Download Genetics - Spring Branch ISD

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Genetics Class Notes
Reproduction
Reproduction is common to all living things. When organisms reproduce they
make more of their own kind.
Offspring are the products of reproduction.
Every organism requires a set of genetic instructions for specifying its traits or characteristics.
What is a trait?
Trait
A characteristic that a parent
organism passes on to its
offspring through genetic
material
Examples:
Eye Color
Hair Color
Leaf Shape
BIG IDEA: When organisms reproduce, many traits or characteristics are passed to the new
organism.
Heredity
Heredity is the passage of genetic instructions from one generation of organisms to the next
generation.
Genetics is the study or science of heredity.
Class Notes Page 1
What is DNA?
DNA
Structure
discovered by
Watson and Crick
1.Nucleic Acid
2.Macromolecule:
C, N, H, O, P
3. Organic
Double Helix Shaped
(Twisted Ladder shape)
Sides of Ladder
Sugars and Phosphates
1. Located in the
cell’s nucleus
2. Packaged in
Chromosomes
Rungs of Ladder
Nitrogen bases ; Bases connected to
Sugar molecules
DNA language is built on the alphabet of A, T, C, G. The sequence or order of these nitrogen
bases forms the genetic code.
BIG IDEA DNA stores and transmits the genetic information from one generation to the next.
Class Notes Page 2
What is a chromosome?
DNA is packaged into bundles called chromosomes.
What is the relationship between traits, genes, chromosomes, and alleles?
A gene is a section of DNA on a chromosome that codes for a specific trait.
Alleles are different forms of a gene that provide the code for specific inherited traits.
Examples:hair color, eye color, leaf shape
The code in the DNA of the gene determines the type of allele (ex: shortness or tallness) that will be
present in the gene.
Gregor Mendel, the father of genetics, noticed that genes always come in pairs. Every organism that
reproduces sexually receives two genes for each trait. They receive one gene from the mother and
one gene from the father for a specific trait.
BIG IDEAS
 An organism receives two genes for each trait, one from each parent.
 One of the genes may be stronger; the trait of the stronger gene shows up and is called the
dominant gene. The trait of the weaker gene is “hidden” or does not show up and is called the
recessive
gene.
Dad
Mom
DominantUpper case
RecessiveLower Case
Brown
Blue
Brown
Class Notes Page 3
What is the language of genetics?
A capital letter is used to represent a dominant allele.
A lower case letter is used to represent a recessive allele.
Example: In the color of pea plant flowers, purple is the dominant allele and white is the
recessive allele.
Dominant_Purple (P)
Genetics Term
Recessive__White (p)_
Example: Flower Color
Genotype
Definition
the genetic makeup of an
organism; the type of genes
Phenotype
the external or physical
appearance of an organism
White
Purple
Homozygous
an organism with two identical
alleles for a trait
PP and pp
an organism with both a
dominant and a recessive
allele for a trait
Heterozygous
Pp, PP, pp
Pp
How do you predict heredity?
A Punnett square is a chart used to predict the genetic outcomes of offspring.
The letters on the outside of the square represent the alleles of the parents.
The letters on the inside of the square represent the possible combinations of alleles among the
offspring.
Parent
Parent
Offspring
Class Notes Page 4
L
l
L
l
LL
Ll
Ll
ll
3/4
1/4
75
25
25
50
25
Tall
LL
Short
w
w
W
W
Ww
Ww
Ww
Ww
4/4
0
ll
100
0
0
100
0
Long
Ll
Ww
Class Notes Page 5
What are the characteristics of Asexual Reproduction?
Number of Parents
Inheritance of
Genetic Material
Offspring
Advantage/Disadvantage
One parent
One set of genetic material is passed to offspring
Identical to the parents
Advantage: Produces a large number of offspring rapidly
Disadvantage: Offspring are not genetically diverse
Binary Fission:


Single celled organisms
(prokaryote)
Reproduces by dividing in half
Vegetative Propagation:

Processes



Plant asexual reproduction
Examples
Produce runners
Bulbs
Potato eyes
Budding:


Eukaryote
New organism grows directly
out of parent’s body
Class Notes Page 6
What are the characteristics of Sexual Reproduction?
Number of Parents
Inheritance of
Genetic Material
Offspring
Two parents
Two sets of genetic material are passed to the offspring
Offspring inherits traits from both parents
Advantage: Offspring are genetically diverse; diversity helps
organisms survive when their environment changes
Advantage/Disadvantage
Disadvantage: Cannot reproduce quickly
Process
Organisms
Male sperm cell unites with female egg cell
Most animals
Seed plants
Class Notes Page 7
There are two X’s
Female
male
There is an X and a Y
X
Y
X
X
X
XX
XX
Y
XY
XY
Class Notes Page 8