chapter 2 Flashcards
Three main periods of prenatal development
Three main periods of prenatal development
Germinal period
Embryonic period
Fetal period
conception occurs when
a sperm and ovum form a zygote, two cells become one
-no matter how conception occurs, the zygote, divides and multiples from shell, implants not automatic, sometimes never implants
Germinal period:
Germinal period: First 14 days
Zygote begins duplication and division within hours of conception.
–Development of the placenta
–Implantation (about 10 days after conception)
–Organism grows rapidly
Embryonic period:
Embryonic period: Third through eighth week
Embryo
–Primitive streak becomes the neural tube and later forms the brain and spine of the CNS.-day 14`
–Head takes shape.
–Eyes, ears, nose, and mouth form.
Heart begins to pulsate.
–Extremities develop and webbed fingers and toes separate.
-3rd week after conception-mass of inner cells takes shape=embryo
Fetal period:
Fetal period: Ninth week until birth
Fetus
–Genitals form and sex hormones cause differences in fetal brain organization.
–By three months, the fetus weighs about 3 ounces.
–Experiences the period of greatest brain growth during the fourth, fifth, and sixth months
end of embryonic period
23rd pair of chromosomes produce hormones that cause the reproductive organs to develop inside-affect development of brain and body
-baby can be born with “ambiguous genitals”
uncertain sex, Childs sex is not abundantly clear. need to look at 23rd pair of chromosomes
Age of viability
Age of viability-increases as baby stays in womb longer
-Age at which a preterm newborn may survive outside the mother’s uterus if medical care is available
-About 22 weeks after conception
-Brain is able to regulate basic body functions (e.g., breathing).
From Zygote to Newborn summary
The Germinal Period
An estimated 65 percent of all zygotes do not grow or implant properly and
thus do not survive the germinal period.
The Embryonic Period
About 20 percent of all embryos are aborted spontaneously. This is usually
called an early miscarriage, a term that implies something wrong with the
woman when in fact the most common reason for a spontaneous abortion
is a chromosomal abnormality.
The Fetal Period
About 5 percent of all fetuses are aborted spontaneously before viability at
22 weeks or are stillborn, defined as born dead after 22 weeks. This is much
more common in poor nations.
Birth
Because of all these factors, only about 27 percent of all zygotes grow and
survive to become living newborn babies.
Chromosomal and genetic problems
92 percent of people:
-About half of all zygotes:
99 percent of newborns:
Chromosomal and genetic problems
-92 percent of people: no serious inherited condition
-About half of all zygotes: more or fewer than 46 chromosomes; spontaneously abortion
-99 percent of newborns: have 46 chromosomes
Entire added chromosome
Chromosomal and genetic problems
Entire added chromosome (recognizable syndrome)
-Trisomy
–Patau syndrome/13th site: 1 in 10,000 newborns
–Edwards syndrome/18th site: 1 in 5,000
–Down syndrome/21st site: 1 in 700
–Alzheimer’s disease (AD) by middle age: 21st site and increase of amyloid plaque
Problems of the 23rd pair
Problems of the 23rd pair
–One in every 300 infants born with only one sex chromosome (no Y) or with three or more.
–Cognition, fertility, and sexual maturation are affected.
turners
only one sex chromosome is present
Gene disorders
Gene disorders
-Phenotype is only affected when inherited gene is dominant or when both parents carry recessive gene.
-Some dominant disorders begin in adulthood (fatal dominant childhood conditions cannot be passed on).
-Recessive disorders are more common.
—Early-onset Alzheimer’s disease
—One form of muscular dystrophy
—Marfan syndrome
—Huntington’s chorea
X-lined recessive conditions
-Hemophilia
-Duchenne muscular dystrophy
-Fragile-X syndrome-inherited intellectual disability
Common genetic disorders
Multiple genes
Common genetic disorders- they are common because carriers benefited from the gene, which makes the gene frequent in pop.
–Cystic fibrosis
–Thalassemia
–Sickle-cell disease
-protects against malaria
Multiple genes
–Most important human traits (for health, intelligence, emotions, and so on) are result of several genes, not a single one. (anxiety, depression)
–These genes came from ancestors who lived in many places.
