Transcript Mendel's Laws of Heredity - West-MEC

Mendel’s Laws of Heredity
Why we look the way we look...
History
 Principles of genetics were developed in the mid 19th
century by Gregor Mendel an Austrian Monk.
 Gregor developed these principles without ANY
scientific equipment - only his mind!
 Gregor experimented with pea plants, by crossing
various strains and observing the characteristics of
their offspring.
History cont…
Studied the following characteristics:
Pea color (Green, yellow)
Pea shape (round, wrinkled)
 Pea shape (round, wrinkled)
Flower color (purple, white)
Plant height (tall, short)
History cont…
 Made the following
observations (example
given is pea shape)
 When he crossed a round
pea and wrinkled pea, the
offspring (F1 gen.) always
had round peas.
 When he crossed these F1
plants, however, he would
get offspring which
produced round and
wrinkled peas in a 3:1
ratio.
Genetic Vocabulary
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Genetics: The scientific study of heredity
Genes: Point on a chromosome that controls the trait.
Allele: Alternate forms of a gene/factor. A or a
Genotype: combination of alleles an organism has. (genetic
traits)
Phenotype: How an organism appears. (physical traits)
Dominant: An allele which is expressed (masks the other).
Recessive: An allele which is present but remains
unexpressed (masked)
Homozygous: Both alleles for a trait are the same.
Heterozygous: The organism's alleles for a trait are
different.
Genetic Vocabulary
 Probability : The mathematical chance that an event will
happen.
 Meiosis :The cell division that produces sex cells.
 Mutation : A change in the type or order of the bases in an
organism DNA: deletion, insertion or substitution.
 Natural Selection : The process by which organisms with
favorable traits survive and reproduce at a higher rate than
organisms without favorable traits.
 Evolution :The process by which population accumulate
inherited changes over time.
Punnett Squares
Genetic problems can be easily solved using a tool
called a Punnett square.
Tool for calculating genetic probabilities
A Punnett square
Punnett Squares Vocabulary
 Punnett Squares : The chart used to show the possible ways
genes are combined when passed from parents to offspring.
 Dominant genes are UPPER CASE (T)
 Recessive genes are lower case (t)
 Each parent has two genes for a trait. (TT), (Tt) or
(tt).
 There can be a possible four combinations for each
cross.
Punnett Squares Vocabulary Cont…
GENOTYPE: The gene combination
 Homozygous – Pure dominate or pure recessive
 Heterozygous – Hybrid a mixed
PHEOTYPE :The physical appearance
 Dominate trait
 Recessive trait
 Combination of two traits (incomplete dominance)
INCOMPLETE DOMINANCE : Occurs when
two inherited traits combine and show up as a
third trait.
 What is Incomplete Dominance?
-- Occurs Incomplete dominance is a type of
inheritance in which one allele for a
specific trait is not completely dominant
over the other allele. This results in a
combined phenotype (expressed physical
trait).
Example, if you cross pollinate red and
white snapdragon plants, the dominant
allele that produces the red color is not
completely dominant over the recessive
allele that produces the white color. The
resulting offspring are pink.
Monohybrid cross
(cross with only 1 trait)
 Problem:
 Using this is a several step process, look at the
following example
 Tallness (T) is dominant over shortness (t) in
pea plants. A Homozygous tall plant (TT) is
crossed with a short plant (tt). What is the
genotypic makeup of the offspring? The
phenotypic makeup?
Punnett process
1. Determine alleles of each
parent, these are given as TT,
and tt respectively.
2. Take each possible allele of each
parent, separate them, and
place each allele either along
the top, or along the side of the
punnett square.
Punnett process continued
Lastly, write the letter for
each allele across each
column or down each
row.
The resultant mix is the
genotype for the
offspring. In this case,
each offspring has a Tt
(heterozygous tall)
genotype, and simply a
"Tall" phenotype.
Punnett process continued
Here we have some more
interesting results: First we
now have 3 genotypes (TT,
Tt, & tt) in a 1:2:1
genotypic ratio. We now
have 2 different phenotypes
(Tall & short) in a 3:1
Phenotypic ratio. This is
the common outcome from
such crosses.
Dihybrid crosses
 Dihybrid crosses are made when phenotypes and
genotypes composed of 2 independent alleles are
analyzed.
 Process is very similar to monohybrid crosses.
 Example:
 2 traits are being analyzed
 Plant height (Tt) with tall being dominant to
short,
 Flower color (Ww) with Purple flowers being
dominant to white.
Dihybrid cross example
The cross with a pure-breeding (homozygous) Tall,
Purple plant with a pure-breeding Short, white
plant should look like this.
F1 generation
You don’t look like…..
Have you ever been told that
you resemble one parent more
than the other? The reason for
this may be due to having
received more dominate genes
from the parent you resemble.
However, you receive half of
all your chromosomes and
genes from each parent.
Each parent passes to you 23
chromosomes for a total of 46
chromosomes.
“Oh’ Boy A Take Home Lab!”
STRATEGY:
 You will examine ten of your genetic traits.
 You will examine your parents for these same traits.
 You can then compare how similar or how different
you are to each parent.
PROCEDURE:
Use the handout that Ms. Olson has given to you to
complete the assigned task (lab). Complete the
column marked YOU for the genetic traits to be
examined. Ask your lab partner to assist you in
describing certain traits that you may not be able to
see, such as ear lobe shape or hair whorl.
TRAIT
DESCRIPTION
Handedness
Left or right
YOU
FATHER
MOTHER
TRAIT DESCRIPTION
Sight
Nearsighted
or
normal
YOU
FATHER
MOTHER
TRAIT
DESCRIPTION
Eye color
Blue or not
Brown eyes
Blue eyes
YOU
Green eyes
FATHER
MOTHER
Hazel eyes
TRAIT
DESCRIPTION
Dimples
Yes or No
Mario
Lopez
Josh
Holloway
YOU
FATHER
Zinta
MOTHER
Jada Smith
TRAIT
DESCRIPTION
Freckles
Present
or
Absent
YOU
FATHER
MOTHER
TRAIT
DESCRIPTION
Allergies
Yes or No
YOU
FATHER
MOTHER
Food
Pollen
Animal hair
dander
Medication
TRAIT
HairWhorl
DESCRIPTION
Clockwise
or
Counter-clockwise
YOU
FATHER
MOTHER
TRAIT
Ear lobe
DESCRIPTION
YOU
FATHER
MOTHER
Free
or
Attached
Unattached
Attached
Unattached
Unattached
Attached
TRAIT
Eye shape
DESCRIPTION
Close set, Deep set,
Hooded, Almond,
Down turned,
Protruding
YOU
FATHER
MOTHER
TRAIT
DESCRIPTION
Tongue
Roller
or
Non-roller
Rollers
YOU
FATHER
MOTHER