Dixon Exam 2 Study Guide Lecture 11 1 Be able to distinguish between the genetic consequences of sexual and asexual reproduction In asexual reproduction a single individual is the sole parent and passes copies of all of its DNA to the offspring creating a direct clone this does not allow for any genetic variation unless a mutation arises the genomes are virtually exact copies of the parent s genome In sexual reproduction two parents give rise to an offspring that has unique combinations of genes inherited from the 2 parents they are variations of a common theme of family resemblance but not exact replicas Genetic variation is the most important consequence of sexual reproduction 2 Be able to distinguish the cellular processes behind asexual mitosis and sexual meiosis reproduction Mitosis results in 2 diploid cells and Meiosis results in 4 haploid cells 3 Know that chromosomes exist as homologous pairs in diploids Diploid means it has 2 chromosome sets and is abbreviated 2n 4 Be able to explain why meiosis produces haploid daughter cells from diploid parents Gametes are the only cells not produced by mitosis During meiosis the number of chromosomes are halved therefore creating haploid cells If the cells were to undergo mitosis instead of meiosis they would be diploid like the somatic cells and have a double number set of chromosomes this type of cell division reduces the number of sets of chromosomes from 2 to 1 in the gametes counterbalancing the doubling that occurs during fertilization 5 Know that sexual life cycles alternate meiosis and fertilization this contributes to genetic variation among offspring 6 Be able to explain how sexual life cycles vary in the timing of meiosis and fertilization 3 main types of sexual life cycles Humans most other animals gametes are the only haploid cells meiosis occurs in germ cells during the production of gametes which undergo no further cell division prior to fertilization After fertilization the diploid zygote divides by mitosis producing a multicellular organism that is diploid Plants some algae alternation of generations includes both haploid and diploid stages that are multicellular The multicellular diploid stage is the sporophyte Meiosis in the sporophyte produces haploid cells called spores Unlike a gamete a haploid spore doesn t fuse with another cell but divides mitotically generating a multicellular haploid stage known as a gametophyte Therefore in this type of cell cycle alternation of generations the sporophyte generation produces a gametophyte as its offspring and the gametophyte generation produces the next sporophyte generation The third type is common in most fungi and some protists After gametes fuse and form a diploid zygote meiosis occurs without a multicellular diploid offspring developing Meiosis produces not gametes but haploid cells that then divide by mitosis and give rise to either unicellular descendants or a haploid multicellular adult organism The haploid organism carries out further mitoses producing the gamete cells The only diploid stage found in these species is the single celled zygote Note that either haploid or diploid cells can divide by mitosis depending on the type of life cycle Only diploid cells can undergo meiosis because haploid cells have a single set of chromosomes that cannot be further reduced Terms to know Haploid gametes contain a single set of chromosomes have a haploid half Diploid a cell with two chromosome sets has a diploid double number of set of chromosomes n cells 2n Homologous chromosome same length centromere position and staining pattern Both chromosomes of each pair carry genes controlling the same inherited characteristics Sister chromatid generated when a single chromosome is replicated into two copies of itself these copies being called sister chromatid Gametes reproductive cells sperm eggs Zygote fertilized egg Meiosis produces the gametes Fertilization joining of the egg and sperm Gonad ovaries in females testes in males organs tat produce gametes Sexual reproduction two parents give rise to an offspring that have unique combinations of genes inherited from the parents Asexual reproduction a single individual is the sole parent and passes copies of all its genes to its offspring without the fusion of gametes Clone a group of genetically identical individuals Spore typically one celled reproductive unit capable of giving rise to a new individual without sexual fusion Extra things to know Mitosis genetically identical daughter cells Development growth and asexual reproduction Meiosis daughter cells contain a subset of parent cell s genes Preconditions for sexual Reproduction formation of gametes Homologous chromosomes genetically similar but not necessarily identical Sister chromatids of same chromosome genetically identical result of S phase of cell cycle VERY IMPORTANT diploidy vs haploidy has NOTHING to do with sister chromatids Lecture 12 1 Be able to explain how meiosis produces haploid daughter cells by separating homologous pairs of chromosomes so that one homolog goes to each cell reduces number of chromosomes by half and introduces genetic variability amongst the gametes 2 Know that meiosis consists of two stages meiosis I and meiosis II Meiosis I separates homologous chromosomes Meiosis II separates sister chromatids 3 Know that the end product of meiosis is 4 haploid cells 4 Know the names of the stages of meiosis and what happens in each 5 Know that the pairing of homologs and crossing over both occur in prophase I and be able to explain the significance of both Homologous chromosomes are chromosome pairs of the same length centromere position and staining pattern with genes for the same characteristics at corresponding loci One homologous chromosome is inherited from the organism s mother the other from the organism s father They pair synapse during meiosis or cell division that occurs as part of the creation of gametes Each chromosome pair contains genes for the same biological features such as eye color at the same locations loci on the chromosome Each pair however can contain the same allele both alleles for blue eyes or different alleles one allele for blue eyes and one allele for brown eyes for each feature Crossing over is when homologous pairs of chromosomes exchange genetic information between them in Prophase I of meiosis The importance is that it creates vast numbers of possible combinations of alleles in the gametes 6 Be able explain how the random
View Full Document
Unlocking...