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Chapter 2 ConceptionAnswer all parts of the questions in your OWN words. Please feel free to use your textbook and any other course materials to assist you in this assignment.Discuss the relationship between genotype and phenotype. Provide an example of each to support your analysis. Your friend Min Yan is currently pregnant and attempting to learn about common birth complications and/or whether or not homebirth is a good option for her. She is 25 years old, in good health, and expecting her first child. Help her by first describing two birth complications and then discuss why a home delivery may be a viable option in her case.Jen is 20 years old, pregnant, and eats well, but she is under a lot of prolonged, extreme stress. Her friend Angelina, who is also pregnant, is 42 years old and has a very poor diet, but is under little stress. What prediction could you make concerning the postbirth health of each of these women’s babies?Alisha is in for her weekly prenatal check-up. Her OB/GYN physician is going over some potential environmental threats to her baby. Describe any three the doctor might discuss with Alisha that govern how teratogens could affect her baby’s development. (Alisha lives in Miami and recently traveled to Brazil and the Carribean). Additionally, identify an additional disease, one drug, and another environmental hazard that is known to negatively impact prenatal development. Be sure to describe the specific impact of each teratogen.Describe the three basic stages of childbirth in terms of time, purpose, and symptoms.Down syndrome and Turner’s syndrome are two genetic disorders that involve abnormal chromosomes. Identify the exact chromosomal aberration and the impact of the aberration on development for each syndrome.Length of gestation (i.e., number of weeks in utero) and weight at birth are both related to birth risk. Demonstrate your awareness of key related concepts by discussing the concepts of prematurity, low birth weight, and extremely low birth weight.A new genetic disorder called “ HARID” disease is found to involve heterozygous alleles, is recessive, and is characterized by incomplete dominance. Discuss the implications of this description concerning the inheritance of this disorder.Describe why in vitro fertilization and eugenics represent controversial issues in human development.Beth is 12 weeks pregnant and concerned that her fetus may have a genetic disorder. Describe two techniques that a physician could use to determine whether Beth’s concerns are warranted. Also, discuss how fetal therapy could be used to deal with a disorder if one is identified.
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Chapter Two
Biological Foundations: Heredity, Prenatal
Development, and Birth
© 2019 Cengage. All rights reserved.
2.1 In the Beginning: Learning
Objectives
• What are chromosomes and genes? How do
they carry hereditary information from one
generation to the next?
• What are common problems involving
chromosomes, and what are their
consequences?
• How is children’s heredity influenced by the
environment in which they grow up?
© 2019 Cengage. All rights reserved.
Mechanisms of Heredity:
Chromosomes
• Mechanisms of heredity:
– Human eggs contain 23 chromosomes selected
from the mother’s 46
– Human sperm contain 23 chromosomes selected
from the father’s 46
– Think of it as mixing two hands of cards
(1 from mother and 1 from father), shuffling this mix,
and then dealing a hand of cards
– The dealt hand is your 23 pairs of chromosomes
© 2019 Cengage. All rights reserved.
Mechanisms of Heredity: Egg and
Sperm United
• The human egg and sperm unite, resulting in a
zygote that contains a complete set of 23 paired
chromosomes (46 in total)
• The 46 chromosomes contain around 25,000
genes
• Autosomes are the first 22 pairs of
chromosomes
• Sex chromosomes: 23rd pair determines the
child’s sex
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Mechanisms of Heredity: Sex
Chromosomes
• Sex chromosomes (23rd pair)
– Males: XY chromosomes
▪ X from mother and Y from father
– Females: XX chromosomes
▪ X from mother and X from father
© 2019 Cengage. All rights reserved.
Mechanisms of Heredity: DNA
• DNA: each chromosome consists of one DNA
molecule
– DNA is instructional code for cells to create amino
acids, proteins, and enzymes
– DNA instructional code is a double string of chemical
compounds
▪ A (adenine)
▪ T (thymine)
▪ G (guanine)
▪ C (cytosine)
© 2019 Cengage. All rights reserved.
The Organization of DNA
• DNA: order of A, C, T, and G and the number of
each creates the code
• Gene: a group of compounds that provides a
specific set of biochemical instructions
© 2019 Cengage. All rights reserved.
Mechanisms of Heredity:
Genotype and Phenotype
• Genotype: complete set of genes one has
inherited
• Phenotype: combination of genotype and
environmental influences resulting in the actual
expression of traits
– Physical
– Behavioral
– Psychological
© 2019 Cengage. All rights reserved.
Mechanisms of Heredity: Alleles
• The interaction of genes on each pair of
chromosomes produces traits
• Each chromosome of a pair contains one
parent’s gene contribution to a specific trait
• Alleles: different forms in which genes come
– Each allele carries instructions for a specific variation
on a trait
© 2019 Cengage. All rights reserved.
