Anatomy Exam 4- Development and Heredity

Development involves:

• fertilization

• embryonic development and circulation

• pregnancy effects on mother

• birth

Heredity contains:

• genes and variation

• patterns of inheritance

• environmental factors determining inheritance

• genetic screening and counseling

Fertilization:

• sperm cells struggle through female reproductive system to reach 20 oocyte

• only a few thousand (out of many millions) reach the oviduct

• only one may be lucky enough to reach 20 oocyte and penetrate:

Acrosomal reaction:

allows sperm to penetrate Zona Pellucida and membrane

• enzymes within acrosome of sperm dissolve zone pellucida

Prevention of Polyspermy (more than one sperm):

• oocyte membrane block

• cortical reaction

Oocyte Membrane Block:

extra sperm are unable to bind to membrane

Cortical Reaction:

further blocks sperm from binding

• also hardens the Zone Pellucida

Meiosis II finishes in the egg, forming an ovum:

• fertilization

• zygote

Fertilization occurs when:

sperm and ovum nuclei combining

Zygote:

diploid, single-celled embryo results

What is the acrosomal reaction?

The release of enzymes from sperm that digest pathways through the zona pellucida

Cleavage:

rapid mitotic divisions of embryo

• blastomeres

• morula

Blastomeres:

early daughter cells of cleavage mitotic divisions

Morula:

solid ball of embro cells, 16 cell stage at least

Blastocyst:

forms eventually, fluid filled capsule made of two basic parts

• inner cell mass or embryoblast

• trophoblast

Inner cell mass or embryoblast:

solid wad of inner cells

Trophoblast:

sphere of cells around embryoblast and fluid

Implantation:

Blastocyst embeds in endometrium

• embryo secretes Human Chorionic Gonadotropin (hCG)

• this preserves corpus luteum

• corpus luteum continues to produce progesterone and estrogen

• these hormones preserve the endometrium, preventing menstruation

Placenta:

forms partly embryonic and partly maternal

• chorionic villi

• decidua basali

Chorionic villi:

embryonic portion

Decidua basalis:

maternal portion

• decidua capsularis- contains embryo

Extramebryonic membranes:

form early to support/supply the embryo

• amnion

• yolk sac

• allantois

• chorion

Amnion:

filled with amniotic fluid to provide buoyancy, protection

• same function in shelled-egg producing amniotes

Yolk sac:

partially forms gut and initial RBC production (hematopoiesis)

• provides nutrition to embryo in shelled-egg producing amniotes

Allantois:

forms most umbilical cord

• acts as a waste sac in shelled-egg producing amniotes

Chorion:

forms embryonic portion of placenta

• acts as a gas exchange membrane in shelled-egg producing amniotes

Gastrulation:

folding and differentiation of tissues into primary germ layers

• endoderm

• ectoderm

• mesoderm

Endoderm:

forms inner linings of digestive tract, respiratory system

Ectoderm:

forms epidermis and nervous system via neurulation

Mesoderm:

forms everything else (muscle, bone, majority of most organs)

Fetal circulation:

• placenta

• ductus venosus

• foramen ovale

• ductus arteriosus

• umbilical arteries

• umbilical vein

Placenta:

exchange with mother

• O2, CO2, nutrients, wastes via umbilical arteries/vein

Ductus Venosus:

• connects umbilical vein to vena cava

• mostly bypasses liver

Foramen ovale:

connects atria

• distributes O2 to left and right sides

Ductus arteriosus:

• connects pulmonary trunk and aorta

• distributes O2 to left and right sides

Umbilical arteries:

blood to placenta

Umbilical vein:

blood to embryo

• to fetus from week 9 onward

What hormone prevents degeneration of the corpus luteum?

