Grade 9 Bio - Mitosis + Meiosis

What are 5 reasons a cell reproduces?

Reproduction, growth, development, replacement, and repair

Things copied during cell reproduction include…

DNA

organelles

cell membrane

lots of other molecules

A dividing cell…

duplicates its DNA.

The DNA starts as _________ in the nucleus.

chromatin

Why does chromatin become chromosomes for cell division?

If you tried to divide it like that, it could tangle & break.

Chromosomes are found in cells that…

are ready to divide.

DNA in chromatin form must be ______ __ into chromosomes before division

coiled up

Chromosomes

rod-shaped structure of DNA molecules, wrapped around proteins called histones

What is the purpose of histones in chromosomes?

To maintain shape

Chromatid

Each half of a duplicated chromosome.

Chromatids form as…

DNA making a copy of itself.

When the cell divides, each of the new cells will receive ___ _________ from each chromosome

one chromatid

What is the waist of chromatids?

Centromere

Sex chromosomes

responsible for development of reproductive organs and characteristics of an organism

Autosomes

all other chromosomes, besides the sex chromosomes

The pair of autosomes together are called…

homologous chromosomes

Diploid cells…

have a full set of chromosomes, containing both chromosomes for each homologous pair.

Haploid cells…

have half the number of chromosomes that are present in diploid cells.

Mitosis

division of the nucleus in somatic (body) cells

Mitosis results in…

new cells with genetic material identical to the original cell.

Cytokinesis

division of the cytoplasm

Meiosis

division reducing the chromosome number in half to form gametes

Cell Cycle

Repeating events that make up the life of a cell

Interphase

Time between divisions.

What are the three phases of interphase?

G1, S, G2

In G1…

cells grow to full size.

In S…

DNA is copied.

In G2…

cell gets ready for cell division.

G0 phase

Cells do not copy their DNA and do not prepare for cell division

What is an example of cells that enter the G0 phase?

Nerve Cells

When do cells enter G0 phase?

After they finish mitosis.

Chromatin

DNA wrapped around proteins (mess). How DNA is found most of the time.

Sister Chromatid

½ of a replicated chromosome.

Centromere

Protein disc that helps with division

What are the four phases of mitosis?

Prophase, Metaphase, Anaphase, Telophase

During prophase…

• the nucleus disappears

• chromatin becomes chromosomes

• spindle fibers form

During metaphase…

• chromosomes line up in the middle

• spindle fibers attach to centromere

During anaphase…

• spindle fibers shorten, pulling away chromosomes

During telophase…

• nucleus reforms

• chromosomes become chromatin

• spindle fibers disappear

During cytokinesis…

• either a cleavage furrow or cell plate is formed

• ends with 2 daughter cells

Prophase

Prepare

Metaphase

Middle

Anaphase

Apart

Telophase

Two nuclei

Does the cell cycle occur in prokaryotes or eukaryotes?

Eukaryotes

What process NEVER occurs in interphase?

Cell Division

Cells obtain ________ and duplicate or copy their __________ or genetic material during interphase.

nutrients, chromatids

Telomere

A region of repetitive DNA sequences at the end of a chromosome that maintains chromosomal stability and prevents chromosomal degradation

Centromere vs Centrioles

Centrioles are paired barrel-shaped organelles located in the cytoplasm of animal cells near the nuclear envelope. The centromere is the central region of the chromosome which consists of highly constricted DNA.

Since proteins and _______ are being made during g1, there is a great amount of ______ _________ occuring.

enzymes, protein synthesis

What are body cells called?

Somatic Cells

What are reproductive cells known as?

Germ Cells

Centriole

A barrel-shaped organelle which lives normally within the centrosome

Cell growth can be turned on and off within the cell by proteins called _______.

cyclins

Cancer

A disorder in which cells lose the ability to control their growth and division.

Malignant

invasive, cancerous cells; spreading the message of rapid growth to other cells

Metastasis

spreading of malignant cells

Carcinoma

External or internal body coverings.

Sarcoma

Tissues that support the body.

Leukemia and lymphoma

Blood-forming tissues.

What is the difference between cell division in an animal cell and cell division in a plant cell?

In animals, cytokinesis takes place through the formation of a furrow in the plasma membrane whereas, in the case of plants, cytokinesis takes place through the formation of a cell wall.

Diploid

Containing two complete sets of chromosomes, one from each parent

Haploid

A cell that contains a single set of chromosomes

What is crossing over?

the exchange of genes between homologous chromosomes, resulting in a mixture of parental characteristics in offspring

When does crossing over occur?

Prophase I

What is the purpose of meiosis?

To produce gametes.

Fertilization

A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.

Asexual Reproduction

The formation of offspring from one parent

Sexual Reproduction

Formation of offspring from two parents

Zygote

A diploid cell resulting from the fusion of two haploid gametes

WHat would happen if we made gametes through mitosis?

We would have 92 chromosomes and die.

Are gametes haploid or diploid?

Haploid

True or False: haploid n + haploid n = diploid 2n

True

Meiosis

Process of nuclear division that cuts the chromosome number in half.

How many rounds of cell division are there in meiosis?

Two

How many rounds of cell division are in mitosis?

One

How many haploid gametes are formed after mitosis?

Four

True or False: Meiosis is described as “reduction duplication.”

False

How many polar bodies are formed when a female sex cell goes through meiosis?

Three

Polar Body

A nonfunctional cell formed at the same time as an egg cell.

Homologous chromosomes

A pair of chromosomes holding information controlling the same inherited characteristics

What happens in prophase I in meiosis??

• Nucleus and nucleolus break down.

• The chromatin condenses into chromosomes.

• spindle fibers appear

• Homologous chromosomes containing the two chromatids come together to form tetrads, joining at their centromeres.

• “crossing over” occurs, which creates genetic variation.

What happens in metaphase I?

• Tetrads line up in the middle of the cell along the metaphase plate

• Spindle fibers attach each homologous chromosome.

What happens in anaphase I?

• Tetrads are separated by spindle fibers, sending the homologous chromosomes to opposite ends of the cell

• Independent Assortment: genetic material is pulled apart at random

What happens during telophase I?

• Nuclei are separated

• Nuclear membranes form again

• New cells are haploid, containing half the amount of DNA

• One of each homologous pair

• Telophase I is followed by Cytokinesis I, when cytoplasm is separated.

What happens during prophase II?

Same as prophase in mitosis.

What happens during metaphase II?

Same as metaphase in mitosis.

What happens during anaphase II?

Same as anaphase in mitosis.

What happens during telophase II?

Same as telophase in mitosis?

How many chromosomes are there in a cell before meiosis?

46

How many chromosomes are there in a cell after the first phase of meiosis?

23

How many chromosomes are there in a cell after the second phase of meiosis?

23 chromosomes

How many chromatids are there in a cell before meiosis?

92

How many chromatids are there in a cell after the first phase of meiosis?

46

How many chromatids are there in a cell after the second phase of meiosis?

23 chromatids

Meiosis allows for ___________ over time.

consistency

Spermatogenesis

Original cell produces four haploid, unique sperm cells by meiosis

Oogenesis

Original cell produces one egg cell and three polar bodies by meiosis

Egg cell receives most of the original cell’s cytoplasm