Genes and Medical Genetics Chapter 2
Genotype and Phenotype <ul><li>Genotype  = all the genes that an individual has </li></ul><ul><li>Phenotype  = physical ap...
Genotype (con’t) <ul><ul><li>Alleles can be dominant (capital letter) or recessive (lower case letter). </li></ul></ul><ul...
<ul><ul><li>Example – in humans unattached earlobe is dominant over attached earlobes </li></ul></ul><ul><li>Could use cap...
<ul><li>When the two alleles are both dominant it is called a  homozygous dominant   genotype </li></ul><ul><ul><li>The ph...
Forming gametes (gametogenesis) <ul><li>Recall: gametes have ½ normal # of chromosomes </li></ul><ul><li>Happens when chro...
<ul><li>Genotypes </li></ul><ul><li>WW or Ww  ww </li></ul><ul><li>EE or Ee  ee </li></ul><ul><li>SS or Ss  ss </li></ul><...
Genetic Crosses ( One-trait Crosses) <ul><li>If know genotype of parents, can predict chances of having a child with certa...
One-trait  Crosses (con’t) <ul><li>If both parents are heterozygous (Dad is Ee, and Mom is Ee), what are the chances that ...
<ul><li>What if one parent is Ee and the other is ee? </li></ul><ul><li>Each child will have a 50% chance of having unatta...
Genetic Crosses (Two -trait Crosses) <ul><li>What if want to look at two traits at the same time?  </li></ul><ul><ul><li>E...
<ul><li>Expected phenotypic ratio for a dyhibrid cross is always 9:3:3:1 </li></ul><ul><li>Can use this expected ratio to ...
Autosomal Dominant Disorders <ul><li>Genetic disorders are caused by mutations </li></ul><ul><li>Mutations  – permanent ch...
Autosomal Dominant Disorders <ul><li>Neurofibromatosis </li></ul><ul><ul><li>Most common genetic disorders (1 in 3,500 new...
Autosomal Dominant Disorders <ul><li>Huntington Disease </li></ul><ul><ul><li>Neurological (nervous system) disorder that ...
Autosomal Recessive Disorders <ul><li>Cystic Fibrosis (CF) </li></ul><ul><ul><li>Most common lethal genetic disease among ...
Fig. 02-08 Treatment for CF
Autosomal Recessive Disorders <ul><li>Phenylketonuria (PKU) </li></ul><ul><ul><li>Not so common as CF </li></ul></ul><ul><...
Autosomal Recessive Disorders <ul><li>Tay-Sachs Disease </li></ul><ul><ul><li>Usually occurs in Jewish people </li></ul></...
Autosomal Recessive Disorders <ul><li>Albinism </li></ul><ul><ul><li>Person unable to produce pigment  melanin    colors ...
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Genetics pp

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Genetics pp

  1. 1. Genes and Medical Genetics Chapter 2
  2. 2. Genotype and Phenotype <ul><li>Genotype = all the genes that an individual has </li></ul><ul><li>Phenotype = physical appearance of the individual </li></ul>Pictures of Jennifer Aniston
  3. 3. Genotype (con’t) <ul><ul><li>Alleles can be dominant (capital letter) or recessive (lower case letter). </li></ul></ul><ul><ul><li>Alternate forms of a gene having the same position (locus) on a pair of matching chromosomes that control the same trait are called alleles </li></ul></ul><ul><ul><li>An individual has two alleles for each trait because a chromosome pair carries alleles for the same traits </li></ul></ul><ul><ul><li>How many alleles for each trait will be in the gametes? </li></ul></ul>
  4. 4. <ul><ul><li>Example – in humans unattached earlobe is dominant over attached earlobes </li></ul></ul><ul><li>Could use capital E to show dominant allele and lower case e to show recessive (non-dominant) allele </li></ul><ul><li>Note: it is customary to designate alleles by the same letter, with uppercase to signify dominant and lowercase to signify recessive </li></ul>Fig. 02-01
  5. 5. <ul><li>When the two alleles are both dominant it is called a homozygous dominant genotype </li></ul><ul><ul><li>The phenotype will be unattached earlobes </li></ul></ul><ul><li>When the two alleles are both recessive it is called homozygous recessive </li></ul><ul><ul><li>The phenotype will be attached earlobes </li></ul></ul><ul><li>When the two alleles are different (one dominant, one recessive) it is called a heterozygous genotype </li></ul><ul><ul><li>The phenotype will be ________________. </li></ul></ul>Fig. 02-01
