CHAPTER 15 THE CHROMOSOMAL BASIS OF INHERITANCE

1
CHAPTER 15 THE CHROMOSOMAL BASIS OF INHERITANCE
2

• MENDELS FACTORS (OR GENES) ARE LOCATED ON
  CHROMOSOMES
• IT IS THE CHROMOSOMES THAT SORT AND SEGREGATE
  INDEPENDENTLY

3
(No Transcript)
4

• T. H. MORGAN
• EARLY 1900S _at_ COLUMBIA UNIV
• DROSOPHILA MELANOGASTER (FRUIT FLY)
• EASILY CULTURED
• PROLIFIC BREEDERS
• SHORT GENERATION
• ONLY 4 PAIR OF CHROMOSOMES
• 3 PAIR OF AUTOSOMES
• 1 PAIR OF SEX CHROMOSOMES
• EASILY SEEN UNDER A LIGHT MICROSCOPE

5

• WILD TYPE
• THE NORMAL PHENOTYPE
• MOST FREQUENTLY FOUND
• DESIGNATED BY SUPERSCRIPT ()

6

• MUTANT PHENOTYPE
• DUE TO MUTATION OF THE WILD TYPE GENE
• ALTERNATIVE PHENOTYPE
• GENE SYMBOL IS BASED ON THE FIRST MUTANT
• FIRST LETTER IS LOWER CASE

7

• SEX LINKAGE
• MORGAN DEDUCED THAT EYE COLOR IS ON THE X
  CHROMOSOME
• IF ONLY ON THE X THAN THE FEMALE CARRIES 2
  COPIES OF THE GENE AND MALES ONLY ONE COPY
• SINCE THE MUTANT ALLELE IS RECESSIVE A WHITE EYE
  MALE MUST HAVE THE ALLELE ON BOTH X
  CHROMOSOMES, WHICH WOULD NOT BE POSSIBLE IN
  MORGANS EXPERIMENTS
• WHITE EYED MALES HAVE NO WILD TYPE ALLELE (RED)
  TO MASK THE RECESSIVE MUTANT ALLELE, SO A SINGLE
  COPY OF THE MUTANT ALLELE WOULD BE WHITE EYES

8
(No Transcript)
9

• SEX LINKED GENES
• GENES THAT ARE LOCATED ON THE X CHROMOSOME

10

• LINKED GENES
• GENES LOCATED ON THE SAME CHROMOSOME
• TEND TO BE INHERITED TOGETHER
• DO NOT SORT INDEPENDENTLY
• MOVE TOGETHER THROUGH MEIOSIS AND FERTILIZATION
• WILL NOT PRODUCE 9331 RATIOS IN DIHYBRID
  CROSSES

11
(No Transcript)
12

• GENETIC RECOMBINATION
• PRODUCTION OF OFFSPRING WITH NEW COMBOS OF
  TRAITS
• RESULT IS FROM MEIOSIS AND RANDOM FERTILIZATION

13
(No Transcript)
14
(No Transcript)
15
(No Transcript)
16

• MENDELS WORK
• INDEPENDENT ASSORTMENT
• 2 PROGENY TYPES
• PARENTAL TYPE SAME PHENOTYPE AS PARENTS
• RECOMBINANTS PHENOTYPE THAT DIFFERS FROM THE
  PARENTS

17

• MORGANS DIHYBRID TEST CROSS RESULTS
• 15.5
• RESULTS SHOW THAT CROSSING OVER ACCOUNTS FOR
  RECOMBINATION OF LINKED GENES

18

• CHROMOSOMAL MAPPING
• MORGANS WORK SHOWED THAT SOME GENES ARE LINKED
  MORE TIGHTLY THAN OTHERS
• ALRED H. STURDEVANT
• MORGANS STUDENT
• ASSUMED THAT IF CROSSING OVER OCCURS RANDOMLY
• THAN THE PROBABILITY OF CROSSING OVER BETWEEN 2
  GENES MUST BE DIRECTLY PROPORTIONAL TO THE
  DISTANCE BETWEEN THEM

19

• RECOMBINANT FREQUENCIES
• MAY BE USED TO CONSTRUCT A GENETIC MAP
• MAP UNIT 1 RECOMBINATION FREQUENCY
• CENTIMORGANS TODAYS MAP UNITS
• CYTOLOGICAL MAPPING
• THE ACTUAL LOCATION OF GENES AND THE REAL
  DISTANCE BETWEEN THEM
• DIFFERENT MAP CREATED AS OPPOSED TO THE MAP BASED
  ON CROSSOVER FREQUENCIES

