1
Q
How is sexual reproduction Expensive?
A
- Finding a mate
- Assess mate potential
- Produce gametes
- Mating
- Carry and care for offspring
- Possibility of unsuccessful mating
- Balance between parental investment & reproductive success so fewer offspring
- More complicated so higher chance it goes wrong but have more variation
2
Q
Types of Variation in Sexual reproduction
A
- Recombination
- Independent assortment
- Random fertilization
3
Q
Why is mitochondria only from the female gamete?
A
- Only the sperm nucleus enters the egg because if it let a whole cell into the egg it would also be able to let in bacteria so it only lets a part of the sperm in
- Evolution from bacteria where they transfer gene material not the whole cell
- Sexual dimorphism decreases risk of self-fertilization (natural fail safe)
- To avoid risk of infection other cells/organelles are not allowed into egg
4
Q
Advantage: group selection
A
- Greater variation
- Variety comes with the probability that some offspring will survive in a changing environment
- Ex: Irish potato famine had no variation in its crop so one virus could wipe most of the potatoes out
5
Q
Advantage: environmental effects on life history
- Asexual vs Sexual
A
- Asexual= highly variable environments
o Reproduce quickly so can survive at various environments
o Short lives to ensure reproduction
o High rate of reproduction and mutations
o Take antibiotics every 12 hours because it will kill the bacteria at its exponential stage of growth - Sexual
o Longer lives so better for stable environments because cant respond to rapid change
o Variable phenotypes ensure some success
6
Q
chromosomes
eukaryote vs prokaryote
A
- Prokaryotes: genetic material is a small circular DNA
- Eukaryotes: more genetic material organized un chromatin, which condenses in chromosomes during nuclear division
7
Q
Karyotype Test
A
- Karyotype is a test to identify and evaluate the size and shape and number of chromosomes in a sample of cells
- Karyotype analysis process
o Force cells into mitosis then stop at metaphase stage to view the condense chromosomes
o Heterochromatin: dark, condenses DNA, not expressed
o Euchromatin: light bands, expressed
8
Q
chromosome abnormalities
A
- evolutionary constraint
- Numerical abnormalities
o Written as: # of ch, sex ch, + extra, ex: 47, XY, +18
o Aneuploidy : loss or gain of 1 chromosome
o Monosomy: loss of 1 chromosome and only survivable one is Turner syndrome with one X chromosome only
o 2 types of trisomy : dosage affect prevents survival of most trisomy
1. Autosomes (21, 18, 13)
2. Sex chromosomes
-XXX: turn off 2 X - Kleinfelter: 47, XXY turn off 1 X
- Jacobs: 47, XYY has no problems with carrying to term because it doesn’t code for anything important but does seem to increase testosterone and antisocial behavior because its at an increase in prison populations
9
Q
Chromosome Abnormality in Newborns
A
- 50% of all spontaneous miscarriages have chromosomal abnormality & 80% of those in 1st trimester
- 0.5-1% live births have chromosome abnormalities
- Miscarriage is high due to the types of genes and the dosage effect
10
Q
Non-Disjunction
A
- Separation in meiosis 1 is unsuccessful leading to gametes with more and less than normal amounts of genetic info
- 50/50% chance of a trisomy or a monosomy
11
Q
Non-Disjunction and Age
A
- Older women’s chromosomes have been formed inside of them since they were born and are released when they ovulate and the longer it takes to fertilize them the longer the chromosomes will have spent being stuck together and lower the chances they will pull apart
- 90 % maternal ND because have carried eggs since their own birth
- 5% paternal ND because the sperm is on a cycle creating new ones about every 6 weeks
- 4% Robertsonian translation
- 1% mosaicism
12
Q
Robertsonian Translocation at meiosis
A
- First, they Lose short arms of 2 chromosomes and fuse together to make a new chromosome
- Now have a 14, 21, and 14/21
