Meiosis

Ovum

A mature egg cell formed from the division of the secondary oocyte.

Asexual Reproduction of cells Ex. mitosis , binary fission

Asexual reproduction - single parent produces offspring Mitosis: single parent cells produce 2 identical daughter cells All offspring are genetically identical to one another and to parent

. Crossing over is a very important event in Prophase I of meiosis! What happens during crossing over and what is the significance?

Crossing over is the process of homologous chromosomes exchanging genetic information. The significance of this is that no matter which chromosomes the zygote gets it will have genetic information from both parents of the owner of the gamete cells. Non-sister chromatids = homologous pairs crossing over Helps with genetic diversity

Telophase I & Cytokinesis

Duplicated chromosomes arrive at opposite poles Nuclear membrane forms around the chromosomes. Usually followed by cytokinesis

Metaphase II

Duplicated chromosomes line up midway between spindle poles at the metaphase plate

Fertliization

Fusion of two gametes to form a zygote

Gamete Formation

Gametes are sex cells (sperm, egg(ovum)) Arise from germ cells in reproductive organs

Process for producing gametes

Germ Cell → Meiosis I → Meiosis II → Gamete

Meiosis I

Goal: separate homologous chromosomes diploid → haploid

Meiosis II

Goal: separate sister chromatids haploid → haploid

Fertilization

Male and female gametes uniteand nuclei fuse Fusion of two haploid nuclei produces diploid cell called a zygote Random chance of sperm fertilizing egg increases variation in offspring

If you had three chromosomes then what is the chance of getting a particular combination of chromosomes at the end meosis 2

2 to the 3rd

Homologous chromosomes line up across from each other along the equator of the cell in _______.

Metaphase I

Effects of Crossing Over

Non sister chromatids can switch genetic information After crossing over, each chromosome contains both maternal and paternal segments Creates new allele combinations in offspring

Are germ cells haploid or diploid?

diploid

in Changing environments offspring of what kind of reproducers have an evolutionary advantage

sexual reprouction

Diploid or haploid: After fertilization takes place

diploid

Diploid or haploid: after mitosis is complete

diploid

Diploid or haploid: body cell

diploid

What is the value of variation?

more likely to have an adaptation and not go extinct

The DNA sequence of any gene may different from....

the corresponding gene of the homologous chromosomes

What do you notice about the size of the two resulting cells at the end of cytokinesis 1 in females?

✅ One of the cells formed is bigger than the other one.

how many molecules is a chromsome

1

Not taking into account crossing over how many possible combinations of chromosomes are there?

2 to the 23rd

In humans how many instances of crossing over are there during meiosis?

46-95

What is the chance of getting a paternal or maternal chromosome in gamete?

50% because of random alignment/chromosome segregation

spermatogonium

A diploid cell male germ cell before growth and DNA replication

primary spermatocyte

A diploid cell that undergoes mitosis and cytoplasmic division to create the secondary spermatocytes

oogonium

A diploid female germ cell before growth and DNA replication

Red queen hypothesis

Sexual reproduction is widespread because of pressure for constant change resulting from compretative species interactions

2 haploid (N) daughter cells form

Telophase I

How do the genetic contents of cells resulting from Mitosis and Meiosis differ?

The cells resulting from mitosis are all genetically identical to each other and the parent cell while the cells resulting from meiosis are genetically different from each other and the parent germ cell.

Where are germ cells located?

gonads

secondary oocyte

haploid cell resulting from the division of the primary oocyte. Will undergo meiosis 2 and cytokinesis 1 to form the ovum and another polar body.

secondary spermatocytes

haploid cells that complete meiosis II to produce 4 haploid spermatids

somatic cells have what type of chromosomes

homologous chromosomes

male and female reproductive organs

male: testes. female: ovaries

spermatazoa

mature, sperm, haploid, male gamete

meiois gives rise to ___________

new combinations of parental alleles

gametogenesis

production of gametes

Spermatogenesis

production of sperm

sexual reprudction

reproductive mode by which offspring arise form 2 parents and inherit genes.

What is the reason for different-looking organisms in sexually reproducing organisms?

Allele differences

spindle fibers pull homologous chromosomes apart and each chromosome moves to the opposite pole

Anaphase I

Sister chromatids separate from each other

Anaphase II

individual chromatids separate and move to opposite poles of the cell

Anaphase II

sister chromatids separate from each other

Anaphase II

What type of reproduction requires more phosphorus? Why?

