Relative dominance in major plant lineages Gametophyte 1N, produces gametes Sporophyte 2N, produces spores Non-vascular-to-vascular Spores-to-seeds Cones-to-flowers Motile-to-non-motile sperm

Fig. 37.3

Types of cell division Mitosis: –growth, development & repair –Asexual reproduction (yields identical cells) –Occurs in somatic (body) cells Meiosis –Sexual reproduction (yields different cells) –Occurs in specific reproductive cells

A comparison of mitosis and meiosis (Part 1)

Meiosis Type of cell division that halves number of chromosomes Process of 2 successive divisions –Chromosome number reduced in prophase I and anaphase I Product is gamete, essential for sexual reproduction

Meiosis occurs in gametophytes male = pollen grain – located within pollen sacs inside anther female = embryo sac –ovules contained within ovary –embryo sac within ovule Female gametophyte Male gametophyte

Fig a

Overview of meiosis: how meiosis reduces chromosome number

Results of alternative arrangements of two homologous chromosome pairs on the metaphase plate in meiosis I

Crossing Over exchange of genetic material between homologous portions of 2 non-sister chromatids (prophase I) Increases genetic diversity Results of crossing over during meiosis

Evolutionary advantage asexual reproduction (mitosis) –easy, rapid, effective way to reproduce –useful in stable environment –lack of genetic diversity among offspring sexual reproduction (meiosis) –promotes genetic variability –useful in dynamic environment

Alternation of Generations

Overview of angiosperm life cycle Monecious or diecious Polar nuclei  endosperm

Spores vs. Seeds 1N, haploid No embryo No nutritive tissue 2N, diploid Embryo Nutritive tissue –(endosperm, 3N)

Plant Classification Binomial nomenclature – (genus & species epithets) Devised by Carolus Linnaeus in ca Species grouped by reproductive traits More recently based on DNA sequences

Plant Evolution How did we get so many species? Just what is a species?

Fig. 1.5

Fig. 1.1

Fig. 1.6

Fig. 15.4

Fig Convergent evolution

Theory of Natural Selection Over-reproduction Struggle for existence Survival & reproduction of the fittest Inheritance & accumulation of favorable traits

Descent with modification

Remember: - Natural selection occurs because of interactions between organisms and their environments. Because the environment varies in time & place, NS is situation dependent. - Natural selection works to increase or decrease the occurrence of heritable traits. It “filters” existing variation, but does not generate variation. -Individuals are selected, but populations evolve. - Populations are members of a species that interbreed. - A population is the smallest unit that can evolve.

Evolution of insecticide resistance in insect populations.

Evolution of drug resistance in HIV

Artificial selection: diverse vegetables derived from wild mustard

5. Evidence of evolution Fossil record Convergent form & function Biogeography Homologous structures Embryological development Molecular (DNA) sequences

Embryological evidence: all vertebrates have pharyngeal pouches – gills.

Molecular evidence: e.g., DNA/RNA is universal for the genetic code. Other evidence: homologies basically follow the tree of life. More closely related organisms have more homologous molecules.

Evolution terms Phenotype (expression of genes) vs. genotype (genetic make-up) Micro (within a species) & macro (among species) changes Evolution refers to changes in a population, not changes in an individual Evolution (change) usually leads to adaptation of a species to environment (acclimation refers to changes in an individual)

Sources of variation Mutation in DNA sequences –Ca. 1 in 100,000 genes; most harmful –Most are harmful; some neutral or helpful Migration Genetic drift (in small populations) Reproductive isolation –E.g., geographical, mechanical, temporal Non-random mating (e.g., sexual selection) Hybridization Polyploidy

Fig Geographic Isolation of Western & Eastern Redbud Species

Fig Reproductive Isolation of Dutchmen’s Breeches and Squirrel Corn

Fig Mechanical Isolation in Orchids

Fig. 15.9

Fig Hybridization & polyploidy is very common in plants

Fig. 43.2

Fig. 43.3a

Fig. 43.3b