Genetics Guided Notes
To be used with Genetics PowerPoint
History of Genetics:
Gregor Mendel:
- Austrian monk lived from 1822-1884
- Mendel developed principles of heredity
without any knowledge of genes or
chromosomes
- His principles were established through
experiments with pea plants
Why was Mendel so successful with pea plants?
•Used pure breeding, contrasting traits
•Studied characteristics one at a time for many
generations
•Used mathematics in analyzing his results
•Obtained large numbers of offspring
•Chose pea plants which normally self-fertilize
•Used scientific method
•Inexpensive
Define genes: factors that control organism’s traits.
-the part of chromosome that contains the genetic code.
Every organism requires a set of coded instructions for specifying its traits
For offspring to resemble their parents, their must be a reliable way to transfer hereditary information from one generation to the next
Genetic Terms:
• ( ): the alleles on homologous chromosomes are the same
• : ( ): the alleles on homologous chromosomes are different
•parental generation (P): the two original organisms being crossed - usually pure
•first filial generation(F1):the first generation of offspring from the parents
•second filial generation(F2):generation of offspring arising from the first filial generation
Genotype: the ______makeup of an organism
•Homozygous Dominant: ____
•Homozygous Recessive: ____
•Heterozygous: ____
Phenotype: the ______of an organism
Describes what the organism looks like
TT - ______
tt - ______
Tt - ______
______:
a model used to predict the
results of a genetic cross
Three Laws by Mendel:
1. Law of Dominance: a pattern of heredity in which one allele of a gene may express
itself by masking the presence of the other allele
Define Dominant Trait:
Define Recessive Trait:
Example:
______x ______ ______
Example of Dominance:
R = red
r = white
Problem: Cross homozygous dominant with homozygous recessive
______x ______
What are the results?
Phenotype:
____ % red, ____ %white
Genotype:
____ % homozygous or heterzygous
2. Law of Segregation and Recombination Mendel’s Second Law:
When gametes are formed during meiosis three things happen. What are they?
When gametes are formed during meiosis:
There is a random segregation of homologous chromosomes
Random segregation of sister chromatids & alleles
The result: new gene combinations are likely to be produced
Segregation means separation and can lead to genetic recombination.
Example of Segregation:
Problem: Cross two offspring from the 1st filial generation (both are heterozygous)
______x ______
Results?
Phenotype:
_____% red, ____% white
Phenotypic ratio:
___ red : ___ white
Genotype:
___% homozygous dominant
___% homozygous recessive
___% heterozygous
3. Law of Independent Assortment Mendel’s Third Law
Scenario: Two different traits located on two different chromosomes
Explain what two things can happen to these traits during meiosis:
•They segregate randomly during meiosis
•May be inherited independently of each other
The cross of two organisms heterozygous for a trait is known as a dihybrid cross
Punnett Square Problem #3: Dihybrid Cross
T = tallt = short
Q = wrinkledq = smooth
Problem: Cross homozygous tall and homozygous wrinkled seeds with homozygous short and homozygous smooth seeds
Genotypes for this cross: TTQQ x ttqq
What are the phenotypes for these plants?
Punnett Square Problem #3: Dihybrid Cross
Genotypes for this cross: TtQq x TtQq
T = tallt = short
Q = wrinkledq = smooth
What are the phenotypes for these plants?
Incomplete Inheritance:
Two examples of Incomplete Inheritance:
Incomplete Dominance & Codominance
Define Incomplete Dominance:
Name one example of incomplete dominance
______
Define Codominance:
Name the first example of Codominance:
______
Example of Codominance:
Problem:
Cross offspring from 1st cross (2 heterozygous parents)
Problem 3: Cross two
heterozygous parents
R = red
r = white__ __ x __ __
Results:
Phenotype: ___% red, white___%
Phenotypic Ratio: __ : _ __
Genotype: ___% heterozygous
___% homozygous dominant
___% homozygous recessive
R = red __ __ x __ __
r = white
Results:
Phenotype: ___% red, white___%
Phenotypic Ratio: _____ : ______
Genotype: ___% heterozygous
___% homozygous dominant
___% homozygous recessive
Problem: Cross two heterozygous parents.
R = red __ __ x __ __
r = white
Results:
Phenotype:
___% red, ___& red and white, ___% white
Phenotypic Ratio:
__ ___ : ______: ______
Genotype: ___% heterozygous
___% homozygous dominant
___% homozygous recessive
Problem: Cross two heterozygous parents.
R = red __ __ x __ __
r = white
Results:
Phenotype:
___% red, ___& pink, ___% white
Genotype: ___% heterozygous
___% homozygous dominant
___% homozygous recessive
Traits that are controlled by more than 2 alleles
Results in multiple phenotypes
Examples:
Pigeons Blood groups in humans
BA dominant over B Four blood types A B AB & O
BA and B are dominant over
Polygenic Inheritance
A pattern of a trait that is controlled by 2 or more genes.
Phenotype express a range of variability.
Examples:Stem length, human height, eye color & skin color
Stem length for a totally recessive plant is____ cm.
aabbcc = 4 cmAABBcc = cm
Aabbcc = cmAABBCc = cm
AAbbcc = cmAABBCC = cm
AABbcc = cm
Gene Expression
Influence of External Environment:
Examples: Temp., nutrition, light, chemicals
Color of rabbit in the summertime: brown
Color of rabbit in the winter: white
The temperature effects what color fur (or what proteins) are expressed
Temp also determines the sex of a gator
Light determines color of bacteria
Influence of Internal Environment:
Examples: Hormonal influences
•Horn size in mountain sheep
•Male pattern baldness
•Peacock feathers
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