PowerLecture: Chapter 11

PowerLecture:Chapter 11 Observing Patterns in Inherited Traits

Section 11.0: Weblinks and InfoTrac See the latest Weblinks and InfoTrac articles for this chapter online

Videos: CNN Ask your Thomson Sales Representative for these volumes on CD or VHS • Biology, 2003, Vol. 7. Tastier Tomatoes (2:53)

Impacts, Issues: In Pursuit of a Better Rose • Roses have been around for at least 40 million years • Researchers are working to create genetic maps for rose chromosomes

Fig. 11-1, p.168

p.169

Impacts, Issues: In Pursuit of a Better Rose • Knowing the location of desirable genes on chromosomes helps rose breeders mix the beauty of cultivated varieties with disease resistance of wild varieties

Earlobe Variation • Whether a person has attached or detached earlobes depends on a single gene • Attached earlobes: two copies of the recessive allele for this gene • Detached earlobes: either one or two copies of the dominant allele

Early Ideas about Heredity • People knew that sperm and eggs transmitted information about traits • Blending theory • Problem: • Would expect variation to disappear • Variation in traits persists

Gregor Mendel • Strong background in plant breeding and mathematics • Using pea plants, found indirect but observable evidence of how parents transmit genes to offspring

Gregor Mendel • The founder of modern genetics Fig. 11-2, p.170

a Garden pea flower, cut in half. Sperm form in pollen grains, which originate in male floral parts (stamens). Eggs develop, fertilization takes place, and seeds mature in female floral parts (carpels). b Pollen from a plant that breeds true for purple flowers is brushed onto a floral bud of a plant that breeds true for white flowers. The white flower had its stamens snipped off. This is one way to assure cross-fertilization of plants. c Later, seeds develop inside pods of the cross-fertilized plant. An embryo within each seed develops into a mature pea plant. d Each new plant’s flower color is indirect but observable evidence that hereditary material has been transmitted from the parent plants. Fig. 11-3, p.170

Gregor Mendel Crossing garden pea plants

Genes • Units of information about specific traits • Passed from parents to offspring • Each has a specific location (locus) on a chromosome

Alleles • Different molecular forms of a gene • Arise by mutation • Dominant allele masks a recessive allele that is paired with it

Allele Combinations • Homozygous • having two identical alleles at a locus • AA or aa • Heterozygous • having two different alleles at a locus • Aa

Genetic Terms A pair of homologous chromosomes A gene locus A pair of alleles Three pairs of genes Figure 11.4Page 171

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

Genetic Terms Genetic terms

Genotype & Phenotype • Genotype refers to particular genes an individual carries • Phenotype refers to an individual’s observable traits • Cannot always determine genotype by observing phenotype

Tracking Generations • Parental generation P mates to produce • First-generation offspring F1 mate to produce • Second-generation offspring F2

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

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

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 Monohybrid Cross Results Monohybrid cross

Mendel’s Monohybrid Cross Results F2 ratios interaction

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

True-breeding homozygous recessive parent plant F1PHENOTYPES aa True-breeding homozygous dominant parent plant Aa Aa a a Aa Aa A AA A Aa Aa Aa Aa An F1 plant self-fertilizes and produces gametes: F2PHENOTYPES Aa AA Aa A a A AA Aa a Aa aa Aa aa Monohybrid CrossIllustrated Figure 11.7Page 173

Monohybrid CrossIllustrated Testcross

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

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 • Individual that shows dominant phenotype is crossed with individual with recessive phenotype • Examining offspring allows you to determine the genotype of the dominant individual

Homozygous recessive Homozygous recessive a a a a A A Aa Aa Aa Aa a A aa Aa aa Aa Punnett Squares of Test Crosses Two phenotypes All dominant phenotype

Punnett Squares of Test Crosses POSSIBLE EVENT: PROBABLE OUTCOME: sperm A meets egg A sperm A meets egg a sperm a meets egg A sperm a meets egg a 1/4 AA offspring 1/4 Aa 1/4 Aa 1/4 aa p.173

aa Aa aa a A a A A a A a A A A A Aa AA Aa a a a a Aa aa Aa aa Punnett Squares of Test Crosses female gametes male gametes Fig. 11-7a, p.173

female gametes male gametes Aa aa a A a A A a A a Aa AA Aa A A A A a aa Aa aa Aa aa a a a Punnett Squares of Test Crosses Stepped Art Fig. 11-7a, p.173

Punnett Squares of Test Crosses True-breeding homozygous recessive parent plant F1 PHENOTYPES aa True-breeding homozygous dominant parent plant Aa Aa a a Aa Aa A AA Aa Aa A 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 AA Aa A Aa aa a Aa aa Fig. 11-7b2, p.173

Dihybrid Cross Experimental cross between individuals that are homozygous for different versions of two traits

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 X AaBb 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 1/16 AaBb 1/16 AAbb 1/16 Aabb 1/4 Ab 1/16 AABb 1/16 white-flowered, dwarf 1/16 AaBB 1/16 aaBB 1/16 aaBb 1/4 aB 1/16 AaBb 1/16 Aabb 1/16 aaBb 1/16 aabb 1/16 AaBb 1/4 ab

AABB purple- flowered tall parent (homozygous dominant) aabb white- flowered dwarf parent (homozygous recessive) X AB ab F1 OUTCOME: All of the F1 plants are AaBb heterozygotes (purple flowers, tall stems). AaBb Fig. 11-9a, p.175

1/4 1/4 1/4 1/4 meiosis, gamete formation AB Ab aB ab 1/4 1/16 1/16 1/16 1/16 AABB AABb AaBB AaBb AB 1/4 1/16 1/16 1/16 1/16 Ab AABb AAbb AaBb Aabb 1/16 1/16 1/16 1/16 AaBB AaBb aaBB aaBb aB 1/16 1/16 1/16 1/16 1/4 AaBb Aabb aaBb aabb ab Fig. 11-9b, p.175

Dihybrid Cross: F2 Results Dihybrid cross

Independent Assortment • Mendel concluded that the two “units” for the first trait were to be assorted into gametes independently of the two “units” for the other trait • Members of each pair of homologous chromosomes are sorted into gametes 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

Independent Assortment Nucleus of a diploid (2n) reproductive cell with two pairs of homologous chromosomes Possible alignments of the two homologous chromosomes during metaphase I of meiosis The resulting alignments at metaphase II Allelic combinations possible in gametes 1/4 AB 1/4 ab 1/4 Ab 1/4 aB Fig. 11-8, p.174

PowerLecture: Chapter 11