Asexually reproducing animals because DNA contains phosphorus and asexually reducting reproducing organisms tend to have more copies of the DNA

How/when is the diploid number restored?

At fertilization

Random Alignment

Between prophase I and metaphase I, chromosome pairs align randomly at metaphase plate Initial contact between spindle fiber and either maternal or paternal chromosome is random

Zygote

Cell formed by the fusion of two gametes at fertilization; the first cell of a new individual

What does crossing over do

Changes allele combinations and introduces new traits

What molecule is responsible for storing the genetic information in the chromosomes?

DNA is responsible for storing genetic information in the chromosomes.

If a diploid cell containing 28 chromosomes undergoes Meiosis, how many chromosomes will each daughter cell have?

Each daughter cell will have 14 chromosomes.

✅ 5. Meiosis does PMAT twice! That means there is a prophase I and a prophase II. There is a metaphase I and a metaphase II. Etc... If the cartoon below has chromosomes in the middle of the cell, how would you know whether it was in metaphase I or metaphase II?

In metaphase I the homologous chromosomes are lined up next to each other in pairs. In metaphase two the chromosomes are lined up "single file" with the spindles attached the the sister chromatids.

cells undergo a round of DNA replication

Interphase (s phase)

Possible Chromosome Combinations

Maternal and paternal chromosomes are randomly aligned

Duplicated chromosomes line up along the equator of the cell during ________.

Metaphase 2

Random Alignment happens

Metaphase I

Mitosis vs. Meiosis: Is there a difference in DNA between the parent cell and the daughter cell for this type of cell division?

Mitosis: NO, genetically identical Meiosis: Yes, genetically different

Mitosis vs. Meiosis: Is there a change in chromosome number for this type of cell division?

Mitosis: No, the number of chromosomes remains diploid Meiosis: Yes, each daughter cell haas half the genetic information, they are haploid.

Many invasive species have a need for what? Why?

Phosphorous which is plentiful in polluted areas because a lot of them are asexual reproducers.

Each chromosome is connected to a spindle fiber

Prophase ----> telophase

Crossing over occurs

Prophase 1

Crossing over taking place during...

Prophase 1

Chromosomes become visible

Prophase I or II - Meiosis I or II

Effect of sex reproduction on harmful mutations

Sexually reproducing species have a better chance Of weathering the effects of harmful mutations

Prophase II

Spindle fibers attach to duplicated chromosomes Nuclear membrane breaks down. Interphase does not come before this phase!!!

Anaphase 1

Spindle fibers pull homologs towards spindle poles

What are the largest and smallest cells in the human body

The ovum is the largest cell in the human body. In contrast, the sperm cell is the smallest cell in the human body.

Gamete formation in plants

In plants, haploid germ cells are formed by mitosis then gametes from when these cells divide by mitosis

What chromosome will a microtubule bind to?

Microtubules bind to the first centromere they contact regardless of whether it is maternal or paternal. That chromosome will get pulled to the pole that the spindle fiber is attached to.

first polar body

One of the products of meiosis I in oogenesis; contains half the chromosomes but very little of the cytoplasm. Will undergo meiosis 2 to form 2 more polar bodies

Crossing over

Process by which homologous chromosomes exchange corresponding segments of DNA during prophase one of meiosis

After _________ and _______ there are four haploid cells.

Telophase 2 and cytokinesis 2

What would happen if organisms produced reproductive cells though mitosis instead of meiosis?

The cells would be diploid and the offspring would have double the chromosomes as the parent. Also lack of genetic diversity.

Meiosis: Two Divisions

Two consecutive nuclear divisions Meiosis I - splits apart homologous chromosomes Meiosis II - splits apart sister chromatids DNA is not duplicated between divisions Interphase does not occur between 2nd division (Meiosis I & Meiosis II) 4 haploid nuclei form = 4 genetically different daughter cells

Telophase II & Cytokinesis

Unduplicated chromosomes arrive at opposite ends of cell Nuclear envelopes form around chromosome sets Cytoplasm divides Four haploid genetically different cells result

✅3. A cell that begins meiosis has 23 chromosomes inherited from the mother (shown in green in the cartoon below) and 23 chromosomes inherited from the father (shown in blue in the cartoon below). In the process of meiosis, chromosomes begin to match up in homologous pairs. How would you know if two chromosomes were homologous?

