animal genetics E1

83 flashcards · Biology · by Baher Nazar Gul

1. Genetics

   •study of Heredity •Study of biologically inherited traits •Provides explanation for similarity among organisms •Also provides explanation for diversity among organisms

2. Gregor Mendel

   1866

3. Many directions

   Mutant study Population genetics Evolutionary processes Genes and pathways

4. Disciplines of Genetics

   Classical Cytogenetics Molecular Population Quantitative

5. classical

   transmission of genes from generation to generation

6. Cytogenetics

   – Study of chromosomes

7. Molecular

   Molecular structure and function of genes

8. Population

   Study of heredity in groups of individuals

9. Quantitative

   Study of heredity of traits that could be measured

10. DNA

    •The genetic material of most living organisms •Exceptions – RNA viruses

11. genome

    The total DNA component of an organism

13. Chromosomes

    Threadlike structure within the nucleus of a cell •Contains DNA •Prokaryotes – usually single circular chromosome •Eukaryotes – number of linear chromosomes •Some extranuclearDNA found in Eukaryotes

14. Gene Expression

    • Process by which a gene produces its product and the product carries out its function • Proteins - the product of gene expression • Beadle and Tatum – genes provide instructions for making specific proteins • One gene – One enzyme hypothesis

15. Proteins

    • Long polypeptide chains • Composed of amino acids • Order of the amino acids dictate shape and functionality of the protein • Production of proteins require two steps – Transcription – Translation

17. Transcription

18. RNA

    • Ribonucleic Acid • Single Stranded • Uracil instead of Thymine

19. • Messenger RNA

    – Takes information from DNA to ribosome

20. • Ribosomal RNA

    – Major constituent of ribosomes

21. • Transfer RNA

    – Transfers appropriate amino acid

23. Genetic Code

    • 20 amino acids in proteins and only four bases in DNA • Each amino acid is specified by a three nucleotide sequence – codon

24. Genetic Variation

    • Any given gene can exist in several forms that differ from each other • These different forms of a gene are called alleles • At protein level allelic variation becomes protein variation

25. Sources of Genetic Variation

    • Mutation – Spontaneous or induced • Recombination – Meiosis – conjugation • Selection – Changes the frequency of a gene in a population • All three are necessary for the process of evolution

26. Haplosufficient

    When the normal function is obtained with only one copy of a normal gene present

27. Cellular Reproduction

    Reproduction is the basis of heredity Genes must be passed on to offspring

28. Eukaryotes

    True nucleus Animals plants, protozoa, yeast, algae

29. Prokaryotes

    No true nucleus bacteria

31. Eukaryotic Chromosomes

    •Multiple Linear Chromosomes •Usually in pairs – Diploid (2N) •Reproductive Cells – one set of chromosomes – haploid (N)

32. genome

    The complete complement of genetic information in a haploid chromosome set

34. Sex Chromosomes

    Animals and some plants have male and female cells with distinct chromosome sets One sex has a matched pair of chromosomes (e.g., XX in human females) The other sex has an unmatched pair (XY in human males)

35. Chromosomes Revisited

    Discovered in 1880s •Thread like substance found in the nucleus of almost all cells – contains DNA •Segregates in an orderly fashion in to daughter cells

36. Chromosomes Revisited

    •Chromosome number is fixed in a species Chromosome complement •Most eukaryotes are diploid Exceptions - yeast •Number varies among species

37. Types of Chromosomes

    Autosomes Found in homologous pairs in all somatic cells •Sex Chromosomes Paired in only one sex X and Y chromosomes

39. Multicellular organisms contain trillions of cells Develops from a single fertilized egg

40. Two different processes of cell division

    Mitosis –maintains the chromosome number Meiosis –halves the chromosome number

41. Cell Cycle

    Growth •Mitosis – nuclear division •Cytokinesis – cell division

43. Interphase

    • Individual chromosomes are diffused • DNA is replicated • Sister chromatids formed

44. Mitosis

    • Prophase – Organization of chromosomes • Metaphase – Chromosomes line up • Anaphase – Chromosomes divide • Telophase – Completion of mitosis

45. Prophase

    • Nucleolus disappear • Chromosomes condense • Spindle begin to form • Chromatid – one half of replicated chromosome

47. Metaphase

    •Kinetochore microtubules orient the chromosomes •Chromosomes lineup on metaphase plate

48. Anaphase

    •Centromeres of sister chromatids separate •Daughter chromosomes move towards the poles

49. Telophase

    •Reverse condensation of chromosomes •Nuclear envelope reforms •Spindle microtubules disappear

50. Cytokinesis

51. Meiosis

    •Only in diploid cells •Involves two divisions of the nucleus but only one duplication of chromosomes •First and second meiotic division Meiosis I Meiosis II •Diploid to haploid

52. Meiosis I

    •Chromosome number is reduced from diploid to haploid •Prophase I •Metaphase I •Anaphase I •Telophase I

53. Prophase I

    •Similar to that of mitosis except for crossing -over of homologous chromosomes •Reciprocal exchange of segments between homologous chromosomes •Four stages