20

• CROSSING OVER
• RECOMBINATION OF LINKED GENES DURING MEIOSIS,
  WHICH WILL FORM NEW ALLELE COMBINATIONS

21

• CHROMOSOMAL BASIS OF SEX IN HUMANS
• MAMMALS HAVE AN X-Y MECHANISM TO DETERMINE SEX
  AT FERTILIZATION
• HETEROGAMETE XY
• HOMOGAMETE XX
• EACH GAMETE WILL CARRY ONLY 1 SEX CHROMOSOME
• Y DETERMINES THE SEX OF THE ZYGOTE
• SRY SEX DETERMINING REGION
• TESTES DEVELOP DUE TO THE PRESENCE OF THIS GENE
• MAY CODE FOR OTHER GENES TOO
• NO SRY OVARIES DEVELOPE

22
(No Transcript)
23

• SEX LINKED DISORDERS
• X CHROMOSOME IS LARGER THAN THE Y CHROMOSOME,
  AS A RESULT OF THIS STRUCTURAL DIFFERENCE THERE
  ARE MORE X LINKED THAN Y LINKED TRAITS
• THERE IS NO HOMOLOGOUS LOCI ON THE Y
• MOST GENES ON THE Y ENCODE FOR MALE TRAITS ONLY
• MALE, GETS THE X FROM MOTHER
• FATHER IS UNABLE TO PASS SEX LINKED TRAITS TO HIS
  SONS
• MOTHER IS ABLE TO PASS SEX LINKED TRAITS TO BOTH
  SONS AND DAUGHTERS
• IF SEX LINKED TRAIT IS DUE TO A RECESSIVE ALLELE
  A FEMALE WILL ONLY EXPRESS IT PHENOTYPICALLY IF
  SHE IS HOMOZYGOUS FOR THAT TRAIT

24
(No Transcript)
25

• HEMIZYGOUS
• CONDITION WHERE 1 COPY OF A GENE IS PRESENT IN A
  DIPLOID ORGANISM
• MALES ARE HEMIZYGOUS
• MORE MALES THAN FEMALES HAVE SEX LINKED DISORDERS
• CARRIERS
• FEMALE HETEROZYGOTES FOR THAT TRAIT

26

• X INANCTIVATION IN FEMALES
• FULLY FUNCTIONING FEMALE WITH ONLY 1 X ACTIVE
• MARY F. LYON LYON HYPOTHESIS
• BARR BODIES INACTIVE X CHROMOSOME
• MOST BARR BODIES, GENES ARE NOT EXPRESSED
• REACTIVATED IN GONADAL CELLS UNDERGOING MEIOSIS
• FORMATION OF BARR BODIES IS COMPLETELY RANDOM

27

• FEMALES ARE A MOSAIC OF 2 CELL TYPES
• ACTIVE MATERNAL X
• ACTIVE PATERNAL X
• X CHROMOSOME INACTIVATION IS ASSOCIATED WITH
  DNA METHYLATION (CH3) AT CYTOSINE
• XIST INACTIVE SPECIFIC TRANSCRIPT
• INACTIVATES THE X CHROMOSOME
• RECENT DISCOVERED GENE THAT IS ACTIVE ONLY ON
  BARR BODIES

28

• ALTERED CHROMOSOME NUMBER
• NONDISJUNCTION
• FAILURE OF HOMOLOGOUS CHROMOSOMES TO SEPARATE
  DURING MEIOSIS I OR II
• OCCASIONALLY IN MITOSIS

29
(No Transcript)
30

• ANEUPLOIDY
• ABNORMAL NUMBER OF CHROMOSOMES
• A NORMAL GAMETE UNITES WITH AN ABNORMAL GAMETE
  WHICH WAS A PRODUCT OF NONDISJUNCTION
• TRISOMIC 2n1, TRIPLICATE CHROMOSOME NUMBER
• MONOSOMIC 2n-1, MISSING A CHROMOSOME

31

• POLYPLOIDY
• MORE THAN 2 COMPETE SETS OF CHROMOSOMES
• TRIPLOIDY 3n
• TETRAPLOIDY 4n
• THESE RARELY OCCUR IN ANIMALS, OCCUR IN PLANTS.
• PLANTS MAY APPEAR PHENOTYPICALLY NORMAL

