Development and Inheritance

(Chapter 29)

Lecture Materials

for

Amy Warenda Czura, Ph.D.

Suffolk County Community College

Eastern Campus

Primary Sources for figures and content:

Marieb, E. N. Human Anatomy & Physiology 6th ed. San Francisco: Pearson Benjamin

Cummings, 2004.

Martini, F. H. Fundamentals of Anatomy & Physiology 6th ed. San Francisco: Pearson

Benjamin Cummings, 2004.

Development and Inheritance

Fertilization (on handout)

Prenatal Development (on handout)

Gestational trophoblastic neoplasia =

trophoblast cells grow as a tumor,

normal placenta and embryo do not form

2. Embryonic development (week 1-8)

(on handout)

A. Gastrulation (week 2-3)

(on handout)

Amy Warenda Czura, Ph.D. 1 SCCC BIO132 Chapter 29 Lecture Notes

B. Placentation (week 2-12)

(on handout)

Placenta as endocrine organ:

(fetal tissue secretes hormones)

1. Human Chorionic Gonadotropin (hCG):

maintains corpus luteum !

progesterone ! maintain uterine lining

2. Human Placental Lactogen (hPL):

3. Placental Prolactin:

-both prepare mammary glands for milk

production

4. Relaxin: - " flexibility of pubic symphysis

- dilates cervix

- suppresses release of oxytocin to

delay labor

5. Progesterone: prevents mensus

6. Estrogen: levels increase 3rd trimester,

stimulates labor and delivery

C. Organogenesis

(on handout)

Summary of Gestation

1. First Trimester (month 0-3)

-zygote formation -- embryogenesis

-rudiments of all organ systems and

structures are formed

2. Second Trimester (month 4-6)

-rapid growth and development

-amnion and chorion fuse =

amniochorionic membrane (“amniotic

sac”)

-most organ systems complete

development

3. Third Trimester (month 7-9)

-period of weight gain

-adipose tissue forms

-organ systems become fully functional

Amy Warenda Czura, Ph.D. 2 SCCC BIO132 Chapter 29 Lecture Notes

Pregnancy and Maternal Systems

1. Physical changes

-reproductive organs more vascularized

-uterus expands

-abdominal organs push diaphragm into

thoracic cavity

-shift in center of gravity ! lordosis

-mammary glands increase, produce milk

2. Functional changes

-GI system: -nausea

-heartburn

-constipation

-Urinary system:

-"GFR (by 50%)

- incontinence

-Respiratory system:

- "respiratory rate and tidal volume

- #residual volume

-Cardiovascular system:

- "blood volume (25-40%)

- " BP

- " CO (20-40%)

-Metabolism:

-nutrient requirements increase 10-30%

-hunger

Parturition

-280 days from last menstruation

-through pregnancy progesterone inhibits

smooth muscle

-last few weeks, estrogen increases causing:

1. oxytocin receptors in myometrium

2. antagonistic effect on progesterone

-weak irregular contractions occur

(Braxton-Hicks contractions / false labor)

-near birth, fetal pituitary releases oxytocin !

triggers prostaglandin release by

placenta, both cause powerful uterine

contractions

-contractions trigger maternal release of

oxytocin (positive feedback loop) !

labor

Stages of labor

1. Dilation stage (labor onset to cervix dilated)

-uterine contractions 10-30min intervals, last

10-30sec, force fetus toward vagina

-cervix softens, thins, dilates (10cm =full)

2. Expulsion stage (full dilation to delivery)

-contractions 1-3 min intervals, last up to 1min

-continues until fetus is delivered (20-50min)

3. Placental stage

-30min post birth: contractions + compression

of uterine blood vessels causes placenta

to detach from endometrium

-afterbirth (placenta + fetal membranes) exits

-amniochorionic membrane ruptures

-contractions increase

Amy Warenda Czura, Ph.D. 3 SCCC BIO132 Chapter 29 Lecture Notes

Complications to fetus

1. Teratogens: cause congenital abnormailities

-most damaging first 8 weeks

2. Spontaneous abortion: termination of

pregnancy due to chromosomal defects

or inadequate hormone levels

3. Premature labor: labor and delivery before

fetus fully developed

-before week 28: survival poor, respiratory,

cardiovascular and urinary systems not

complete

-survival rates increase

with birth weight

4. Difficult deliveries

A. face up: slow, requires

assistance (vacuum, forceps)

B. dystocia: small pelvis, slows/stops birth,

can cause brain damage: CP or epilepsy

may require Cesarean section

C. breech: buttocks first, head trapped in

cervix (same problems as above)

Multiple Births (natural)

-twins 1:89

-triplets 1:8000

-quadruplets 1:705,000

-most due to multiple oocytes ovulated

Twins

1. Dizygotic twins (fraternal)

-72% of all twins

-two fertilized ovum: children as different as

any siblings

2. Monozygotic twins (identical)

-division of single zygote

-8% divide immediately post fertilization:

each has own chorion and amnion

-65-75% divide 4-8 days post fertilization:

share chorion but have own amnion,

may or may not share placenta

-1% divide after day 8: share amnion, chorion,

and single placenta (risk one fetus

dominates nutrients)

-after day 12 = conjoined twins

Lactation

-3rd trimester: "estrogen + lactogen ! "PRH

! "prolactin = secretion by mammary

glands

-initially ! colostrum = high protein, low fat,

IgA rich

-1 week post delivery ! milk = lipids, sugars,

ions, vitamins, complement, lysozyme:

750C/L (infant consumes ~850ml/day,

640C)

-after delivery prolactin #, milk production

depends on mechanical stimulation:

suckling ! "PRH ! "prolactin !

"milk production for next feeding

-suckling also triggers milk letdown reflex: !