  6. 6. Forming gametes (gametogenesis) <ul><li>Recall: gametes have ½ normal # of chromosomes </li></ul><ul><li>Happens when chromosome pair separates during meiosis </li></ul><ul><li>Since alleles are on chromosomes, they also separate during meiosis, thus gametes only carry one allele for each trait. </li></ul><ul><ul><li>Ex. If individual was Ee, and produced four gametes, ½ would be E and ½ would be e. </li></ul></ul>(Chromosomes already doubled) Fig. 02-02 Gametogenesis
  7. 7. <ul><li>Genotypes </li></ul><ul><li>WW or Ww ww </li></ul><ul><li>EE or Ee ee </li></ul><ul><li>SS or Ss ss </li></ul><ul><li>FF or Ff ff </li></ul>Fig. 02-03 Common Inherited Character -istics in Humans Phenotypes
  8. 8. Genetic Crosses ( One-trait Crosses) <ul><li>If know genotype of parents, can predict chances of having a child with certain genotypes (and thus certain phenotypes). </li></ul><ul><ul><li>Ex. If one parent is homozygous dominant (EE) the chance of having a child with unattached earlobes is 100% because parent only has dominant allele (E) to pass on to baby. </li></ul></ul><ul><ul><li>But, if both parents are homozygous recessive (ee), the chance of having a child with attached earlobes is 100% because parents only have recessive allele (e) to pass on to baby. </li></ul></ul>
  9. 9. One-trait Crosses (con’t) <ul><li>If both parents are heterozygous (Dad is Ee, and Mom is Ee), what are the chances that baby will have unattached or attached earlobes? </li></ul><ul><li>Determine using a Punnett Square </li></ul><ul><li>Each child will have a 75% chance of dominant phenotype (unattached), and 25% chance of having recessive phenotype (attached). </li></ul>Fig. 02-04 Heterozygous-by- Heterozygous cross Punnett Square
  10. 10. <ul><li>What if one parent is Ee and the other is ee? </li></ul><ul><li>Each child will have a 50% chance of having unattached earlobes </li></ul>One-trait crosses (con’t) Fig. 02-05 Heterozygous By Homozygous cross Punnett Square
  11. 11. Genetic Crosses (Two -trait Crosses) <ul><li>What if want to look at two traits at the same time? </li></ul><ul><ul><li>Ex. Widow’s peak (W) and short fingers (S) (both dominant traits). </li></ul></ul><ul><li>If one parent is homozygous for widow’s peak and short fingers (WWSS) and other is homozygous for straight hairline and long fingers (wwss), what will </li></ul><ul><ul><li>Children look like? </li></ul></ul><ul><ul><li>Grandchildren look like? </li></ul></ul>
  12. 12. <ul><li>Expected phenotypic ratio for a dyhibrid cross is always 9:3:3:1 </li></ul><ul><li>Can use this expected ratio to predict chances of each child receiving a certain phenotype </li></ul><ul><ul><li>Ex. Chance of getting two dominant phenotypes together is 9 out of 16 </li></ul></ul><ul><ul><li>Chance of getting two recessive phenotypes is 1 out of 16 </li></ul></ul>Fig. 02-06 Dihybrid cross using Punnett Square
  13. 13. Autosomal Dominant Disorders <ul><li>Genetic disorders are caused by mutations </li></ul><ul><li>Mutations – permanent changes in genes (DNA) </li></ul><ul><li>If disorder is autosomal dominant  mutation is a single allele, and heterozygotes will exhibit the disorder </li></ul><ul><li>If know genotype of parents, can determine chances of children having the disorder (see Table 2.2, p. 26) </li></ul><ul><li>Can provide genetic counseling to parents who can make decision about best courses of action (Chapter 4). </li></ul>
  14. 14. Autosomal Dominant Disorders <ul><li>Neurofibromatosis </li></ul><ul><ul><li>Most common genetic disorders (1 in 3,500 newborns, all races and ethnicities) </li></ul></ul><ul><ul><li>Symptoms </li></ul></ul><ul><ul><ul><li>Large tan spots on skin that get darker with age </li></ul></ul></ul><ul><ul><ul><li>Small, benign (?) tumors (neurofibromas) often occur in nerves </li></ul></ul></ul><ul><ul><ul><li>If severe case </li></ul></ul></ul><ul><ul><ul><ul><li>Skeletal deformities (including a large head) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>May develop eye and ear tumors  become blind and deaf </li></ul></ul></ul></ul><ul><ul><ul><li>Children with non-severe symptoms may still have learning disabilities and be hyperactive </li></ul></ul></ul><ul><ul><li>Gene for neurofibromatosis has been located on chromosome 17 </li></ul></ul><ul><ul><li>Found that gene controls production of protein that usually blocks cell growth </li></ul></ul><ul><ul><li>If gene not working  certain cells grow out of control =_______________ . </li></ul></ul>
