Genetics...

Genetic Vocabulary

gene-a distinct unit of hereditary information found in chromosomes

traits-a characteristic of an organism, genetically or environmentally determined

allele-different forms of a gene for a particular trait

genotype-the genetic makeup of an organism

phenotype-the physical traits that appear as a result of the organism's genetic makeup

dominant-the inherited characteristic that appears in an organism

recessive-the inherited characteristic that is not seen in an organism, often masked by the dominant characteristic

homozygous-having two identical alleles for a particular trait

heterozygous-having two different alleles for a particular trait

karyotype-method of organizing chromosomes according to their numbers, size, and types

mitosis-process where the nucleus divides but maintains the chromosome number

cell cycle-pattern of growth and synthesis

includes cell reproduction

DNA-hereditary material of most organisms, found in genes

-made up of base pairs: ACGT

chromatin-DNA wound around small groups of proteins

-condenses during mitosis to form chromosomes

chromosomes-rodlike structures that contain genes

-found in cell's nucleus

NB#1: DNA IS MADE UP OF BASE PAIRS

NB#2: GENES ARE MADE UP OF DNA

NB#3: GENES ARE ON CHROMOSOMES

Cell Cycle:

Stages:

G1-Growth

S-synthesis of DNA

G2-growth-2 (preparing proteins for cell division

M-Mitosis (cell division)

G1...

(G0-cells that opt out of the process entirely remain in "G1" indefinitely are said to be in G0)

chromatid-single strand of chromosome that is duplicated prior to cell division

centromere-region that connects two chromatid sisters

HUMAN GENOME PROJECT

-quest to map all 3B base pairs that are believed to exist in humans

-23 pairs of chromosomes

-each chromosome contains thousands of genes

-project is estimated to take over 5 yrs of continuous work and about $5B!

Competition from private companies....

4 groups now in competition

Chapter 20

MITOSIS AND ASEXUAL REPRODUCTION

-all cells arise from other cells

-cells can reproduce in one of two ways

1. asexual reproduction, requires no special reproductive cells or organs, and involves only one parent cell

2. sexual reproduction, requires special reproductive cells and

organs, and involves two parent cells

-a cell with a distinct nucleus has two division processes

1. mitosis, is the process where the nucleus divides

2. cytokinesis, is the process where the cytoplasm divides

MITOSIS

Changes in the Nucleus

-the nucleus controls cell division

-chromosomes, DNA containing structures, are found in the nucleus

-each type of organism has a specific number of chromosomes

eg. humans = 46

potato = 48

Stages and Drawing mitosis....

Stages of Mitosis

-continuous process, involving four/five stages

1. interphase, "resting phase", cell is actually growing and doubling chromosomes

2. prophase, chromosomes become visible (karyotypes), and microtubules called asters, which form spindles, are produced by the cell's centrioles

-each strand of doubled chromosome is called a chromatid, and is joined by a centromere

3. metaphase, centromeres of the duplicated chromosomes line up at the equator of the cell

(best karyotypes-a chemical can stop process here for "picture")

4. anaphase, duplicated chromosomes move to opposite poles of the cell, with the help of the microtubules

5. telophase, chromosomes become threadlike and not distinctly visible

Cytokinesis in Animal Cells

-cytoplasm division, begins during late anaphase, and finishes during telophase, producing two daughter cells

Mitosis and Cytokinesis in Plant Cells

-very vivid in growing regions of roots and stems

-basic processes same as in animals, except

-plant cells have no centrioles, and form no asters

-rigid cell walls do not divide, instead, a cell plate forms across the middle of the cell

Time Span of Mitotic division

-varies among organisms

-on average, human cells divide in about 24hrs

-specialized cells like nerve and muscle cells seldom or never divide

Control of Mitotic Cell Division

-in unicellular organisms, increase in cell size triggers mitotic division

-in complex organisms, growth and repair needs trigger mitotic division

-uncontrolled cell growth is called cancer

ASEXUAL REPRODUCTION

-takes place by mitotic division

-produces cells that are almost identical to parent cell

-rapid and produces many offspring

-includes several methods:

Binary Fission

-simplest form of asexual reproduction, used by one-celled organisms like bacteria and protozoa

Budding

-parent organism divides into two unequal parts, yeast, hydra, sponges and some worms use this method

Spore Formation

-spores, single specialized cells

-released from parent and grow to form new individuals

-formed sexual or asexual formation

eg. breadmold

Regeneration

-ability to regrow lost parts, not used to reproduce

-although can grow new organism from pieces, not used as a usual method of reproduction

Vegetative Reproduction

-asexual reproduction involving roots, stems and leaves

(seeds are sexual reproduction)

-natural vegetative reproduction, involves several means:

-onions and tulips use bulbs

-waterchestnuts use corms (type of bulb)

-potatoes use tubers

-strawberries and crabgrass use runners

-cattails and waterlilies use rhizomes

-artificial vegetative reproduction, were developed by farmers and gardeners

-roses are grown from cuttings

-raspberries are reproduced by layering

-seedless oranges are grown by grafting

(advantages: no genetic variation, only way to get seedless fruit)