Meiosis Cornell notes

Meiosis animation video https://www.youtube.com/watch?v=rqPMp0U0HOA

Each one of us have characteristics passed on to us from our parents Each characteristics we have is called a trait The DNA on the chromosomes are arranged in segments called genes Each chromosome consist of hundreds of genes

Sex cells formed by meiosis SEXUAL REPRODUCTION Sex cells formed by meiosis Requires 2 parents Offspring not identical Meiosis A kind of cell division that results in gametes (sex cells) with half the number of chromosomes Gametes In order to maintain the same chromosomes # from generation to generation, an organism produces gametes (sex cells) that have half the # of chromosomes Haploid Haploid means HALF, as in the number of chromosomes, written as n

Homologous Chromosomes * Human body cells have 46 chromosomes * Human body cells have 23 homologous pairs Meiosis and Fertilization One haploid gamete combines with another haploid gamete. As a result of fertilization, the cell now will contain a total of 2n chromosomes

The union of an egg and a sperm Fertilization n 2n The union of an egg and a sperm

Homologous chromosomes

Phases of Meiosis (2 cell divisions ) Interphase Chromosomes replicate Chromatin condenses

Phases of Meiosis (2 Cell divisions – Meiosis I & Meiosis II) MEIOSIS I Prophase I Pairing of homologous chromosomes, crossing over occurs, nuclear envelope breaks down, and spindles form

Metaphase I Spindle fibers attach to homologous chromosomes (pairs) and line up in the middle of the cell. Anaphase I The fibers pull the homologous chromosomes apart. Chromosomes move toward opposite sides of the cell.

Telophase I During Telophase I and cytokinesis, the spindles break down, chromosomes uncoil and form two new nuclei, the cell divides (2 daughter cells) **** The Chromosome number is reduced to half during Meiosis I forming haploid (n) daughter cells

MEIOSIS II Prophase II Chromosomes condense, spindle fibers form in each new cell, Spindle fibers attach to chromosomes Metaphase II Chromosomes line up in the middle of the cell

Anaphase II Sister chromatids separate and move towards opposite sides of the cell Telophase II Cells divide, resulting in 4 haploid cells – gametes (sex cells)

Meiosis Parent cell – chromosome pair Chromosomes copied 1st division - pairs split 2nd division – produces 4 gamete cells with ½ the original no. of chromosomes

Summary 3 to 4 sentences of meiosis notes

Mitosis, Meiosis, or Neither Number 1 - 6

What process is this?

How this sperm cell was created

DNA replication happens before this process.

When the sperm actually meets the egg.

I’m a single celled paramecium. Time to reproduce!

DNA replication happens before this process.

ANSWERS! Number 1 - 6

What process is this? Mitosis

How this sperm cell was created Meiosis

DNA replication happens before this process. Mitosis

When the sperm actually meets the egg. Neither! (Fertilization)

I’m a single celled paramecium. Time to reproduce! Mitosis

DNA replication happens before this process. Meiosis