- 6 possible game combos where 50/50% lead to death or survival
- Outcomes lead to unbalanced genetic material
- Normal: 14, 21 (1/3 chance for the survival gametes)
- Normal carrier: 14/21 will have normal phenotype but be a carrier for Robertsonian
- Down syndrome: 14/21, 21 leads to this because get 2 copies of 21 from mom and 1 from dad during fertilization
- Lethal combos are: 14 alone, 21 alone, & 14, 14/21 which leads to a 14 trisomy
13
Q
Mosaicism
- 2 cases
A
- Presence of 2 or more cell lines with different genetic makeup in an individual
- Milder form of down syndrome because some cells in the body have Down and some don’t
- 2 cases:
1. Nondisjunction during early division after fertilization causing some cells to have trisomy and others to not
2. Start with a Down syndrome embryo where some cells revert back and lose the extra chromosome after fertilization
14
Q
Down Syndrome
A
- Trisomy of 21
- Symptoms: low IQ, behavior/cognitive retardation, congenital heart and GI tract defects, epicanthal folds, broad nasal bridge, short stature, smooth philtrum, early onset of Alzheimer’s
- Same rate of incidence in the last 100 years because of the increases in maternal age leads to an increase in non-disjunction but incidence of trisomy stays low because of abortion (we can detect early on if baby has trisomy)
15
Q
Sex Determination
A
- Organisms that have sexual reproduction usually have 2 sexes
- Many systems in nature determine the sex
1. Environmental parameters: alligators develop sex based on the temp at which they are incubated
2. XX vs XO: increase elegans, the presence of 2 copies of the sex chromosome determines a female and one sex chromosome makes a male
3. XX vs XY: humans, most mammals, some insects where XX= F, XY = M
16
Q
Barr Body
A
- Lyonization: the inactivation of the extra X chromosome into a Barr body, occurs early in embryonic development, random inactivation, inactivation is transmitted to daughter cells
- F= XX & M=XY (only 1 X)
- Inactivation of one X chromosome prevents females from having twice as many X chromosome gene products as males
- Inactivation if one X chromosome only takes place in somatic nuclei
- Ex: calico cats fur color because only females have XX
17
Q
Turner Syndrome
A
- Only monosomy compatible with life
- 45, XO (no barr body)
- Phenotypically female
- Webbed neck
- Ovarian formation failure so no period and sterile
- Short in stature because they have less SHOX genes (dosage effect)
- Normal IQ
- Impaired social cognition
- Associated disorders: renal problems, Hashimoto’s thyroiditis (autoimmune hypothyroidism), cardiac problems
18
Q
Klinefelter Syndrome
A
- 47, XXY (inactivate 1 X to limit dosage effect)
- Phenotypically male
- Learning difficulties
- Increased antisocial and criminal behavior (in XYY too)
- 50% normal fertility
- Taller than average because they have more SHOX genes in the barr body (dosage effect)
- Slightly lower IQ
19
Q
Women with XXX
A
- Low IQ
- Tall stature
- Normal fertility
- Learning disability and antisocial behavior
20
Q
Effects of Differences in Sex Development
A
- Crucial aspect of development
- Differences of Sex Development Effects
1. Congenital conditions where chromosomal, gonadal or anatomical sex is atypical (physical and genetic se don’t match)
2. Lifelong emotional and psychological consequences
3. Develop as a consequence of our evolutionary history
4. Cultural taboo/ignorance
21
Q
SRY = Sex determining region on Y chromosome
A
- M & F reproductive tracts arise from the same embryonic tissue
- If SRY is present, then Sertoli cells are expressed leading to the differentiation of Leydig cells which produce testosterone (which goes toward M formation) and inhibition of female genitalia development
- If no SRY then go to ovaries
- By default you develop F but if anything disrupts the factors in the pathways it can lead to a change in internal and external genitalia
- Q: What happens if a patient has XX but the SRY is translocated onto and an X chromosome?
