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Questions and Answers
What are the building blocks of DNA?
Genes
Which process occurs to form gametes?
Dizygotic twins come from a single zygote that split up.
False
How many chromosomes do gametes contain?
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What is the role of the placenta?
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Homozygous refers to having the same ______ for a gene.
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What type of diseases are X-Linked?
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What syndrome is mentioned as a chromosomal abnormality?
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What does the zygote develop into in Week 1?
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What structures begin to form in Week 2 to support the zygote?
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Neural tube, which develops into the _____ and _____, appears during Weeks 3-4.
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By Week 12, external genitalia are formed.
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What covers the fetal skin between Weeks 13-24?
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At what point is the baby considered to have a good chance of survival if born?
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The embryonic period is when serious defects are least likely to occur.
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What is the leading preventable cause of intellectual disabilities?
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Which of the following is NOT a symptom of Fetal Alcohol Syndrome (FAS)?
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Preeclampsia typically occurs in the _____ and _____ trimesters.
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Study Notes
Fertilization & Conception
- DNA is organized into genes, which are segments located along chromosomes.
- Chromosomes in body cells pair up, copying themselves and forming an X shape.
- Crossing over occurs during meiosis, exchanging segments between chromosomes to create new gene combinations.
- Meiosis results in gametes that contain half the DNA, totaling 23 chromosomes.
Fertilization Process
- Fertilization leads to the formation of a zygote with 23 pairs of chromosomes (46 total).
- Monozygotic twins originate from a single zygote that divides into two.
- Dizygotic twins arise from two separate eggs fertilized by two distinct sperm.
- The 23rd pair of chromosomes determines the sex of the offspring (XX for females, XY for males).
Conception & Implantation
- The zygote undergoes cell division to form a blastocyst, which implants into the uterine lining.
- The placenta develops to facilitate the exchange of nutrients and oxygen to the growing organism, while removing waste through the umbilical cord.
Genetic Interactions
- Alleles are variations of genes that influence individuals' genotypes and phenotypes.
- Homozygous refers to having the same allele for a gene, whereas heterozygous means having different alleles.
- Dominant alleles can mask the expression of recessive alleles; Bb genotype individuals may carry recessive traits without exhibiting them.
X-Linked Diseases
- X-linked diseases are linked to genes on the X chromosome and are often recessive.
- Females can be carriers of X-linked conditions without showing symptoms if they have a normal dominant allele.
- Males are more likely to express the disease because they have only one X chromosome, lacking a dominant allele for protection.
Chromosomal Abnormalities
- Down syndrome is an example of a chromosomal abnormality characterized by the presence of an extra chromosome 21.
Stages of Development
- Week 1: Zygote rapidly multiplies into a blastocyst.
- Week 2: Implantation of the blastocyst; formation of supporting structures like the amnion, chorion, placenta, and umbilical cord to nourish and protect the embryo.
- Weeks 3-4: Development of neural tube, which will become the primitive brain and spinal cord.
- Weeks 5-8: Formation of external body structures (face, arms, legs) and internal organs; production of neurons begins by Week 7, allowing the embryo to respond to touch and move.
- Weeks 9-12: Rapid size increase of the fetus; development of behavioral capacities; formation of external genitals enables sex detection by Week 12.
- Weeks 13-24: Layer of vernix (protective coating) covers the skin; lanugo (fine hair) develops; fetal movements are felt; fetus shows sensitivity to light and sound; brain cortical infolding and myelination begin.
- Weeks 22-26: Age of viability indicates increased chances of survival if born at this stage.
- Weeks 25-38: Significant cerebral cortex enlargement indicates rapid brain development; development of personality linked to fetal activity; maternal antibodies transferred for disease protection; fetus becomes more responsive to external stimuli; by Week 34, distinct sleep/wake patterns emerge.
Sensitive Periods
- Zygotic period: High risk of death.
- Embryonic period: Most serious defects occur due to foundational organ structure development.
- Fetal period: Likely resulting damage from teratogens is minor in comparison.
Teratogens
- Environmental agents such as diseases, pollutants, and substance abuse that can cause birth defects.
- Teratogenic effects depend on timing of exposure, dosage, number of agents, and genetic predispositions.
- Genetic variability may explain different responses to teratogens, seen in fraternal twins.
Use of Alcohol
- Fetal Alcohol Spectrum Disorder (FASD) is the leading preventable cause of intellectual disabilities.
- Fetal Alcohol Syndrome (FAS): Characterized by slow growth, three facial abnormalities, and brain injuries.
- Partial Fetal Alcohol Syndrome (pFAS): Requires only two of the three facial features of FAS. Alcohol-Related Neurodevelopmental Disorder (ARND) involves neurological impairment without physical symptoms.
Use of Tobacco
- Chemicals from tobacco impair fetal oxygen supply, affecting crucial organ development.
- Nicotine causes blood flow constriction; carbon monoxide is damaging to the central nervous system.
- Associated effects: low birth weight and higher risks of learning disabilities.
Prenatal Complications
- Preeclampsia: High blood pressure, weight gain, swelling; typically arises in the second and third trimesters.
- Increased complication risk after maternal age 40.
- Low birth weight significantly correlates with increased mortality and complications after birth; related to drug and tobacco use.
- Maternal emotional stress can redirect blood supply from the uterus, causing possible oxygen deprivation and fetal disorders.
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Description
This quiz covers the processes of fertilization and conception, focusing on DNA, genes, and chromosomes. It discusses the formation of gametes through meiosis and the significance of crossing over in genetic variation. Explore how zygotes are formed and the implications for monozygotic twins.
