Presentation on theme: "Meiosis is the Basis of Sexual Reproduction"— Presentation transcript:
1 Meiosis is the Basis of Sexual Reproduction Chapter 6Meiosis is the Basis of Sexual Reproduction
2 Sexual ReproductionRequires two parents and results in genetic variationProduces offspring that are genetically different from each other, from parents and from any other member of their species.Genetic variation occurs because the offspring inherits half of its genetic material from the female parent and the other half of its genetic material from the male parent.
3 Terminology: Sexual Reproduction Haploid: half the genetic contentHalf of the genetic material or (Haploid) are carried in gametes which are specialized cells needed for reproduction.Gametes often referred to as sex cells.Fertilization: male sex cell combines with female sex cell to produce a zygote (diploid)Diploid: Genetic content equal to the parentEmbryo: the zygote undergoes mitosis and cell division to produce an embryo.
4 MeiosisMeiosis occurs in gametes (eggs and sperm) and is a process that produces eggs and sperm with half the number of chromosomes as body cells.Meiosis occurs in two parts, Meiosis I and Meiosis II.Interphase occurs before Meiosis I begins (this is when the cell increases in size, makes proteins and organelles, and DNA duplicates: Basically the cell gets ready to divide)
5 Meiosis I:Similar to mitosis, EXCEPT in meiosis I, a pair of matching chromosomes (one from each parent) called a homologous pair, lines up at the equatorThe homologous pair separates and moves to opposite poles, and two daughter cells are formed at the end of Meiosis IThe phases are called Prophase I, Metaphase I, Anaphase I, Telophase I
6 Prophase I: Metaphase I: Homologous chromosomes shorten and thicken and the membrane around the nucleus disappears.Metaphase I:Homologous pairs are lined up at the equator of the cell
7 Anaphase I: Telophase I: Homologous pairs move to opposite poles of the cell.Telophase I:Membrane for the nucleus forms around each set of chromosomes. Now there are two nuclei in one cell and the cell is ready to divide again.
9 Meiosis II: DNA is NOT replicated again before Meiosis II. Meiosis II is like mitosis because in both processes, the chromatids of each chromosome are pulled to opposite poles.The stages are Prophase II, Metaphase II, Anaphase II and Telophase IIEach daughter cell inherits one chromatid from each chromosome.End result is 4 haploid cells, each with half the number of chromosomes as the original parent cell.
11 Comparing Mitosis and Meiosis Core LabComparing Mitosis and Meiosis
12 Similarities and Differences between Mitosis and Meiosis: In body cellsIn sex organs to produce sex cellsTwo daughter cellsFour daughter cellsSame number of chromosomes as parent cellOne half the number of chromosomes as parent cellAsexual ReproductionSexual Reproduction
13 Methods of Fertilization External Fertilization: a sperm cell and an egg cell unite outside the bodies of the parents.Example: fish, mosses and fernsHow do mosses reproduce?The male and female organs develop on the end of the stems or branches of the plantFertilization cannot occur without water.Sperm cells produced by the moss either swim across the damp ground or are splashed by raindrops into female parts of the plantsFertilization results in a new plant
15 How do flowering plants reproduce? Internal Fertilization: sperm cells are deposited inside the female’s body where they meet an eggHow do flowering plants reproduce?Internal fertilization occurs through a process called pollinationPollination is the transfer of male gametes in structures called pollen from the male reproductive part (stamen) to the female reproductive part of a plant (pistol)After pollen lands on the pistol, structures form to deliver the sperm cells to the egg cells.Zygote forms, grows into an embryo and is nourished by the food stored in the seed. The seed’s outer covering protects the embryo.
17 Sexual Reproduction in Insects Internal fertilizationMetamorphosis: a change in the form of an insect as it maturesIncomplete Metamorphosis: involves subtle changes through three life stages: egg, nymph, and adultThese changes are mostly due to growingThe nymph (immature) phases look much like smaller versions of the adultThe nymph is usually wingless and unable to reproduceThe nymph has to moult (shed exoskeleton) in order to grow and develop wings and reproductive organs
19 Another type of internal sexual reproduction Complete Metamorphosis: a change in the form of an insect as it matures. The adult form of the insect is completely different from the larval stage.Occurs in 4 stages: egg, larvae, pupa, adult.The larva (grub or caterpillar) is wingless and wormlikeThe larva’s job is to eat and growAfter several moultings, the larva enters the pupa stage and energy reserves are used in reorganizing organs and developing new adult structures such a wings.Adult’s main purpose is to reproduce and in many species the adult does not eat.
