Reproduction and Meiosis How organisms make new individuals

Asexual reproduction Requires 1 parent, no sexes Uses mitosis

Budding Multi-cellular offspring grows off of parent Ex. Hydra

Binary Fission A single cell Protista divides into two cells forming two new organisms by mitosis Ex. amoeba

Sexual Reproduction Requires 2 parents Uses a process called meiosis Male produces sperm with half the DNA Female produces eggs with half the DNA Combined - Sperm and eggs come together to form new individual zygote with whole DNA

Fertilization The combining of the male sperm and the female egg

External fertilization When the fertilization occurs outside of the body. Ex. Male fish releases sperm over female eggs in water – called spawning

Internal Fertilization When fertilization occurs inside the females body Ex. Human, mammals, reptiles, birds

Plant reproduction Also sexual Male and female usually on same plant Conifers have male and female cones

Gametes Male gamete – Sperm Millions produced at one time very small have a flagella to swim Produced in Testes Female gamete – Egg Only one produced at a time Very large free moving Produced in Ovaries

Zygote When sperm and egg unite, they combine chromosomes for a zygote with 2 sets of chromosomes. The offspring has a combination of the genetic instructions from both parents

v Haploid = Each gamete has ½ the number of chromosomes of the parents. Diploid = two sets of chromosome. The normal number Egg and sperm form a diploid zygote

Chromosomes DNA wound up on histone proteins for sorting during mitosis

Karyotype A method of visually organizing an individuals chromosomes Aids in identifying chromosome abnormalities

Autosomes All the Non sex chromosomes Humans have 22 autosomes pairs

Sex Chromosomes X and Y – Different, not homologous Determine male or female Presence of a Y causes development as a male

Meiosis Meiosis is the process for the formation of Gametes Meiosis is similar to mitosis but there is a second Complete division Occurs ONLY in sex organs

Gameteogenesis Formation of gametes by meiosis. In male 4 sperm are produced, In female only 1 egg and 3 polar bodies are produced

Meiosis I First stage of meiosis Homologous Chromosomes line up and go to separate cells. Chromatids do NOT split at Centromere

Meiosis II Immediately follows telophase I NO new DNA replication occurs Each homologue splits at centromere, with only one chromatid to each cell

                                    Prophase I Chromosomes appear, centrioles, spindle fibers etc

Tetrads The two sets of homologous chromosomes that organize together during prophase I Provides for crossing over and recombination between homologues

Crossing over Occurs during prophase I into metaphase Homologous Chromosomes switch some pieces (Recombine) between different chromatids to increase genetic diversity Chisamata – where homologues connect and cross over

Metaphase I Chromosome Tetrads line up NOTE - matching pairs line side by side (in mitosis, each chromosome is separate)

Anaphase I Chromosome PAIRS separate (In mitosis each chromatid separates from sister)

Telophase I 2 cells separate following cytokinesis Meiosis II IMMEDIATELY follows

Prophase II Each of the 2 cells prepares to divide again

Metaphase II Chromosomes line up along middle

Anaphase II Sister Chromatids separate                       

Telophase II Four haploid daughter cells are produced Each daughter cell has half the number of chromosomes from the parent cell (haploid)

Interesting fact Because each of the 23 pairs of chromosomes can line up in two different ways one person can produce more than 8 million different kinds of eggs or sperm.  When fertilization occurs, 70 trillion different zygotes are possible! You are 1 in 70 trillion

Meiosis overview

Comparison Mitosis Meiosis 1  2 cells 1  4 cells Diploid  diploid Goe through Once Homologues line up separately No crossing over Chromatids separate during anaphase Produces identical cells with full DNA Meiosis 1  4 cells Diploid  haploid Goes through Twice Homologues line up together in tetrads Crossing over Chromatids do not separate during anaphase I, only anaphase II Produces gametes with half DNA

Animation of meiosis