Genetics REV - The Genetics of Child Development I. GENETIC...

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The Genetics of Child Development I. GENETIC FOUNDATIONS A. The Genetic Code l. Chromosomes : "colored bodies" carrying genetic material contained in the nucleus of all cells except red blood cells Humans have 23 pairs (n = 46) Chimpanzees have 24 pairs Horses have 32 pairs Mice have 20 pairs 2. Genes : multiple genes per chromosome; most genes lead to production of some protein. Genes composed of: 1
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3. DNA (deoxyribonucleic acid) : genes differ in length of the segments of DNA --Double helix structure (twisted ladder); uncoiled set of 23 chromosomes would be 3 feet long (in each cell) --Sides of ladder: alternating sugar and phosphate molecules in two threads wound around each other. --Ladder rungs consist of pairs of nucleotides (nitrogen-based molecules) attached to the sugar units of the sides: Adenine (A) paired with Thymine (T) Cytosine (C) with Guanine (G) --sequence of pairings determines the genetic instructions --chromosome 1 has 263 million bases; smallest (chrom. 21) has 50 million 2
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bases ( Human Genome project ) 3
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4. Karyotype : depicts homologous pairs (except for the XY pair in males)--in humans, 22 of the pairs are known as autosomes , and l pair are sex chromosomes . 5. Gametes : sex cells (egg, sperm) contain only 23 chromosomes each 6. Mitosis : process by which DNA duplicates itself --DNA ladder splits down the middle, leaving each exposed base free to pick up its complementary mate from the cell cytoplasm --sister chromatids attached at centromere then separate during cell division e.g., Zygote (fertilized egg) replicates in 4
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first 24 hours 5
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7. Meiosis : process by which gametes, or sex cells are formed --Cell with 46 chromosomes replicates itself (but doesn't split from sister chromosome) -- Crossing Over : pairs of chromosomes exhange corresponding segments to create new genetic combinations --Cell then divides, then divides again to leave 4 cells with 23 chromosomes each 8. Alleles : the different forms/versions of each gene (e.g., Brown-eye, blue-eye, green-eye, etc.) --occur at the same locus on the autosomes, one each from mother and father 6
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9. Genotype : one's genetic inheritance (e.g., BB or Bb or bb for eye color) homozygous : having same two alleles for a trait (e.g., BB or bb) heterozygous : having two different alleles for a trait (e.g., Bb) 10. Phenotype : one's expression of a trait (e.g., Brown eyes vs. blue eyes) 11. Monozygotic Twins share a genotype (mono- = one zygote); dizygotic (fraternal) twins do not 7
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II. GENETIC INHERITANCE A. Autosomes : 1. Dominant Traits : supercede expression of recessive traits 2. RecessiveTraits : Exhibited only when inherit two alleles (only one allele makes one a carrier) Dominant Recessive Brown eyes Gray, green, blue Curly hair Straight hair Brown hair blond or light hair Non-red hair (BR,bl) Red hair thick lips thin lips dimples no dimples farsightedness normal vision Rh-positive blood Rh-negative blood 8
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3. Co-dominance : With some traits, a combination of the alleles is phenotypically
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Genetics REV - The Genetics of Child Development I. GENETIC...

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