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Grade 9 Science Chapter 4.notebook
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Grade 9 Science
Unit 3: ReproductionChapter 4
Dec 3012:01 PM
The Function of the NucleusThe nucleus is the organelle that is responsible for heredity and for controlling the functions of the cell
The control centre of the cell
The nucleus contains the master set of instructions that determines what each cell will become, how it will function, when it will grow and divide, and when it will die
Chromosomes are inside the nucleus (we'll get back to this later :)
Grade 9 Science Chapter 4.notebook
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Responsible for Heredity
1) Trait: a particular feature that can vary in size of form from individual to individuals within a species
Traits are inherited from biological parents
2) Heredity: the process through which patterns of traits are passed on from an individual to its offspring
Dec 3012:42 PM
Examples of TraitsTraits # of students
with trait 1# of students with trait 2
No cleft vs. cleft chin
Widow's peak vs. straight hairline
Dimples vs. no dimples
Detached vs. attached earlobes
Freckles vs. no freckles
Tongue rolling vs. not rolling
Straight thumb vs. hitch hiker's
Left thumb over right with interlacing fingers vs. right over
left
Hair on back of hand vs. none
Arm crossing ‐ left vs. right
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DNADNA carries the instructions in the nucleus
DNA is a long double‐stranded molecule, it forms a helix structure (a twisted ladder)
The sides of the DNA ladder are made of sugar and phosphate
The steps are made of four nitrogen bases:1) Adenine (A)2) Guanine (G)3) Cytosine (C)4) Thymine (T)
**NOTE: A always joins with T and G always joins with C
DNA MOLECULE
Dec 3012:22 PM
Read the article glowing genes on page 120 of your textbook!!
http://www.youtube.com/watch?v=88kMwpC7CCg
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ChromosomesWhen a cell is ready to divide, each strand of loosely coiled DNA folds up further into a compact, X‐shaped structure called a chromosome
Chromosomes within the nucleus are found in pairs
Most humans have 23 pairs of chromosomes, including one pair that determines gender
Dec 3012:01 PM
GenesGenes are found on chromosomes
Genes are small segments of DNA located at specific places on a chromosome
They store information needed to produce proteins used by body cells
Genes can vary in length from hundreds to thousands of bases, the arrangement of bases will determine the protein produced
Each chromosome contains thousands of genes
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ProteinsProteins determine what body cells will become and how they will function
Specialized cells will form tissues; tissues will form organs
Specialized proteins called enzymes speed up the hundreds of chemical reactions that occur within each cell
Ex. Digestive enzymes
Some proteins act as chemical messengers called hormones Ex. Growth hormone
Bookwork: Page 121: 1‐13
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MutationsA gene mutation is a change in the specific order of the bases that make up a particular gene
A base may be:‐ Added‐ Deleted‐ Substituted for another
Open your book to page 123 and do Activity 4‐2A: Identify the Mutation
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Effects of Mutations1) Positive Mutation: benefits an individual
Ex. Resistance to disease
2) Negative Mutation: harms the individual; reduces the probability that the individual will produce offspring or survive in their environment
Ex. Sickle cell anemia or cystic fibrosis
3) Neutral Mutation: does not affect the individual; things that produce variety in a species but do not give individuals advantage over one another
Ex. Hair color or eye color or blood type
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MutagensA mutagen is a substance or factor that can cause mutations in DNA
Ex. Cigarette smoke, X‐rays, pollutants
Mutagens can be caused by:1) Nature
Ex. Solar radiation or radioactive gases2) Human Activity
Ex. Chemical or nuclear radiation
Bookwork: Page 131: 1‐15