Lecture 11: Meiosis

What is the definition of heredity?

The transmission of traits from one generation to the next, also known as inheritance.

What term describes the differences observed between individuals?

Variation

Define 'genetics'.

The study of heredity and hereditary variation

What are gametes

Reproductive cells that transmit genes from one generation to the next.

In _____ reproduction, a single parent produces offspring.

Asexual

How do multicellular organisms reproduce asexually?

Through budding or fragmentation

In asexual reproduction, what is the genetic relationship between the offspring and the parent?

They are clones, genetically identical to the parent and to each other

What are a few advantages of asexual reproduction?

It is faster and it requires less energy than sexual reproduction

If a diploid (2n) parent undergoes asexual reproduction, what is the ploidy of the two offspring?

Also diploid (2n)

What is the primary advantage of sexual reproduction?

It makes genetic variation

What is a zygote

It is a diploid cell from fusing two gametes during fertilization

The fusion of two gametes is known as

Fertilization

What is a major cost of sexual reproduction

It takes a lot of time an energy

What is 'genome dilution' in sexual reproduction

The offspring only receive half of a parents genes

Meiosis is described as a 'reduction division' because it halves what?

The chromosome number

What is the overall outcome of meiosis starting from one diploid (2n) cell?

It produces four haploid (n) cells, which are now gametes

What crucial event happens during the Interphase that precedes meiosis?

The chromosomes duplicate (during s phase)

After chromosomes duplicate in interphase, each chromosome consists of two_____

Sister chromatids 

In a human cell (2n=46), how many chromosomes and chromatids enter meiosis after interphase?

46 chromosomes and 92 chromatids

What major event characterizes meiosis 1

The homologous chromosomes separate from each other

During which phase of meiosis does the cells ploidy get reduced from diploid to haploid? (meiosis I or II)

Meiosis I the ploidy changes from 2 diploid cells to 2 haploid cells

What unique event occurs during Prophase I that doesn’t happen in Mitosis

Crossing over and synapsis

What is a tetrad?

It is two homologous chromosomes held together 

What is the main purpose of synapsis during Prophase 1

It’s so that there can be crossing over of the homologous pairs

Define crossing over

It is the exchange of genetic material between tetrads (happens in prophase 1)

What is the primary result of crossing over?

It makes a new combination of genes, this is important for diversity

What aligns at the metaphase plate during metaphase 1

The tetrads

What is the main point of Anaphase 1

The homologous chromosomes being split up by the spindle fibers

During anaphase 1 what structures remain connected and move to the same pole

The sister chromatids

What is the result of telophase 1 and cytokinesis

Two haploid cells with duplicated chromosomes

At the end of telophase 1, how many chromosomes in each of the two cells?

23 chromsomes

At the end of Telophase I,  how many chromatids are in the two cells?

46 chromatids

What is the stage between the first and second meiotic divisions?

Interkinesis

What critical process does NOT occur during interkinesis

There is no DNA replication during interkinesis

What happens during interkinesis?

It is just the time in between the first and second meiotic divisions

What separates during the second meiotic division? (Meiosis II)

Sister chromatids separate into daughter cells

Meiosis II is very similar to…?

Mitosis

Does the ploidy of the cell change during Meiosis II

No it doesnt change, it stays haploid

At the end of Meiosis II, how many chromosomes are in each of the 4 daughter cells?

23 chromosomes

At the end of meiosis II how many chromatids are in each daughter cell

0, the “chromatids” are now considered an individual chromsome

What is the final outcome of the entire process of Meiosis (I & II)

4 haploid daughter cells

Which process does the chromosome number get reduced by ½?

Meiosis

What structures separate during anaphase of mitosis?

The sister chromatids

In anaphase 1 of meiosis what is being separated?

Tetrads

Does Mitosis or Meiosis create genetically identical daughter cells

Mitosis

Does homologous pairing occur in mitosis?

No, only in Meiosis I

Can Mitosis occur in haploid cells?

Yes

To form a zygote you must…

Fuse 2 gametes

What is the main difference between the offspring of sexual vs. asexual reproduction

Offspring of sexual reproduction are genetically unique; offspring of asexual reproduction are all identical clones

During which phase of Meiosis does crossing over happen?

Only in Prophase 1

How does the orientation of tetrads in metaphase 1 contribute to variation

The direction each chromosome faces is all random, this is independent assortment