A: the patient would be genetically female but would develop male sex organs
22
Q
Differences in sex development
A
- Patients that acquire mutations on the gene coding for proteins involved in sex determination
- Called XX DSD (anything but fully F) and XY DSD (anything but fully M)
- Hopefully no more gender reassignment before puberty
23
Q
2 extreme examples of differences in sex development
A
- 46 XY Complete Gonadal Dysgenesis = cant develop internal/external M genitalia
- Female appearance with normal uterus and fallopian tubes
- No ovaries
- 15-20% caused by a mutation or deletion on the SRY
- Sterile - 46, XX Gonadal Dysgenesis
- Male or ambiguous genitalia
- Translocation of SRY onto another chromosome (often the X chromosome)
- Often have Male gender identity
- Sterile
24
Q
qualities of human reproductive strategy
A
- High investment, few offspring
- Single births norm
- Infanticide of multiples (usually F)
- Factor driving offspring # is amount of resources
- 2 examples of populations with no family planning or contraceptives
1. Kung: Botswana, 4.7 births, fewer resources
2. Hadza: Tanzania, 6 births, more resources
25
cost of fecundity
- Study of 19th century Bavarian villages
- Longer birth intervals = higher chance of survival for the younger sibling
- Which links back to amount of resources & poverty
26
mate choice
- In males the # of offspring increases with an increase in the # of mates but not for women
- Female reproduction is more expensive than in males
- So females tend to be more selective than males about mates
- **Bateman’s Principle:** women are more selective than men are because reproduction is more expensive for them
27
Human Male Mating strategies
- Goal: maximizing mating opportunities while also ensuring offspring survival
- Monogamy = ensures survival of offspring but a tradeoff with opportunity to have more offspring and mates
- Polygamy/polygyny = more offspring but tradeoff with less parental care
- Influencing factors like culture, society, religion
28
Human Female mating strategies
- More selective (Bateman’s Principle)
- Fitness maximized by selecting a mate that can contribute to survival of offspring by having good genes, providing care, being reliable & dependable
29
universal desire in both sexes
-intelligent, kind, understanding, dependable, healthy
- mutual attraction/love
- affinity
- politics & religion
30
Universal sex differences in Desires
- various desirable characteristics
- women desire wealth (resources) because they are looking for a mate than can support their offspring. Examples: education, ambition, social status, somewhat older men
- men desire younger mates (physical appearance) because increase the odds the woman is healthy and can carry offspring to term. Features like full lips, smooth skin, low hip to waist ratio (WHR)
- WHR = wider hips = wider birth canal = easier birth
31
link b/w wealth & reproductive success
- Study among tribal Turkman of Iran
- Wealthier half of population had increased fertility
- Sexual selection: wealth leads to more sexual success
- But this correlation doesn’t hold for capitalist, urbanized cultures
32
sexual dimorphism
- result of ?
- 5 traits
- Result of natural and sexual selection
- Some traits are:
1. Body size and composition
2. Anatomy
3. Onset of puberty
4. Mortality rates
5. Menstruation
33
Body Comp differences b/w M/F
- Males = more muscle & less fat
- Females = more fat because in the past it is a good indicator they can carry pregnancy to term
- Evolutionarily linked to reproductive success
34
Effects of Sexual Dimorphism on facial attractiveness
- Theoretically: enhancing sexual dimorphism will increase attractive ness but they were wrong because women liked feminized men more as they perceived them as less cold and dishonest
- Subjects asked to choose most attractive facial feature on the average, feminized, and masculinized options
- Feminized men were chosen more because women perceived them as less “cold and dishonest”
- Selection pressure is limiting sexual dimorphism and encouraging neoteny (retention of juvenile features)
35
Larger brains = Less Sexual Dimorphism
- Larger brains required prolonged growth = which requires more maternal care = which in turn needs more support from father = which affects the social structure of human society = less sexual dimorphism because don’t have to fight for mates anymore
- We no longer need extreme sexual dimorphism like in early hominids as in harem scenarios because there is no reason to fight for mating rights since an increase in sociality and social groups due to brain size increase
36
competition and sexual selection
- Sexual selection and competition