32

• ALTERED CHROMOSOME STRUCTURE
• DELETION LOSS OF A FRAGMENT
• DUPLICATION SEGMENT GETS REPEATED
• INVERSION FRAGMENT REATTACHES IN REVERSE ORDER
• TRANSLOCATION FRAGMENT JOINS A NON-HOMOLOGOUS
  CHROMOSOME
• HOMOZYGOUS DELETIONS SINGLE X IN A MALE,
  NEGATIVE SOMETIMES LETHAL
• POSITION EFFECT GENE EXPRESSION IS INFLUENCED
  BY ITS LOCATION AND SUROUNDING GENES

33
(No Transcript)
34

• HUMAN NONDISJUNCTON DISORDERS
• WE HAVE THE ABILITY TO TEST PRIOR TO BIRTH
• DOWNS SYNDROME TRISOMY 21
• PATAUS SYNDROME TRISOMY 13
• EDWARDS SYNDROME TRISOMY 10

35

• SEX CHROMOSOME ANEUPLOIDY
• KLEINFELTERS SYNDROME
• MALE
• GENOTYPE - XXY, XXYY, XXXY
• PHENOTYPE
• MALE BODY (SORT OF)
• BREAST ENLARGMENT,
• NORMAL INTELLEGENCE
• SMALL SEX ORGANS, STERILE

36

• MALES WITH EXTRA Y
• XYY GENOTYPE
• PHENOTYPE NORMAL MALE, TALLER THAN AVERAGE

37

• TURNERS SYNDROME
• X0 GENEOTYPE
• PHENOTYPE
• SHORT
• STERILE
• SECONDARY SEX CHARACTERISTICS FAIL TO DEVELOP

38

• TRIPLE X SYNDROME
• NORMAL PHENOTYPE
• XXX GENOTYPE
• CANNOT BE DISTINGUISHED BETWEEN XX PHENOTYPE

39

• CRI DU CHAT SYNDROME
• CRY OF THE CAT
• DELETION OF CHROMOSOME 5
• MENTALLY RETARDED
• SMALL HEAD
• UNUSUAL FACIAL FEATURES
• CRIES SOUNDS LIKE A CAT
• EARLY DEATH

40

• CHRONIC MYELOGENOUS LEUKEMIA
• CML
• CANCER
• A PORTION OF CHROMOSOME 22 TRANSLOCATES WITH
  CHROMOSOME 9

41

• DOWNS TRANSLOCATION PART OF A THIRD CHROMOSOME
  AT 21 TRANSLOCATES AND ATTACHES TO 15

42

• GENOMIC IMPRINTING
• A PROCESS BY WHICH CERTAIN GENES WILL BE
  EXPRESSED DEPENDING ON WERE THE ALLELE WAS
  RECEIVED FROM (SPERM OR EGG)

43
(No Transcript)
44

• PRADER WILLI SYNDROME
• DELETION FROM PATERNAL CHROMOSOME 15
• RETARDATION, OBESITY, SHORT SMALL HANDS AND FEET
• ANGELMANS SYNDROME
• DELETION FROM MATERNAL 15
• MOTOR AND MENTAL SYMTOMS
• UNCONTROLLED SPONTANEOUS LAUGHTER

45

• TRIPLET REPEATS
• SECTIONS OF DNA WHERE A SPECIFIC TRIPLET OF
  NUCLEOTIDES IS REPEATED MANY TIMES
• MAY OCCUR NORMALLY
• THE PROGRESSIVE ADDITION MAY LEAD TO
• HUNTINGTONS DISEASE
• FRAGILE X SYNDROME

46

• FRAGILE X
• 1-1500 MALES
• 1-2500 FEMALES
• MOST COMMON FORM OF MENTAL RETARDATION
• ABNORMAL X CHROMOSOME TIP HANGS ON THE REST OF
  THE CHROMOSOME BY A THIN THREAD OF DNA
• CONTAINS THE TRIPLET REPEAT CGG

47

• EXCEPTIONS
• SOME EXTRA NUCLEAR GENES MAY BE FOUND IN THE
  CYTOPLASM
• PLASTIDS AND MITOCHONDRIA NOT DISTRIBUTED BY
  SEGREGATION OF CHROMOSOMES DURING MEIOSIS
• PLANTS ZYGOTE RECEIVES PLASTIDS FROM THE OVUM,
  NOT POLLEN
• MAMMALS MITOCHONDRIA GETS ITS DNA ONLY FROM
  MATERNAL GENES AS WELL