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Twins conceived by the union of two different ova or a single ovum that has split are called , or , twins; twins resulting from division of a single zygote after fertilization are called , or , twins. |
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are coils of DNA that carry , or small segments of DNA located in definite positions on their . |
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Normally at conception the fertilized zygote is made up of 23 chromosomes from the and 23 chromosomes from the , resulting in 22 pairs of and a 23rd pair that determines the child’s . |
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A is a person’s genetic makeup, containing both expressed and unexpressed characteristics; the , the person’s observable characteristics, is influenced by the person’s and . |
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In certain recessive disorders linked to genes on the sex chromosomes show up differently in male and female children. |
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The most common chromosomal abnormality results in , also called because its usually caused by an extra 21st chromosome or translocation of part of the 21st chromosome. |
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studies measure the degree to which biological relatives share certain traits; studies look at the similarities between adopted children and their adoptive and biological families; and studies compare pairs of monozygotic twins and same sex dizygotic twins. |
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Monozygotic twins have higher rates for certain traits than dizygotic twins, meaning they have a statistically greater tendency to show the same traits. |
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Even identical twins have their own unique, or , environment in which they grow up, resulting in influences that affect one child differently than another. |
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is a severe disorder of brain functioning characterized by lack of normal social interaction, impaired communication and imagination, and repetitive, obsessive behaviors. Children with a milder form of the disorder, ’s disorder, have higher intellectual functioning but still have difficulty understanding social and emotional cues. |
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According to the principle, development proceeds from the head to the lower part of the trunk; according to the principle, development proceeds from parts of the body near the center before moving to the extremities. |
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factors are those that are capable of causing birth defects. |
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Among the methods of assessing an unborn baby’s well being are , involving high frequency transvaginal probes and digital imaging processing; , sampling amniotic fluid to detect genetic or chromosomal disorders; of tissues from the ends of villi to test for defects; by inserting a needle into blood vessels of the umbilical cord; and to check for brain or spinal cord defects. |
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