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PSYC 2290 A04 Lecture 3

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  1. PSYC 2290 A04 Lecture 3 • Read Chapter 3 in Berk, 5th edition • Biological Basis of Development • Genes, Phenotypes & Disorders • Prenatal Development • Film: Mystery of Birth • Enhanced Prenatal Learning • Film: Brave New Babies Lecture 3

  2. PSYC 2290 A04 Lecture 3 • Class Business • Read Berk Chapter 3 & web resources: • http://vig.pearsoned.ca/catalog/academic/product/0,1144,020542063X,00.html • >Companion Website>Welcome>Select Chapter at V along top > Go > Activities, etc • Notes: http://home.cc.umanitoba.ca/~mckeen/ • Instructions for Assignment 2 Lecture 3

  3. Biological Basis of Behaviour Genetic Foundations • Human development can be described as the process by which an individual's genotype comes to be expressed as the phenotype. Lecture 3

  4. Genetic Foundation • GENOTYPE: • Genetic constitution of an individual • Genetic material inherited from ancestors • No two people have the same genotype • Exception? Lecture 3

  5. Genetic Foundation PHENOTYPE: • Expression of genotype in observable characteristics of an individual • We observe the phenotype, not the genotype. • Some examples of phenotypes? Lecture 3

  6. Genetic Foundation GENES • are basic units of inheritance • indirectly influence behaviour • via proteins and physiological systems • are located on chromosomes at a specific location • called a locus • thousands of genes on each chromosome Lecture 3

  7. Genetic Foundation CHROMOSOMES • a necklace of genes • located in cell nucleus • Human cells contain 46 chromosomes. • Containing 30,000 – 50,000 genes • The complete set of genes • Comprise an individuals' genotype Lecture 3

  8. Chromosomes are in pairs • most chromosomes in body exist as pairs (exception - reproductive/gametes) • within each pair, a gene on one chromosome is matched by a gene at the same locus on the companion chromosome • genes at a single locus govern the same phenomena Lecture 3

  9. Homozygotes and Heterozygotes Alleles: • A gene is composed of a pair of alleles • So, child has 2 alleles for every gene • one from mother, and one from father • For that gene, if allele from each parent is same, • child is homozygousat that locus • If allele from each parent is different, • child is heterozygous Lecture 3

  10. Homozygotes and Heterozygotes EXAMPLE – • "A" represents one allele (curly hair) • "a" represents one allele (straight hair), • following combinations can occur: AA, aa, Aa, aA • homozygous: • AA (homozygous) will have ? hair (phenotype) • aa (homozygous) will have ? hair (phenotype) Lecture 3

  11. Homozygotes and Heterozygotes • What about the child with Aa or aA? • What happens when you have heterozygous alleles? • eg, if a child has alleles to have curly hair from both parents • is she homo- or hetero-zygousfor curly trait? • If she has curly allele from one parent and straight allele from other, • is she is homo- or hetero-zygous? • What is her phenotype? (straight or curly hair) Lecture 3

  12. Homozygotes and Heterozygotes • For a trait determined by a single gene-pair (the simplest case), • There are 3 ways a heterozygous combination of alleles can be expressed in a person's phenotype: Lecture 3

  13. Homozygotes and Heterozygotes • 1. Intermediate • phenotype has attributes in between the two individual alleles • eg, a very tall parent and a very short parent produce a child of average height. • for our hair example, curly-haired parent and straight-haired parent have a child with wavy hair. Lecture 3

  14. Homozygotes and Heterozygotes • 2.Combined • phenotype has attributes carried by both alleles. • in the hair example, • a child with a curly-haired parent and a straight-haired parent would have some curly hair & some straight hair. Lecture 3

  15. Homozygotes and Heterozygotes • 3. Dominant/recessive – • thephenotype has attributes associated with only one of the alleles. • ie, One allele will be dominant over the other • and more likely be expressed phenotypically • If "A" is a dominant gene, and "a" is a recessive gene, then phenotype Aa will be the same as the phenotype AA. Lecture 3

  16. Dominant / Recessive Inheritance • In the hair example, • we know curly hair (A) is dominant over straight hair (a); • so someone with genotype Aa will have ? hair • and will not differ phenotypically from someone with a AA genotype. • So, when there is dominance among alleles, a person will only show the recessive trait when they are homozygous (aa) Lecture 3

  17. Table of well known dominant and recessive characteristics Dominant TraitsRecessive Traits • Curly hair straight hair • Dark hair light hair • Rh+ blood type Rh- blood type • Normal vision near-sightedness • Far-sightedness normal vision • cheek dimples no dimples • normal blood clotting hemophilia • normal metabolism phenylketonuria (PKU) • normal blood cells sickle-cell anemia • Huntingdon's Chorea normal CNS • N respiration, digestion cystic fibrosis Lecture 3

  18. RECESSIVE DISORDER • Eg, PKU - phenylketonuria • disorder caused by a recessive gene • ~ 1/20 people carries the recessive allele for PKU (p) • enzyme missing - necessary to metabolize proteins found in milk • Child has 2 recessive genes for PKU (pp) • is unable to convert phenylalanine to tyrosine • > accumulation of phenylpyruvic acid in body. • damages child's developing nervous system • infant appears normal at birth, but with gradual build up • results in mental retardation Lecture 3

  19. Recessive gene transmission • If heterozygote (Np) carrier of recessive gene disorder has a child with one who carries two dominant normal alleles (NN): Lecture 3

  20. PKU: Normal parent, Carrier parent • If heterozygote (Np) carrier parent with recessive gene disorder has a child with parent who carries two dominant normal alleles (NN) • The children have a ____% chance of being a carrier. • Their children will be unaffected by PKU. Lecture 3

