Plant Reproduction and Inheritance 2023 PDF

CHAPTER 5 PLANT REPRODUCTION & INHERITANCE At the end of this chapter, students should be able to:  Define asexual and sexual reproduction  Discuss the advantages and disadvantages of asexual reproduction and sexual reproduction  State Mendel’s Laws and its principle.  Reproduction...

CHAPTER 5 PLANT REPRODUCTION & INHERITANCE At the end of this chapter, students should be able to:  Define asexual and sexual reproduction  Discuss the advantages and disadvantages of asexual reproduction and sexual reproduction  State Mendel’s Laws and its principle.  Reproduction Plant reproduction is the process by which plants generate or producing new individuals, or offspring from its parents. It is an inherent characteristic of all living organism to continue or maintain their races by the mechanism of reproduction. Modes of Reproduction in Plants ASEXUAL Does not involve sex cell and fertilization A single organism produces new individuals New offspring produced by mitosis & genetically identical to his parents New plant arises from vegetative parts No spore or no seed formation SEXUAL By means of sex, fertilization, fusion of gametes Involves 2 gametes fuse to form a zygote Process of gamete formation involve meiosis division Offspring are not genetically identical to his parents New plant arises through reproductive part = flower Fruits and seeds are formed Asexual reproduction  involves only one parent,  does not involve seeds or the fusion of gametes  part of a plant’s such as stem, leaves and roots can become new plants.  Produces offspring / clones genetically identical to the parent,  Allows plants to be produced much faster than sexual reproduction. Asexual reproduction Asexual reproduction occurs through:  Spore formation  Vegetative Propagation,  Budding,  Fragmentation SPORE FORMATION A spore is a reproductive structure that is adapted for dispersion & surviving for extended periods of time in unfavorable conditions. are usually haploid & unicellular are produce by meiosis in the sporophyte are usually small, light and easily dispersed algae, fungi, mosses, and ferns VEGETATIVE PROPAGATION  Most plants have roots, stems and leaves.  These are called the vegetative parts of a plant.  Vegetative Propagation is a type of asexual reproduction in which new plants are produced from roots, stems, leaves and buds.  Since reproduction is through the vegetative parts of the plant, it is known as vegetative propagation. 🞂 Can happen: 1.naturally e.g. runners, tubers, plantlets, bulbs 2.Can be done artificially by growers. Eg: Bryophyllum (sprout leaf plant) has buds in the margins of leaves. If a leaf of this plant falls on a moist soil, each bud can give rise to a new plant Bryophyllum (sprout NATURAL VS ARTIFICIAL PROPAGTION Natural vegetative Artificial vegetative propagation propagation Definition Refer to the natural Refers to the artificial development of a new plant development of new plants by without human intervention means of human intervention Occurrenc Naturally occurs in plant Occurs under the influence of e man Methods Occurs through roots, Occurs through budding, bulbs, corms, tubers, grafting, layering, cutting, suckers, rhizomes, runners, tissue culture etc plantlet, etc Role Helps to avoid physical Helps to maintain desirable barriers in sexual characters over generation reproduction Example Garlic, taro, banana Rubber, roses, bougainvillea VEGETATIVE PROPAGATION Vegetative propagation may form new plants from the following structures: 1.stems, such as runners in strawberries 2.roots, such as root tubers in sweet potato 3.leaves, in sansevieria 4.buds, in bulbs such as onions or daffodils Developmental Structures of Natural Vegetative Propagation in Plants Developmental structure Type of Structure Modified stems that horizontally grow along the ground Rhizomes surface or underground Ex: Lilies, irises, orchids, and certain grasses Modified stems that horizontally grow on or under the surface Runners/Stolons of the ground Ex: Strawberry and currants Bulbs Swollen, underground stems Ex: Garlic, onion, lilies, daffodils, tulips, and shallots Vegetative structures developed from root or stems Tubers Ex: Stem tubers – Potatoes and yams Root tubers – Sweet potatoes and dahlias Corms Enlarged, bulb-like underground stems Ex: Taro, gladiolus, and crocus Plant shoots arisen from underground buds Suckers/Root sprouts Ex: Apple, cherry, and banana trees, hazel, shrubs, raspberries, gooseberries, and rose Vegetative structures developed at the margin of leaves Plantlets Ex: Kalanchoe, spider plant, hawkweed, dandelion, some citrus, some orchids, and many kinds of grass Bulbils Flower-like structures Ex: Garlic 1. Natural Vegetative propagation Based on using vegetative organ (stem, root, leaf) or parts of existing stock by forming adventitious root and adventitious shoot to generate new plants. This daughter plants will have traits identical to parent plant and called as clone. Asexual growth by modified stem: rhizome, tuber, bulb, stolon or runner, corm, suckers Rhizome, tuber, bulb, corm - acts as food storage Without special food storage - runners, suckers, leaf buds  Tuber Rhizome Bulbs Corm Sucker s Runner Methods of Natural Propagation: Modified stem a) Runners 🞂 Horizontal stem which grows or runs over the soil surface. 