PowerLecture: Chapter 11 Observing Patterns in Inherited Traits

Early Ideas about Heredity Blending theory Problem: Variation in traits persists

Gregor Mendel Fig. 11-2, p.170

Genes Fig. 12-2, p.188

Allele Combinations Homozygous Heterozygous

A pair of homologous chromosomes, each in the unduplicated state (most often, one from a male parent and its partner from a female parent) A gene locus (plural, loci), the location for a specific gene on a chromosome. Alleles are at corresponding loci on a pair of homologous chromosomes A pair of alleles may be identical or nonidentical. They are represented in the text by letters such as D or d Three pairs of genes (at three loci on this pair of homologous chromosomes); same thing as three pairs of alleles Fig. 11-4, p.171

Genotype & Phenotype Genotype - the particular genes an individual carries Phenotype - an individual’s observable traits

Probability The chance that each outcome of a given event will occur is proportional to the number of ways that event can be reached

Tracking Generations Parental generation P mates to produce First filial F1 mate to produce Second filial F2

Experimental intercross between Monohybrid Crosses Experimental intercross between two F1 heterozygotes AA X aa Aa (F1 monohybrids) Aa X Aa ?

Monohybrid Cross Illustrated True-breeding homozygous recessive parent plant homozygous dominant An F1 plant self-fertilizes and produces gametes: F1 PHENOTYPES F2 PHENOTYPES aa Aa AA A a Monohybrid Cross Illustrated Figure 11.7 Page 173

Mendel’s Monohybrid Cross Results 5,474 round 1,850 wrinkled 6,022 yellow 2,001 green 882 inflated 299 wrinkled 428 green 152 yellow F2 plants showed dominant-to-recessive ratio that averaged 3:1 705 purple 224 white 651 long stem 207 at tip 787 tall 277 dwarf Fig. 11-6, p. 172

F2 Dominant-to- Recessive Ratio Trait Studied Dominant Form Recessive Form F2 Dominant-to- Recessive Ratio SEED SHAPE 5,474 round 1,850 wrinkled 2.96:1 SEED COLOR 6,022 yellow 2,001 green 3.01:1 POD SHAPE 882 inflated 299 wrinkled 2.95:1 POD COLOR 428 green 152 yellow 2.82:1 FLOWER COLOR 705 purple 224 white 3.15:1 FLOWER POSITION 651 long stem 207 at tip 3.14:1 STEM LENGTH 787 tall 277 dwarf 2.84:1 Fig. 11-6, p.172

Mendel’s Theory of Segregation An individual inherits a unit of information (allele) about a trait from each parent During gamete formation, the alleles segregate from each other

Mendel’s Theory of Segregation Homozygous dominant parent Homozygous recessive parent Mendel’s Theory of Segregation (chromosomes duplicated before meiosis) meiosis I meiosis II (gametes) (gametes) fertilization produces heterozygous offspring Fig. 11-5, p.172

Test Cross dominant phenotype crossed with recessive phenotype Examining offspring determines genotype of dominant individual

Punnett Squares of Test Crosses True-breeding homozygous recessive parent plant F1 PHENOTYPES aa True-breeding homozygous dominant parent plant Aa Aa a a A Aa Aa AA A Aa Aa Aa Aa Fig. 11-7b1, p.173

Punnett Squares of Test Crosses An F1 plant self-fertilizes and produces gametes: F2 PHENOTYPES Aa AA Aa A a A AA Aa a Aa aa Aa aa Fig. 11-7b2, p.173

Dihybrid Cross: F1 Results purple flowers, tall white flowers, dwarf TRUE- BREEDING PARENTS: AABB x aabb GAMETES: AB AB ab ab AaBb F1 HYBRID OFFSPRING: All purple-flowered, tall

Dihybrid Cross: F2 Results AaBb X AaBb 1/4 AB 1/4 Ab 1/4 aB 1/4 ab 9/16 purple-flowered, tall 1/4 AB 1/16 AABB 1/16 AABb 1/16 AaBB 1/16 AaBb 3/16 purple-flowered, dwarf 3/16 white-flowered, tall 1/4 Ab 1/16 AABb 1/16 AAbb 1/16 AaBb 1/16 Aabb 1/16 white-flowered, dwarf 1/4 aB 1/16 AaBB 1/16 AaBb 1/16 aaBB 1/16 aaBb 1/16 AaBb 1/16 Aabb 1/16 aaBb 1/16 aabb 1/4 ab

Independent Assortment Mendel concluded that “units” one trait assorted independently of the “units” for the other trait homologous chromosomes are sorted at random during meiosis

Independent Assortment Metaphase I: OR A A a a A A a a B B b b b b B B Metaphase II: A A a a A A a a B B b b b b B B Gametes: B B b b b b B B A A a a A A a a 1/4 AB 1/4 ab 1/4 Ab 1/4 aB

