Download Genetics Notes

Genetics
-the scientific study of inheritance
inheritance- the process in which genetic
material is passed from parents to their
offspring
Gregor Mendel

Austrian monkstudied pea plants
 Mathematical basis
for experiments
 Kept careful records
of numbers
 Studied simple traits
(seed color, shape,
flower color, height,
etc.)
Monohybrid Cross

A cross between two parents that
are identical in all but one
characteristic.
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Example: cross a short pea
plant and a tall pea plant
P is parent generation,
F1 is first filial generation,
F2 is second filial generation
Result of cross: F1-all tall, F2-3
tall:1 short
Modern Genetics
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Allele: Alternate forms of the same gene. Each
trait has two alleles:

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Dominant: masks the effects of the recessive (ex. T)
Recessive: is masked by the dominant (ex. t)
Modern Genetics cont’d

Gene Locus: the place on a
homologous pair of chromosomes
where the alleles occur, one on each
chromosome.
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Homozygous (true-breeding): Both
copies of the allele are identical (TT
or tt)
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Heterozygous: Each copy of the
allele is unique (Tt)
Genotype vs. Phenotype

Genotype: the alleles an individual receives at
fertilization. TT is homozygous dominant, tt is
homozygous recessive, and Tt is heterozygous.

Phenotype: refers to the physical characteristics of an
individual. Homozygous dominant and heterozygous
individuals both show the dominant phenotype (tall),
while homozygous recessive shows the recessive
phenotype (short).
Classes of chromosomes
autosomal
chromosomes
sex
chromosomes
Genetics of Sex

In humans & other mammals, there are 2 sex
chromosomes: X & Y

2 X chromosomes
• develop as a female: XX

X
Y
X
XX
XY
X
XX
XY
an X & Y chromosome
• develop as a male: XY
50% female : 50% male
Sex-Linked Traits

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Sex-linked traits are produced by genes only on the X
chromosome.
They can be Dominant or Recessive.

A = dominant a = recessive
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What would be the genotypes of a male and female that have a Sexlinked Dominant trait and do not express the trait?
Expresses Trait:
Male - XA Y
Female - XA XA or XA Xa
No Expression:
Male - Xa Y
Female - Xa Xa
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What would be the genotypes of a male and female that have a Sexlinked Recessive trait and do not express the trait?
Expresses Trait:
Male - Xa Y
Female - Xa Xa
No Expression:
Male - XA Y
Female - XA XA or XA Xa
(Carrier)
Most Sex-linked traits are Recessive!
Dihybrid Cross

A cross between two
individuals that differ from
each other in regards to
two traits.

Ex: pod color and pea
color: GGYY and ggyy.
• F1 generation will be GgYy.
Polygenic Inheritance
 phenotype
determined by combination
effects of 2 or more genes at a different
loci on different chromosomes.
 Phenotypes usually found on

a bell-shaped curve
human traits
•
•
•
•
•
skin color
height
weight
intelligence
behaviors

Multiple alleles- more than 2 forms of a gene controlling
the expression of a trait
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Ex: Blood type:
• In humans, 3 alleles: A,B,O

Co-dominance- A pattern of inheritance in which the
phenotypic effect of two alleles in a heterozygous
genotype express each phenotype of each allele fully
and equally; a phenotype which would not be expressed
in any other genotypic combination.

Ex: Checkered chickens have both white and black feathers.
Environmental Effects
 Phenotype
is controlled by
both environment & genes
Human skin color is influenced
by both genetics &
environmental conditions
Coat color in arctic
fox influenced by
heat sensitive alleles
Color of Hydrangea flowers
is influenced by soil pH
What are Chromosomal Mutations?
Damage to chromosomes due to physical or chemical disturbances or errors
during meiosis.

Mutations might also be inherited from the sex cells of your parents. If you
inherit a mutation from your parent, all of your DNA will be made with the
mutation already in it.
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The only way to inherit mutations from your parent is through sex cells – not
through other types of cells.

Ex: Skin cancer is not passed on to your kid.
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Mutations may cause certain types of diseases or make you susceptible to
certain types of diseases.
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Two Types of Chromosome Mutations:
1.
Chromosome Structure
2.
Chromosome Number
Problems with Chromosome Structure:
2 main types of chromosome structure mutations:
1. Point mutation - A point mutation is a simple change in
one base of the gene sequence. This is equivalent to
changing one letter in a sentence.
2. Frameshift mutation- a change in the bases that causes
the sequence to be read in different sets of codons.
Equivalent to changing the spacing of the sentence.
Gene Mutations
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Nonsense substitution- a change in 1 base that changes an amino
acid to a stop codon
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Silent substitution- a change in 1 base that does not cause a change
in the amino acid produced OR a change in the DNA that causes a
change in the protein, but not the function of the protein.
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Missense substitution- a change in 1 base that changes the amino
acid produced
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Deletion- a deletion of a base
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Insertion- an addition of a base
Chromosomal Mutations
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translocation- a portion of a chromosome breaks
off and attaches to a non-homologous
chromosome
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inversion- a portion of a chromosome breaks off
and reattaches “upside down”
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deletion- a portion of a chromosome breaks off
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duplication- a portion of a chromosome is
duplicated
Problems with Chromosome Number
nondisjunction – members of homologous
chromosomes do not move apart in Meiosis I or
sister chromatids do not separate during Meiosis II
leaves one cell with too few chromosomes and
one cell with too many.
monosomy – only one of a particular type of chromosome (2n -1)
trisomy – having three of a particular type of chromosome (2n + 1)
polyploidy – having more than two sets of chromosomes; triploids (3n =
3 of each type of chromosome), tetraploids (4n = 4 of each type of
chromosome).
Biotechnology

-any procedure or methodology that uses biological
systems or living organisms to develop or modify either
products or processes for specific use.

Genetic engineering- a technology that includes the
process of manipulating or altering the genetic material
of a cell resulting in desirable functions or outcomes that
would not occur naturally.

genetically modified organism- an organism whose genetic
material has been altered through some genetic engineering
technology or technique.
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gene therapy- the intentional insertion, alteration, or deletion of
genes within an individual’s cells and tissues for the purpose of
treating a disease.
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gene splicing- a type of gene recombination in which the DNA is
intentionally broken and recombined using laboratory techniques
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Cloning- a process in which a cell, cell product, or organism is
copied from an original source
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DNA cloning- making exact copy of a DNA fragment
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Reproductive cloning- transfer of genetic material from the
nucleus of a donor adult cell to an egg that has had its nucleus
removed ; the embryo is an exact genetic copy of the donor
organism.
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Therapeutic cloning- using STEM cells for use in research
• STEM cells- undifferentiated cells; have not decided “what they want to be”
when they “grow up”