Download Bio 11

Chp. 11: Introduction to Genetics
11.1 The Work of Gregor Mendel
HW: Read, Quiz Tomorrow
11.2 Probability and Punnett Square
A. Punnett Squares – used to predict and
compare genetic variations that will result
from a cross
1. Homozygous – 2 identical alleles
a. Dominant – RR, more likely to
be seen
b. Recessive – rr, less likely to
be seen
2. Heterozygous – 2 diff. alleles, Rr
a. Trait is still dom.
3. Phenotype – physical trait you
see (brown eyes, green pods)
4. Genotype – genetic makeup (Rr,
RR,rr)
B. Probability – likelihood that an event will
occur
1. Principle of probability predict the
outcome of genetic crosses
2. What is the probability that you
will flip a coin and land heads up 4x
in a row?
a. ½ * ½ * ½ * ½= 1/16
C. Probabilities Predict Averages
1. Predicts the average outcome for
large events
2. In 100 plants in a Heterozygous
Cross 75 will be Tall and 25 will be
short
11.3 Exploring Mendelian Genetics
A. Independent Assortment
1. The 2 Factor Cross: F1
a. Mendel crossed true breeding
plants that produced only round
yellow peas.
i. Round and Yellow alleles
are dominant to wrinkled
and green alleles
2. The 2 Factor Cross: F2
a. Mendel took the hybrid plants
from F1 and crossed them (all
were RrYy)
b. Results were in a ratio of
9:3:3:1
3. Independent Assortment - genes
from different traits separate
independently during the formation
of gametes (sex cells)
a. Accounts for many genetic
variations in plants, animals and
other organisms.
B. Summary of Mendel’s Principles
1. Inheritance of specific traits is
determined by genes. Genes are
passed from parents to offspring.
2. Some forms of the gene may be
dominant and others may be
recessive.
3. In most sexually reproducing
organisms, each adult has 2 copies
of the gene (1 from each parent).
These genes segregate from each
other when gametes are formed.
4. Alleles for different genes usually
segregate independently of one
another.
C. Beyond Dominant and Recessive Alleles
1. Some alleles are neither
dominant nor recessive; some
traits are controlled by multiple
alleles or genes.
a. Incomplete Dominance –
cases in which 1 allele is not
completely dominant
i. Red (RR) and White (WW)
plants crossed to get Pink
(RW)
b. Codominance – both alleles
contribute to the phenotype
i. Chicken Feathers
a. White-WW
b. Black –BB
c. Speckled – BW
c. Multiple Alleles – some genes
have more then 2 alleles
i. Rabbits
a. 4 possible coat colors
ii. Blood Types
d. Polygenic Traits – traits
controlled by 2 or more genes
i. Human Skin Color
a. At least 4 different
genes control this trait