Download Chapter 3 Science Notes

Chapter 3 Goals:
-Heredity is the passing of physical characteristics, or traits, from parents to their kids. In science,
we call kids “offspring”.
-Your parents and grandparents passed on traits to you like hair color and eye color
-You do not look exactly like your parents because you get half of your genes from your mom and
half of your genes from your dad. A gene is the thing that controls traits.
-Sometimes a gene is dominant, and that means it is very strong. A dominant gene will mean a
trait will appear. The gene for brown hair is dominant. That means if you get a gene from your
parents for brown hair, you will have brown hair.
-Sometimes a gene is recessive, and that means it is weaker. You have to get a recessive gene
from your mom and a recessive gene from your dad for the trait to appear.
-A Punnett square helps us to determine the chance or probability that we will get a certain gene
from each parent.
green y is recessive for green pod color. Lower
case y
yellow Y is dominant for yellow pod color. Capital Y
-This Punnett square shows one parent with 2 recessive (yy) genes for pod color.
-This Punnett square shows one parent with 1 recessive (y) and 1 dominant (Y) gene for pod color
**when 2 letters go a walkin’ the big one does the talking.
-This means that the only way an offspring (baby plant) can be born showing the recessive trait is
that it has to have 2 lowercase letters
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Patterns of Inheritance-Ch 3 Lesson 3
Key concept: most traits are the result of complex patterns of inheritance.
Incomplete dominance - neither allele is completely dominant
Example: Red flower R and white flower W make a pink flower
Codominance - both alleles are equally dominant
Example: White chicken W and black chicken B make a spotted chicken
Chromosomes and Inheritance - Chapter 3 Lesson 4
Key concept: Genes pass from parents to offspring on chromosomes
Human body cells have 46 chromosomes (23 pairs).
Human sex cells (egg or sperm) have 23 chromosomes.
Sex cells have half the number of chromosomes as body cells so that when they join together, we get
the full number of chromosomes people need.
-body cells 46 chromosomes; sex cells have half that number
egg cell
23 chromosomes
+
sperm cell
23 chromosomes
__________________________
human
46 chromosomes
DNA - Chapter 4
-Genes are made up of DNA
-DNA is looks like a twisted ladder and carries the information that tells us if we are boy or girl, short
or tall, blond hair or brown hair.
-The order of bases (colored pieces of the ladder) is a unique code like a bar code. It is specific to us.
Only identical twins have the same DNA.
-Each base only pairs up with a particular base
A goes with T
C goes with G
The sides are made up of sugars (brown) and phosphates (purple)
Mutations - Chapter 4 Lesson 3
Sometimes genes can be changed. The letters might not line up or match correctly. When this
happens, we have mutations. Mutations are changes in the DNA.
-Mutations can be helpful or harmful. Those mutated genes can be passed down to offspring if the
mutation occurs in the sex cell.
Cancer
-Cancer is when cells grow and divide uncontrollably, damaging the body around it. Something
damaged the DNA and caused a mutation. That mutation makes the cell grow and develop quickly.
-Some factors can cause cancer such as smoking or a family history or cancer.
-Some treatments can destroy the cancer cells so they do not live to grow and copy anymore.