Transcript Genetics - nimitz163

Genetics
Chapter 8
 Three Principles of Mendel:

 Principle of dominance & recessiveness.- In
heterozygous individuals, ONLY the dominant
allele achieves expression. The recessive
allele is present but remains unexpressed. In
order to express a recessive allele, one has to
be homozygous for the trait (they must have 2
recessive alleles) pg. 119 #5

 Principle of segregation.-The members of
each pair of alleles separate when gametes
are formed. A gamete will receive one allele or
the other. pg. 122

 Principle of independent assortment.-2 or
more pairs of alleles segregate independently
of one another during gamete formation.
Pg.122
Origins of Genetics
Heredity
The passing of characters from
parents to offspring
Character
Inherited characteristic (ex.
flower color)
Trait
 Single form of a characteristic
(ex. purple flower)
Genes
Control the expression of traits
(i.e. flower color)
Have two parts - alleles
One allele is from Mom other from
Dad.
Alleles
 Dominant - the expressed allele
of the gene
Capital letter
Ex. P
 Recessive - the allele that was not
expressed
Lower case letter
Ex. P
 Homozygous (Homo = same)
Two alleles are the same
Ex. PP or pp
 Heterozygous (Hetero = different)
The alleles are different
Ex. Pp
Modern Terms
 Genotype
The set of alleles for a Gene
 Ex. PP, Pp or pp
 Phenotype
 Physical appearance
 Ex. Purple or White Flowers
The dominant allele determines
phenotype
 Ex. Pp  Purple Flower or PP  Purple
Flower
If both alleles are recessive then the
individual will express the recessive
phenotype.
 Ex. pp  White Flower
Probability
 The likelihood that a specific event will
occur
Expressed in multiples ways:
 Fractions
 Percentages
 Decimals
 Ratios
 Probability =
½
50%
.5
3:1 or 3 to 1
# of one kind of possible outcome
Total # of all possible outcomes
Incomplete Dominance
Inheritance that is intermediate
between two parents
Ex. Snapdragon with red flowers are
crossed with a snapdragon with white
flowers  a snap dragon with pink
flowers is produced.
Neither the allele for red flowers nor the
allele for white flowers is dominant.
Codominance
Case in which both forms of the
character are displayed.
Ex. The ABO blood groups
Neither IA nor IB are dominant is
dominant over the other.
Both are dominant over i.
When both IA and IB are present
they are codominant and the
individual is type AB
Blood Typing
Blood Types
A
IA
IB
i
AB
B
O
IA
IB
i
IAIA
IAIB
IAi
IAIB
IBIB
IBi
IAi
IBi
ii
Sex-Linked Traits
Body cell has 46 chromosomes 44 autosomes, 2 sex chromosomes.
Gamete (egg/sperm) has 23
chromosomes –
22 autosomes, 1 sex chromosome
Sex-Linked Gene
A gene located only on the X or Y
Most are carried on the X
chromosome
Males have only one X chromosome
Male who carries a recessive allele
on the X chromosome will exhibit the
sex-linked condition
Hemophilia
(Heme: blood, philia: liking
of)
Condition that impairs the
blood’s ability to clot
A sex-linked trait
Carriers and victims contain
the recessive allele on their
X-chromosomes
Only females can be carriers
 XHXh
Because males only have
one X chromosome
Males CAN NOT be carriers
only victims.
Genetic Disorders
Sickle Cell Anemia
Recessive disorder among
African Americans
Caused by a mutated allele that
produces a defective hemoglobin
protein.
Hemoglobin in RBC’s bind and
transport oxygen through the body
Genetic Disorders
Cystic Fibrosis
Fatal hereditary recessive
disorder among Caucasians.
Clogging of the airways and lungs
with thick mucus and the blockage
of ducts of the liver and pancreas.
There is no known cure.
 Gene Mutations: changes to the DNA
that result in a change in the protein.

 Mutagen: substance or condition that
causes or increases the rate of
mutation. Ex: viruses, x-rays,
cigarettes, etc…

 Mutation: permanent change in the
genetic material of a cell.

 codon of a gene. – set of 3 DNA bases
 Ex: GAG to GUG


D. Frameshift Mutation: insertion
or deletion of a nitrogen base that
produces a type of gene mutation.
Genetic Disorders
Albinism
Recessive
Body is unable to produce an
enzyme necessary to make
melanin.
Melanin is a pigment that gives
color to hair, skin and eyes
Chromosome
Rearrangements:

 Inversion: when part of a chromosome is broken &
becomes reinserted backwards.

 Translocation: A broken piece of chromosome
attaches to a chromosome of a different pair.

 Deletion: when part of a chromosome breaks off
and is lost.


D. Nondisjunction: homologous
chromosomes fail to separate.

 Monosomy: only has one chromosome of a pair.
Lethal


G. Trisomy: 3 copies of a chromosome. Ex.
Down’s Syndrome
Pedigrees
A family history that shows
how a trait is inherited over
several generations
Helps to track down the
carriers (heterozygotes) of
recessive disorders.
Reading Pedigrees
A shaded box –
affected male …………
A shaded circle-
affected female……….
A clear box
-
normal male…………..
A clear circle
-
normal female………...