Lesson 3: Sexual Reproduction

Question 1

what is sexual reproduction

Answer 1

form of reproduction in which individuals are produced from the fusion of two sex cells (sex cells usually come from two different parent organisms)

Question 2

advantages to sexual reproduction and provide examples

Answer 2

• individuals that rely on sexual reproduction can adapt to a changing environment, due to their genetic variability which is not possible in organisms that reproduce asexually
• this can support the long term survival of a species

for instance, a pack of rabbits are residing somewhere, when wolves suddenly come into their environment and reside there too- the rabbits that run fast will survive and the rabbits that dont will not survive
- basically, if all rabbits were slow and genetically identical, as soon as the wolves come, they would all die and the species would have less chance of survival and possibly go extinct

Question 2

disadvantages to sexual reproduction

Answer 2

• specialized organs are required to produce the sex cells
• specialized mating calls or bright colours to attract mates can also attract predators
• may require the loss of resources, like nectar in flowers
• the combining of genetic information may make the offspring weak and unable to survive

Question 3

what are the two key processes in sexual reproduction

Answer 3

• formation of haploid cells, or gametes, which contain genetic information from the parents
• two sex cells joining together to form a zygote, the first cell of a genetically unique individual, through fertilization

Question 4

what is meiosis

Answer 4

this is the process through which haploid gametes are formed; it involves two divisions that produces 4 haploid gametes from 1 diploid parent cell

Question 5

gametogenesis

Answer 5

formation of sex cells

Question 6

what are the two types of gametogenesis in humans

Answer 6

• formation of sperm by spermatogenesis
• formation of egg cells or ova by oogenesis

Question 7

growth stage: interphase

Answer 7

• cell grows to nearly twice in size
• nucleus makes a copy of its DNA
• organelles are also replicated

Question 8

meiosis 1: prophase 1

Answer 8

• chromatin condenses into chromosomes
• nuclear membrane dissolves
• centrioles move to opposite sides of the cells
• spindle fibers begin to grow

Question 9

meiosis 1: prophase 1 (what are tetrads and how are they formed- through what process are they fomed)

Answer 9

homologous chromosomes come together and intertwine to form a tetrad by a process called synapsis

Question 10

what is a tetrad

Answer 10

four sister chromatids together is called a tetrad

Question 11

meiosis 1: prophase 1 (crossing over, what is it and how does it occur)

Answer 11

crossing over may occur at this stage
- when intertwined chromatids from different chromosomes break off and reattach at the chiasmata
- this causes an exchange of genetic material at certain sections
- it works to mix or recombine genetic information, further increasing the genetic variation in the gene pool

Question 12

meiosis 1: metaphase 1

Answer 12

the tetrads migrate towards the center of the cell, called the equatorial plate
- spindle fibers are attached at the centromeres of the chromosomes
- the tetrads align their centromeres in the middle of the cell

Question 13

meiosis 1: anaphase 1

Answer 13

homologous chromosomes move to opposite poles of the cell when the spindle fibers shorten
- this means that only one of the two chromosomes from each homologous pair will be in each new daughter cell and therefore are genetically unique
- ex: each of your sperm or egg has only the chromosome you received from your mom or your dad, not both

Question 14

meiosis 1: telophase 1

Answer 14

the nuclear membranes reform, spindle fibers dissolve, and the cell begins to divide via the first cycle of cytokinesis (each new cell has only 1 and not 2 duplicated copy of a chromosome at this point)
- only the maternal or paternal chromosome is in each new cell
- therefore, cells are haploid

Question 15

meiosis 2: prophase 2

Answer 15

each haploid cell has one chromosome made of two sister chromatids at this point
- the sister chromatids are not genetically identical due to crossing over that occurred during prophase 1
- nuclear membrane dissolves, centrioles move to opposite poles, and spindle fibers reform

Question 16

meiosis 2: metaphase 2

Answer 16

the chromosome move to the center of the cell, called the equatorial plate
- accomplished through spindle fiber attachment at the centromeres
- the chromosomes align their centromeres in the middle of the cell

Question 17

meiosis 2: anaphase 2

Answer 17

sister chromatids now seperate and move to opposite poles of the cell
- each cell now has a single sister chromatid, not a duplicate copy
- these will not be identical due to the genetic exchange that occurred in crossing over

Question 18

meiosis 2: telophase 2

Answer 18

the nuclear membrane reforms around the chromatids, the DNA relaxes into chromatin, and the spindle fibers dissolve

Question 19

meiosis 2: cytokinesis for the second time

Answer 19

cytoplasm splits and results in 4 haploid daughter cells that are not identical

Question 20

what allows for genetic variation in meiosis

Answer 20

• crossing over in prophase 1
• in metaphase 1 and 2, it is random as to which side each chromosome goes to

Question 21

what is the male reproductive cell called

Answer 21

sperm (contains 50% of the father’s genes)

Question 22

what is the female reproductive cell called

Answer 22

the egg (contains 50% of the mother’s genes)

Question 23

fertilization

Answer 23

when the two cells join together, the genetic material combines (essentially the joining of reproductive cells is fertilization)

Question 24

diffferent types of fertilizations?

Answer 24

• some animals like humans go through internal fertilization, where the egg is fertilized inside the body; the offspring develop inside the mother
• some animals like fish have external fertilization; the female releases her eggs, then the male fish spreads his sperm over her eggs- the young basically develop outside of the body