54. Prophase I

    •Leptonema Chromosomes condense Cell gets committed to meiosis Homologous chromosomes pair •Zygonema Synapsis occur Tetrads form

55. Prophase I

    •Pachynema Chromosomes get more condensed and thick Crossing over takes place •Diplonema Synapsed chromosomes begin to separate Held together by chiasmata Stage where human oocytes remain most of their lives

56. Crossing-Over

58. Gene Segregation in Meiosis

    •Three significant results •Haploid cells are produced (1N) •Random alignment of maternally and paternally derived chromosomes 2n-1 possible combinations

59. Meiosis in Animals

    •Gametogenesis •Spermatogenesis Meiosis in males to produce spermatozoa Occurs continuously •Oogenesis In females to produce oocytes Arrested in meiosis I until ovulation

61. Sex Determination

    Sex is determined by number of different mechanisms •Sexual Reproduction Allows formation of offspring that are genetically distinct from their parents •Sex (gender) Sexual phenotype, typically two Male and female

62. Sex Chromosomes in Mammals

    Female – XX •Male – XY •Male determines the sex of the offspring All normal egg cells carry one X ½ normal sperm cells carry one X ½ normal sperm cells carry one Y •Male – heterogametic sex •Female – homogametic sex

63. •Exception to male heterogametic status

    Birds ZW sex determination Males – ZZ Females – ZW •Also in fish, reptiles, moths and butterflies •XX/XO system of sex determination Fruit flies, grasshoppers

64. Environment dependent sex determination

    Crocodiles, some reptiles and fish

65. Sequential hermaphroditism

    Slipper limpets Each animal could be both male and female but not at the same time Starts as male changes to female

66. Sex Determination

    Genotypic Sex determination Y chromosome mechanism of sex determination Humans and other mammals X chromosome autosome balance system Drosophila C.elegans Ratio between X and rest Y needed for male fertility

67. Sex Chromosomes

    •Controls the development switch that determines the sex of the organism •Many other autosomal genes involved in male and female development •X carries many genes with function unrelated to sexual differentiation •Y – few genes

68. Sex-linked Genes

    Many genes located on sex chromosomes •Mainly on X •Violation of the principle that genes come in pairs – one from each parent •X chromosome inactivation seen in female mammals

69. X – inactivation

    •Calico Cat •“Random” inactivation of coat color gene •Lyonization

70. Chromosome Theory of Inheritance

    •First proposed based on association •Thomas Hunt Morgan –1910 •Drosophila Sex linkage

72. Sex- linked traits in humans

    •X-linked – on the X chromosome More than 100 known traits Could be dominant or recessive •Y-linked – on the Y chromosome Holandric traits

73. Some X -linked traits

    Hemophilia A •Hemophilia B •Icthyosis •Color blindness •Duchene muscular dystrophy •Hunter syndrome •G-6-PD deficiency

74. X-linked Recessive Inheritance

    Females usually must be homozygous to exhibit the trait •Affected males transmit the trait to all the daughters but not to sons •Many more males than females exhibit the characteristic •All sons of affected mothers will have the trait sons of carrier mother should be ½ with trait and ½ without trait •Carrier females will have ½ normal daughters and ½ normal carrier daughters •Affected male and normal female unions will produce normal sons but all daughters will be carriers

75. X-linked Dominant Traits

    •Observed in both males and females •All daughters of affected males display the trait •No sons of affected males should exhibit the trait unless the mother is affected as well

76. Y linked Inheritance

    •Carried on Y with no counterpart in X •Every son of an affected male should exhibit the trait •No daughter should ever inherit the trait •Examples? Y-linked diseases •Azoosperma – complete inability to produce sperm (USP9Y) •Abnormal or absent testicular development (SRY) •Retinitis Pigmentosa –progressive loss of sight. Night blindness -loss of peripheral vision -blindness (RPY) •Cattle infertility due to translocation of Y fragments

77. Early evidence for the Y chromosome mechanism came from studies of chromosome non-disjunction •Abnormal sex chromosome complement

78. Turner Syndrome

    XO •45,X •1:1000 female births •99% embryos do not develop to term •Infertility, skeletal abnormalities, web -neck, •Learning difficulties (not retarded), spatial relationships •Evidence that two X chromosomes necessary for female development •Mice and horses (dogs)

79. Klinefelter Syndrome

    •XXY, XXXY, •47,XXY •1:500 male conceptions •Male, tall, sterile, poor growth of body and facial hair, gynecomastia, •Advanced maternal age?

80. Polysomy of sex chromosomes slightly better tolerated due to X chromosome inactivation

    XXX – (Trisomy X) Phenotypically normal, some times mild mental retardation •XYY – ( double Y) male, tend to be tall, fertile, slightly higher incidence of mental impairment, slightly higher among prison populations

81. X-Inactivation

    Need for gene dosage compensation between sexes •X Chromosome inactivation •Barr bodies – inactive X chromosomes

82. X-Inactivation

    •Occurs ~16th day after fertilization in humans •~500-1000 cells •All descendent cells carry on the inactivated pattern •All females are “mosaic” for X -inactivation

83. Determination of “Maleness”

    •Testis determining factor •Identified by studying “sex reversal” individuals •SRY gene