You would know if chromosomes were homologous because they would be the same size and shape, have the same centromere location and have the same genes on them.

primary oocyte

a cell that undergoes meiosis 1 and cytokinesis I to form the first polar body and the secondary oocyte

Alleles

forms of a gene with slightly different DNA sequences; may encode for slightly different versions of the gene's product

Germ cells

immature reproductive cell that gives reise to haploid gametes whien it divides

Errors in meiosis are the cause of chromosome abnormality. Errors that occur when a pair of homologous chromosomes or sister chromosomes fail to separate is called....

nondisjunction

asexulal reproduction

single organism makes 2 identical organisms

What would happen if meiosis did not occur

the chromosome number would double every generation.

alleles control...

trait expression

Telophase 1

Two sets of chromosomes reach spindle poles, new nuclear membrane forms and DNA loosens. The nuclei are haploid and the chromosomes are duplicated

homologous chromosomes are separated during...

Anaphase 1

Sister chromatids are separated during _____.

Anaphase 2

✅ 1. The purpose of meiosis is to make gametes, also known as sperm and egg cells. In humans, your body cells have 46 chromosomes. How many chromosomes are in a sperm or egg cell if, when they come together to form a fertilized zygote, there are 46 chromosomes?

23 chromosomes in sperm and egg

What fraction of genetic information does asexual reproduction pass on? What about sexual reproduction?

Asexual reproduction passes on all the greens and sex reproduction passes on 1/2

Describe a similarity and difference between Meiosis I and Meiosis II.

Both Meiosis I and Meiosis II end with haploid cells and go through prophase, metaphase, anaphase and telophase. On the other hand, meiosis I separates the homologous chromosomes while meiosis II separates the sister chromatids.

Homologous Chromosomes Carry Different Alleles

Cells with two of each chromosome are diploid cells ex. Human body (somatic) cells have 23 pairs of chromosomes...how many chromosomes total? Chromosome pairs: one from mom, one from dad Paternal and maternal homologous chromosomes carry different alleles (versions of genes) Ex: eye color (trait) - one chromosome may code for blue eyes and the other chromosome code for brown eyes

Chromosome Number

Chromosome number - total number of chromosomes in cell Germ cells (parent cells in meiosis, found in repro. organs) are diploid (2n) Gametes produced from germ cells are haploid (n) Meiosis cuts the chromosome number in half!

Metaphase 1

Chromosomes aligned in the middle in homologous pairs

Meiosis does not always occur without any difficulties. Describe what occurs during nondisjunction and the effect on the resulting cells

Every chromosome contains essential genetic information. Nondisjunction is when chromosomes stay together instead of pulling apart.

Anaphase I

Homologous chromosomes separate Sister chromatids remain attached (each chromosome still duplicated)

What regions can genetic information be swapped in during crossing over

Many chromosomes can solve any region. Some regions are more common than others. It happens between nonsister chromatids -- one materal + one paternal

gametes

Mature, haploid reproductive cell -- egg or sperm

homologous chromosomes line up in the center of the cell

Metaphase I

Chromosomes line up in the middle of the cell in haploid cells

Metaphase I or II

Compare the number and type of cells that result from Mitosis vs. Meiosis.

Mitosis produces 2 diploid somatic cells while meiosis produces 4 haploid gametes.

Mitosis vs. Meiosis: How many rounds of division are in this type of cell division?

Mitosis: 1 round of division Meiosis: 2 rounds of division

Mitosis vs. Meiosis: How many daughter cells are produced from this type of cell division?

Mitosis: 2 diploid identical cells Meiosis: 4 haploid genetically different cells.

Mitosis vs. Meiosis: How many phases are involved in this type of cell division?

Mitosis: 4 phases: prophase, metaphase, anaphase, telophase Meiosis: 8 phases: Prophase I and II Metaphase I and II Anaphase I and II Telophase I and II

Mitosis vs. Meiosis: Where does this type of cell division take place?

Mitosis: Body cells Meiosis: Germ cells / reproductive organs

Mitosis vs. Meiosis: What is the function of this type of nuclear division?

Mitosis: Growth and repair. Meiosis: Reproduction

Is there DNA replication between divisions?

