Questions and Answers
At what age might a child with Down syndrome walk?
About 2 years
What is the frequency of Klinefelter's syndrome?
1 in 500 male births
What physical characteristic is common in individuals with Turner's syndrome?
Short stature
What is the frequency of XXX syndrome?
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What is a common intellectual characteristic of individuals with XYY syndrome?
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What is a reproductive characteristic of individuals with Klinefelter's syndrome?
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What is one of the emotions that parents may experience when expecting a child?
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What is the inherited condition that affects people of African heritage?
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What is one of the functions of red blood cells?
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Why is it especially worrisome for parents to find out their child has sickle-cell disease?
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What is one of the reasons parents might be concerned about their baby's health?
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Why is it important to understand the genetic bases of child development?
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What is one of the reasons sickle-cell disease is painful?
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What is the purpose of learning about genetic disorders like sickle-cell disease?
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What is the characteristic of an individual with sickle-cell trait?
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What is endogamy, and what does it prefer?
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What is clinal variation, and where is it observed?
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What is the approximate frequency of sickle-cell disease in children of African heritage?
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What is the unique benefit of having the sickle-cell allele?
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What is the mode of transmission of malaria?
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What is the relationship between the sickle-cell trait and malaria?
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What is a common genetic disorder that affects individuals of African heritage?
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What is the abnormal shape of red blood cells in individuals with sickle-cell disease?
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What is the function of white blood cells in the body?
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What is the thread-like structure inside the nucleus of every cell that comprises DNA?
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What is the term for specific segments of DNA that have different functions?
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How many individual chromosomes are present in each egg or sperm cell?
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What is the process by which egg and sperm cells are produced with half the amount of genetic material?
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What would happen if an egg and sperm each had a full complement of genetic material (46 chromosomes)?
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Why is it important for each egg and sperm cell to contribute half the necessary genetic material for development?
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What is the primary effect of albinism on an individual's visual system?
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What is the characteristic of cystic fibrosis that leads to lung infections?
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What is the effect of phenylalanine accumulation in individuals with PKU?
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What is the genetic cause of Tay-Sachs disease?
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What is the typical consequence of having an extra, missing, or damaged chromosome?
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What is the chromosomal cause of Down syndrome?
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What is a characteristic of babies with Down syndrome during the first several months?
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What is a common developmental challenge experienced by individuals with Down syndrome?
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Study Notes
Genetic Disorders
- A child with Down syndrome may develop at a slower pace, sitting up without help at around 1 year, walking at 2, and talking at 3, which is behind children without Down syndrome.
Chromosomal Disorders
- Klinefelter's syndrome: XXY, occurs in 1 in 500 male births, characterized by tall stature, small testicles, sterility, and below-average intelligence.
- XYY syndrome: XYY, occurs in 1 in 1000 male births, characterized by tall stature, and below-average intelligence in some cases.
- Turner's syndrome: X, occurs in 1 in 2500-5000 female births, characterized by short stature, limited development of secondary sex characteristics, and problems with spatial relations.
- XXX syndrome: XXX, occurs in 1 in 500-1200 female births, characterized by normal stature, but delayed motor and language development.
Sickle-Cell Disease
- Sickle-cell disease is an inherited condition that affects many people, particularly those of African heritage, and can be life-threatening.
- Red blood cells in sickle-cell disease patients are long and curved, stiff, and misshapen, blocking oxygen flow and the body's natural defense against bacteria.
- Inherited through a combination of genes, sickle-cell disease is more common in people of African heritage due to the protective effect of the sickle-cell allele against malaria.
Heredity and Chromosomes
- Chromosomes are thread-like structures containing DNA, present in every cell's nucleus, and carry genetic material.
- Each chromosome contains many genes, which instruct cells on how to make proteins.
- Gametes (eggs or sperm) contain 23 individual chromosomes, and when they combine, they form 23 pairs of chromosomes, necessary for human development.
- Meiosis is the process by which egg and sperm cells are produced, containing half the genetic material, to ensure a full complement of 46 chromosomes in the resulting person.
Inherited Traits
- Sickle-cell trait: a characteristic of individuals with one dominant and one recessive allele, resulting in partial expression of sickle-cell anemia.
- Endogamy: a preference for mating with people from one's own social or cultural group.
- Clinal variation: continuous genetic variation observed between geographic regions.
Single Gene Traits
- Examples of dominant and recessive phenotypes include:
- Curly hair vs. straight hair
- Dark hair vs. blond hair
- Thick lips vs. thin lips
- Cheek dimples vs. no dimples
- Normal hearing vs. deafness
- Normal vision vs. near-sightedness
- Normal color vision vs. red-green color blindness
- Type A blood vs. Type O blood
Global Perspective
- Sickle-cell disease affects about 1 in 400 children of African heritage, but is rare in children of Western or Eastern European heritage.
- The sickle-cell allele provides protection against malaria, which is common in warm climates, including many parts of Africa.
Other Genetic Disorders
- Albinism: affects 1 in 10,000 to 1 in 20,000 births, characterized by skin lacking melanin, causing visual problems and sensitivity to light.
- Cystic fibrosis: affects 1 in 2500 births among European North Americans, characterized by excess mucus clogging digestive and respiratory tracts.
- Phenylketonuria (PKU): affects 1 in 10,000 births, characterized by the accumulation of phenylalanine, an amino acid, causing cognitive delay.
- Tay-Sachs disease: affects 1 in 3000 births among Jews of European descent, characterized by the degeneration of the nervous system, causing deafness, blindness, cognitive delay, and death.
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