NeoMendelian Genetics

1
Neo-Mendelian Genetics

• 1. Incomplete Dominance
• 2. Co-dominance
• 3. Multiple alleles
• 4. Epistasis
• 5. Sex-limited Phenotypes
• 6. Sex-influenced Phenotypes
• 7. Penetrance and Expressivity
• 8. X-linked
• 9. Temperature

2
Neo-Mendelian Genetics

• Incomplete Dominance
• A. Intermediate phenotype
• B. No dominant phenotype
• Red Snapdragon X White Snapdragon
• All F1 pink
• F1 X F1(all heterozygous pink)
• F2 1 red, 2 pink, 1 white

3
(No Transcript)
4
(No Transcript)
5
Neo-Mendelian Genetics

• Codominance (multiple alleles)
• A. Both alleles are expressed
• B. Any given gene may have more than two
• alleles
• C. Karl Landsteiner discovered ABO
• blood type
• D. I isoagglutinogen

6
Neo-Mendelian Genetics

• E. 4 blood phenotypes by 3 alleles
• F. IA, IB, ii
• G. Type A person will have A antigen on
• erythrocyte and anti-B antibody
• H. Type O person will have no antigens
• and both AB antibodies
• I. Universal donor O
• J. Universal recipient AB

7
(No Transcript)
8
Neo-Mendelian Genetics

• Background on Human Blood Groups
• 1. A and B antigens are carbohydrate groups
• bound to lipid molecules
• 2. Most people have H-substance consisting
• of 3 sugars Gal, N-acetylglucosamine,
• and fucose

9
Neo-Mendelian Genetics

• Background on Human Blood Groups
• 3. IA allele responsible for an enzyme
• that attaches N-acetylgalactosamine
• to the H-substance
• 4. IB allele responsible for an enzyme
• that attaches galactose to the H-substance
• 5. i allele responsible for no addition
• of a sugar

10
(No Transcript)
11
Neo-Mendelian Genetics

• Bombay Phenotype
• A. Woman is Bombay phenotypically O
• B. Her parents were AB
• C. Genetically the woman was B
• D. Rare recessive mutation h
• E. H-substance lacked fucose
• F. IA or IB alleles could not recognize
  
• H-substance

12
Neo-Mendelian Genetics

• Secretor Locus
• A. Ability to secrete A/B antigens into body
• secretions
• B. Influenced by a dominant allele Se/Se or Se/se

13

• What happens when more than
• one gene interacts to control the expression of
  a phenotype?

14
(No Transcript)
15
Epistasis

• A. Modification of 9 3 3 1
• B. Genes exerting influence on another gene
• C. Example 1 9 7
• White-flowered sweet peas
• AAbb X aaBB F1 AaBb all purple
• AaBb X AaBb F2 9 purple and 7
  white
• presence of at least one dominant allele of each
  of two gene pairs is essential in order for
  flowers to be purple

16
(No Transcript)
17
Epistasis

• Example 2 12 3 1
• Fruit color in summer squash
• - dominant alleles of one locus masks expression
  at the second locus
• A-B-(or bb) White aabb green
• aaB- Yellow
• AaBb X AaBb F1 12 white, 3 yellow, 1 green

18
Epistasis

• Example 3 9 6 1
• Summer Squash
• - dominant allele at either locus ensures a
  sphere shaped fruit/both genes are influenced
  equivalently
• AABB(disc) X aabb(long) F1 all disc
• AaBb X AaBb F2 9 disc, 6 sphere, 1 long

19
(No Transcript)
20
Epistasis

• Example 4 13 3
• White Leghorn Chickens (CCII) X White Wyandotte
  chickens (ccii) F1 CcIi (white feathers)
• CcIi X CcIi F2 13 white, 3 colored
• C allele necessary for colored feathers
• I allele inhibitor of feather coloration
• I allele dominant over C allele

21
Epistasis

• Example 5 9 4 3
• Agouti coat color
• A dominant allele for agouti hair color
• aa- black coat color
• C- dominant allele necessary for hair pigment
• cc albino

22
Epistasis

• AACC agouti
• AaCc agouti
• aaC- black
• aacc albino
• AACC X aacc F1 AaCc
• AaCc X AaCc F2 9 agouti, 4 albino, 3 black

23
(No Transcript)
24
Epistasis

• Example 6 9 3 3 1
• 1. Very similar ratios as the F2 offspring of a
  dihybrid cross.
• 2. If Rose mates with Single, Rose is
  completely dominant over Single (F1 all Rose, F2
  31, RoseSingle)
• 3. If Pea mates with Single, Pea is completely
  dominant over Single (F1 all Pea, F2 31,
  PeaSingle)
• 4. If Rose and Pea mate, all F1 walnut. When
  two
• walnuts mate from F1, F2 expresses
• 9 walnut 3 rose 3 pea 1 single

25
(No Transcript)
26
X Linkage

• A. Documented in 1910 by Thomas Morgan
• B. studies of white eye mutation in Drosophila
• C. X and Y chromosomes pair during meiosis at
  regions called pseudoautosomal regions (PAR)

27
X Linkage

• D. Y chromosome believed to be largely blank
• E. Located on only one X chromosome
• F. Reciprocal cross same conditions different
  sexes
• G. Phenotypic traits controlled by recessive X
  linked genes are passed from homozygous mother to
  all sons Crisscross pattern of inheritance

28
X Linkage

• H. Morgans work supported chromosomes theory of
  inheritance (genes transmitted on specific
  chromosomes)

29
Sex Influences Phenotype

• A. Sex-limited inheritance - only one sex can
  express phenotype
• B. Sex-influenced inheritance - sex determines
  how phenotype is seen
• C. Autosomal genes involved
• D. Hormones involved

30
Sex Influences Phenotype

• Example 1 Hen feathers or Cock Feathers
• Female Male
• hh hen feathers hh cock feathers
• sex limited

31
Sex Influences Phenotype

• Example 2 Pattern Baldness
• Female Male
• BB Bald Bald
• Bb Not Bald Bald
• bb Not Bald Not
  Bald
• even BB in females is less pronounced than in
  males

32
(No Transcript)
33
(No Transcript)
34
Modification of Gene Expression

• A. Penetrance - percentage of individuals that
  show at least some degree of expression of a
  mutant genotype
• B. Expressivity - range of expression of mutant
  genotype
• C. Genetic Background
• 1. Suppression - no expression of a mutant
  phenotype
• 2. Position effect - physical location of gene

35
(No Transcript)
36
Modification of Gene Expression

• D. Temperature Effect
  Primrose Red flowers _at_ 23oC
• White flowers _at_ 18oC
• Himalayan Rabbits - dark fur around areas that
  are cooler, light fur around areas that are
  warmer. Pigment enzyme functional at lower
  temperatures.

37
Modification of Gene Expression

• Nutritional Effect (nutritional mutants)
  inactivity of enzymes of a biosynthetic pathway
• -useful to genetic studies in bacteria
• -phenylketonuria
• -galactosemia
• -lactose intolerance

38
Modification of Gene Expression

• Onset of Genetic Expression
• stage of an organisms life spanwhere a gene is
  expressed
• Tay Sachs disease(aut. Rec.) by age 3
• Lesch-Nyhan Syndrome (X-linked rec) 8 months
• Duchenne Muscular Dystrophy(X-inked rec) 3 to 5
  years
• Huntington Disease (aut. Dom) 38 years

39
Modification of Gene Expression

• Gene expression and the resultant phenotype are
  often modified through the interactions between
  an individuals particular genotype and the
  internal and external environment