21 Comparing Complete and Incomplete Metamorphosis Number of Parents2Type of ReproductionSexual (internal)Number of Stages in Life Cycle43Habitat??
22 Advantages and Disadvantages of Sexual Reproduction Little energy required to find a mate for external fertilizationMore energy required to find a mate for internal fertilizationExternal fertilization, greater numbers of offspringInternal fertilization fewer offspring are producedInternal fertilization, there is more protection to the embryo and more prenatal careExternal fertilization, offspring are unprotected and are often preyed uponGreater genetic variation. More likely to survive disease or other threats that appear in a populationSome good traits may not be passed from parent to offspring
23 Compare/Contrast Sexual and Asexual Reproduction Number of Parent Cells12Gametes (eggs or sperm)None (cell divides)2 (cells unite to from a zygote)Variation in offspringLesserGreaterAmount of Energy requiredParental care
24 Male Reproductive System StructureFunctionTestesProduce sperm (male gametes) by meiosis and release hormonesScrotumProtects the testes, keeping them at a cooler temperatureVas deferensMuscular tubes in which sperm mixes with fluids to produce semen as the sperm move from the testes to the urethraUrethraOpening through which sperm leave the bodyPenisContains the urethra for the delivery of sperm
26 Female Reproductive System StructureFunctionOvariesProduce eggs (female gametes) by meiosis and release hormonesOviducts/Fallopian tubesLocation of fertilization. Connect the ovaries to the uterusUterusProtects and nourishes the zygote during development. Connects the oviducts to the cervixCervixSperm travel through this opening on the way to the uterus. It opens (dilates) to allow the baby to leave the body during childbirthVaginaSperm are deposited here. Opening though which the baby leaves the body, or where unfertilized eggs leave the body.
28 Stages of Human Development FertilizationFirst Trimester(weeks 1 – 12)Second Trimester(weeks )Third Trimester(weeks 25-38)-occurs in fallopian tube-egg and sperm unite to produce a zygote-movement from fallopian tube to uterus occurs-zygote now called an embryo, attaches to uterine wall-placenta and amniotic sac form-embryo becomes a fetus-by the end of this trimester, all major organs have begun to develop-skeleton forms-nervous system begins to function-mother begins to feel movement-organs continue to develop-rapid increase in size-immune system develops-increased movementNote: Once fertilization occurs, mitosis controls the growth and development from the zygote into adulthood.
29 Possibly ask a public health nurse to address the next two slides and last few slides on reproductive systems
30 Visible Signs of Pregnancy These signs vary from one person to another.Signs include:Menstrual flow stopsWidening of the hipsEnlargement of the breastsMorning sicknessWeight gainCravings
31 Major Shifts in Scientific Understanding of Genetics Gregor Mendel (mid 1800’s):Experimented with inherited traits in pea plants.Working with several generations, he showed that traits were inherited from parent plantsHe isolated the parts in the seeds that passed on the traits of color and shape
32 Major Shifts… Francis Crick and James Watson (1953) Described the structure of DNAShowed that DNA is an organization of genes into a double helix shape, like a twisted ladderThe specific makeup of this ladder helped explain how a cell could make exact copies.The ladder came apart and each side acted as a template on which a new side could form
33 Major Shifts… Human Genome Project: Genome: consists of the full set of genetic material that makes up an organismScientists around the world collaborated for about 20 years to identify every gene in the human DNAA big surprise was how few genes make up human cells. Only one sixth the estimated numberAnother surprise, how alike the genes of very different animals are
34 Major Shifts… Genetic Engineering Scientists are now selectively taking fertilized eggs with particular genes (such as gender, or absence of particular disease like Huntington’s disease) and implanting them into the female parent.This is embryo screening to select a certain offspring.Definitely some ethical issues arise from this process
35 Genetic Conditions that Cannot be Cured Down Syndrome: the results of a chromosome mutationCaused by an extra chromosomePeople with this syndrome have characteristic facial features and shorter statureEmbryo screening currently exists for this condition but if an individual is born with this condition it is incurable.
36 Genetic Conditions … Cystic Fibrosis Embryo screening exists for this condition.Caused by a mutationProtein that is responsible for moving a substance (chloride ion) into and out of the cell is not made correctlyMucus thickening in the lungs occurs and breathing is difficultLung infections can occur more easily
37 Genetic Conditions… Allderdice Syndrome A local example, restricted to an isolated community of Sandy point on the west coast (later resettled to St. George’s)Caused by an inverted insertion of a chromosomeLeads to low birth weight, and and facial abnormalities and psychomotor dysfunction
38 Evaluate information and evidence gathered on the topic of genetics and genetic engineering ???????