Mechanisms of Heredity:
Homozygous/Heterozygous Alleles
• Homozygous alleles: When alleles are the
same, both parents have contributed similar
genes for a trait
▪ Example: both parents contribute the allele instructions for
the same colored eyes
• Heterozygous alleles: The parents have
contributed different versions of the trait
▪ Example: one parent contributes the allele for blue eyes and
the other for brown eyes
© 2019 Cengage. All rights reserved.
Mechanisms of Heredity: Dominant
vs. Recessive Alleles (1 of 2)
• Certain alleles are dominant over other alleles
– The dominant allele’s instructions are followed, but
the recessive is ignored
• Other alleles are recessive
– Recessive instructions are followed only if both alleles
are recessive (one form of a homozygous condition)
© 2019 Cengage. All rights reserved.
Mechanisms of Heredity: Dominant
vs. Recessive Alleles (2 of 2)
• Incomplete dominance can lead to a
phenotype that falls in between the phenotype
associated with either the dominant or the
recessive allele
– Example: a mild form of the sickle-cell trait that
appears under vigorous physical exertion
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Single-Gene Inheritance
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Two Types of Genetic Disorders
• Inherited disorders: often involve two recessive
alleles
– Examples: sickle-cell disease, PKU
…but some involve a dominant allele
– Example: Huntington’s disease
• Abnormal chromosomes: extra, missing, or
damaged chromosomes that result in abnormal
development
– Examples: Down syndrome, Turner’s syndrome,
Klinefelter’s syndrome
© 2019 Cengage. All rights reserved.
Heredity, Environment, and
Development (1 of 2)
• Behavioral genetics
– Studies the inheritance of behavioral and
psychological traits
– Complex, because most traits are the result of many
genes (alleles pairs) instead of only one gene or
alleles pair
© 2019 Cengage. All rights reserved.
Heredity, Environment, and
Development (2 of 2)
• Polygenetic inheritance
– When many genes affect the phenotype of a physical,
psychological, or behavioral trait
• strongly expressed with more alleles that are dominant in the
combination and weakly expressed with more recessive
alleles in the combination
© 2019 Cengage. All rights reserved.
Behavioral Genetics: Mechanisms
and Methods (1 of 2)
• Dizygotic or fraternal twins: result from two
different eggs fertilized by two different sperm
– No more genetically similar than other siblings
• Monozygotic or identical twins: result from the
union of one egg and one sperm that splits in
two soon after conception
– Are genetically identical
• Either type of twin may share much of the same
experience and environment
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Behavioral Genetics: Mechanisms
and Methods (2 of 2)
• Scientists compare identical and fraternal twins
to measure the influence of heredity
• Adoption studies compare adopted children to
their biological parents (heredity) and adoptive
parents (environment)
• DNA sampling creates a profile to see if the
genotype is associated with behavior
phenotypes.
– Example: genes linked to disabilities in reading and
mathematics
© 2019 Cengage. All rights reserved.
Paths from Genes to Behavior
• Heredity and environment interact dynamically
throughout development
– Heritability coefficients
• Genes can influence the kind of environment to
which a person is exposed
– Niche picking
• Environmental influences typically make children
within a family different
– Nonshared environmental influences
© 2019 Cengage. All rights reserved.
2.2 From Conception to Birth:
Learning Objectives
• What happens to a fertilized egg in the first two
weeks after conception?
• When do body structures and internal organs
emerge in prenatal development?
• When do body systems begin to function well
enough to support life?
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Periods of Prenatal Development
• Prenatal development takes an average of 38
weeks
– Time measured from date of conception
▪ Usually occurs about two weeks after woman’s last
menstrual period
• Divided into three periods:
– Period of the zygote (weeks 1-2)
– Period of the embryo (weeks 3-8)
– Period of the fetus (weeks 9-38)
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Periods of Prenatal Development:
The Zygote
• Period of the zygote (weeks 1-2):
– After fertilization (natural or in vitro), the zygote travels
down the fallopian tube and is implanted in the uterine
wall
– Implantation triggers hormonal changes to prevent
menstruation
– Center of zygote contains the germ disc
▪ Cells that develop into a baby
– Other cells form the placenta, which supports the
baby’s development
© 2019 Cengage. All rights reserved.
Events of the Period of the Zygote
© 2019 Cengage. All rights reserved.
Periods of Prenatal Development:
The Embryo (1 of 3)
• Period of the embryo (weeks 3-8):
– Body structures, internal organs, and the three layers
of the embryo develop:
▪ Ectoderm (outer layer: becomes hair, skin, nervous system)
▪ Mesoderm (middle layer: becomes muscles, bones,
circulatory system)
▪ Endoderm (inner layer: becomes digestive system and lungs)
© 2019 Cengage. All rights reserved.
Periods of Prenatal Development:
The Embryo (2 of 3)
• Period of the embryo (weeks 3-8):
– The amniotic sac fills with fluid; the umbilical cord
connects the embryo to the placenta
– The umbilical cord’s blood vessels join the placenta to
the embryo
▪ Allow exchange of nutrients, oxygen, vitamins, and waste
products between mother and embryo
© 2019 Cengage. All rights reserved.
