Transcript GENETICS

GENETICS
The Science of
Heredity
TRAIT
A characteristic that an
organism can pass on to
its
offspring through its
genes.
GENE
A segment of DNA on a
chromosome that codes
for
a specific trait.
DOMINANT ALLELE
An allele whose trait
always
shows up in the organism
when the allele is
present.
PROBABILITY
The likelihood that a
particular event will
happen.
PUNNETT SQUARE
A chart that shows all the
possible combinations of
alleles that can result from
a
genetic cross.
GENOTYPE
An organism’s genetic
makeup or allele
combinations.
PHENOTYPE
An organism’s
physical appearance,
or visible traits.
MUTATION
A change in a gene or
chromosome.
FATHER OF GENETICS
Gregor Mendel’s work
was the foundation of
genetics

Understand why offspring
have traits similar to
those of their parents.
ST
1
Mendel cross-pollinated
purebred tall pea plants
with purebred short pea
plants.
Traits are controlled by
alleles of genes.

Organisms inherit one allele
from each parent.
Some alleles are dominant
 capital letter.
Some alleles are recessive
 lowercase letter.
The principles of probability
can be used to predict the
results of genetic crosses

The likelihood that a
particular event will
happen.
Geneticists use
Punnett squares

to show all the possible
outcomes of a genetic cross
and to determine the
probability of a
particular outcome.
PHENOTYPE
PHYSICAL
APPEARANCE
VISIBLE TRAIT
GENOTYPE
GENETIC MAKE-UP
ALLELE
COMBINATIONS
HOMOZYGOUS
HETEROZYGOUS
CODOMINANCE
The alleles are
neither dominant nor
recessive.
HOW DO GENES EXPRESS
THEMSELVES ?
An organism has two
alleles for each trait . . .
They may be dominant or
recessive.
ONLY THE DOMINANT
ALLELE IS EXPRESSED
!
The genotype of a black
rabbit is either two dominant
alleles (BB) or one dominant
allele & one recessive allele
(Bb); the genotype of a
brown rabbit consists of two
recessive alleles (bb).
USING PUNNETT SQUARES
Used to identify possible
combinations of dominant and
recessive alleles in offspring.

Used to calculate the
probability that an offspring
will inherit a certain trait.
USING PUNNETT SQUARES
1) Divide a square into four
sections.
2) Write the letters that
represent the alleles of the
parents across the top &
down the side of the square.
USING PUNNETT SQUARES
3) Combine the alleles from one
parent with those from the
other in every combination.
4) The letters in the Punnett
square show the genotypes of
the offspring.
LAW OF DOMINANCE
The trait that appears is the
dominant trait and the hidden
trait is the recessive trait.
IN
RABBITS, THE ALLELES FOR BLACK COAT
COLOR
(B)
IS DOMINANT OVER THE ALLELE
FOR BROWN COAT COLOR (B).
RABBITS
(BB)
ARE MATED.
PREDICT ABOUT THE
TWO
WHAT
OFFSPRING?
BLACK
CAN YOU
_____________________________________
A) Most of the offspring will be brown.
B) Most of the offspring will be black.
C) All of the offspring will be black.
D) All of the offspring will be brown.
WHAT IS A PUREBRED PLANT?
_______________________________________
WHY WAS IT IMPORTANT FOR MENDEL TO
PREVENT HIS PEA PLANTS FROM SELF
POLLINATING?
_______________________________________
IS
YELLOW SEED COLOR CONTROLLED BY
A DOMINANT ALLELE OR A RECESSIVE
ALLELE?
WHAT
TYPE OF ALLELE CONTROLS
PINCHED POD SHAPE?
______________________________________
WHAT
COMBINATION OF ALLELES MUST THE
WHITE RABBIT HAVE?
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IF A PEA PLANT HAS A TALL STEM, WHAT
POSSIBLE COMBINATIONS OF ALLELES
COULD IT HAVE?
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WHAT IS A DOMINANT ALLELE? WHAT IS A
RECESSIVE ALLELE?
GIVE
AN EXAMPLE OF EACH.
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THE
ALLELE FOR ROUND SEED IS
REPRESENTED BY
SUPPOSE
R.
THAT A PEA PLANT
INHERITED TWO RECESSIVE ALLELES
FOR WRINKLED SEEDS.
HOW
WOULD YOU WRITE THE
SYMBOLS FOR ITS ALLELES?
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