Meiosis

Question 1

How many sets of chromosomes do eukaryotes have?

Answer 1

Most eukaryotes have two sets of homologous chromosomes (“diploid”)

Question 2

How many chromosomes do humans have?

Answer 2

Humans have 46 chromosomes, but in fact 23 pairs (n = 23, 2n = 46)

Question 3

What are haploid organisms?

Answer 3

Organisms that have only 1 set of chromosomes (1n) are called “haploid”

Question 4

What is the maternal set of chromosomes

Answer 4

The set of chromosomes you get from your mother

Question 5

What is the paternal set of chromosomes?

Answer 5

The set of chromosomes you get from your father

Question 6

What is the Centromere?

Answer 6

The region of a chromosome to which the microtubules of the spindle attach, via the kinetochore, during cell division.

Question 7

What are the different types of chromatids in a 2n set of chromosomes.

Answer 7

• The sister chromatids of one duplicated chromosome
• The non-sister chromatids in a homologous pair
• The pair of homologous chromosomes (one is maternal the other is paternal)

Question 8

Draw and label a diagram of the different chromatids in a 2n set of chromosomes.

Answer 8

https://docs.google.com/document/d/1Nzo4FTzXCbwOZjpoc_J_4IF3gsOXPcoyC2BowELmx0U/edit?usp=sharing

Question 9

What is sexual reproduction?

Answer 9

The fusion of two cells from different individuals

Question 10

What would happen if you fused two diploid cells?

Answer 10

If you fused two diploid cells the offspring would have double the amount of chromosomes and therefore double the amount of genes to copy every time a new cell is made and thus it is inefficient. For example:
2n + 2n = 4n then the next generation of 4n would produce double their amount of chromosomes, for example:
4n + 4n = 8n and so on until it simply becomes to slow for the baby to grow because it has to copy so many chromosomes before it can make a new cell.

Question 11

For sexual reproduction to be possible what needs to be produced?

Answer 11

Organisms need to produce cells with half the number of chromosomes as the parental cell = “gametes”

Question 12

What is the difference between Mitosis and Meiosis?

Answer 12

Mitosis: Produces two genetically identical diploid cells (ie, each has 2n chromosomes)

Meiosis: Produces four haploid cells with half the number of chromosomes as parent cell (ie, each has 1n chromosome)

Question 13

What is the first step of Meiosis?

Answer 13

The chromosomes duplicate so that there are two paternal chromosomes and two maternal chromosomes.

Question 14

What is the second step of Meiosis?

Answer 14

• “Meiosis 1”
• The homologous chromosomes separate into separate cells
• These are called haploid cells with the duplicated chromosomes inside them

Question 15

What is the third step of Meiosis?

Answer 15

• “Meiosis 2”

- The sister chromatids separate into their own cells creating a gamete.

Question 16

Draw and label a diagram of the Meiosis cycle

Answer 16

https://docs.google.com/document/d/1Nzo4FTzXCbwOZjpoc_J_4IF3gsOXPcoyC2BowELmx0U/edit?usp=sharing

Question 17

What are the basic steps of the human life cycle in relation to Meiosis and Mitosis?

Answer 17

• The first step is meiosis, where the ovaries and the testis create the gametes.
• Second is fertilisation, or, the fusion of the gametes
• Third is Mitosis which is the development of the organism

Question 18

What are the three types of sexual life cycles?

Answer 18

• Animals
• Plants and most algea
• Most fungi and some protists

Question 19

What are the basic steps of the plant sexual life cycle?

Answer 19

• Many plants have two parts, the sporophyte and the gametophyte.
• The cycle starts with the sporophyte where Meiosis happens, the sporophyte will shoot out spores which are the gametes of the plant
• Next, under optimum conditions, Mitosis will begin to happen. This means that the spores grow and develop into gametophytes
• The gametophytes continue to undergo mitosis until another hapliod cell (aka gamete) comes along and fertilises it
• After it is fertilised the sporophyte part of the plant begins to grow (mitosis) thus starting the cycle over

Question 20

What are the basic steps of the fungi sexual life cycle?

Answer 20

• The first step is Meiosis
• Once the games have been produced they undergo mitosis and develop into either unicellular or multicellular organisms
• Once they are organisms they are able to find other haploid cells (gametes) and begin fertilisation
• After fertilisation the organism undergoes more mitosis until it is able to reproduce, itself.

Question 21

What happens in Meiosis 1?

Answer 21

Separation of homologous chromosomes and reduction of the number by half (ie, 2n → n) - There is no DNA replication in this part:

Question 22

Which phases are part of Meiosis 1?

Answer 22

– Prophase I and Prometaphase I
– Metaphase I
– Anaphase I
– Telophase I and cytokinesis

Question 23

What is the main goal of Meiosis 2?

Answer 23

Separate sister chromatids (~ mitosis)

Question 24

Which phases are in Meiosis 2?

Answer 24

– Prophase II and Prometaphase II
– Metaphase II
– Anaphase II
– Telophase II and cytokinesis

Question 25

What happens in Prophase I (and Prometaphase I)

Answer 25

– Can take several days
– Synapsis form
– There is crossing over

Question 26

What are synapsis (in regards to Meiosis)?

Answer 26

Homologous pairs of chromosomes that bind together (forming “tetrads”)

Question 27

What is a tetrad?

Answer 27

A tetrad is a pair of homologous chromosomes that bind together by the chiasmata (the middle section of a chromosome)

Question 28

What is crossing over (in regards to Meiosis)?

Answer 28

Exchange of large sections of chromosomes between pairs (cross-over region is called “chiasmata”)

Question 29

What happens during Metaphase 1?

Answer 29

Tetrads align along the metaphase plate

Question 30

What happens during Ananphase 1?

Answer 30

Attachment between homologous chromosomes break down, and homologous chromosomes move towards opposite poles

Question 31

What happens during Telophase 1 and Cytokinesis?

Answer 31

Cells split, forming 2 haploid daughter cells with n chromosome (each with 2 chromatids)

Question 32

What happens during Meiosis 2?

Answer 32

• No DNA replication occurs b/w meiosis I & II

- Meiosis II very similar to mitosis because it produces 4 haploid cells with n chromosome (each with 1 chromatid)

Question 33

What type of reproduction is Mitosis?

Answer 33

Asexual reproduction (by mitosis)
– Produces 2 identical daughter cells (clones)
– Allows reproduction from a single cell

Question 34

What type of reproduction is Meiosis?

Answer 34

Sexual reproduction (by meiosis)
– Produces 4 haploid daughter cells (“gametes”), genetically different from parent and from each other
– Requires 2 organisms, each providing 1 haploid (male provides sperm, female provides egg)

Question 35

What are the advantages of Meiosis?

Answer 35

Meiosis produces much greater genetic diversity than mitosis:
– Independent assortment → new combinations
– Crossing over → mixing chromosomes

Question 36

Why is genetic diversity advantageous?

Answer 36

Genetic diversity provides greater flexibility to adapt

to changes in the environment

Question 37

How do mitochondria reproduce and how are they inherited by offspring?

Answer 37

• Mitochondria (and chloroplasts) have their own DNA, and divide by binary fission
• In sexual reproduction, mitochondria are inherited exclusively from the mother (mitochondria in sperm are destroyed by egg after fertilisation)