Genetics
Chapter 5
Life Science
Bell work Ch5 L.1
Heredity: passing of traits from parents to
offspring
Genetics: the study of how traits are passed
from parent to offspring
Dominant trait: observed when offspring have
either one or two dominant factors
Recessive trait: genetic factor that is blocked
by presence of a dominant factor
Launch lab p.149 (work in pairs)
● Lets look at three traits
o
o
o
Unattached vs attached earlobes
Curved vs straight thumb
Left over right vs right over left thumb
● Why might some students have types of
traits that others don’t?
● If a person has dimples, do you think their
offspring will have them too? Explain.
● What determines the traits you inherit?
Gregor Mendel
● Father of genetics
● Experiments with
pea plants helped
explain recessive
and dominant traits
o
How two people with
brown eyes can have
a child with blue eyes
Mendel’s experimental methods
● Controlled breeding
experiments using pea
plants
Reproduce quickly
Easily observable traits
 flower color
 wrinkled/smooth peas
o Controllable breeding
 he decided which plants (and
which traits) were interbred
o
o
Pollination in pea plants
● Fertilization
o when pollen lands on pistil of
flower
o Sperm from pollen fertilizes egg in
pistil
● Self-pollinate
o pollen from one plant fertilizes
flowers on that same plant
● Cross-pollination
o pollen from one plant fertilizes
flowers on a different plant (he did
this manually)
 naturally= wind, insects etc.
True-breeding plant
● A plant who self-pollinates and the offspring
all have the same selected trait(s) as the
parent
● Example: self-pollinate a plant with wrinkled
seeds, offspring all have wrinkled seeds
Mendel’s results
● First-generation crosses (using true breeding
●
plants)
o True breeding purple flower plants all had purple
flower offspring= AS EXPECTED
o True breeding white flower plants all had white
flower offspring= AS EXPECTED
First-generation crosses (combining white true
breeder with purple true breeder)
o Hybrid offspring had ALL purple flowers= NOT
EXPECTED
Mendel results
Second generation (hybrid) crosses
● First generation plants were all hybrids= had
different forms of the same trait
● Now cross two hybrids
o
White flowers reappeared in the offspring even
though both parents had purple flowers
● Same results with other traits/hybrids
Patterns emerge
● Second generations all had the same 3:1
ratio
o
o
3 purple flowers to 1 white flower
Purple flowers grew from this cross 3x more often
than white flowers
Other hybrid crosses with 3:1 ratio
●
●
●
●
●
●
●
Purple:white
Flowers on side:flowers on end of stem
yellow seed:green seed
round seed:wrinkled seed
Smooth pod:bumpy pod
Green pod: yellow pod
Long stem: short stem
Mendel’s conclusions
● In purple hybrid flowers, the purple trait seemed
to block the white trait
o
o
genetic factor that blocks another= dominant trait
 purple flower is a dominant trait
 Only one dominant trait is enough to show the
dominant factor
genetic factor that is blocked by a dominant factor=
recessive factor
 white flower is a recessive trait
 ***white flowers only present when two recessive
traits are present
Homework Ch5 L.1
● p.156 #1-10
● Study for quiz
● EXTRA CREDIT FOR TEST WILL NOW BE
CHAPTER OUTLINE DUE TEST DAY
Bellwork Ch5 L.2
Gene: section on a chromosome that has genetic information for one trait
Allele: different forms of a gene
Phenotype: how a trait appears or is expressed (purple vs white flower)
Genotype: the two alleles that control the phenotype of a trait
Homozygous: when the two alleles of a gene are the same
Heterozygous: when the two alleles of a gene are different
Punnet Square: model used to predict possible genotypes and phenotypes of
offspring
Incomplete dominance: when offspring phenotype is a combination of parents’
phenotype
Codominance: when both types of the allele are observed in the phenotype
Polygenetic inheritance: when multiple genes determine the phenotype of a trait
What controls traits?
● Two factors control traits
o
o
One from mother
 from egg
One from father
 from sperm
● What are the factors?
o
o
Chromosomes- contain DNA
Exist as pairs
 One from mom and one from dad
Genes and Alleles
● Chromosome have information about hundreds
of traits
o
The section on a chromosome that has genetic
information for one trait= gene
●
Example: gene for flower color or wrinkled/smooth seeds
● Alleles= different forms of a gene
o
You get two forms of the trait- one from mom and one
from dad
 Example: two alleles for purple flowers or one allele
for purple flower and one allele for white flower
Genotype and Phenotype
● Phenotype: how a trait appears
o
We can see that the flowers are purple or white
 Gene codes for flower color and the phenotype is
white or purple
● Genotype: the two alleles that control the
phenotype of a trait
o
In other words, how we would write it down
 Example: if purple= P (capitalized) and white=p
(lower case) then a heterozygous organism would
have the genotype Pp
Genotype cont’d
● Symbols
o
o
Uppercase= dominant allele (written first if present)
Lowercase= recessive allele
● Homozygous
o
When the two alleles of a gene are the same
 Both upper case or both lower case
● Heterozygous
o
When the two alleles of a gene are different
 One upper case and one lower case
Genotype practice
If a purple flower is dominant over a white
flower, (and we are using the letter P or p to
represent the alleles) what are the genotypes
for:
● purple flowers?