o Between males for access to females so increased risk taking to access mates
o Between females for most desirable mates
- Crucial factor that determines the survival of the genes
- Still present today and affects health & mortality
o Pathway #7 of ultimate mechanisms for disease risk
37
sexual selection and male mortality
- Evolutionary perspective
- Males evolved to:
o Compete effectively with other males
o Demonstrate to females they are the optimal mate
- However humans have also evolved to live in stable social groups with rules that facilitate coexistence in the group
38
mortality difference: longevity
- Females typically live longer (over 80)
- Males are more vulnerable to extrinsic causes of death
o Violence/aggression
o Smoking and alcohol
o Risk takers
o Most diseases
- Why? Because males evolved to take more risks to get mates
39
cardiovascular disease and estrogen
- Hypertension (high BP)
o Young males
o Post menopausal females
- Estrogen provides protection by lowering inflammation which enhances vasodilation (decreases heart attack risk) which reduces oxidation which is all optimal for pregnancy
- Estrogen slows atherosclerosis
40
3 reproductive strategies
oviparity
ovoviviparity
viviparity
41
Oviparity
1. Oviparity: females lay eggs that develop and hatch in the external environment
- Eggs are autonomous
- More offspring
- Reduced parental investment
- Ex: chickens
42
Ovoviviparity
2. Ovoviviparity: females retain developing embryo in eggs inside their body and give birth to offspring
- Developing embryo does not have access to mother’s circulatory system
- Feeds on yolk
- Ex: sharks
43
viviparity
3. Viviparity: females retain developing embryo inside their body and give birth to offspring
- Get nourishment from mother
- Developing embryos have access to mother’s circulatory system
- Fewer offspring
- Higher parental investment
44
menstruation in females
- Not all mammals menstruate
- Thickening of the endometrium to prepare for implantation
o Regulated by hormones
o Decidualization
o Caused by progesterone
o To prepare for implantation from blastocyst
o No implantation = progesterone drops and endometrium sheds
- Non menstruating species: thickening only occurs with implantation
- Some species reabsorb the endometrium (ex: horses)
45
human menstruation vs seasonal breeders
- Humans evolved in tropical regions with limited seasonality so we can procreate at any time of the year
- Higher energetic cost to have period every month but it is worth it
- Seasonal breeders (depending on where they evolved)
o Need to reproduce to give birth in the favorable season because more nutrients are available during that season
o Adjust the biorhythm based on day length & temp
o Monoestrous: 1 cycle per year
o Usually evolved in cold climate so give birth in spring because more nutrients
46
menstruation hypothesis
- Decidualization evolved to protect against invasive/malformed fetal tissue
- Assesses quality of embryo
- If the embryo is not viable it can be shed from the uterus (miscarried)
- Profet’s sperm hypothesis – “cleanse uterus”
o Uterus sheds harmful pathogens introduced by sperm
o Yet antibodies could respond to this, and it would be less costly so why shed pathogens
- Menstruation removes residual sperm in the uterus
o Yet it only happens once a month so it’s not very often
47
menstruation linked to reproductive cancers
- Hunter gatherers: 100- 150 menstrual cycles per lifetime
- Western Women: 450-500 menstrual cycles per lifetime
- This excessive number of periods causes constant fluctuations of estrogen and progesterone
- Women who have their period earlier have increased risk of reproductive cancers because of hormone fluctuations
48
lactational amenorrhea
- Study in Dogon women in Mali
- Higher average number of births = longer lactational periods = less periods = less hormone fluctuation = lower reproductive cancer risks
- Average 8.6 births per woman
- Average of 2 menses in 2 years
- Lactational amenorrhea
- Low incidence of reproductive cancers
- Modern women have an increased risk of reproductive cancers because of
1. Longer reproductive lives = more periods
2. Shorter lactation periods
3. Less offspring so more periods
49
4 embryonic membranes
1. Yolk sac : only used in early gestation
2. Allantois: nutrition, excretion, and umbilical cord development
3. Chorion
- Blood to get nutrients from mother
- Outermost membrane
- Contributes to the development of the placenta
4. Amnion Sack
- Contains fluid to absorb shock
- Innermost membrane
50
placenta (general)
- Placenta is a highly evolved structure that allows an efficient exchange of substances to support fetal growth
