Download Chapter 3-1 • Definitions: - Genetics: the scientific study of heredity

Chapter 3-1
• Definitions:
- Genetics: the scientific study of heredity
- Heredity: the passing of traits from parent to offspring
- Trait: different physical characteristics
- Purebred: an organism that always produces offspring with the
same form of a trait as the parent
- Gene: factor that controls traits
- Allele: different forms of a gene
- Dominant Allele: its trait always shows when the allele is
present
- Recessive Allele: is masked by the dominant allele
- Hybrid: having two different alleles for a trait
• Mendel
- is called the “Father of Genetics”
- used pea plants in his experiments because
a. we get many offspring in one generation and in short time
b. traits come in either of 2 forms
- crossed 2 plants by taking pollen from the male flower and
transferring to the female flower of the same kind of plant
- his experiments:
- Notes:
a. Each organism inherits 2 alleles from parents, one from
mom and one from dad.
b. Tall allele + Tall allele = Tall
Tall allele + Short allele = Tall
Short allele + Short allele = Short
Chapter 3-2
• Punnett Square: tool to show all the possible outcomes of a genetic
cross and determine the probability of an outcome
• Phenotype: physical appearance or visible trait, ex. Tall, green
• Genotype: genetic makeup or allele combination, ex. TT, Tt, GG
• Purebred: same alleles; also known as homozygous, ex. TT, tt
• Hybrid: different alleles; also known as heterozygous, ex. Tt
• Codominance: see pg. 99, figure 11
The alleles are not dominant or recessive; neither allele is masked;
both alleles appear.
Chapter 3-3
• The sex cells include the female cells or the eggs and the male cells or
the sperm.
• The grasshopper egg contains 12 chromosomes; the grasshopper
sperm also contains 12 chromosomes. When the egg and sperm join
in fertilization, the fertilized egg has 12 plus 12 or 24 chromosomes
(12 pairs); one in each pair coming from dad and one from mom.
• Chromosome Theory of Inheritance: genes are passed from parent to
offspring on the chromosomes.
• Meiosis: process by which chromosome # is reduced when forming
sex cells
• You can use a Punnett Square to show the events of meiosis. The
alleles separate when sex cells form.
• Chromosomes are made of genes joined together like beads on a
string.
• Many genes means many traits.
• On a chromosome pair the genes are in the same order; however the
alleles can be different on each one.
Chapter 3-4
• Introduction
Genes contain DNA and therefore many of the nitrogen bases that
line up in a specific order.
This order forms a genetic code which determines the type of amino
acids.
Amino acids are the building blocks of proteins.
Proteins determine your traits.
• Role of RNA
RNA stands for Ribonucleic acid.
RNA carries the genetic code from the DNA in the nucleus to the
ribosomes in the cytoplasm where proteins are made.
Differences between RNA and DNA
sugar
strand
Nitrogen bases
location
DNA
Deoxyribose
2
A, T, C, G
nucleus
function
has the genetic code
-
RNA
Ribose
1
A, U (Uracil), C, G
made in the nucleus;
goes to cytoplasm
carries the genetic code
from DNA to the
ribosomes in the
cytoplasm
Types of RNA:
a. messenger RNA (m-RNA) which carries the genetic code from
DNA to the ribosome in the cytoplasm
b. transfer RNA (t-RNA) which carries amino acids needed to
make proteins
• Protein Synthesis (translation)
DNA unzips.
One of the strands of DNA directs the making of m-RNA by pairing
the bases (A-U and C-G); this process is called transcription.
m-RNA leaves the nucleus to go to the ribosomes in the cytoplasm.
t-RNA picks up amino acids according to a 3-letter code, called
codon, and attaches on the m-RNA.
Amino acids join to from proteins.
• Mutation: a change in a gene or chromosome resulting in
- a change in the protein made
- this changes the phenotype
- therefore the trait is changed
Gene mutation happens during DNA replication when the Nbases are changed.
Chromosome mutation happens during meiosis when
chromosomes fail to separate correctly resulting in too many or
too few chromosomes.
Mutations can cause genetic variety.
Some mutations are harmful resulting in less chance of survival
or reproduction; others are helpful resulting in more chance of
survival or reproduction; others are neutral. Whether a
mutation is harmful or helpful partly depends on the
environment.