● white flowers?
Modeling inheritance
● Can predict the ratio of inheriting specific genes
o
Ratio of phenotypes and genotypes can be different
● Punnett square: model used to predict what the
genotypes of the offspring will be
o
need genotypes of parents
● Analyzing Punnett square:
o
Gives probability for each phenotype but the phenotype
of one offspring has no effect on probability of the next
offspring
Practice filling out a Punnett square
● What are the genotypes of the offspring?
● What are the phenotypes of the offspring?
● Are the ratios of the genotypes and
phenotypes the same?
Pedigree
● Shows phenotypes of genetically related
family members
o
o
Can show inherited traits in a family
Can help determine genotype
 You can figure out if the traits are dominant or
recessive
 You can figure out if the individuals are
homozygous or heterozygous for the trait
Pedigree practice
Complex patterns of inheritance
● Types of dominance
Complete dominance
 This is what we have been doing
o Incomplete dominance
 Combination of parental
phenotypes
 Red flowers crossed with white
flowers produces pink flowers
o Co-dominance
 Both alleles expressed equally
(NOT MIXED)
o
Complex patterns of inheritance cont’d
● Multiple alleles: genes have more than two alleles
o
Example: blood.
 There are three possible alleles: A, B, O.
 Offspring only inherit two total but there are three
possibilities
● Polygenic inheritance
o
A trait that is affected by more than one gene
 Example: eye color, height, skin color etc.
● Environment also affects what genes are expressed
Homework Ch5 L.2
● P.167 #1-9
● Study for quiz
Bellwork Ch5 L.3
DNA: an organism's genetic material
Nucleotide: a molecule made of a nitrogen base, a sugar and a
phosphate group
Replication: the process of copying the DNA molecule to make
another DNA molecule
RNA: a type of nucleic acid that carries the code for making proteins
from the nucleus to the cytoplasm.
Transcription: the process of making mRNA from DNA
Translation: the process of making protein from RNA
Mutation: a change in the nucleotide sequence of a gene
Launch Lab p.170
● Work individually
● Solve the code and answer the three
questions
● Write your full first and last name on the
paper
● TURN IT IN
The structure of DNA
● Genes provide the
directions for the cell so it
can assemble molecules
● Genes are segments on
DNA
● DNA is arranged in a tight
coiled coil structure
o First you have the double
helix= think of this like a twisted
zipper or a twisted ladder
o Then that double helix is
twisted around into a coil shape
Four nucleotides shape DNA
● Nucleotide has a sugar,
phosphate and nitrogen group.
o Nitrogen groups interact with each
other to form the teeth of the zipper or
the rungs on the ladder
o The phosphate and sugar groups
form the sides of the zipper or ladder
● Four nucleotides (A:T and G:C)
o
o
o
o
Adenine
Thymine
Guanine
Cytosine
How DNA replicates
● DNA is in chromosomes so
chromosomes have to be
replicated
● Steps in DNA replication
o
o
o
DNA coiled strand separates to
expose nitrogen bases
Free nucleotides come in and
pair with exposed nitrogen bases
Two identical DNA strands are
produced
Making proteins
● Junk DNA
o 97% of DNA is not used to
make proteins. It does not
form genes.
● The role of RNA
o nucleic acid that carries code
for making proteins from
nucleus to cytoplasm
o Single stranded, has Uracil
(U) instead of Thymine (T),
ribose instead of
deoxyribose.
Transcription
● The process of making
mRNA from DNA
● Steps
o
o
o
Separate double stranded
DNA
Pair RNA nucleotides to
exposed nitrogen bases
RNA removes itself from
DNA template and moves
to cytoplasm
Three kinds of RNA
● mRNA
o
o
messenger RNA
Used as the instructions to make proteins
● rRNA
o
o
ribosomal RNA
Used to make up the ribosome, help form chemical
bonds between amino acids in protein production
● tRNA
o
o
transfer RNA
Used to carry amino acids during protein production
Translation
● making a protein from mRNA
o
Three nitrogen bases from RNA make one amino
acid in a protein
 three nitrogen bases in mRNA is called a codon
●
o
64 codons but 20 amino acids
o
more than one codon codes for the same amino acid
o
One codon signals the start of translation
o
Three different codons signal for the stop of translation

Theses do not code for an amino acid
The order of the bases determines the order of the
amino acids
Codons and amino acids
Mutations
● A change in the
nucleotide sequence of a
gene
o
Most of them are corrected
● Some occur naturally,
some can be triggered
o
X-ray, UV light, radioactive
material, some chemicals
Types of mutations
● All change the sequence of
nitrogen base pairs
o can bring about a premature
STOP
o can code for a different protein
● Deletion
o Delete one nitrogen base
● Insertion
o Add one nitrogen base
● Substitution
o Change one nitrogen base for
another one (can be the same
one)
One step up about mutations
● What kind of mutation (from the three we just
did) is the “worst”?
o
Why?
● Are all mutations bad?
● Do all mutations have some sort of effect?
o
Good or bad?
Homework Ch5 L.3
●
●
●
●
p. 177 #1-10
Study for quiz
Start studying for Ch5 exam
Start Extra Credit
o
Outline of all of Ch5
● Practice test problems (will not be collected)
o
p. 181-185