No

Sexual Reproduction of cellsEx. meiosis

Sexual reproduction - 2 parent cells involved in producing offspring Meiosis is the production of gametes: egg and sperm cells Meiosis allows for fertilization to maintain - chromosome number: when sperm cell fertilizes the egg cell, correct # of chromosomes for zygote Produces genetic variation among offspring - non-identical daughter cells Variation in traits is the basis for evolutionary change

Anaphase II

Sister chromatids separate to become unduplicated chromosomes

How does meiosis create haploid cells?

Sorting chromosomes into separate nuclei twice

anaphase 2

Spindle fibers pulll chromosomes towards the spindle poles. Chromosomes are now unduplicated.

4 haploid (N) daughter cells form

Telophase I

three polar bodies

Three haploid cells created by the division of the first polar body and the secondary oocyte.

Sexual Reproduction and Genetic Variation

Two functions of meiosis provide variation in traits: crossing over random alignment

spermatocyte

a male germ cell that might go through meiosis to form a sperm cell

Unicellular organism such as bacteria depend on asexual reproduction. Why is sexual reproduction so common in higher multicellular organisms such as humans?

bc multicellular organisms need more diversity given they are more likely to have a larger, more variable habitat.

Sexular reproduction

combination of 2 gametes which are haploid -- mitosis halfs the chromosomes number

Diploid or haploid: dividing body cell

diploid

Diploid or haploid: step one of meiosis

diploid

gametes come from ____

division of germ cells

Diploid or haploid: Sex cells

haploid

Diploid or haploid: Step Three( Anaphase II ) of meiosis II

haploid

Diploid or haploid: When meiosis is complete

haploid

Diploid or haploid: end of Step Three( Anaphase I ) of meiosis

haploid

spindle fibers attach to the homologous chromosome pairs

prophase I

Individual chromatids move to each end of the cell

✅ Anaphase II - Meiosis II

Why are egg cells are large and sperm cells are small?

✅ I think that egg cells are large and sperm cells are small because egg cells stay and develop in the female and can actually turn into a zygote while male cells have to be able to move.

Nuclear envelope re-forms

✅ Telophase I or II - Meiosis I or II

What is the largest cell called?

✅ The larger cell is called the ovum.

IN oogenesis: What are the small cells called?

✅ The small cells are called polar bodies. Polar bodies are small cells that develop as a byproduct of meiosis in females. In humans and most other animals, these cells play no significant role and soon die.

Continue through meiosis until you finish telophase II and cytokinesis II. IN females: What do you notice about the four cells now?

✅ There is one cell that is larger than the rest.

How does this compare to the two cells at the end of telophase I and cytokinesis I in male cells?

✅ Unlike the female cells at the end of cytokinesis I, the immature reproductive cells are the same size.

Metaphase I

Chromosomes are moved to middle of cell Spindle is fully formed Random assortment of homologous chromosome pairs at the metaphase plate (cell equator) - another way variation is created within a species

Prophase 2

Chromosomes condense in nuclear membrane breaks up. Spindle fibers attach to sister chromatids

prophase 1

Chromosomes condense, nuclear envelope breaks up, crossing over occurs, spindle microtubules attach

Metaphase 2

Chromosomes lined up in the middle of the cell

telophase 2

Chromosomes reach spindle poles. DNA loosens and nuclear membrane forms. Four haploid cells with an duplicated chromosomes.

Recap: Factors contributing to variation among offspring

Crossing over during prophase I Random alignment of chromosomes at metaphase I Random combination of gametes at fertilization

Crossing Over

Each chromosome attaches to its homologue forming a tetrad All four chromatids are closely aligned Non Sister chromosomes exchange segments

Prophase I

Each duplicated chromosome pairs with homologue forming tetrad Homologues swap segments (crossing over) Each chromosome becomes attached to spindle

Environmental change and reproduction

Environmental changes the norm and sexual reproduction allows for the best adapted organisms to reproduce the most

Crossing Over

Homologous chromosomes swap genes. This is one way variation is created within species.

✅2. Interphase must occur once before meiosis can happen. (Same thing for mitosis). What would happen if interphase didn't occur first?

If interphase didn't occur first then the DNA would not be duplicate and the daughter cells would not have the correct genetic material. Also, the cell would not grow so the daughter cells would not have the correct amounts of cytoplasm and organells.

Gamete formation in animals

In animals meiosis in diploid cells makes gametes