🞂 The terminal bud sends up new shoots & down new roots from it. 🞂 e.g. strawberries Methods of Natural Propagation: Modified stem b) Stem tubers 🞂 The tips of these underground stems become swollen with stored food - starch. 🞂 The swollen tips are called tubers. 🞂 The “eyes” are lateral buds that produce new shoots and roots using the stored food. 🞂 E.g. Potatoes Methods of Natural Propagation: Modified root a) Root Tubers 🞂 fibrous roots which swell with stored food 🞂 the tubers break off & grow into a new plant 🞂 e.g. tapioca Methods of Natural Propagation: Modified root b)Tap Roots 🞂 are swollen roots for food storage in plants, 🞂 storage in biennial plants. 🞂 e.g. carrot and turnip,  Methods of Natural Propagation: Modified leaves a)Plantlets 🞂 Some plants produce small plants on the side of their leaves. 🞂 When they reach a certain size, they fall off and grow into new plants. 🞂 e.g. cacti and Bryophyllum  Methods of Natural Propagation: Modified leaves b) Bulbs 🞂 A bulb (an underground bud) has a reduced stem, roots, 🞂 fleshy leaves swollen with stored food and a main bud in the centre which grows into a new plant 🞂 e.g. onion, daffodil, tulip 2. Artificial Vegetative propagation  Artificial vegetative propagation is usually used for the propagation (or reproduction) of those plants which produce either very few seeds or do not produce viable seeds.  Examples: Banana, Pineapple, Orange, Grape, Rose, etc.  Artificial propagation can be conducted via: 1) Cuttings – stem, leaf, root 2) Grafting – stem 3) Layering – stem/shoot 4) Budding – bud 5) Micropropagation : Tissue culture – stem, leaf, root 2. Artificial Vegetative propagation  Cutting Grafting Buddin Micro propagation /Tissue culture ADVANTAGES & DISADVANTAGES OF ASEXUAL REPRODUCTION ADVANTAGES DISADVANTAGES 🞂 Using only a single parent to 🞂 All offspring are identical to generate new offspring parents thus no quality 🞂 Producing large number of improvement. offspring 🞂 Organisms are unable to adapt 🞂 Can be produce in a short to changing conditions. time 🞂 Susceptible to disease as no 🞂 Do not need pollinator agent genetic variation 🞂 Compete for food as they 🞂 New offspring are genetically produced in colony identical to his parents SEXUAL REPRODUCTION  Sexual reproduction is involving two haploid gametes (n) fuse to form a diploid zygote (2n), which then grows into a new offspring which are genetically different from the parent.  Plant produce reproductive organs called flower  Sexual cell called gametes are made in the reproductive organs  Flower have specialized structures which are either female or male reproductive organ  Male reproductive organ make pollen grain  Female reproductive organs contain egg cells in the ovule inside the ovary  The gametes fuse in a process called fertilization  After fertilization, fruit and seed developed from part of the former flower Overview of the Flower Flower is a component of the shoot system and is the characteristic feature of angiosperms. Flower is responsible for the development of and seed and fruits. It is the plant's reproductive structure. They are usually bright colored to attract insects for pollination. Flowers that are not colorful are pollinated by wind. All flowers have the basic plan having four main parts: sepals, petals, stamens and carpels. The stamen is the male part of the plant and carpel is the female part of the plant. Structure of the Flower Stamen Male part of the Carpel flower Female part of Anther: produce the flower pollen grain Stigma: sticky Filament: landing site for support anther pollen grains above female Style: slender reproductive tube; transport organs pollen to ovary Petal Ovary: contain Often larger and ovules; develop brightly colored. The into fruit after petals fertilization collectively are Ovule: contain known as the egg cell which Corolla and help develops into attracting insects seed when for pollination fertilized Sepal Receptacle Protect of flower parts The stem portion, it is while in bud. found at the base in the Combination of sepals center of the flower. called Calyx Sexual Reproduction in Plants: Pollination CROSS POLLINATION SELF POLLINATION  also called allogamy,  occurs when pollen from  occurs only when pollen