Chapter 13- Meiosis Flashcards
What are the similarities and differences between cell division and the life cycle of sexually reproducing organisms?
Cell division is when a single cell splits into two daughter cells while the life cycle of sexual organisms involves alternating phases of cell division which results in genetic diversity
Both processes involve DNA replication and some for of division
What are the origins of homologous chromosomes and their replication during meiosis?
Human females have a homologous pair of X chromosomes (XX) and males have X and Y (XY)
Homologous chromosomes separate in meiosis I; during crossing over non sister chromatids of homologous chromosomes exchange DNA segments
What are the three types of sexual life cycles?
Haploid dominant, diploid dominant and alternation of generations
What are the stages of meiosis I?
Prophase I: Chromones begin to condense, each pair of chromosomes forms a tetrad
Metaphase I: Tetrads line up at the metaphase plate with one chromosome facing each pole
Anaphase I: Pairs of homologous chromosomes separate; one chromie moves towards each pole
Telophase I: Each half of the cell has a haploid set of chromies; each chromie still consists of two sister chromatids
Cytokinesis: Usually occurs simultaneously and forms two haploid daughter cells
What are the stages of Meiosis II?
Prophase II: A spindle apparatus forms, in later prophase II chromies move towards the metaphase plate
Metaphase II: The sister chromatids are arranged at the metaphase plate; sister chromatids are no longer genetically identical due to crossing over
Anaphase II: Sister chromatids separate, now newly individual chromies move towards opposite poles
Telophase II: The chromosomes arrive at opposite poles, the nucleus forms and the chromies begin decondensing
Cytokinesis: Separates the cytoplasm
What are the sources of genetic variation in sexual reproduction?
1: Reshuffling of alleles during sexual reproduction produces genetic variation
- Independent assortment of chromies, crossing over and random fertilization
- Random fertilization is when any sperm can fuse with any ovum
- Sexual reproduction in general adds to the genetic variation in an environment which originates from mutations
What are the mechanisms and outcomes of nondisjunction in meiosis I and meiosis II?
Nondisjunction refers to the failure of homologous chromosomes in meiosis or sister chromatids (meiosis II) to separate properly during cell division; leads to gametes with abnormal chromosome numbers
In meiosis I this results in all four gametes being affected; in meiosis II only 2 of the 4 are affected
