Observable Patterns of Inheritance

1
Observable Patterns of Inheritance

• Starr/Taggarts
• Biology
• The Unity and Diversity of Life, 9e
• Chapter 11

2
Key Concepts

• Genes are units of information about inherited
  traits
• Each gene has a particular location on a
  chromosome
• Paired genes are moved apart during meiosis
• Gregor Mendel discovered and reported evidence of
  gene segregation

3
Key Concepts

• Homologous chromosomes are independently
  distributed and assorted during meiosis
• Contrasting traits are specified by nonidentical
  alleles
• Alleles may be dominant, recessive, or
  codominant, and some can influence adjacent genes
• Environmental factors can induce variations in
  traits

4
Mendels Insight into Patterns of Inheritance

• Mendels Experimental Approach
• Garden pea plant

5
Terms Used in Genetics

• Genes
• Alleles
• Hybrid
• Homozygous
• Heterozygous
• Dominant
• Recessive
• Genotype
• Phenotype
• Generations
• P, F1, F2

6
Mendels Theory of Segregation

• Monohybrid cross
• Gene segregation

7
Trait Studied
Dominant Form
Recessive Form
F2 Dominant-to- Recessive Ratio
SEED SHAPE
2.961
5,474 round
1,850 wrinkled
SEED COLOR
3.011
6,022 yellow
2,001 green
POD SHAPE
2.951
299 wrinkled
882 inflated
POD COLOR
2.821
152 yellow
428 green
FLOWER COLOR
3.151
705 purple
224 white
FLOWER POSITION
3.141
651 long stem
207 at tip
STEM LENGTH
2.841
787 tall
277 dwarf
8
Probability and Punnet Squares

• A possibility of outcomes and crosses
• Test crosses
• Unknown genotype crossed with homozygous recessive

9
Mendels Monohybrid Cross
10
Mendels Monohybrid Cross
11
TRUE- BREEDING PARENTS
purple flowers, tall
white flowers, dwarf
x
AABB
aabb
GAMETES
AB
AB
ab
ab
AaBb
F1 HYBRID OFFSPRING
In-text, p. 180
12
AABB purple- flowered tall parent (homozygous domi
nant)
aabb white- flowered dwarf parent (homozygous rece
ssive)
F1 OUTCOME All F1 plants purple-flowered,
tall (AaBb heterozygotes)
AaBb
AaBb
meiosis, gamete formation
1/4
1/4
1/4
1/4
1/4
1/16
1/16
1/16
1/16
AABB
AABb
AaBB
AaBb
1/4
1/16
1/16
1/16
1/16
AABb
AAbb
AaBb
Aabb
1/4
1/16
1/16
1/16
1/16
AaBb
aaBB
aaBb
AaBB
1/4
1/16
1/16
1/16
1/16
AaBb
aabb
Aabb
aaBb
Fig. 11.9, p. 181
Possible outcomes of cross-fertilization
13
Mendels Theory of Segregation

• Diploid cells have pairs of genes or homologous
  chromosomes
• During meiosis the two genes segregate and wind
  up in different gametes

14
Independent Assortment
15
Theory in Modern Form

• Independent Assortment
• Gametes require genes independently of how other
  pairs of genes were sorted out
• Variety of Offspring

16
Dominance Relation

• Incomplete Dominance
• Red snapdragon crossed with white snapdragon
  ---------gt Pink F1
• Codominance
• Multiple allele system
• ABO Blood types

17
homozygous parent
homozygous parent
F1 offspring heterozygous for flower color
F2 offspring - 3 phenotypes in 121 ratio
Fig. 11.10, p. 182
18
Multiple Effects of Single Genes

• Pleiotropy
• Effects two or more traits
• Sickle Cell Anemia

19
Interactions Between Gene Pairs

• Epistasis
• Fur color in mammals
• Melanin production
• Albinism
• Comb shape in chickens

20
RRpp (rose comb)
rrPP (pea comb)
RrPp (all walnut comb)
P
F1
X
X
9/16 walnut (RRPP, RRPp, RrPP, or RrPp)
3/16 rose (RRpp or Rrpp)
3/16 pea (rrPP or rrPp)
1/16 single (rrpp)
F2
WALNUT COMB
ROSE COMB
PEA COMB
SINGLE COMB
Fig. 11.15, p. 185
21
Less Predictable Variation in Traits

• Camptodactyly
• Continuous variation
• Eye color
• Height

22
Fig. 11.16, p. 186
23
Examples of Environmental Effects on Phenotypes

• Himalayan Rabbit Siamese Cat
• Less melanin in warm body regions. Heat makes
  enzyme in melanin production pathway less active
• Hydrangea color
• Color ranges from blue to pink, depending on
  acidity of soil

24
Fig. 11.19, p. 188
25
In Conclusion

• Gene is unit of information about a heritable
  trait
• Mendel provided indirect evidence of dominant and
  recessive genes
• F1 offspring form monohybrid crosses
• AA x aa -----gt Aa
• Crosses from F1 result in F2 offspring with
  phenotypes having a 31 ratio

26
In Conclusion

• Theory of segregation states that genes of each
  pair segregate during meiosis and wind up in
  different gametes
• Dihybrid crosses result in 9331 phenotypic
  ratio
• Theory of Independent Assortment states that gene
  pairs independently sort out into different
  gametes regardless of other gene pairs of other
  chromosomes

27
In Conclusion

• Four factors influence gene expression
• Degrees of dominance
• Products of pairs of genes may interact
• One gene may effect two or more traits
• Environment
• developed by M. Roig