Human chorionic gonadotropin

Pregnancy effects on mother:

• uterus enlarges and presses on other abdominal organs

» urination becomes more frequent

» morning sickness, heartburn, and constipation may occur

• pelvis widens and becomes more flexible

• breasts enlarge and prepare to lactate

• tidal volume of respiratory system increases

• blood volume increases and CO an BP can vary

Labor:

three stages of childbirth occurring at around 9 months

1.) dilation stage

2.) expulsion stage

3.) placental stage

Dilation Stage:

cervix dilates as it relaxes and baby’s head pushes on it

Expulsion Stage:

storing uterine contractions expel baby (oxytocin helps)

Placental Stage:

the placenta (afterbirth) is expelled

Lactation- Colostrum:

(high in protein) produced initially

• proper lactation (producing milk) begins after 2 or 3 days

• production stimulated by prolactin, ejection by oxytocin

Gene expression can be controlled by:

other genes

Genetics:

study of the mechanism of heredity

Diploid number (46) of chromosomes in all cells except :

gametes

• 23 pairs of homologous chromosomes

• 1 pair of sex chromosomes that determine genetic sex (XX= female and XY= male)

• 22 pairs of autosomes that guide expression of most other traits

Karyotype:

diploid chromosomal complement displayed in homologous pairs

Genome:

genetic (DNA) makeup; two sets of genetic instructions (maternal and paternal)

Alleles:

genes that occur at same locus (location) on homologous chromosomes

• DNA sequence can be same or different

• homozygous: alleles are same for single trait, AA or aa

• heterozygous: alleles are different for single trait, Aa

Genotype:

genetic makeup of a person for a trait

• for double-jointed example, person can have three possible genotypes: JJ, Jj, jj

Phenotype:

physical expression of genotype

• for double-jointed example:

• person with genotypes JJ or Jj will have double- jointed thumbs (J is dominant)

• person with genotype jj will not have double-jointed thumbs

Independent assortment:

• alleles of two different traits on two different chromosomes are distributed independently

Example: Bb is on one chromosome, Jj on another

• whether you inherit a B or b is independent of if you get a J or j

Crossing over:

during prophase 1 of meiosis, homologous chromosomes exchange DNA making unique chromosomes

Random fertilization:

eggs by sperm

Dominant-Recessive:

one allele (dominant) masks (suppress) expression of its recessive partner

• dominant trait is expressed even if other allele codes for recessive trait

Example: JJ or Jj will result in double-jointed thumbs

• recessive traits is expressed only if both alleles are recessive

Incomplete dominance:

Heterozygous have intermediate phenotype combination both

Example: sickle-cell anemia

• SS= normal hemoglobin (Hb) made

• Ss= sickle-cell trait: both mutated and normal Hb are made; person can suffer sickle-cell crisis under in longer low oxygen conditions

• ss= sickle-cell anemia: makes only mutated Hb; person is more susceptible to sickle-cell crisis even with short O2 reduction

Multiple-allele:

genes that exhibit more than two allele forms

• ex: ABO blood typing with three alleles: Ia, Ib, and I

Sex-linked:

genes that are located on sex chromosome X or Y

• mostly X (has > 1400 genes, Y has = 200 genes), X-linked genes

X-linked trait: expresion more common in males

• recessive alleles are always expressed in males because only have 1 copy

ex: colorblindness, hemophilia

Maternal factos on gene expression:

alter normal gene expression during development

• drugs or pathogens

• EX: in 60s, meds for morning sickness (thalidomide) caused by embryos to develop finger-like appendages

After birth effects on gene expression:

• poor infant nutrition negatively impacts brain growth, body development, and height

» even if have “tall genes”, growth can be stunted

• hormonal deficits during childhood can affect growth and development

» ex: congenital hypothyroidism- dwarfism due to low TH secretion

Genetic screening:

used to detect genetic conditions before birth, helps parents determine if a trait will be passed on

Carrier recognition:

identify if parents is heterozygous (carrier) for a disorder

• pedigree- traces the trait through generation

• blood tests can detect some unexpressed recessive traits

Fetal testing:

sample amniotic fluid for a disease

Human gene therapy:

edit genes and deliver corrected genes