Sex Determination and chromosomes numbers & human genetic traits

Question 1

disjunction

Answer 1

• term for when chromosomes separate into different cells in division

Question 2

nondisjunction

Answer 2

• when some mistake happens in chromosome separation

- particular chromosome has been lost

Question 3

primary nondisjunction

Answer 3

• 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

Question 4

secondary nondisjunction

Answer 4

• 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

Question 5

somy

Answer 5

• wrong number of chromosomes

Question 6

Trisomic

Answer 6

• 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

Question 7

Trisomic 21/down syndrome

Answer 7

• 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

Question 8

Aneuploid

Answer 8

• a number of chromosomes other than the normal number (especially seen in cancers)

Question 9

ploidy

Answer 9

• describes that number of haploid sets of chromosomes (haploid, diploid, triploid)

Question 10

triploid

Answer 10

• 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

Question 11

Klinefelter syndrome

Answer 11

• 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

Question 12

examples of dominant traits

Answer 12

• dimples
• widow’s peak
• freckles
• cleft chin
• hair on arms

Question 13

examples of recessive traits

Answer 13

• no freckles
• straight hairlines
• no dimples
• round chin
• no hair

Question 14

Incontinentia pigmenti (IP)

Answer 14

• causes a pigment change- blotchy areas

Question 15

Hypertrichosis

Answer 15

• sex-linked dominant

- hair all over body

Question 16

Phenylketonuria (PKU)

Answer 16

• 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

Question 17

primordial dwarfism

Answer 17

• body proportions are normal but smaller, small pointy noise and high pitched voice

Question 18

Achondroplastic dwarfism

Answer 18

• 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

Question 19

Dwarfism: Pycnodystosis

Answer 19

• Soft spot at top of head (fontanelle)
• Autosomal recessive
• Height 4’ 11”
• Fragile bones
• Short fingers at tips
• Parents first cousins

Question 20

Disorders of hand/finger formation

Answer 20

• brachydactyly- fingers deformed, also have intellectual deficit
• polydactyly- has extra fingers
• syndactyly- fingers fused together

Question 21

Ehlers-Danlos

Answer 21

• collagen dysfunction
• Skin stretches
• Joints unstable and loose

Question 22

Marfan Syndrome

Answer 22

• 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

Question 23

Y chromosome

Answer 23

• 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

Question 24

Turner’s syndrome

Answer 24

• Just X
• Webbed neck, extra skin folds
• Underdeveloped secondary sex characteristics
• Low fertility

Question 25

Jacobs Syndrome, XYY

Answer 25

• 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

Question 26

Mechanisms for extra X chromosome

Answer 26

• 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

Question 27

Gene dosage compensation

Answer 27

• 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

Question 28

Barr Body

Answer 28

• 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

Question 29

Random X-inactivation (cats)

Answer 29

• 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

Question 30

Random X-inactivation in females

Answer 30

• 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

Question 31

normal process of sex-determination (sexual differentiation)

Answer 31

• 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

Question 32

Guevodoces

Answer 32

• 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

Question 33

Androgen Insensitivity Syndrome (Testicular Feminization Syndrome)

Answer 33

• 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

Question 34

Congenital adrenal hyperplasia

Answer 34

• 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

Question 35

Degrees of virilization

Answer 35

• 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

Question 36

twin boy circumcision study

Answer 36

• 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