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Important Vocabulary Heredity
Allele
Genetics
Hybrid
Dominant
Recessive
Punnett square
Genotype
Phenotype
Homozygous
Heterozygous
Inheriting Traits Heredity: the passing of traits to offspring
An organism is a collection of traits inherited from its parent or parents
What is genetics? Alleles: different forms of a trait that make up a gene
pair When a pair of chromosomes separate during meiosis, the
alleles of a gene pair also separate into different sex cells As a result, every sex cell has one allele for each trait
Genetics: the study of how traits are inherited through the interactions of alleles
http://glencoe.mcgraw-hill.com/sites/0078693918/student_view0/concepts_in_motion.html#
(Click on Meiosis and Fertilization)
Mendel- The Father of Genetics
Gregor Mendel Austrian monk who studied
math and science Became the gardener at a
monastery Predicted the types of flowers
and fruits that would result from crossbreeding two plants
Began experimenting with peas in 1856 Shared results 8 years later
with other scientists
http://science.discovery.com/tv-shows/greatest-discoveries/videos/100-greatest-discoveries-shorts-genetics.htm
Mendel- The Father of Genetics
Mendel was the first scientist to trace one trait through several generations
Genetics in a Garden Each time Mendel studied a plant, he crossed two
plants with different expressions of the trait He found that the new plants all looked like one of the
two parents These new plants were called “hybrids”
Hybrid: receives different genetic information, or different alleles, for a trait from each parent
Purebred: organism that always produces the same traits generation after generation
Dominant and Recessive Factors
Mendel found that tall plants that were crossed with short plants produced seeds that were all tall plants Mendel called the tall form the
“dominant” factor
Dominant: dominates, or covers up, another allele Dominant alleles are written in
capital letters Ex. B = purple flower
Recessive: allele that seems to “disappear” or is covered up Recessive alleles are written in lower
case letters Ex. b = white flower
Using Probability to Make Predictions
Mendel dealt with probabilities His results were more accurate because he worked
with many plants– about 30,000 pea plants! This increased Mendel’s chances of seeing a
repeatable pattern
Punnett square: tool used to predict the results in Mendelian genetics
Punnett Squares In Punnett squares, letters symbolize
alleles Remember, capital letters represent
dominant alleles and lowercase letters represent recessive alleles
The letters form a code for the genetic makeup an organism
Genotype: genetic make up of an organism (BB, Bb, bb)
Phenotype: the way an organism looks and behaves based on their genotype (purple flower or white flower)
Alleles Determine Traits Most cells in your body have
at least two alleles for every trait Located on chromosomes
within each cell’s nucleus
Homozygous: an organism that has two alleles that are the same Example: BB or bb
Heterozygous: an organism that has two different alleles Example: Bb
Making a Punnett Square
Make a grid like this one:
One parent’s alleles are placed on the top, second parent’s alleles place along the side like this (one letter per column/row):
Each square is filled in with one allele donated by each parent.
Make sure the capital (or dominant) allele is placed before the lowercase (or recessive) allele.
In this Punnett square, the probability of each genotype is: BB: 25% or ¼ Bb: 50% or ½ bb: 25% or 1/4
B b
B
b
B b
B BB bB
b bB bb
B b
B BB Bb
b Bb bb
Principles of Heredity It took Mendel years of detailed observation, careful
analysis, and repeated experimentation to conclude his ideas of heredity. The following tables sums them up in three principles:
Video Links http://www.youtube.com/watch?v=xc2wbIDfO7E
http://learn.genetics.utah.edu/content/begin/traits/tour_trait.html
http://learn.genetics.utah.edu/content/begin/traits/tour_heredity.html