Periods of Prenatal Development:
The Embryo (3 of 3)
• Growth of the embryo follows two important
principles:
– the cephalocaudal principle, where the head
develops before the rest of the body
– the proximodistal principle, in which growth of parts
near the center of the body occurs before those that
are more distant.
© 2019 Cengage. All rights reserved.
Periods of Prenatal Development:
The Fetus (1 of 2)
• Period of the fetus (weeks 9-38):
– Begins at week 9 and ends at birth
• Fetus becomes much larger and bodily systems
begin to function
• Final development of many systems essential to
human life occurs
– All regions of the brain grow, particularly the cerebral
cortex
– Week 9: differentiation of the ovaries and testes
© 2019 Cengage. All rights reserved.
Periods of Prenatal Development:
The Fetus (2 of 2)
• Period of the fetus (weeks 9-38)
– Week 12: circulatory system begins to function
– Week 16: movements felt by mother
– Week 20: eyebrow, eyelashes, scalp hair
▪ Skin thickens and is covered by protective greasy substance
(vernix)
– Weeks 22-28: age of viability
– Weeks 22 and beyond: senses active; fetus can
remember voices, music, tastes
© 2019 Cengage. All rights reserved.
2.3 Influences on Prenatal
Development: Learning Objectives
• How is prenatal development influenced by a
pregnant woman’s age, her nutrition, and the
stress she experiences while pregnant?
• How do diseases, drugs, and environmental
hazards sometimes affect prenatal
development?
• What general principles affect the ways that
prenatal development can be harmed?
• How can prenatal development be monitored?
Can abnormal prenatal development be
corrected?
© 2019 Cengage. All rights reserved.
General Risk Factors
• Nutrition
– A pregnant woman should increase both her caloric
and nutrient intake
• Stress
– Causes greater harm when experienced early in
pregnancy
• Mother’s age
– Prenatal development is most likely to proceed
normally when women are between 20 and 35 years
of age
© 2019 Cengage. All rights reserved.
Teratogens: Drugs, Diseases, and
Environmental Hazards (1 of 3)
• Teratogens: drugs, diseases, or environmental
hazards causing abnormal prenatal
development
• Drugs (Examples: alcohol, aspirin, caffeine, and
nicotine)
– Fetal alcohol spectrum disorder (FASD)
– Nicotine use increases likelihood of miscarriage, low
birth weight, birth defects
© 2019 Cengage. All rights reserved.
Teratogens: Drugs, Diseases, and
Environmental Hazards (2 of 3)
• Diseases (Examples: AIDS, cytomegalovirus,
genital herpes, rubella (German measles),
syphilis)
– Some (cytomegalovirus, rubella, syphilis) attack the
fetus directly through the placenta; others (AIDS,
genital herpes) attack the fetus during birth
– Medications that may help treat a woman after she
becomes ill do not prevent damage to the fetus
© 2019 Cengage. All rights reserved.
Teratogens: Drugs, Diseases, and
Environmental Hazards (3 of 3)
• Environmental Hazards (Examples: air
pollution, lead, PCBs, X rays)
• Exposing the fetus to environmental hazards
such as polluted air, lead, and PCBs can affect
both physical and mental development of the
fetus before birth and of the child after birth
• Can also lead to the child’s developing health
issues such as leukemia after birth
© 2019 Cengage. All rights reserved.
How Teratogens Influence Prenatal
Development
• The effect of the teratogen depends upon the
genotype of the organism
• The impact of teratogens changes over the
course of prenatal development
• Each teratogen affects a specific aspect of
prenatal development
• The impact of teratogens depends on the
dosage
• Damage from teratogens is not always evident
at birth
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Prenatal Diagnosis and Treatment
• Genetic counseling
– Helps to assess the chances of inherited disorders
• Prenatal diagnosis
– Ultrasound
– Amniocentesis
– Chorionic villus sampling
– Non-invasive prenatal testing (NIPT)
▪ samples genetic material that reflects the fetal genotype for
testing
© 2019 Cengage. All rights reserved.
Prenatal Diagnosis and Treatment:
Fetal Medicine
• Fetal therapy
– Administering medicine to the fetus
– Fetal surgery to correct spina bifida and circulatory
problems
– Genetic engineering involves replacing defective
genes with synthetic normal genes
▪ CRISPR: experimental technique that allows scientists to edit
hereditary material.
© 2019 Cengage. All rights reserved.
2.4 Labor and Delivery: Learning
Objectives
• What are the different phases of labor and
delivery?
• What are “natural” ways of coping with the pain
of childbirth? Is childbirth at home safe?
• What adjustments do parents face after a baby’s
birth?
• What are some complications that can occur
during birth?
• What contributes to infant mortality in developed
and less developed countries?
© 2019 Cengage. All rights reserved.
Stages of Labor
• Stage 1 (12-24 hours before birth):
– Contractions become increasingly stronger and more
rhythmic
– Cervix enlarges to ~10 centimeters
• Stage 2 (
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