Chapter 8

Explain how independent segregation of chromosomes in meiosis and random fertilization leads to genetic variability.

...

Compare asexual and sexual reproduction in terms of characteristics of offspring, advantages and disadvantages and examples of.

Sexual Reproduction is the process by which a new organism develops from joining of male and female sex cells (sperm and ova respectively). An organism that reproduces sexually requires a partner, with the offspring sharing characteristics from each parent. Examples include mammals, most reptiles, and flowering plants. Pros of Sexual Reproduction In sexual reproduction, unlike in asexual reproduction two parents are involved. Two gamete cells are involved. Fertilization takes place mixing the genetic material together. One of the main advantages of sexual reproduction is that there is a large chance of an evolution taking place. Thus the species would be able to adapt to new environmental conditions. Also new species could be born. Another advantage is that a new character is formed with the mixed gametes of the parents so there is a chance that the parent's diseases would not be received by the offspring. Cons of Sexual Reproduction One of the disadvantages is that only half the population (females) is capable of gestation. Another one of the disadvantages is that two parents have to be involved in the process. Also having to find a mate and producing gamete cells is also another disadvantage. Fertilization has to take place and there is no guarantee that the nucleus of the male sex cell would fuse with the female sex cell. Also this takes a long time and there is no grantee that an offspring would be born. Asexual Reproduction is the process by which a single organism produces a new organism identical to itself. An asexually reproducing organism does not require a partner to produce offspring. Examples include bacteria, nonflowering plants and some reptiles. Pros of Asexual Reproduction There are many advantages of asexual reproduction. One of them is that only one parent is needed. There is a large guarantee that the offspring would be born. It takes a very short period and genetic material need not be produce. Fertilization is not there. They have identical characteristics as their parents. They are always of the same species. Asexual reproduction is more reliable because there are less steps to follow so less can go wrong. Cons of Asexual Reproduction One of the cons of asexual reproduction is that there is almost no chance of an evolution taking place. The offspring would almost always be of the same species and would be identical to the parents, so diseases and bad qualities are also passed down directly from the parents to the offspring. One of the common disadvantages of plants using the vegetative method is that there will be a struggle for light, space, nutrients and soil so most plants will remain less healthy.

Explain cancer in terms of the cell cycle.

uncontrollable cell growth/ division.

Explain when and how crossing-over occurs and how that affects genetic variability.

An exchange of corresponding segments between two homologous chromosomes, begins in prophase 1 in Meiosis.

Explain what a karyotype is and what key information does it provide?

An ordered display of magnified image of individual's chromosomes arranged in pairs, shows chromosomes in metaphase of mitosis.

Describe what is meant by a homologous chromosome.

Both carry genes controlling the same inherited characteristics.

Describe the structure of DNA in eukaryotic cells and the structure and function of chromosomes.

DNA is coiled because of a double helix and is made up of nucleotides. Chromosomes contain the long strands of DNA* that carry genetic information. They are the unit of DNA replication in living cells. Eukaryotic cells, with their much larger genomes, have multiple, linear chromosomes. The length and linear nature of eukaryotic chromosomes increases the challenge of keeping the genetic material organised and of passing the proper amount of DNA to each daughter cell during mitosis. During cell division, eukaryotic chromosomes condense into highly coiled 4 armed structures. The tight coiling and high degree of organisation in this supercoiled DNA facilitates proper segregation during mitosis and cell division. The following illustration explores the structure, classification and features of a eukaryotic chromosome.

Differentiate between diploid and haploid in the life cycle of a cell and give an example of each.

Diploid- 2 homologous set of chromosomes, humans are diploid organisms. Haploid- A cell with a single chromosome set

Compare cytokinesis between plants and animals

In animal cells, cytokinesis is accomplished by the formation of a cleavage furrow, which gradually "pinches" the cell in half. In plant cells, cytokinesis is accomplished by the formation of a cell plate that gradually divides the cell in half; it eventually thickens to become a new cell wall.

Describe the eukaryotic cell cycle in terms of stages and events and compare the relative amount of time a cell spends in each stage

Interphase is longest phase (90% of the cell cycle), divided into three sub-phases(G1,S, and G2). Only during the S phase does the cell replicate its DNA for the next cell division. Interphase lasts about 23 hours. But keep in mind a cell can go into G0 phase which keeps the cell from dividing. Prophase(chromatin forms into the visible chromosomes, this takes about 15 minutes). Prometaphase(nuclear envelope dissolves, kinetochore microtubles are seen attached to the centromeres on each chromosome, lasts about 15 minutes). Metaphase( this is the longest stage, 20 minutes, when the chromosomes are lined up in the center of the cell) Anaphase( last probably three minutes tops, this is when the chromosomes split and become daughter chromosomes). Telophase and Cytokinesis( Two sets of chromosomes on each side of the cell form their own nuclei and at the same time the cytoplasm of the cell cleaves into two daughter cells. this last less than ten minutes.)

Describe the key events of each mitotic stage and identify cells undergoing each stage

Interphase, prophase, prometaphase, metaphase, anaphase, telophase and cytokinesis

Describe the key events of each meiotic stage and identify cells undergoing each stage.

Interphase- same as mitosis Prophase 1- most complex phase in meiosis, chromatin coils up-become visible under microscope. Metaphase 1- chromosome tetrads aligned on the metaphase plate, spinale microtubles- attach to kinetochores- poised to move to opposite ends. Anaphase 1- chromosomes move to either poles of the cell, only tetrad split up. Telophase 1/cytokinesis- chromosome arrive at the poles of the cell, chromosomes uncoil, nuclear envelop re-forms.

Mutations are caused by mutagens and include inversions, deletions, and translocations.

Inversions- a fragment reattaches to the original chromosomes but in the reverse direction, less likely to produce harmful affects. Deletions- Fragments of a chromosome is lost (missing DNA) Translocations- attachment of a chromosomal fragment to a non-homologous chromosomes.

Identify the overall functions of meiotic division and give examples of when and where it would take place.

Meiotic division- a type of cell division that produces haploid gametes in diploid organisms.

What is a non-disjunction event and what are the consequences?

Members of a chromosome pair fail to separate, it can happen in Meiosis 1 or 2. If it is combined with a normal gamete it will produce a zygote with abnormal number of chromosomes.

Identify the overall functions of mitotic division and give examples of when and where it would take place.

Mitosis is the type of division that gives rise to daughter cells for the purpose of tissue growth, regeneration or asexual (vegetative) reproduction. After mitosis and cytokinesis the daughter cells contain the same information for properties for heredity as the mother cell (they are genetically identical).

Compare and contrast mitosis and meiosis in terms of function, offspring, and genetic variation.

Mitosis- growth tissue repair, and asexual reproduction, daughter cells are identical to the mother cells Meiosis-needed for sexual reproduction, makes haploid daughter cells.

Explain how anchorage, cell density and chemical growth factors affect cell division

density dependent inhibition crowded cells stop growing; decreased availability of resources stops cell division ex: skin cells on top layer that make us 'leak proof' anchorage dependence in order to divide, most animal cells must be attached to the extracellular matrix of a tissue; cells must be anchored to a tissue to divide; rouge cells can't divide chemical growth factors