Inherited vs. Acquired
Traits
n
http://www.youtube.com/watch?v=egXIk_4-qMY&feature=fvw
n Make a two lists:
n What traits have you inherited
Mendel’s Garden
Female Male
Mendel’s Pea Plants
(His Experimental System)
n Mendel chose the garden pea for
several reasons
n Many different varieties were
available
n Small and easy to grow
n Short generation time and
lots of offspring
n Both male and female
reproductive organs are enclosed within the pea
Mendel’s
Methods
n Plant Breeding using
Cross-pollination
n When 2 plants are
crossed, a hybrid results
1 Removed stamens from purple flower White Stamens Carpel Purple PARENTS (P) OFF-SPRING
(F1)
2 Transferred pollen
from stamens of white flower to carpel of purple flower
3 Pollinated carpel matured into pod
Mendel’s Experimental
Design
n Mendel selected seven
characteristics or traits to study, each of which had two
Theories About Heredity
in the 1800’s
n Fluid competition
n Spontaneous generation
n Preformed miniature humans in sperm
Mendel’s Principles
n Genes are passed from parents to offspring
n Principle of Dominance
n Some genes are dominant and some are recessive and
the dominant gene determines the appearance
n Principle of Segregation
n Each organism has two versions of each gene and one
Mendel’s Crosses
P=Parent Generation
F1=First Filial Generation
X
Mendel always began with true-breeding
plants. These plants ONLY produced
There Are Many Alternative
Forms of a Gene
n Each person has 2 versions of
every gene
n Each different gene is
represented by a letter
n B = brown hair and b = red
hair
n Y = yellow pea and
Dominant Genes
Determine Appearance
n Usually some versions of a gene
are dominant and others are recessive
n The dominant version
determines the appearance of the individual
n YY = yellow,
n Yy = yellow
Dominate Versions of Genes Are
Not Always More Common
n Dominance does NOT describe how common an allele
is.
n Dominance DOES describe the version that determines
appearance.
n Examples of some Uncommon dominant traits:
n Huntington’s Disease
n Dwarfism
n Six fingers
n Webbed fingers
n Baldness
Probability And Punnett
Squares
Unit 3 Chapter 11.1
Y y
Y
Probability is the
Likelihood of an Event
n The probability of a coin landing heads-up is one out
of two or ½
n The probability of a coin landing heads-up a second
time is also one out of two or ½
n Each coin flip is independent. PAST EVENT S DO
NOT AFFECT FUTURE ONES!
n So the probability of a coin landing heads-up 3 times
Gene Segregation is Like a
Coin Toss
y
y
y
y
y
y
y
y
Y
Y
Y
Y
Y
Y
Gametes
=sex cells. They have one
Punnett Squares Help
Make Predictions
Y Y
y
y
Yy Yy
Yy Yy
Parents genes
Possible
offspring
combinations
of genes
Y
Y
y
y
Punnett Squares Help
Make Predictions
n A Yy x Yy results in a 3:1 ratio of yellow:green.
n A Yy x Yy results in a 1:2:1 ratio of YY:Yy:yy
Y y
Y
y
y
Y
Y
y
y
Genotypes Determine
Phenotypes
n The appearance of an individual trait is its
phenotype. (ex. Yellow, green)
n The genetic composition of an individual trait is its
genotype. (ex. YY, Yy, yy)
n Phenotypic Ratio #Dominant : #Recessive
Question
n Round peas (R) are dominant and wrinkled peas (r)
are recessive. What is the genotype of this pea?
a) RR
b) rr
c) Rr
Question
n Can two peas have the same phenotype, but a
different genotype?
a) Yes
Two Organisms Can Have the Same
Phenotype, but Different Genotype
n Heterozygous – Two different
versions of a gene for the same trait (R r). Hybrid for the trait.
n Homozygous – Two identical
versions of a gene for a trait (RR or rr). True-breeding for the trait.
R
r
Beyond Dominant and
Recessive Traits
Incomplete Dominance
n The phenotype of the heterozygous offspring
is intermediate between the homozygous phenotypes
n In Snapdragons, a red parent and a white
parent produce a pink offspring
n Because there is only one copy of R, less
Codominance
n The phenotype of the heterozygous offspring is a
combination of the two homozygotes
n Notice that both colors appear separately, they are not
Multiple Alleles
n In a population, multiple versions of a
gene (more than two) often exist for a characteristic
n The ABO blood group in humans is
determined by a gene with 3 versions
n The different combinations of the three
Polygenic Traits
n Polygenic - one characteristic (i.e. height, eye color,
or skin color) but controlled by many genes.
n These genes contribute in a cumulative way to the
phenotype.
Polygenic: Eye Color
n The number of genes for eye color in
humans is unknown
Polygenic: Skin Color
n This is a three gene model with seven different
skin tones.
n Skin tone is also affected by the UV in the
mouse without the weight-controlling hormone leptin
normal mouse
Many Diseases are
Multifactorial
n Phenotypes are controlled by genes in addition to
environmental and cultural factors.
n Cancer, diabetes, heart disease and obesity are all
multifactorial
n 30% of US adults are obese
n Lifestyle, including diet and exercise, are
environmental components impacting weight
n Many genes influence hunger and metabolism
n For example: Mutations in leptin pathway account for
Sex-Linked Traits
n Traits from a gene on the sex
chromosome
n Human X chromosome has more than
1000 protein-encoding genes
n Human Y chromosomes has only 100
genes
Color Blindness: X-linked
Recessive
n Females have 2 versions for X genes,
males have 1
n Sex-linked disorders usually affect
males
n These disorders can easily ‘hide out’ in
n Red/Green Color Blindness
is one example
n Normal color = ~150 colors
n Red/Green color blind
X-Inactivation
n How do females get the same ‘dosage’ as males for
genes on the X-chromosome?
n One of the two X’s is randomly tightly packaged into
Unit 4 Vocab
n Trait
n True-breeding
n Gene
n Dominant
n Recessive
n Gametes
n Phenotype
n Genotype
n Homozygous
n Heterozygous
n Crossing Over
n Meiosis