"oxytocin ! contraction of

myoepithelial cells for milk ejection

Post-Natal Development

1. Neonatal Period (first 4 weeks)

- lungs take over gas exchange, high

respiratory rate (45 breaths/min)

- ductus arteriosus and foramen ovale close,

high heart rate (120 beats/min)

- digestive system begins function, meconium

cleared

- kidneys begin to filter waste, dilute urine:

inability to concentrate

- body temp fluctuates: hypothalamus learns

thermoregulation

- metabolic rate 2X adult (per weight)

2. Infancy (1 month - 2 years)

- rapid growth and change in body proportions

- organs and features become more adult like

3. Childhood (2 years - adolescence)

- growth continues driven by GH and thyroid

hormones

Amy Warenda Czura, Ph.D. 4 SCCC BIO132 Chapter 29 Lecture Notes

4. Adolescence (puberty - maturity)

- period of sexual and physical maturation

driven by sex hormones

5. Senescence (maturity - death)

-aging: changes reduce functional abilities of

cells and systems ultimately affecting

homeostasis

Human Genetics

Gene = functional unit of DNA: encodes

product (protein)

-all somatic cells contain same 46

chromosomes as original zygote

-differentiated cells only express certain genes

and turn off others

Genotype = all genes in a cell or person

Phenotype = anatomical or physiological

characteristics due to the genotype

Patterns of Inheritance

-somatic cells ! 23 pairs homologus

chromosomes (egg + sperm):

1 pair = sex chromosomes

XX = female XY = male

22 pair = autosomal: somatic characters

-genes on same locus (place) of homologus

chromosomes called alleles (version of

the gene)

-alleles can code for the same or alternate

versions of same gene

Autosomal Chromosome Alleles

- Homozygous = same allele on both

chromosomes: genotype and phenotype

match

- Heterozygous = two different alleles of the

gene: phenotype depends on the

relationship between alleles:

1. Dominant – one allele determines

phenotype regardless of other

2. Recessive – requires homozygous

alleles to cause phenotype

3. Incomplete dominance – intermediate

phenotype

4. Codominace – expression of two or

more alleles over another

Simple Inheritance

-phenotype determined by interaction between

single set of alleles

-use Punnett square to calculate probability of

offspring (graph for mixing alleles)

-dominant = capital letter

-recessive = lowercase letter

e.g. Cystic fibrosis: recessive disorder

Mom = sick ! homozygous recessive (ff)

Dad = appears normal (FF or Ff)

f f

F

F

Ff

Ff

Ff

Ff

f f

F

f

Ff

ff

Ff

ff

If Dad heterozygote, 50%

chance of sick kids,

50%carriers

If Dad homozygous

dominant, 0% chance sick

kids, 100% are carriers

e.g. Blood types

Mom = heterozygous type A (IAi)

Dad = heterozygous type B (IBi)

IA i

IB

i

IAIB

IAi

IBi

ii

25% chance type AB (IAIB)

25% chance type A (IAi)

25% chance type B (IBi)

25% chance type O (ii)

Amy Warenda Czura, Ph.D. 5 SCCC BIO132 Chapter 29 Lecture Notes

Sex Linked Inheritance

-phenotype determined by somatic genes

located on sex chromosome: X-linked

-X-linked disorders more common in males

since they have only one X

-female requires two copies of recessive gene

to have disorder (dad must have it)

e.g. color blindness

Mom = carrier of color blindness (X Xc)

Dad = normal (XY)

Polygenic Inheritance

-phenotype determined by interaction of

several genes, hard to predict

1. suppression: one gene suppresses other so

it does not contribute to phenotype

XcX

X

Y

XcXXX

XY XcY

50% chance of color

blind sons

all daughters normal

vision but 50% are

carriers

2. complementary gene action: two dominant

alleles from different genes interact to

produce different phenotype than either

alone

Nature vs. Nurture

-genotype ! phenotype: other genes and

environment alter outcome

-penetrance = % individuals in population

with genotype that show phenotype

-expressivity = extent of expression of any

allele (often only one allele is expressed

or one is expressed more than the other)

-genomic imprinting = different phenotype

effects depending on if egg or sperm

allele is expressed

Individual Variation

1. Genetic Recombination

-meiosis: synapsis + cross over swap genes on

homologus chromosomes (random)

-each person can make ~8.5 million different

gametes

Defects in gamete formation:

A. translocation defect: cross over between

different chromosomes, genes are lost

B. extra/missing chromosomes: unequal

separation during meiosis

1. trisomy: one gamete has two copies

of a chromosome so zygote ends

up with three

2. monosomy: one gamete missing a

chromosome so zygote has only

one copy

-most chromosomal abnormalities are fatal

2. Mutation

-spontaneous mutation = error rate of DNA

replication (1: 109bases)

-nonfatal mutations create variability: different

alleles

-dominant bad mutations: 50% zygotes fail at

cleavage, 10% don’t reach month 5

-recessive bad mutations: silent until

combined with another recessive

Amy Warenda Czura, Ph.D. 6 SCCC BIO132 Chapter 29 Lecture Notes

Genetic Screening and Counseling

-counseling = risk analysis for parents who

know genetic disorder is in their family:

tests determine parent genotypes to

predict offspring

-fetal testing:

1. Amniocentesis: cells collected from

amniotic fluid, analyzed for genetic

disorders, only after week 14

2. Chorionic villi sampling: cells collected

from chorion, as early as week 8

3. In vitro fertilization:

-one cell extracted at the eight cell stage

morula for genetic screening

-healthy seven-cell embryos can be chosen

based on genetic profile and implanted,

will develop normally

Amy Warenda Czura, Ph.D. 7 SCCC BIO132 Chapter 29 Lecture Notes