- Cost: fetal and maternal circulation are close in proximity (NO mixing)
- Risk of immunological responses = immune compromised so lowered immune response so mother’s immune system doesn’t attack the fetus
- Placenta inhibits ovulation to avoid the waste of a second offspring
51
Placenta and fetal/mother interaction
- Nutrients diffuse from mothers blood to fetus
- Waste products diffuse from fetus to mother
- Maternal antibodies actively transported across placenta
- Maternal transferrin releases iron that is taken up by transferrin receptors = baby uses the iron stored up from the mother in utero for first 6 months of life = baby post 6 month eats iron on their own
- Most bacteria are blocked
- Many viruses can pass including rubella, chicken pox, mono, zika
- Many drugs and toxins pass including alcohol, heroin, mercury, warfarin
- Placental secretion of hormones: progesterone & HCG and estrogen & CRH
52
Preeclampsia
- Complex pathogenesis
- Mom and fetus form placenta with both of their tissues
- Leading cause of maternal mortality and potentially fatal fetal mortality
- Dysfunctional development of uterine spiral arteries leading to placental hypoperfusion, ischemia, inflammation and systemic vasoconstriction in the mother and can impair fetal development
- Some signs are hypertension, renal damage, proteinuria (protein in urine), hemolysis, elevated liver enzymes
- treatment = delivering the baby
53
Preeclampsia Occurrence
- 5-10% only in humans because larger brains require a more invasive/complex placenta because we need more nutrients for brain growth
- Increased risk for first pregnancy and decreases in later pregnancies
- Over 40% risk in multiples because of the impaired remodeling of the tissue
- Cause: immunological difference between mother and fetus (incompatible)
54
Why has Preeclampsia persisted?
- Preeclampsia is less common when women have more babies with the same partner so increased monogamy is favorable
- A thin layer separating fetal and maternal blood allows for an efficient exchange of nutrients
- Decrease after first affected pregnancy (with same partner)
- Favors a stable relationship = monogamy = lower risk
- Benefits: mild increase in hypertension (but not later on in pregnancy) causes increased nutrient delivery, improves offspring growth and expected health
55
vertebral column
- adult = 26 bones (7, 12, 5, 5, 3-5)
- Transmits weight of trunk to the lower limbs
- Surrounds and protects the spinal cord
- Serves as attachment sites for muscles of the neck and back
o Thoracic and sacral curvatures (primary): convex posteriorly
o Cervical and lumbar curvatures (secondary): concave posteriorly
- Allowed bipedalism by having a spring like effect for carrying our weight
56
Curvatures
- Baby is born with a C shaped spine
- Curvatures are allowed by the wedging of the vertebra
- Lower vertebrae are larger to support more weight
- Primary curvatures (thoracic and sacral) are present at birth
- Secondary curvatures (cervical and lumbar) develop when baby begins to lift the head and walk
- Humans have 5 lumbar vertebrae while chimps have 4
57
intervertebral Disc Herniation
- Half of expecting women develop lower back pain at some point during pregnancy
- An increased curvature of lumbar vertebrae can help restore the center of gravity but can also contribute to back pain and increases risk for herniated discs
- Pathway 5 of evolutionary constraints
It is a prolapse of an intervertebral disc through a tear in the surrounding annulus fibrous
- A herniated disc can put pressure on and irritate the neighboring spinal nerves
- Each disc absorbs the stress and shock and prevents the vertebrae from grinding against one another
- The lumbar curvature is more accentuated during pregnancy
58
Obstetric Dilemma
- wide (for easy birth) vs. narrow (for walking) pelvis
- narrow = risky strategy because of gestation, birth , parental investment, avg birth takes 9 hours the first time and needs assistance
- Reconfiguration of the birth canal to be narrower because of bipedalism yet the brain was expanding
- Delayed closure of sutures and fontanelles in the skull
- Sutures are fibrous tissue that connects skull bones allowing:
o Skull bones to slide during birth to facilitate the passage through the birth canal
o Remain open for the first few years of life to allow brain growth
59
Evidence for Obstetric Dilemma
- Pubic symphysis is a cartilaginous joint that can stretch up to 9mm during birth
- During pregnancy hormones (relaxin) contribute to structural changes in the symphysis which allow it to lengthen during birth
- Assistance is universal cross culturally
60
Obstetric Dilemma Clinical application
