Meiosis and Sexual Reproduction Notes To be used with Meiosis and Sexual Reproduction Guided Notes

Genes and Heredity Heredity - the passing of traits from parents to offspring. Genetics - the study of heredity (the passing of traits) Each human cell contains 30 thousand different genes

Karyotype Karyotype is a chart of an organism’s chromosomes. All 30,000 genes are located on 23 pairs of chromosomes.

Genes and Heredity Genes: Factors that control organism traits or characteristics. Part of a chromosome containing the genetic code Passed on from parent to offspring.

Alleles T t t T Alleles: part of a gene that is located on a chromosome. Example: Height(gene): tallness or shortness(alleles) The alleles determine how each gene is expressed. At least two alleles for one gene. Locus: Location of gene on a chromosome. T T t t

Meiosis Meiosis: A type of cell division where the chromosome number is reduced to half. The process in which cells undergo two dividing phases to form gametes. Meiosis only produces sex cells (gametes).

Meiosis Gametes are your sex cells. Your egg and sperm cells. Sexual reproduction (sperm + egg)produces a zygote.

Meiosis

Diploid vs. Haploid Diploid Number (2n): the number of chromosomes found in all body cells. Humans 46. Haploid Number (n): 1/2 the diploid number of chromosomes. Humans 23. found in the egg and sperm cells of a species DIPLOID HAPLOID

Diploid vs. Haploid Organism Diploid # Haploid # Human 46 Chimpanzee 48 Dog 78 Fruit fly 8 Garden pea 14 Adder’s fern 1260 23 24 39 4 7 630

Terms Gametes: eggs or sperm Gonads: specialized organs in higher animals where the gametes are made Ovaries: female gonads Testes: male gonads

Meiosis Interphase Preparation phase Organelles & cell grows Chromatin duplicates Non dividing phase

Chromatin-Chromosome-Homologous Chromosome Sister Chromatid Chromosome Homologous Chromosome

Homologous Chromosomes: -a pair of chromosomes that contain genes for the same traits. -one chromosome is from mom the other from dad. -same size & centromeres are in same location.

Homologous chromosomes pair up according to: 1. same genes 2. size 3. centromere loci

Prophase I Homologous chromosomes become visible & pair up Prophase I Homologous chromosomes become visible & pair up. The nuclear membrane starts to disappear. Centrioles are present.

Prophase I Synapsis: the meeting of homologous chromosomes Tetrads: the two pairs of homologous chromosomes Crossing Over: the exchange of chromosome pieces Crossing over increases the variability of the offspring This is why the offspring of sexual reproduction show many variations - Crossing over occurs only during prophase

Metaphase I Centrioles move to poles extending spindle fibers Metaphase I Centrioles move to poles extending spindle fibers. Homologous chromosomes attach to spindle fibers in middle of cell.

Anaphase I Cell is egg shaped Homologous chromosomes pull apart.

Telophase I/Cytokenesis Complete cell division Cell is figure eight in shape.

End of Meiosis I Cytokenesis - cytoplasmic division of the cell occurs ends the first stage of meiosis At the end of meiosis I there are two cells each daughter cell contains the diploid number of chromosomes

Meiosis II Meiosis II: Similar to mitosis but no interphase & chromosome replication. No pairing of homologous chromosomes. Single chromosomes line up during metaphase II. Diploid (2n) is reduced to haploid (n)

Meiosis

Mitosis vs. Meiosis

Problems during Meiosis Normally, homologous chromosomes separate and move toward opposite poles of the cell. Problems during anaphase: this disorder is called non Disjunction Nondisjunction: the failure of homologous chromosomes to separate

Nondisjunction Down's syndrome: results from the nondisjunction of chromosome 21 individual has an extra 21st chromosome

Down’s Syndrome Rates

Mistakes in Mitosis can be Good polyploidy: having an entire extra set of chromosomes Will result in the 3n or 4n number of chromosomes - Many plants are a result of polyploidy; banana & day lily

Summary Meiosis is very similar to two divisions of mitosis. The diploid number (2n) of chromosomes is reduced by half to the haploid number (n) Eggs and sperm are formed Crossing Over occurs—lots of variation Variations rarely occur in MITOSIS Variations often occur in MEIOSIS Gaccione likes little boys and girls on Tuesdays only

Results of Meiosis Mitosis is associated with growth, replacement and asexual reproduction Meiosis is associated with sexual reproduction & reduces the # of chromosomes in half Spermatogenesis: the production of sperm Produces 4 sperm Oogenesis: the production of ova or eggs Produces one egg and three polar bodies Penis