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

Before Meiosis lets look back at Mitosis

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

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. All of your genes are located on 23 pairs of chromosomes

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

Chromosomes 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.

Amniocentesis Amniocentesis: a medical procedure used in prenatal diagnosis of chromosomal abnormalities. Chromosomes are taken from the amniotic fluid.

Karyotype The chromosomes from the amniotic fluid are then placed on a karyotype. A karyotype is a chart of an organism’s chromosomes.

Karyotype Next, the chromosomes are matched up according to: 1. if they came from mom or dad. 2. how tall they are. 3. centromere location.

Karyotype A karyotype can reveal if a person… 1. is, male or female 2. has a normal number of chromosomes 3. has an abnormal number of chromosomes. Example: Down’s syndrome

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. -found in the somatic(body) cells 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 # (body cells) Haploid # (sex cells) Human 46 Chimpanzee 24 Dog 78 Fruit fly 4 Garden pea 14 Adder’s fern 1260 23 48 39 8 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 Meiosis I Meiosis II Has all the phases mitosis has. I P M A T Has all the phases meiosis I has, except Interphase. P M A T

Prophase I of Meiosis During Prophase 1 crossing over takes place. Crossing over is : 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 I

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 of Mitosis & Meiosis 1. Meiosis is very similar to two divisions of mitosis. 2. The diploid number (2n) of chromosomes is reduced by half to the haploid number (n) 3. Eggs and sperm are formed Crossing Over causes lots of variations Variations rarely occur in MITOSIS Variations often occur in MEIOSIS

Summary Mitosis is associated with asexual reproduction. Mitosis takes place in somatic (body) cells. What is produced from mitosis? Two identical daughter cells How many? 4 10. Meiosis is associated with sexual reproduction. Meiosis takes place in sex cells. Meiosis produces gametes and three polar bodies.