- Craniosynostosis is a pathological condition in which the sutures of the cranium are prematurely ossified preventing a proper growth pattern of the skull
- The skull compensates by growing more in the direction parallel to the closed suture
- If the growth is sufficient for the growing brain the child is health but has deformed facial features
- If the growth is not sufficient for the growing brain it may cause intracranial pressure and pathological consequences (low IQ, blindness …)
61
menopause (general)
- Termination of menstruation
- Possibly unique to humans
- Most animals reduce reproduction
- Menopause has been observed in gorillas in captivity so its possibly a byproduct of longer lives and human lifespan is now longer than when humans evolved
- Lowers estrogen and progesterone = no ovulation
- Hunter gatherers = age 40-45, developed countries = age 50-55
- Longer lifespan so menopause so osteoporosis
62
menopause Hypothesis 1: Epiphenomenon
- Epiphenomenon: stems from another factor/phenomenon
- Some factors could be
1. Byproduct of increased lifespan
2. Trade off favoring efficient reproduction earlier on
o Byproduct of prenatal beginning of oogenesis because it leads to decline of oocytes & hormones and an increased risk for non-disjunction. earlier pregnancy's increase chance of coming to term
63
Menopause Hypothesis 2: Adaptive
- No selection after reproduction but inclusive fitness
- Not having more kids at an older age is advantageous so less competition between siblings and older women tend to have more complications with birth
- 2 main hypotheses are the mother hypothesis and the grandmother hypothesis
- More support for the adaptationist views over epiphenomenon
64
Mother Hypothesis
- From Williams 1957
- There is a fitness cost to offspring from competition between siblings
- Fitness cost of premature maternal death
- Fitness cost of pregnancy complications in older mothers
65
Grandmother Hypothesis
- Help daughter raise grandchildren
- Increase survival
- Accumulated knowledge/culture – mom teaches daughter how to raise offspring
66
Osteoporosis
- Symptoms
1. Loss of bone mass
2. Deterioration of bone architecture
3. Increased susceptibility to fracture and morbidity
4. Vertebral compression fractures lead to loss of height, stooped over posture (kyphosis) which affects balance, breathing, causes back pain
- Bone strength depends on bone density & quality (architecture, turnover, mineralization)
67
Steps of Bone remodeling
1. Bone formation: Osteoblasts (bone building cells) deposit collagen and minerals
2. Bone mineralization: osteocytes get smaller and become trapped in tissue
3. Resting phase: osteocytes (are mature osteoblasts and are the majority of cells in bones) stuck in matrix
4. Bone reabsorption: osteoclasts are bone removing cells that secrete HCl and determine bone reabsorption
68
estrogen and bone density
- Bones strongest in 30s
- Decrease in bone mass due to menopause in women but not in men
- More osteoporosis in Asian and Caucasian women
69
Continuous remodeling of bones
- Remodeling replaces about 5-10% of bone each year
- Every time you put more strain on bones more osteogenic cells activate
- The remodeling process is an adaptive mechanism that has allowed humans to adapt to mechanical stimulation so we can deposit more bone as needed
- Bone remodeling is an integral part of the calcium homeostasis system
70
Osteoporosis -- 4 Risk Factors
1. Physical activity: Weight bearing or impact type physical activity
2. Cigarette smoking
- Nicotine and cadmium are toxic to osteoblasts
- Smoking inhibits calcium uptake into intestine
3. Alcohol consumption
- Alcohol inhibits calcium absorption in the intestine
- Toxicity on osteoblasts
- Alcohol inhibits the function of growth hormone (which promotes bone density)
4. Menopause: Estrogen promotes bone mineral density
71
Menopause and osteoporosis
- Genetics account for up to 80% of the variance in peak bone mass
o Asians and Caucasians are at higher risk
- Menopause and osteoporosis
1. Estrogen causes the production of osteoprotegerin aka OPG (bone protecting molecule)
2. OPG inhibits osteoclast differentiation
o Binding of RANK and RANKL activates osteoclasts
3. Menopause causes a drop in estrogen production
4. OPG production drops
5. Increase bone resorption
6. Reduced bone density
72
metopic suture
- A study looked at the metopic suture of an australopithecine
- Metopic suture of chimps and bonobos fuses very shortly after birth
- Metopic sutures of both early and later hominins tend to fuse only after the eruption of the first molars at 2 years of age or later
- In chimpanzees it closes at birth
HBIO405 Exam #2
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