Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Asexual reproduction
Document related concepts
no text concepts found
Transcript
Inheritance of Traits Sexual reproduction In organisms that reproduce sexually, traits are inherited through gametes. Gametes (sperm and eggs) are produced by meiosis. Asexual reproduction Genetically identical clones of the parent. In some exceptions, genetic material can be exchanged between clones. Example: antibiotic resistance in bacteria can be transferred via plasmid DNA. In sexual reproduction, haploid sperm and egg unite to form a diploid zygote. Bacteria reproduce asexually by binary fission. Binary Fission and Budding Asexual reproduction: binary fission. A single parent cell dividing into two daughter cells. Binary fission in the bacterium Staphylococcus Asexual reproduction: budding. Part of the parent body is ‘pinched off’ to produce a small individual exactly like the parent. Budding in Hydra New individual Sexual vs Asexual Reproduction Sexual Reproduction Asexual Reproduction Produces genetic variation. Quick. Usually takes longer than asexual reproduction. No variation, so are more vulnerable when environment changes. Daphnia with eggs. These diploid eggs are produced mitotically and hatch into clones of the adult. Some organisms, e.g. aphids and water fleas (Daphnia), reproduce asexually most of the time, but also go through sexual reproduction as well. Introduction to Meiosis The purpose of meiosis is to produce haploid sex cells (gametes). They have one copy of each chromosome. In humans the haploid number is 23. Meiosis only occurs only in the ovaries and testes. Sperm surround an egg prior to fertilization Meiosis I Interphase DNA replication 2N One chromosome from each homologous pair is donated to each intermediate cell. In prophase 1, homologues pair up to form tetrads in a process called synapsis. The sister chromatids can exchange genetic information during crossing over. Prophase 1 Synapsis and crossing over 2N Metaphase 1 Anaphase 1 separates homologous chromosomes. Tetrads line up on the equator of the cell. 2N Anaphase 1 Telophase 1 1N Intermediate cell Intermediate cell Homologues separate Meiosis II 1N Intermediate cell The second division of meiosis is similar to mitosis. Prophase 2 There is no chromosome duplication in meiosis II. 1N Sister chomatids (now separate chromosomes) are pulled apart and are donated to each gamete cell. Metaphase 2 1N The gametes are haploid (1N). Anaphase 2 Telophase 2 1N Gamete (egg or sperm) Individual chromosomes separate Cell Division: An Overview Spermatogenesis Male embryo Mitosis Male adult 2N 2N Meiosis Sperm 1N Fertilization Zygote Mitosis 2N Mitosis Embryo 2N Somatic cell production Mitosis Female embryo Female adult 2N 2N Meiosis Egg 1N Oogenesis Adult 2N Somatic cell production Aneuploidy Nondisjunction during meiosis can lead to an abnormal chromosome number. These chromosomal defects are known as aneuploidy. XY XX XY XY XXY X XY X XO X X XXY X X XO Aneuploidy in Sex Chromosomes Aneuploidy can result in an abnormal number of sex chromosomes. Turner syndrome affects females. X Klinefelter syndrome affects males. XXY Turner Syndrome karyotype Aneuploidy in Autosomes Aneuploidy can also affect autosomes (non-sex chromosomes). In trisomy, the nucleus of the cells have one extra chromosome (2N+1). Three forms of trisomy survive to birth: Down syndrome (trisosmy 21) Edward syndrome (trisomy 18) Patau syndrome (trisomy 13) Down Syndrome karyotype
