1 / 19

Genetics Congenital & Genetic Disorders

Genetics Congenital & Genetic Disorders. Pathophysiology. Review of Human Genetics. Genes, diploid, alleles, traits Genes = segment of DNA responsible for a particular trait Gene locus = where it’s located on the chromosome Human genome project

gerald
Download Presentation

Genetics Congenital & Genetic Disorders

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. GeneticsCongenital & Genetic Disorders Pathophysiology

  2. Review of Human Genetics • Genes, diploid, alleles, traits • Genes = segment of DNA responsible for a particular trait • Gene locus = where it’s located on the chromosome • Human genome project • Diploid = when one’s chromosomes are in matched pairs • One chromosome in the matched pair ---- from the father • One chromosome in the matched pair from the mother • These sister chromosomes called homologs • Alleles = genes that have the same locus (location) on sister chromosomes • Allele = each form of the same gene • Trait = what both alleles eventually code for • 2 genes(alleles) are responsible for most traits • One from the mother; one from the father • Mitosis & meiosis • Mitosis = process of cell replication where DNA is replicated (“mutations”) • For maintenance and growth of the organism • Chromosomes number stays constant • Meiosis = process of making sex cells (gametes) • For sexual reproduction • Chromosome number is reduced by half SEE NEXT SLIDE

  3. MEIOSIS= nuclear division mechanism with which the parental chromosome number is reduced by half • Thus, going from a diploid cell to a haploid cell • purpose = to make gametes ( sex cells) • Meiosis has 2 divisions (note that mitosis has only one division) 1. MEIOSIS I • phases = Prophase I, Metaphase I, Anaphase I, Telophase I • called “reduction division” • In prophase 1, when homologs synapse --- called “tetrad” since chromosomes are already in chromatid form • Key = Homologs separate 2. MEIOSIS II • phases = Prophase I, Metaphase II, Anaphase II, Telophase II • called “mitotic division” • Key = Chromatids separate

  4. Special Events in Meiosis I • CROSSING OVER • In Prophase I the homologs align up (i.e. synapsis) • Remember that each chromosome is in the chromatid form • non-sister chromatids exchange whole segments or individual genes where they touch (where they touch is called a chiasma) • When the homologs align, there are 4 chromatids that are close together • Key = during Prophase I , alleles are exchanged between homologs via “Crossing Over” • RANDOM ASSORTMENT • In Metaphase I the homologs align at the spindle equator • they align at random • Thus, the male homologs & female homologs are interchanged at random • Remember what genetic products are interchanged: • Crossing Over during Prophase I - - - - - - mixes GENES • Random Assortment during Metaphase I - - mixes CHROMOSOMES

  5. Reasons for Genetic Diversity • [1] random fertilization • Mature woman ovaries = 1 million ova • Mature man sperm = 10 million/ ejaculate • Possibilities = 10 million x 1 million = 10 trillion • [2] crossing over • Occurs in prophase I • Mixes genes • [3] independent assortment • Occurs in metaphase I • Possibilities = for diploid organisms put 2 to the power determined by the haploid number of chromosomes • 223 = 8. 3 million

  6. Vocabulary • Dominant allele = in large case; fully expressed • A dominant allele masks the expression of a recessive allele • Recessive allele = in small case; not expressed unless both alleles are recessive • True breeding(same as homozygous) • All offspring same as parent • The inheritance of identical alleles for a particular trait • Hybrid breeding(same as heterozygous) • The inheritance of non-identical alleles for a particular trait • Trait expression • Homozygous dominant = pair of identical dominant alleles • Homozygous recessive = pair of identical recessive alleles • Heterozygous = pair of non-identical alleles • Genotype = actual genes one has for a trait • Phenotype = the appearance one sees for that particular trait • If appearance is the dominant expression you are either homozygous dominant or heterozygous • If appearance is the recessive expression you can be only homozygous recessive

  7. Inheritance pattern in humans (3 types) [Of 23 pairs of chromosomes: 22 = autosomes, 1 = sex chromosomes] • (1) Autosomal recessive • Commonest type of human inheritance • Ones gets both recessive genes for a trait • The heterozygote is a carrier; thus can skip generations • Incomplete dominance =when carrier has “a little disease” (Ss) • Includes: • Albinism • Sickle-cell anemia • Cystic fibrosis • Tay-Sachs disease • Pnenylketonuria

  8. (2) Autosomal dominant • If have one or both dominant genes, the trait is expressed • There are no carriers • Can get codominance --- human ABO blood type • Includes: • Huntington’s chorea • Polycystic kidneys • Marfan’s syndrome • Polydactyly

  9. (3) X-linked recessive • Clues that hint you are dealing with X-linked recessive trait • Males show phenotype much more than females • A son cannot inherit the recessive allele from his father • A daughter can inherit the recessive allele from her father • If mother a carrier– there is a 50% chance that each son will inherit the allele • Includes: • Color blindness • Hemophilia • Muscular dystrophy

  10. Family pedigree for an X-linked recessive trait

  11. Congenital Diseases • Def: = those diseases present at birth • Note that not all genetic diseases present at birth • Congenital diseases include: • (1) Developmental diseases • Those that arise spontaneously during gestation • Exp = failure of testis to descend • Those that are secondary to environmental problems • From trauma • From poisons (teratogenic agents) • From poor nutrition of mother during gestation • (2) Genetic diseases • Single gene disorders --- nucleotide mutation • Chromosomal defects • Usually occurs during mitosis • Multifactoral disorders • Polygenic (exp = diabetes) • Genetic tendency + environment (exp = lung cancer)

  12. Genetic Diseases • Single gene disorders • Classified by inheritance pattern • Chromosomal diseases • 2 types • Structural change of the chromosome • Deletion = cause most serious problems and/or death • Translocation = broken part of chromosome becomes attached to non-homologous chromosome * Reciprocal or non-reciprocal (see next slide) • Change in chromosome number • Caused during meiosis by nondisjunction • Euploidy = normal number of chromosomes • Aneuploidy = abnormal number of chromosomes * Exp = turner’s syndrome = monosomy X Down’s synd. = Trisomy 21

  13. Multifactoral diseases • May be a combination of environmental factors & genetic tendency • Exp = lung cancer, “not so smart” people, colon cancer • These may be polygenic • Exp = deafness, diabetes • Genetic testing • Karyotype • Gross structure chromosomal map • Genome • Loci specific chromosomal map • Analyzing the genes nucleotides • Blood tests looking for biochemical defect • Amniotic fluid analysis --- looking for biochemical defect

  14. Down’s Syndrome • Called trisomy 21 • Seen more frequently as pregnant woman get older • Key = age 35 when risk increases dramatically • Physical signs • Small, flat head with low-set ears • Slanted eyes sometimes with epicanthal fold • Mouth hangs open with large protruding tongue • Simian crease • Short stature • Space between 1st & 2nd toe • Short little finger • congenital form of mental retardation associated with other findings which include: • congenital heart defects (commonest = ASD) • etiology = genetic defect ( commonest = trisomy 21) • More common in older pregnant women • incidence at age 35 = 1/650 • incidence at age 40 = 1/60 • diagnosis = karyotype

More Related