(n is the number of gene loci at which the parents differ) Tremendous Variation Number of genotypes possible in offspring due to independent assortment and hybrid crossing is 3n (n is the number of gene loci at which the parents differ)

Impact of Mendel’s Work Mendel presented his results in 1865 Paper received little notice Mendel discontinued his experiments in 1871 Paper rediscovered in 1900

Dominance Relations Complete dominance Incomplete dominance Codominance

Incomplete Dominance X All F1 offspring heterozygous for flower color: homozygous parent X homozygous parent All F1 offspring heterozygous for flower color: Cross two of the F1 plants and the F2 offspring will show three phenotypes in a 1:2:1 ratio: Fig. 11-11, p.176

Codominance: ABO Blood Types ABO type Gene codes for enzyme that dictates structure of a blood cell glycolipid Two alleles (IA and IB) are codominant when paired Third allele (i) is recessive to others

ABO Blood Type Range of genotypes: IAIA IBIB or or IAi IAIB IBi ii Fig. 11-10a, p.176

ABO and Transfusions Recipient’s immune system attacks blood cells with unfamiliar glycolipid on surface Type O is universal donor because it has neither type A nor type B glycolipid

Pleiotropy Alleles at a single locus may have effects on two or more traits Marfan syndrome - Mutation in gene for fibrillin affects skeleton, cardiovascular system, lungs, eyes, and skin

Epistasis Interaction between the products of gene pairs Common among genes for hair color in mammals

Epistasis Fig. 11-13, p.177

Coat Color in Retrievers (Epistasis) BBEE X bbee F1 puppies are all BbEe F2 puppies BE Be bE be BE BBEE BBEe BbEE BbEe black Be BBEe BBee BbEe Bbee brown bE BbEE BbEe bbEE bbEe yellow be BbEe Bbee bbEe bbee

Comb Shape in Poultry rose comb pea comb walnut comb single comb X RRpp pea rrPP F1 all walnut RrPp RrPp RrPp F2 9/16 walnut RRPP, RRPp,RrPP, or RrPp 3/16 rose RRpp or Rrpp 3/16 pea rrPP or rrPp 1/16 single rrpp Fig. 11-12, p.177

Crossing Over

Linkage Groups Genes on one type of chromosome travel together Degree of linkage may vary

Full Linkage A B a b x Parents: A B a b AB ab F1 offspring: All AaBb meiosis, gamete formation Equal ratios of two types of gametes: A B a b Figure 11.15 Page 178 50% AB 50% ab

Incomplete Linkage AC ac A C a c x Parents: A C a c F1 offspring: All AaCc meiosis, gamete formation A a A a Unequal ratios of four types of gametes: C c c C parental genotypes recombinant genotypes Figure 11.15 Page 178

Crossover Frequency Proportional to the distance that separates genes B C D Crossing over will disrupt linkage between A and B more often than C and D In-text figure Page 178

Linkage Mapping in Humans Linkage maps based on pedigree analysis through generations Color blindness and hemophilia are very closely linked on X chromosome

Environmental Effects on Plant Phenotype Hydrangea macrophylla Action of gene responsible for floral color is influenced by soil acidity Flower color ranges from pink to blue

Environmental Effects on Plant Phenotype Fig. 11-17a, p.179

Environmental Effects on Plant Phenotype Fig. 11-17b, p.179

Temperature Effects on Phenotype This Rabbit is homozygous for allele producing heat-sensitive version of an enzyme in melanin-producing pathway Melanin is produced in cooler areas of body Figure 11.16 Page 179

This Siamese cat, raised in a cold environment in Moscow in the late 20s, developed a relatively dark coat. An area on his shoulder was shaved, and the cat wore a warm jacket while the fur was growing back. When the shaved hair grew back in, it was white, the same color as the cat's belly, due to the increased temperature under the jacket. This was not due to scarring, as the hair grew in normally colored later.

Campodactyly: Unexpected Phenotypes Effect of allele varies: Bent fingers on both hands Bent fingers on one hand No effect Many factors affect gene expression

Continuous Variation Relatively continuous range of differences in a given trait among individuals More genes and environmental factors affect trait - more continuous variation

Human Variation Some human traits occur as a few discrete types Attached or detached earlobes Many genetic disorders Other traits show continuous variation Height Weight Eye color

Continuous Variation Variation in human eye color Fig. 11-18, p.180

Describing Continuous Variation Range of values for the trait Number of individuals with some value of the trait Range of values for the trait Number of individuals with some value of the trait (line of bell-shaped curve indicates continuous variation in population)

Describing Continuous Variation Fig. 11-20, p.181

Fig. 11-21, p.183