Plant Hybridization & Genetics Plant Propagation

Cross-pollination Pollen from a plant pollinates the flowers of a different plant of the same species. Most species of plants are naturally cross-pollinated.

Pollen Vectors Things that move pollen from one plant to another: Wind Insects Bats

Self-pollination The transfer of pollen from an anther to the stigma of the same flower. Fewer species of plants are naturally self-pollinating. Peas are an example. The petals of the flower enclose the reproductive structures making cross-pollination difficult.

Hybrid The offspring of two different plants of the same or closely related species. Naturally occurring hybrids Artificially (man-made) created hybrids

Naturally Occurring Hybrids White Oak A White Oak B X

Artificially Created Hybrids Artificial hybridization of the Garden Pea

Artificially Created Hybrids: Seed Corn Line B planted later Line A planted early Line A planted early

Artificially Created Hybrids: Seed Corn Male Female Female

Artificially Created Hybrids: Seed Corn Female Male Female

Artificially Created Hybrids: Seed Corn Female Male Female

Artificially Created Hybrids: Seed Corn

Artificial Hybrids Can result from crosses made: Within the same species. Between varieties, cultivars or lines of a species. Between two closely related species within the same plant genus.

Reasons for Hybridizing Plants To improve them! Improve quality Better resistance to diseases and insects Improved hardiness Improved fruit size and quality Improved flower color Improved yield Improved fall color Resistance to herbicides Better flavor Improved storage capabilities

Genotype The genetic makeup of an organism; it’s genes.

Phenotype The outward appearance of an organism; how it looks on the outside.

P = G x E The phenotype of an organism is the result of the interaction between it’s genotype and the environment in which the organism lives. Michael Jordan vs. good corn, bad corn

The Nucleus Command and control center of the cell. Found in both plant and animal cells. Contains chromosomes made of the nucleic acid DNA.

Onion root cells

Genes Segments or sections of chromosomes are referred to as genes. Genes “code” for the various traits that control and regulate all aspects of plant development, growth and appearance.

Genes Just a few examples of what genes code for in plants: Flower color Number of stamens, petals, sepals, etc. Number of ovules in an ovary. Size, shape and color of the fruit. Leaf shape and arrangement Disease resistance Yield, etc…

Genes are segments of chromosomes B C Genes are segments of chromosomes

Monogenic vs. Polygenic Traits Monogenic traits are coded for by a single gene. Eye color in human beings is an example. Polygenic traits are coded for by several to many genes (perhaps hundreds of genes). Yield in corn is an example.

Somatic Cells Over 99% of the cells in our bodies, or in a plant, have the identical number of chromosomes. These “generic” cells are referred to as somatic cells.

Oh gross! The somatic cells in my big toe, for example, have all the genes necessary to make teeth, bones, muscles, a heart, lungs, a liver, etc. The genes are present, just simply not expressed. In fact it is theoretically possible to re-create a whole, new me from a single cell!

Consider that a single root cell has, in it’s nucleus, all the genes needed to make: Chlorophyll Leaves Stems Flowers A whole new plant. Get the picture?

Totipotency The ability to re-create an organism from a single cell. First accomplished in plants using Tobacco (Nicotiana).

Gametes There are places, however, in both people and plants where new cells are created that only contain one-half the normal number of chromosomes. These “sex cells” are called gametes.

Plant Gametes In plants there are 2 different kinds of gametes: Female gamete = egg nucleus (located in an ovule) Male gamete = sperm nucleus (located in a pollen grain)

Fertilization Occurs when male and female gametes unite.

A Human Example… Female Egg 23 chromosomes Male Sperm 23 chromosomes Baby 46 chromosomes

Alleles Plant (and animal) genes come in different forms called alleles. For example a hypothetical gene “A” can come in 2 different alleles: A a

Gene A codes for flower color. Plants would have 2 versions (one from each parent) of gene A in varying combinations: AA = red flowers Aa = red flowers aa = white flowers

A plant with genotype Aa has what color flowers? If these 2 plants were crossed could you predict the percentages of the offspring that would have red and white flowers?

Parent Aa can produce 2 different gametes: A and a Punnett Square Aa X aa Parent Aa can produce 2 different gametes: A and a Parent aa can only produce 1 kind of gamete: a A a Aa aa a

Results 1 out of 2 (50%) offspring will have red flowers. 1 out of 2 (50%) offspring will have white flowers.

A Little More Complicated… Gene A codes for flower color. Gene D codes for plant height: DD = normal height Dd = normal height dd = dwarf What are the gametes that a plant with the genotype AaDd can make?

AaDd D = AD A = Ad d D = aD a d = ad

Try to predict the outcome of the following cross using a Punnett Square: Aadd Flower color and size? Crossed with… aaDd Flower color and size? We’ll do this one on the board!

The End