Download Genes, Chromosomes, and Heredity

Factor - A factor is a gene. Organisms have 2
genes for every trait they show.
Allele – An allele is a version or form of a gene
(dominant vs. recessive)
If an organism’s two genes are the same, it is
homozygous for that trait: Ex: RR or rr
If your two genes are the different, it is
heterozygous for that trait:
Ex: Rr
The two alleles you actually have in your DNA
is your genotype.
Ex: RR, Rr and rr are possible genotypes
The way your alleles are shown on the
outside, or expressed, is known as your
phenotype.
Ex: rolling or not be able to roll is a
phenotype.
The Law of Dominance States that some alleles are
dominant and some alleles are recessive.
A dominant allele will be expressed (show up) in the
phenotype if it is present in the genotype.
A recessive allele will be expressed only if no
dominant allele is present.
Mendel’s law of segregation states that alleles will
separate when gametes (sex cells) are formed, and
they will go to different sex cells.
Mendel’s Experiments…continued….
Independent Assortment
Mendel’s Experiments…continued….
Independent Assortment
Mendel wanted to determine if certain
traits were passed along together (linked).
Ex: Do yellow and round pea traits get
passed along together to offspring?
Do green and wrinkled traits get passed
along together?
The experiment:
Y=Yellow R = Round
y = green r = wrinkled
The experiment:
Y=Yellow R = Round
y = green r = wrinkled
Parents: true breeding for both traits
YYRR
x
yyrr
The experiment:
Y=Yellow R = Round
y = green r = wrinkled
Parents: true breeding for both traits
YYRR
x
yyrr
Poss.
Gam.
YR, YR
yr, yr
The experiment:
Y=Yellow R = Round
y = green r = wrinkled
Parents: true breeding for both traits
YYRR
x
yyrr
Poss.
Gam.
F1
YR, YR
yr, yr
The experiment:
Y=Yellow R = Round
y = green r = wrinkled
Parents: true breeding for both traits
YYRR
x
yyrr
Poss.
Gam.
YR, YR
F1
yr, yr
yr
YR
YR
YyRr YyRr
yr
YyRr YyRr
Phenotype
ratio:
Did this tell Mendel whether or not traits
Are passed along together or linked?
No
Mendel crossed the F1 individuals:
YyRr x YrRr
Mendel crossed the F1 individuals:
YyRr x YrRr
Poss.
Gam.
Mendel crossed the F1 individuals:
YyRr x YyRr
Poss.
Gam.
YR, Yr, yR, yr
YR, Yr, yR, yr
Phenotype ratio: Period 3 Bio – Wait until
tomorrow for Phenotype ratios.
Did this tell Mendel wether or not traits
Are passed along together or linked?
Mendel found that traits were NOT
linked and alleles assort independent
of one another during gamete
formation: the Law of Independent
Assortment
What might be an exception to this law?
An exception to this would be when
genes are found on the same
chromosome.
Carnations: Incomplete Dominance
Snapdragon: Incomplete Dominance
Roan Cattle : Codominance (RW)
Sickle cell anemia: Codominant
clumps
with:
anti-A
anti-B
anti-A
anti-B
none
Genes, Chromosomes, and Heredity
Genes, Chromosomes, and Heredity
In 1902, it was discovered that Mendel’s
genes were found on chromosomes.
Genes, Chromosomes, and Heredity
In 1902, it was discovered that Mendel’s
genes were found on chromosomes.
Chromosomes can be viewed in their
homologous pairs by photographing
them and organizing them into a
picture known as a karyotype.
A normal human karyotype
Humans have 46 chromosomes in 23
pairs. The fist 22 pairs are called
autosomes.
The last pair are called sex
chromosomes:
XX = female (chromosomes are
homologous)
XY = male because a Y is
present. (they are nonhomologous)
Sex linkage – A gene is said to be sexlinked when it is located on the sex
chromosomes. These are most
commonly on the X chromosome.
Sex linkage – A gene is said to be sexlinked when it is located on the sex
chromosomes. These are most
commonly on the X chromosome.
Sex linked traits are more commonly
found in males than in females.
Why??? Look at some examples
Hemophilia – Normal is dominant
Normal genotype:
Male
Female
Hemophilia genotype:
Male
Female
Fruit fly eye color – Red is dominant
over white
Red genotype:
Male
Female
White genotype:
Male
Female
Draw identical twins here
Himalayan rabbit
Siamese Cat
The environment can affect the way
your genes are expressed. This means
that the phenotype is affected.
Chromosomal Mutations
End Result:
Different polypeptide or protein chains
can be made from different
amino acid sequences. These proteins
will have different functions!
Diseases associated with
chromosomal mutations:
- Downs Syndrome
- Kleinfelters disease
- Turner’s Syndrome
MUTATIONS IN THE DNA
Types of mutations:
􀂄Frame Shift - when either insertion or
deletion of one or two nucleotide
bases. When this occurs, the “reading
frame” is changed so that all the
codons read after the mutation are
incorrect.
Disorders that result from DNA
mutations:
􀂄 Sickle Cell Anemia
􀂄 PKU
􀂄 Cystic Fibrosis