is one flower pollinates the delivered to a flower from a same flower or other different plant. flowers of the same plant. Double fertilization  Asexual vs sexual reproduction: Advantages Asexual Sexual Uniformity in offspring Offspring less likely to have mutation show up (genetic variation) Can increase populations Successful traits can be selected rapidly and failed traits can be prevented from passing on for the next generation Does not require a mate for Freedom mate selection reproduction to take place Much faster process Less likely to go extinct Little energy is required Less likely for errors to occur Less danger involved  Asexual vs sexual reproduction: Disadvantages Asexual Sexual Lacks genetic variation and lack Slower process of diversity in offspring because they reproduce offspring genetically identical to parents, the offspring inherit any mutations of the parent. Species more vulnerable to Lots of energy required extinction due to environmental change If parent has disease, offspring Mate required – can be difficult has it too to find Greater chance of error (harmful mutation) Population increases are limited INHERITANCE  Gregor Johann Mendel 1822 – 1884 Responsible for laws governing inheritance of traits He is an Austrian monk Studied the inheritance of traits in pea plants Developed the laws of inheritance Mendel’s work was not recognized until the turn of the 20th century Between 1856 – 1863, he cultivated and tested some 28000 pea plants He found that the plants offspring retained traits of the parents Was known as “father of Genetics” Mendel’s Experiment on inheritance Chromosomes are particular carriers of genetic information These information are encoded by genes These genes consists of nucleotides on a strand of DNA’s double helix. Genes consists information about an organism feature (height, seed, colour leaf shape etc) Each character may appear in two or more forms called a trait The variant form of each trait, known as allele, is a code for each trait. Monohybrid cross involves individuals that have different alleles for a specific gene This type of hybrid cross is based on the law of segregation Monohybrid cross The monohybrid cross is between two parents, using a pair of contrasting character. These characters that are being studies are governed by two multiple variations called locus. A locus is a fixed position on a chromosome, like the position of a gene. When two plants of the same traits are bred with each other, and all their offspring have the same trait, is called “Pure breeding”. In the cross, each parent is chosen to be homozygous for a given trait. The purpose of monohybrid cross It is used to determine the relationship between two alleles. The offspring make up the first filial generation (F1 Gen) Members of F1 are heterozygous Phenotypes of the F1 expresses dominant traits. Crossing the F1, produces the F2 generation with the phenotype ratio of 3:1 Punnett square Invented by Reginald punnet Used to predicts possible outcomes of genetic crosses. The alleles of one parent are written across the top of the square (one allele per box) and those of the other parent are written on the side R = round r = wrinkle Genotype frequency: 25% RR, 50% Rr, 25% rr Phenotype frequency: 75% Round, 25% Wrinkle  Mendel’s Laws 1. Law of Dominance: if two alleles at a locus differ, then one, the dominant allele determines the organism’s appearance; the other, the recessive allele, has no noticeable effect on the organism’s appearance. 2. Law of segregation: the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes. 3. Law of independent assortment: each pair of alleles segregates independently of other pairs of alleles during gamete formation. 1. Law of Dominance In a cross of parent that are pure for contrasting traits, only one form of the trait will appear in the next generation All the offspring will be heterozygous and express only the dominant trait YY x yy yields all Yy (yellow seeds) 2. Law of Segregation During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other Alleles for a trait are then “recombined” at fertilization, producing the genotype for the traits of the offspring. during gamete formation each member of the allelic pair separates from the other member to form the genetic constitution of the gamete. Related to Monohybrid Inheritance. Mendel’s cross of pea plants for color 3. Law of Independent Assortment Alleles for different traits are distributed to sex cells (& offspring) independently of one another Alleles of different genes assort independently of one another during gametes formation. Related to Dihybrid Inheritance. ⮚ Study about the inheritance of two pairs of different traits. ⮚ Example: Seed color and Seed shape This law can be illustrated using Dihybrid crosses