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level: Meiosis and mitosis

Questions and Answers List

level questions: Meiosis and mitosis

QuestionAnswer
Meiosis1. Meiosis produces haploid gametes 2. Gametes fuse during fertilisation to form a zygote. The diploid number is restored. 3. Ensures the diploid number remains the same after every generation.
What is meiosiscell division to produces 4 daughter cells gametes are haploid and genetically different
Diploidpairs of chromosomes that match
HaploidChromosomes that do not match- half the number of chromosomes
Importances of meiosisProduces sex cells which are HAPLOID During fertilisation (egg and sperm fuse) the diploid number is restored This ensures that the diploid number remains the same after every generation (DP = SAME) Meiosis produces genetic variation in offspring which increases the chance of species survival if the environment changes adversely ( SURVIVAL)
What does random fertilisation of haploid gametes DOfurther increases genetic variation within that species
Meiosis brief summaryDiploid cells (2n) divide and divide again into haploid cells (n)
Meiosis1. Meiosis produces haploid gametes 2. Gametes fuse during fertilisation to form a zygote. The diploid number is restored. 3. Ensures the diploid number remains the same after every generation.
InterphaseIn interphase the following occurs: 1) DNA replication occurs 2) Organelles are synthesised 3) Increased protein synthesis occurs 4) Increased rate of respiration (to provide energy for processes 1-3)
ProphaseIn prophase the following occurs: 1) Chromosomes condense so they become shorter and thicker. 2) Nuclear envelope breaks down. IN MEIOSIS BIVALENTS FORM CHROMOSOMES CAN GET TANGLED CAUSING CROSS OVER.
MetaphaseIn metaphase the following occurs: 1) Spindle fibres form. 2) Centromeres attach to spindle fibres. 3) Chromosomes move along the spindle fibres to the middle of the cell.
AnaphaseIn anaphase the following occurs: 1) Centromere splits. 2) Sister chromatids separate. 3) Sister chromatids pulled along spindle fibres to opposite poles of the cell.
TelephaseIn telophase the following occurs: 1) Nuclei reform. 2) DNA becomes chromatin (loose). 3) Spindle fibres begins to break down. 4) Two genetically identical cells are formed. *CYTOKINESIS – the end of mitosis (where the cell splits to form two separate cells).
What causes genetic variation in meiosisCross over independent assortment of homologous chromosomes
What is cross overBivalents form. · Homologous chromosomes twist round each other. · The point of cross over is called a chiasma. · A section of DNA with a block of alleles breaks off, swaps position and reattaches (cross over). · This creates new combinations of alleles
Independent assortment of chromosomesHomologous chromosomes line up in pairs across the cell · Maternal and paternal chromosomes line up randomly within each pair · So that different combinations of chromosomes are produced in the gamete cells · This creates different combinations of alleles.
What is chromosome non disjunctionMutations in the number of chromosomes can arise spontaneously by chromosome non-disjunction during meiosis. CAUSES MUTATIONS
how does non disjunction occur1. Failure of a homologous pair of chromosomes to separate during the first division of meiosis 2. Failure of a pair of sister chromatids to separate during the second division of meiosis
Interphase known as the growth stage whyG1 – growth phase 1 (Increased protein and organelle synthesis) · S phase – DNA replication occurs. · G2 – growth phase 2
Mitosis brief summarycell division to produces 2 genrtcally identical cells 1 division in one cycle 2 new cells produced starting cell is diploid new cell is diploid all cells divide except sex cells
Meiosis brief summarycell divisions to produce 4 genetically different sex cells 2 divisions in one cycle 4 new cells produved starting cell diploid new cell haploid = half number only sex cells divide
Diploid =pairs of chromosomes homologous
Haploid =pairs of chromosomes but different