1 / 35

CHAPTER 5

CHAPTER 5. Genetics: A Review. Mendel’s Investigations. Gregor Johann Mendel (1822-1884) First person to formulate the principles of heredity Mendel chose to work with pure strains of garden peas Ex: dwarf and tall varieties

honorato-cantu
Download Presentation

CHAPTER 5

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. CHAPTER 5 Genetics: A Review

  2. Mendel’s Investigations • Gregor Johann Mendel (1822-1884) • First person to formulate the principles of heredity • Mendel chose to work with pure strains of garden peas • Ex: dwarf and tall varieties • The plants were self-fertilizing but subject to experimental cross-fertilization; all using Meiosis to produce sex cells.

  3. Chromosomal Basis of Inheritance • Meiosis: Reduction Division of Gametes • Sex cells (gametes) transmit genetic information from parents to offspring in sexually reproducing organisms • Chromosomes occur in pairs: homologs • One member is donated by the mother, the other by the father • Homologs • Contain similar genes encoding the same set of characteristics • Usually have the same size and shape • Example: Chromosome #6 from mom and #6 from dad

  4. Chromosomal Basis of Inheritance • Meiosis • Special type of nuclear division • Associated with gamete production • Genetic material replicates once followed by 2 successive nuclear divisions • Produces 4 daughter cells (gametes) • Each with only 1 member of each homologous chromosome pair or 1 set of chromosomes (haploid) (Ex. Only one #6 chromosome in each gamete)

  5. 5-5

  6. Chromosomal Basis of Inheritance • Fertilization • Reestablishes the diploid chromosome number ( Two #6 chromosomes) • Union of egg and sperm produces a zygote

  7. Chromosomal Basis of Inheritance • Meiosis I Prophase I • The two members of each pair of homologs make side-by-side contact • 4 homologous chromosomes lined up is called a tetrad • Homologs cross-over and exchange genetic information to increase variation in animals

  8. Crossing Over - during Meiosis 5-8

  9. Chromosomal Basis of Inheritance Metaphase I • Homologs line up side by side on the metaphase plate Anaphase I • Homologs are separated and moved to opposite poles of cell

  10. Chromosomal Basis of Inheritance Telophase I • Nuclear membrane forms around separated homologs • Each of these cells (now haploid) enter Meiosis II • No interphase between Meiosis I and Meiosis II.

  11. Chromosomal Basis of Inheritance • Meiosis II Prophase II • No crossing-over occurs Metaphase II • All chromosomes line up single file at metaphasic plate

  12. Chromosomal Basis of Inheritance Anaphase II • Centromeres of dyads are replicated and single-stranded chromosomes move toward each pole Telophase II • Nuclear membrane forms around separated chromosomes • Each daughter cell contains one complete haploid set of chromosomes

  13. Chromosomal Basis of Inheritance • Sex Determination in Humans • 46 chromosomes (23 pair) in somatic cells • Pairs 1-22: Autosomes (do not determine sex) • Pair 23: Sex Chromosomes (determine sex) • Two sex chromosomes: X, Y • Males: XY Females: XX Some animals Male is X0 and female is XX (there is no Y chromosome)

  14. Some animals, the absence of a 2nd sex chromosome leads to a male.

  15. In most animals, an XX or XY distribution determines sex.

  16. Mendelian Laws of Inheritance • Mendel’s First Law • The Law of Segregation: • In the formation of gametes (Meiosis), homologous chromosomes separate so that each gamete receives only one member of the pair.

  17. Mendelian Laws of Inheritance • Testcross - (Punnett Square Used) • A testcross is performed to determine the genotype • Crossing an individual of unknown genotype with a homozygous recessive individual

  18. Mendelian Laws of Inheritance • Intermediate Inheritance - (Incomplete Dominance) • Neither allele is completely dominant over the other • The heterozygous phenotype is distinct from those of the parents, often intermediate between them • Ex. Red and White flower = Pink flower • Codominance - Both dominant traits expressed (Ex - white/black spotted cow)

  19. Intermediate Inheritance or Incomplete Dominance

  20. Mendelian Laws of Inheritance • Mendel’s Second Law • Genes located on homologous chromosomes assort independently during meiosis • Pertains to studies of 2 pairs of hereditary factors at the same time • Ex. Pea plant - color and pod size combinations can occur (Yt, YT, yT, yt)

  21. Mendelian Laws of Inheritance • Multiple Alleles • Individuals can have no more than 2 alleles at a given locus (designated sight on chromosome) • Ex: • Freckles • Human ABO blood groups

  22. Mendelian Laws of Inheritance • Gene Interaction • Many different genes can affect a single phenotype: polygenic inheritance • Epistasis: Allele at one locus can mask or prevent the expression of an allele at another locus acting on the same trait • Quantitative inheritance: Characters show variation of 2 extremes (Ex. Skin pigmentation)

  23. Mendelian Laws of Inheritance • Sex-Linked Inheritance • Traits specified by genes located on sex chromosomes • X – Linked Traits • Most sex-linked traits are X-linked • Genes located on the X sex chromosome. • Ex: Red – Green Color Blindness Hemophilia

  24. Color Blindness

  25. Blue 1/2 arrow = Y No trait carried on Y Sex-linked Trait

  26. Mendelian Laws of Inheritance • Autosomal Linkage • Genes on the same chromosome • Said to be linked • Tend to be inherited together • However, linkage groups may be broken up during meiosis (crossing over) •  distance between the 2 loci,  probability that alleles will be inherited together •  distance between the 2 loci,  probability that alleles will be inherited together.

  27. Mendelian Laws of Inheritance • Chromosomal Abnormalities • 5 out of every 1000 humans are born with serious genetic defects attributable to chromosomal anomalies • Changes in chromosome number • Monosomy, Trisomy

  28. Mendelian Laws of Inheritance • Euploidy • Addition or deletion of whole sets of chromosomes • Polyploidy • Most common type of euploidy • The carrying of 3 or more sets of chromosomes by an organism • More common in plants than animals

  29. Mendelian Laws of Inheritance • Changes in Chromosome Structure • Inversion • Portion of a chromosome reversed • Deletion • Entire blocks of genes lost • Translocation • Nonhomologous chromosomes exchange sections • Duplication • Extra section of chromosomes attached

  30. Gene Theory GENE: Nucleotide sequence that encodes a functional polypeptide or RNA sequence

  31. Sources of Phenotypic Variation • Frequency of Mutations • Mutation rate for humans • About every third person carries approximately one new mutation • Although most mutations are harmful, most are recessive and not expressed

More Related