’t have a noticeable disability
- gart gene- may account for mental retardation
8
Q
Aneuploid
A
- a number of chromosomes other than the normal number (especially seen in cancers)
9
Q
ploidy
A
- describes that number of haploid sets of chromosomes (haploid, diploid, triploid)
10
Q
triploid
A
- fertilized by 2 sperm
- both sperm are haploid, and egg is haploid–> end up with 3 copies of every chromosome
- 2X and 1Y
- 3 of every chromosome–> cannot survive
11
Q
Klinefelter syndrome
A
- Aneuploidy in sex chromosomes
- primary or secondary nondisjunction
- Low fertility
- Body proportions sometimes appear more feminine
- Small amount of breast development
- Not severely affected
- Difference between XXY, XXXY, XXXXY?
- No detectable difference
12
Q
examples of dominant traits
A
- dimples
- widow’s peak
- freckles
- cleft chin
- hair on arms
13
Q
examples of recessive traits
A
- no freckles
- straight hairlines
- no dimples
- round chin
- no hair
14
Q
Incontinentia pigmenti (IP)
A
- causes a pigment change- blotchy areas
15
Q
Hypertrichosis
A
- sex-linked dominant
- hair all over body
16
Q
Phenylketonuria (PKU)
A
- autosomal recessive
- Missing the enzyme that normally converts phenylalanine, in excess of that needed for protein synthesis, to tyrosine
- Metabolites of excess phenylalanine become detectable as they spill over in the urine
- If untreated infants develop severe mental retardation and often die as children (interfere with brain development)
- Caught early: eliminate phenylalanine-containing food from the diet until brain development is complete
- all newborn children are tested
17
Q
primordial dwarfism
A
- body proportions are normal but smaller, small pointy noise and high pitched voice
18
Q
Achondroplastic dwarfism
A
- Autosomal dominant – often spontaneous mutation
- defect in connective tissue
- Relatively normal trunk, short proximal limb bones, enlarged forehead, small mid-face, lumbar lordosis
- Exaggerated curvature of back
19
Q
Dwarfism: Pycnodystosis
A
- Soft spot at top of head (fontanelle)
- Autosomal recessive
- Height 4’ 11”
- Fragile bones
- Short fingers at tips
- Parents first cousins
20
Q
Disorders of hand/finger formation
A
- brachydactyly- fingers deformed, also have intellectual deficit
- polydactyly- has extra fingers
- syndactyly- fingers fused together
21
Q
Ehlers-Danlos
A
- collagen dysfunction
- Skin stretches
- Joints unstable and loose
22
Q
Marfan Syndrome
A
- Problems in connective tissue in aorta wall and other issues
- Weakens areas where there would normally be lots of collagen
- -> can cause aorta to swell and burst
- tend to be tall and thin
- autosomal dominant
23
Q
Y chromosome
A
- only has about 85 genes
- has SRY gene= sex determining region of the Y, starts secretion of testosterone
- Tooth enamel formation- sometimes shows visible phenotype
24
Q
Turner’s syndrome
A
- Just X
- Webbed neck, extra skin folds
- Underdeveloped secondary sex characteristics
- Low fertility
25
Q
Jacobs Syndrome, XYY
A
- Prison population experiment
- Presence of XYY was 40X higher in prison population
- But also may not notice because so many people have it, don’t know
26
Q
Mechanisms for extra X chromosome
A
- Dosage- need right number of chromosomes
- Possibilities
1. Some mechanism that increases the expression of the X in men, to balance out the double expression in women? NO
2. Decrease the expression of X genes by ½ in women? NO - Neither one of these (1 or 2) is happening
3. 1 of the 2 Xs in women is inactivated–> condensed and moved into heterochromosome–> this is the mechanism
27
Q
Gene dosage compensation
A
- X inactivation to balance gene dosage between males and females
- Condensed X becomes a black spot just beneath nuclear envelope
- somewhere around 16/32 cells, mechanism kicks in and condenses 1 of the 2 Xs
- Some of descendent cells from then on, the maternal X is inactivated, and the paternal one is activated (and vice versa)
- Will get a random mix of cells in every female, some express paternal, some express maternal
- Blocks of areas in female that will have 1 X on in some cells and the other one in other cells
28
Q
Barr Body
A
- inactivated X chromosome
- Dark sport on side of cell
- Normal females have a single barr body = inactivated X
- Normal males do not inactivate X- no barr body
- No matter how many Xs you have, they are all inactivated except for 1–> so multiple Xs won’t affect much
- X pigment on skin- sometimes see blotchy areas on skin
- Can affect fertility
29
Q
Random X-inactivation (cats)
A
- can affect phenotype
- see blotchy areas of color pigment
- ex. Pigmentation gene is on X chromosome in cats
- as a cat develops and goes through random inactivation process, black genes express on one X chromosome or orange express on orange chromosome
- -> Calico cats- always female cats, since you need the extra X to get blotchy pattern
30
Q
Random X-inactivation in females
A
- random inactivation of maternal and paternal X
- can affect phenotype
ex. pigmentation- blotchy - ex. can have patches of skin that lack sweat glands and hair
31
Q
normal process of sex-determination (sexual differentiation)
A
- male and female about the same until 5 weeks
- 6-8 weeks starts sexual differentiation
- Urethral form
- -> If Y chromosome- will cause germ-line cells to organize into testes and start secreting testosterone–> causes external features to become male-like
- -> If X chromosomes- no signal to develop testes–> inside structure develops into ovaries instead–> causes external features to become female-like
- Bulge develops into penis or clitoris
32
Q
Guevodoces
A
- penis at age 12
- SRY gene not working
- enzyme called 5-alpha reductase that is missing–> Prevents some of the conversion of testosterone into DHT
- DHT causes urethra, prostate, penis and scrotum to develop
- children appear as female, even though they are genetically male
- internal male structures can still develop (without DHT)
- at puberty, testosterone level is so high, some converted to DHT (if a small amount of enzyme), and signal is noticed–> convert into male phenotype at 12, 13 years old–> fully developed penis, some reduce in fertility
- common in Dominican Republic
33
Q
Androgen Insensitivity Syndrome (Testicular Feminization Syndrome)
A
- X linked recessive
- Testosterone receptors non-functional
- have XY chromosomes, but phenotypically look like females
- SRY gene is working, testes form, product testosterone, BUT testosterone receptor (gene) is missing
- Still have testes inside and don’t develop uterus or ovaries–> low shallow vagina
- Don’t start menstruating- often don’t know until puberty
34
Q
Congenital adrenal hyperplasia
A
- most common cause of human intersex
- Pituitary gland (hangs down from bottom of brain and rests in part of skull)
- Enzyme deficiency–> causes reduced synthesis of cortisol
- Levels of cortisol are lower–> hypothalamus senses low on cortisol–> signals to make more ACTH
- ACTH also signal adrenal gland (gets larger) and to make more cell–> adrenal gland also makes androgens
- Androgen hormone causes external genitals to become more masculine looking (virilize)
- -> doesn’t affect boys much, but girls’ tissues will rearrange to look more like boy
35
Q
Degrees of virilization
A
- Range of effects in female reproductive organs depending on virilizing adrenal hyperplasia
- Clitoris will get larger and larger, will create urethral canal
- Extreme conditions–> looks like a penis (mislabeled at the time of birth)
- Ambiguous genitalia–> difficult call
36
Q
twin boy circumcision study
A
- doctor accidentally burned off penis, grew up as a girl
- experts thought it was all environmental and if he grew up as a girl, would be a girl
- eventually had surgery
