Lesson 3: Sexual Reproduction Flashcards
what is sexual reproduction
form of reproduction in which individuals are produced from the fusion of two sex cells (sex cells usually come from two different parent organisms)
advantages to sexual reproduction and provide examples
- individuals that rely on sexual reproduction can adapt to a changing environment, due to their genetic variability which is not possible in organisms that reproduce asexually
- this can support the long term survival of a species
for instance, a pack of rabbits are residing somewhere, when wolves suddenly come into their environment and reside there too- the rabbits that run fast will survive and the rabbits that dont will not survive
- basically, if all rabbits were slow and genetically identical, as soon as the wolves come, they would all die and the species would have less chance of survival and possibly go extinct
disadvantages to sexual reproduction
- specialized organs are required to produce the sex cells
- specialized mating calls or bright colours to attract mates can also attract predators
- may require the loss of resources, like nectar in flowers
- the combining of genetic information may make the offspring weak and unable to survive
what are the two key processes in sexual reproduction
- formation of haploid cells, or gametes, which contain genetic information from the parents
- two sex cells joining together to form a zygote, the first cell of a genetically unique individual, through fertilization
what is meiosis
this is the process through which haploid gametes are formed; it involves two divisions that produces 4 haploid gametes from 1 diploid parent cell
gametogenesis
formation of sex cells
what are the two types of gametogenesis in humans
- formation of sperm by spermatogenesis
- formation of egg cells or ova by oogenesis
growth stage: interphase
- cell grows to nearly twice in size
- nucleus makes a copy of its DNA
- organelles are also replicated
meiosis 1: prophase 1
- chromatin condenses into chromosomes
- nuclear membrane dissolves
- centrioles move to opposite sides of the cells
- spindle fibers begin to grow
meiosis 1: prophase 1 (what are tetrads and how are they formed- through what process are they fomed)
homologous chromosomes come together and intertwine to form a tetrad by a process called synapsis
what is a tetrad
four sister chromatids together is called a tetrad
meiosis 1: prophase 1 (crossing over, what is it and how does it occur)
crossing over may occur at this stage
- when intertwined chromatids from different chromosomes break off and reattach at the chiasmata
- this causes an exchange of genetic material at certain sections
- it works to mix or recombine genetic information, further increasing the genetic variation in the gene pool
meiosis 1: metaphase 1
the tetrads migrate towards the center of the cell, called the equatorial plate
- spindle fibers are attached at the centromeres of the chromosomes
- the tetrads align their centromeres in the middle of the cell
meiosis 1: anaphase 1
homologous chromosomes move to opposite poles of the cell when the spindle fibers shorten
- this means that only one of the two chromosomes from each homologous pair will be in each new daughter cell and therefore are genetically unique
- ex: each of your sperm or egg has only the chromosome you received from your mom or your dad, not both
meiosis 1: telophase 1
the nuclear membranes reform, spindle fibers dissolve, and the cell begins to divide via the first cycle of cytokinesis (each new cell has only 1 and not 2 duplicated copy of a chromosome at this point)
- only the maternal or paternal chromosome is in each new cell
- therefore, cells are haploid