Meosis

What does the multicellular organisms require for development

 both mitosis          and meiosis

sex cells are formed by

meoisis

gametes

 gametes (sex cells) – sperm & egg

meiosis

• Purpose: Produces gametes (sex cells) – sperm & egg
  
  

meiosis involves…

Meiosis involves two distinct divisions, called Meiosis I and Meiosis II

by the end of meosis

• By the end of Meiosis II, the 1 diploid cell that entered meiosis has become 4 haploid cells

diploid

Diploid – a cell that contains homologous chromosomes (one from each parent) 

2N

• Found in somatic or body cells (ex. Skin, digestive tract) - Diploid

Haploid

Haploid – a cell that contains only a single set of chromosomes (one from either parent, not both);

represented by the symbol N or 1N

haploid cells are found in…

• Found in gametes or sex cells – sperm & egg

  • Example:  Humans 🡪 N = 23

homogulus pairs

• During Prophase  I corresponding homologous chromosomes from each parent pair up to form  homologous pairs

crossing over

• When homologous chromosome overlap its called crossing over.

when does crossing over happen

• Crossing over happens when parts of the homologous chromosomes switch places after overlapping

important of crossing over

• Crossing over increases genetic diversity

siblings

• The gene combinations that a person gets from his or her parents will be different, to varying degrees, than the combination a sibling may get.

nondisjunction

During Anaphase I or II if the centrioles do not properly attach the spindle fibers to the homologous chromosome before they start to pull, then a Nondisjunction will occur

a nondisjunction causes

• A Nondisjunction causes the gametes to have the wrong amount of chromosomes.

in male animals

• In male animals (including humans), 4 sperm cells are produced from one meiotic division

in female animals

• In female animals (including humans), the cell divisions at the end of meiosis I & II are uneven, so that 1 large egg is produced along with
  3 other cells, called polar bodies, which are discarded and not involved in reproduction

zygote

Zygote – fertilized egg cell formed form the joining of the gametes (sperm and   egg)

centricoles

Centrioles – Organelles in the cell that help to move chromosomes during cell division

chromotin

Chromatin – What you call the DNA during Interphase, Very easy to access the genes for transcription and translation to create proteins

chromosomes

Chromosome – What you call the DNA during the actual cell division stages (Pro-, Meta-, Ana-, and Telophase). 
    Condensed/packed DNA for easy movement during cell division

chromotid

Chromatid – One of the “arms” of a chromosome ‘X’.  Each chromatid is identical to the other because it is created by replication.
    A chromosome is made of two Sister Chromatids.

spindle fibers

Spindle Fiber – fibers created and used by the centrioles to move the chromosomes around during the division stages.

homogulus chromosomes

Homologous Chromosomes – the same numbered chromosome that pair up from mother and father (ex: mom’s chromosome 1 and dad’s chromosome 1)

crossing over definiton

Crossing Over – A kind of chromosomal mutation that happens in Prophase 1 of meiosis.
    Homologous chromosomes overlap and exchange pieces of the
    chromosome which caused genetic variability.

nondisjuction

Nondisjuction – Happens in either Anaphase 1 or Anaphase 2 of meiosis when one centriole does not connect to the chromosome with a spindle fiber.
    Causes the gametes to have extra or missing chromosomes.

fertilization

Fertilization – The process of making a zygote.  When egg and sperm cells fuse and combine their genetic information (DNA)

number of cells at the beginning of meiosis

1 diploid cell

number of cells at the end of meiosis

4 haploid cells

number of chromosmes at the start of meosis

46

number of chromosomes at the end of meiosis

23

what does meiosis produce

4 unique cells

meiosis produces what type of cells

gamete (sex) cells

mitosis continues throughout an organisms life for..

• The organism grows by adding new cells through mitosis 

3. Mitosis continues throughout an organism's life for:

-growth 

- maintenance (replace old cells)

- Repair damaged tissues

describe meosis

Haploid male and female gametes come together forming a diploid zygote (fertilization)

what happens to the number of chromosomes during meiosis

reduces the number of chromosomes in half such that there is only one copy of all the chromosomes