  21. PKU: Both parents carriers • If two recessive gene heterozygotes have children, they will have a ______% chance of producing a PKU (pp) child with the disorder. Lecture 3

  22. DOMINANT DISORDER Eg, Huntingdon’s Chorea • SINGLE-GENE DOMINANT DISORDER • death may be slow 15 - 20 years • Symptoms - in late stages - uncontrollable movements, staggering, falling, slurred speech • eventually - lose ability to talk, swallow, recall events, intelligence deteriorates • many sufferers are agonizingly aware of their deterioration Lecture 3

  23. Huntingdon’s Chorea • Usually such a lethal, dominant gene would disappear from the population gene pool. • affected person dies before having children. • but, with H, effects of gene don't show up until after the child bearing years • usually between ages of 30 and 50 • by this time people usually have children • & have passed dominant gene on to next generation Lecture 3

  24. Huntingdon’s • Children have a ___% chance of having the disease. • Note: unlike recessive gene diseases, being a carrier of dominant gene disorder means you alsohave the disease. Lecture 3

  25. Huntingdon’s Chorea • There is a test for this disease • a genetic marker can show who has gene • before getting disease • at John Hopkins Hospital - only 64 out of 349 at risks asked to have the testing done • want to find out they don't have it, afraid they do • Question: if you knew you were at risk for Huntingdon’s would you have the test to see if you had the gene done? Lecture 3

  26. Huntingdon’s Chorea Questions: • If you knew you were at risk for Huntingdon’s, would you have the test to see if you had the gene done? • Would you want your children to know? Lecture 3

  27. Raises ethical dilemmas • Career choices? Depression? Suicide? • Relationships in the family? Guilt, sadness • Who should know? • Insurance companies? employers? • may not insure/hire someone who is going to get the disease • Should you have a right to privacy? • Note: Most traits are determined by many genes not just one (polygenetic), • and most dominant genes aren't completely dominant Lecture 3

  28. SEX-LINKED CHARACTERISTICS • Some recessive genes are on X chromosome only. • show up more frequently as recessive characteristics in males. • Why? • Male has only one X chromosome, • if the recessive allele for a defect is present on the X chromosome, the male will show the trait • no equivalent allele on Y chromosome to counteract effect • Females have characteristic only when both X chromosomes have the recessive genes • ie if they are homozygous for recessive gene Lecture 3

  29. Affected father(XaY)Normal mother (XX) • Xa represents affected recessive allele • No evidence of trait in phenotype of offspring • Daughters are carriers. • Sons are normal. ♀ ♂ Lecture 3

  30. Normal father (XY)Carrier mother (XXa) • ? % daughters are carriers. • ? % sons affected. ♀ ♂ Lecture 3

  31. Affected father (XaY), Carrier mother (XXa) • Daughters: • __% affected • __% carriers • Sons: • __% affected • __% normal ♀ ♂ Lecture 3

  32. Normal father (XY), Affected mother (XaXa) • 100% daughters carriers • 100% sons affected • Colour blindness and hemophilia follow this pattern. ♀ ♂ Lecture 3

  33. Baby Xander Xander Dolski 8 weeks Lecture 3

  34. Prenatal Development • Text on fetal positions in utero – from middle ages Lecture 3

  35. Prenatal Development • 17.01 sperm Lecture 3

  36. Prenatal Development • 17.02 ovum Lecture 3

  37. Prenatal Development • Conception begins when sperm penetrates egg to form a zygote • Prenatal development takes 280 days or 40 weeks from 1st day of last menstrual period • 3 periods of development • 1st , 2nd, & 3rd trimester Lecture 3

  38. Prenatal Development • 20.01 Ovum in Fallopian tube • Egg cell enters fallopian tube at 9-16 days of menstrual cycle Lecture 3

  39. Prenatal Development • 20.02 sperm cells • stripping nutrients from around egg Lecture 3

  40. Prenatal Development • 20.03 sperm cell penetrating ovum in Fallopian tube • Fertilization usually takes place within 24 hrs after ovulation - in Fallopian tube Lecture 3

  41. Prenatal Development Period of the zygote • begins with fertilization and ends with implantation of the zygote on the wall of uterus • first two weeks of life Lecture 3

  42. Prenatal Development • 20.05 +20 hours • Fertilization has occurred • Male & female chromosomes line up to combine into 46-chromosome nucleus. Lecture 3

  43. Prenatal Development • 20.06 genotype formed • single cell zygote begins to divide by mitosis • first two cells divide between 24 and 36 hours after fertilization Lecture 3

  44. Prenatal Development • 20.07 8 cells • (we see 4) • many celled zygote called blastocyst • starts trekking down Fallopian tube to uterus Lecture 3

  45. Prenatal Development • 20.08 blastocyst about to exit Fallopian into uterus Lecture 3

  46. Prenatal Development • 20.09 blasto floating in utero Lecture 3

  47. Prenatal Development Blastocyst – has two layers, • Outer layer called trophoblast • will become the placenta, umbilical cord, and the amnion (in next phase) • Inner layer • cells become the developing organism • if all goes well, becomes firmly implanted on wall of uterus Lecture 3

  48. Prenatal Development • 20.10 blasto attaching to uterine wall • usually 10 to 14 days after fertilization Lecture 3

  49. Prenatal Development • 20.11 blasto has landed • Pregnancy begins • Usually 10-14 days after fertilization Lecture 3

  50. Prenatal Development • at implantation, • tendrils from zygote penetrate the blood vessels in the wall of the uterus to develop placenta • forms a physiologically dependent relationship with the mother • relationship will continue throughout the course of prenatal development Lecture 3