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Genetics. Chapter 29. Essential Must Know Terminology. Chromosome : structure of DNA seen in cell division Homologous chromosomes Autosomes : 22 homologs w/o effecting sex Sex chromosomes : 1 homolog determines sex Karyotype : display of homologs Gene : trait determining sequence of DNA

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genetics

Genetics

Chapter 29

essential must know terminology
Essential Must Know Terminology
  • Chromosome: structure of DNA seen in cell division
    • Homologous chromosomes
      • Autosomes: 22 homologs w/o effecting sex
      • Sex chromosomes: 1 homolog determines sex
    • Karyotype: display of homologs
  • Gene: trait determining sequence of DNA
    • Alleles: different or alternate versions
      • Dominant: masks presence of other alleles (A)
      • Recessive: easily masked by other alleles (a)
    • Genotype: allelic combination
      • Homozygous dominant: two dominant alleles (AA)
      • Heterozygous: one dominant and one recessive allele (Aa)
      • Homozygous recessive: two recessive alleles (aa)
    • Phenotype: allelic combination physically seen/shown
sources of genetic variation
Sources of Genetic Variation
  • Segregation
    • Random alignment in metaphase for separation in anaphase
  • Independent assortment
    • Homologs segregate independently of other homologs
  • Crossing over
    • Synapse of tetrad and exchange at chiasma (when?  review)
  • Random fertilization
    • No control over which sperm or egg
solving genetic problems
Solving Genetic Problems
  • Punnett Squares helpful to ‘predict’ probability
    • Each event independent
    • Larger # of offspring = better prediction
    • Key points:
      • All individuals have 2 alleles for EVERY gene
        • 1 from mom and 1 from dad
      • Meiosis produces haploid gametes from diploid cells
        • Aamother = A or a eggs
  • Practicing
    • Place gametes (haploid) of one parent along top, other along the left side
    • Combine all possible female gametes with all possible male gametes = fertilization
    • Boxes with 2 alleles = possible offspring (diploids)
patterns of inheritance
Patterns of Inheritance
  • Dominant-recessive
    • Presence of dominant allele always masks recessive
    • Tongue rolling, freckles, widow’s peak, unattached earlobes
    • Disorders discussed later
  • Incomplete dominance
    • No alleles masked in heterozygote = intermediate phenotype
    • Flower color
    • Sickle cell
      • ssvsSsvs SS
patterns of inheritance cont
Patterns of Inheritance (cont.)
  • Multiple alleles/ Codominance
    • Traits w/ 2+ alleles
    • Varying relationships
    • Blood type
  • Sex-linked
    • Genes on sex chromosomes
    • X-linked when on X only (most)
      • Males only need 1 = hemizyogus
      • Females need 2; 1 = carrier
    • Colorblindness and hemophilia (discussed later)
patterns of inheritance cont1
Patterns of Inheritance (cont.)
  • Polygenic
    • 2+ genes in multiple locations working together
    • Broad spectrum of phenotypes
    • Skin color (3 genes), height, intelligence
      • AABBCC = darkest, aabbcc = lightest, others = in between
  • Environmental relationships
    • Maternal drug use/environment during embryonic development
    • Nutrition and diet
    • Hormonal alterations
abnormal chromosome number disorders
Abnormal Chromosome Number Disorders
  • Normally due to nondisjunction
  • Turner syndrome: female w/ 45 chromosomes (X0)
    • Underdeveloped reproductive organs = sterile, short, broad neck, lack 2° sex characteristics
  • Klinefelter syndrome: male w/ 47 chromosomes (XXY)
    • Underdeveloped reproductive organs = sterile, lack facial hair, some breast enlargement, long appendages
  • Down syndrome: 47 chromosomes (trisomy 21)
    • Slanted eyes, flattened face, short stature, gradient of mental retardartion
autosomal disorders
Autosomal Disorders
  • Dominant
    • Rare because always expressed  embryo/fetal death
    • Huntington’s disease: impairs motor functioning
      • Onset after reproductive age, increase probability of passing
  • Recessive
    • More frequent, because of masking
    • Albinism: lack of pigmentation
    • Cystic fibrosis: thick mucus build up in lungs and GI tract
sex linked disorders
Sex-linked Disorders
  • Need to represent sex chromosome and version
    • XN = trait not present, Xn = trait present
  • Red-green colorblindness
  • Hemophilia
    • Allele for clotting factor VIII mutated
genetic screening
Genetic Screening
  • Pedigrees trace traits through generations
    • Family tree using phenotypic information
  • Fetal testing w/ known risk
    • Amniocentesis
      • Most common; after 14th week
      • Check for genetic markers, enzymes, or karyotypes
    • Chorionic villus sampling
      • 8th week possible, 10th recommended
      • Similar to above