Topic 11 - Reproduction & Meiosis

What is reproduction?

the production of an offspring from an existing organism (e.g. sexual/asexual reproduction)

What is asexual reproduction?

Reproduction without sex/fertilization of egg by sperm that creates offspring that are genetically identical to the parent (e.g. budding/fission)

How is meiosis different between multicellular and unicellular organisms?

Mitosis is used by unicellular organisms as a form of asexual reproduction

Mitosis is used by multicellular organisms for cellular replacement and growth

What are the advantages/disadvantages of asexual reproduction?

Advantages: eliminates the need to find a mate + allows organisms to multiply quickly w/out spending energy to produce sperm/eggs

Disadvantages: less variation which dooms the population equally as they’re susceptible to environmental change

What is sexual reproduction?

fusion of gametes (two sex cells: sperm/egg) to form a zygote + increases variability among offspring (vital towards animal survival if environment changes suddenly)

What is hermaphroditism?

a type of sexual reproduction as sexually reproducing organisms have the ability to produce both egg and sperm

Why is the reduction of chromosomes necessary?

is necessary to maintain the same # of chromosomes through generations

What is meiosis?

a special type of cell division that forms gametes (each gamete has a single set of 23 chromosomes)

Gametes are ___ and Humans/plants/animals are ___

haploid(1n), diploid(2n)

What are the 2 distinct divisions in meiosis?

Meiosis I, II

What type of division is Meiosis I and what is the genetic content of the daughter cells?

Meiosis I is a reduction division

At the end, each daughter cell is haploid (1n) with each chromosome having 2 sister chromatids

What happens during Meiosis II and what is the genetic content of the daughter cells?

During Meiosis II, sister chromatids separate

At the end, each daughter cell has a chromosome with 1 chromatid

What happens in Interphase prior to Meiosis I?

S phase: Chromosome replication creates identical sister chromatids that remain attached at the centromere

What is Prophase I?

• chromosome condenses and nuclear envelope fragments

• homologous chromosomes are brought together by synaptonemal complex whose pairing forms a tetrad

• crossing over occurs

What is crossing over?

exchange of chromosomal segments between homologous non sister chromatids

What happens during Prometaphase I?

• nuclear envelope breaks

• spindle fibers attach to kinetochore in centromeric region

• homologous chromosomes remain attached in tetrad

What happens during Metaphase I?

homologous chromosomes are arranged at the center of the cell in random orientation to create genetic variation among daughter cells (independent assortment)

What is independent assortment?

Mendelian principle that states trait inheritance is independent of each other leading to new combinations of offspring bc homologous chromosomes orient randomly during meiosis (metaphase I) allowing for different gene combinations

What happens during Anaphase I?

microtubules pull tetrads apart

What happens during Telophase I?

DNA decondense + nuclear envelope forms in some species OR cytokinesis takes place without reformation of nuclear envelope in other species

What process is undergone prior to Meiosis II?

Interkinesis (shorter Interphase as there is no S phase)

What happens during Prophase II?

Decondensed chromosomes at the end of Meiosis I are recondensed

What happens during Prometaphase II?

microtubules attach to kinetochores present in each sister chromatid

What happens during Metaphase II?

chromosomes align at the center of the plate

What happens during Anaphase II?

sister chromatids are pulled apart by microtubules

What happens during Telophase II?

chromosomes arrive at opposite ends of the cell and start decondensing + nuclear envelope forms

What is the result of Meiosis II?

4 daughter cells are formed