  15. 15. Autosomal Dominant Disorders <ul><li>Huntington Disease </li></ul><ul><ul><li>Neurological (nervous system) disorder that causes progressive degeneration of brain cells. </li></ul></ul><ul><ul><li>Symptoms </li></ul></ul><ul><ul><ul><li>Most patients appear normal until middle age (may already have children) </li></ul></ul></ul><ul><ul><ul><li>Severe muscle spasms </li></ul></ul></ul><ul><ul><ul><li>Personality disorders </li></ul></ul></ul><ul><ul><li>Treatment – none (patients die in 10 – 15 years after symptoms appear) </li></ul></ul><ul><ul><li>Gene (mutated) located on chromosome 4  causes abnormal protein that clumps inside neurons (nerve cells) </li></ul></ul><ul><ul><li>Test developed for presence but most people do not want to know </li></ul></ul><ul><ul><li>Two minute paper: “Would you want to be tested for a fatal genetic disease? </li></ul></ul><ul><ul><li>Why or why not?” </li></ul></ul>
  16. 16. Autosomal Recessive Disorders <ul><li>Cystic Fibrosis (CF) </li></ul><ul><ul><li>Most common lethal genetic disease among Caucasians in the US </li></ul></ul><ul><ul><li>1 in 20 are a carrier, 1 in 2,500 newborns has it </li></ul></ul><ul><ul><li>Caused by defect in plasma membrane (gene on chromosome 7) </li></ul></ul><ul><ul><li>Symptoms </li></ul></ul><ul><ul><ul><li>Thickened mucous in bronchial tubes (problems breathing) and pancreatic duct (problems digesting) </li></ul></ul></ul><ul><ul><li>Treatment – mucous in lungs manually loosened and other treatments have raised life expectancy to 35-40 years old </li></ul></ul>
  17. 17. Fig. 02-08 Treatment for CF
  18. 18. Autosomal Recessive Disorders <ul><li>Phenylketonuria (PKU) </li></ul><ul><ul><li>Not so common as CF </li></ul></ul><ul><ul><li>Affects nervous system development </li></ul></ul><ul><ul><ul><li>Caused by missing enzyme that normally allows metabolism of the amino acid phenylalanine </li></ul></ul></ul><ul><ul><ul><li>Causes abnormal breakdown product (phenylketone) in urine </li></ul></ul></ul><ul><ul><li>Symptoms – severe mental retardation, black urine </li></ul></ul><ul><ul><ul><li>PKU allele located on chromosome 12  prenatal DNA test can detect it (and elevated phenylalanine in blood) </li></ul></ul></ul><ul><ul><ul><li>If detect  place newborn on diet low in phenylalanine until at least age 7 </li></ul></ul></ul>
  19. 19. Autosomal Recessive Disorders <ul><li>Tay-Sachs Disease </li></ul><ul><ul><li>Usually occurs in Jewish people </li></ul></ul><ul><ul><li>Symptoms </li></ul></ul><ul><ul><ul><li>Development slows at age 4 to 8 months </li></ul></ul></ul><ul><ul><ul><li>Neurological and Psychomotor impairment </li></ul></ul></ul><ul><ul><ul><li>Child gradually becomes blind and helpless, seizures, paralyzed, death by age 3 – 4 years old </li></ul></ul></ul><ul><ul><li>Caused by gene on chromosome 15  caused buildup of nonfunctional lysosomes in neurons </li></ul></ul>
  20. 20. Autosomal Recessive Disorders <ul><li>Albinism </li></ul><ul><ul><li>Person unable to produce pigment melanin  colors skin, hair, eyes </li></ul></ul><ul><ul><li>Symptoms </li></ul></ul><ul><ul><ul><li>White hair, pink eyes, super-white skin </li></ul></ul></ul><ul><ul><ul><li>Vision problems </li></ul></ul></ul><ul><ul><li>Example of epistasis  one gene affects the expression of other genes </li></ul></ul><ul><ul><ul><li>In albino  any gene for coloring cannot be expressed because mutated gene prevents them from producing melanin </li></ul></ul></ul><ul><li>Picture of Johnny Winter </li></ul>

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