Transcript Dominant genotype

Mendelian
Genetics
&
Simple
Inhertiance
So Who’s Mendel?
•
An Austrian monk named Gregor Mendel.
•
Mendel spent his time breeding pea plants.
•
As he did this over & over & over again, he noticed a patterns to the
inheritance of traits from one set of pea plants to the next. By carefully
analyzing his pea plant numbers, he discovered three laws of inheritance.
• Mendel's Laws are as follows:
1. Law of Dominance
2. Law of Segregation
3. Law of Independent Assortment
Genetic vocabulary…
• Genotype: the genes of an
organism (all your genes)
• Phenotype: an organism’s
traits (expression of your genes)
• Allele: variations of a gene
• Represented with letters for
the different types of alleles
(PP, Pp, pp)
• Homozygous: pair of identical
alleles for a character (PP, pp)
• Heterozygous: two different
alleles for a gene (Pp)
Terminology
Dominant & Recessive Genotypes and Phenotypes
Recessive genotype: Both
recessive alleles must be present
(rr).
Dominant genotype: At least one
dominant allele is present (R-).
Character: Tongue Rolling
Being able to roll your tongue is a
dominant phenotype.
___ ___
___ ___
Man pictured to the right: Being able to
roll your tongue is the dominant trait
(phenotype). What would be the dominant
genotype?
Woman pictured to the right: Not being
able to roll your tongue is the recessive
(phenotype). What would be the recessive
genotype?
So what is the baby’s genotype?
___ ___
Genotypes
Mendel's Laws are as follows:
1. Law of Dominance
Dominant traits show in the phenotype
2. Law of Segregation
Alleles separate during Meiosis and are combine to
new alleles at fertilization
3. Law of Independent Assortment
Alleles for different traits are distributed to sex cells
(& offspring) independently of one another.
Mendel’s Laws
Working out
Mendelian Genetics
A Punnett square is a tool for figuring out
what the possible genotypes of
offspring will be.
Lets do a Punnett square for the trait
of bent little finger (dominant genotype):
“Bent Little Finger” (B - )
• David (the Daddy):
courtesy of David and Leo Port
• dominant phenotype [bent finger]
• What is Davids gentoype? _______
David’s Genotype:
• Tami (the Mama):
• Recessive phenotype [straight finger]
• What is my genotype? _____
• Leo (the Baby):
• Dominant phenotype [bent finger]
• What is Leo’s genotype? _______
Tami’s
Genotype:
Punnett Square
So far, we’ve
discussed Simple
Inheritance &
Punnett Squares…
But, of course,
genetic is much
more complicated
than that.
“Degrees” of Dominance
• Incomplete dominance:
F1 generation’s appearance
between the phenotypes of
the 2 parents.
Ex: snapdragons
Incomplete Dominance
• Multiple alleles: more than 2 possible alleles for a gene.
Ex: human blood types (ABO)
• Codominance: two alleles affect the phenotype in
separate, distinguishable ways.
Ex: AB Blood Type
Codominance
Independent Assortment Exercise
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p.2
Only one of each pair is eventually sorted into each
egg or sperm.
Procedure:
• OBJECTIVE: In each of the examples, determine
how many different kinds of gametes may be
formed from the diploid parent cells.
•
ALLELES: The letters within the parent cells
represent genes for a particular trait. The capital
letters A, B, D represent alleles for dominant
traits. While lower case letters a, b, d represent
alleles for recessive traits.
•
WHAT YOU NEED TO DO:
- Fill in the gamete cells with the letter or letters which
represent all the possible hereditary combinations.
- Assume that each pair of genes is located on a
different pair of homologous chromosomes (independent
assortment).
Genetics and Health Science Worksheet
Monohybrid Cross
Parental Generation
p. 3
•
Mendel determined that, in pea plants, tall height (T) is dominant to dwarf (t). This means that
heterozygous plants (Tt) are tall. The allele for tall (T) completely masks the allele for dwarf (t) in
producing the phenotype. This allele relationship is called COMPLETE DOMINANCE.
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You can use a PUNNETT SQUARE to predict the outcome of crossing a homozygous tall plant (TT) with a
dwarf plant (tt). The resulting offspring are called the F1 generation.
Cross the two parents, homozygous dominant tall plant (TT) and recessive dwarf plant (tt).
Parent (TT)
Parent (tt)
F1 Generation
Note: Always put the dominant allele (T) first when writing a genotype (Example - Tt)
What is the expected genotype of the F1 generation? ______________
Describe the expected phenotype(s) of the F1 generation: ___________
Genetics and Health Science Worksheet
Monohybrid Cross
F2 Generation
p. 4
Cross two members of the F1 generation:
Parent (Tt)
Parent (Tt)
F2 Generation
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What is the expected genotype ratio of the F2 generation? ________
What is the expected phenotype ratio of the F2 generation: ________
Genetics and Health Science Worksheet
Incomplete Dominance
Parental Generation
p. 4
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Sometimes, a cross between two individuals, each pure for a particular characteristic, results
in partial expression of both traits in the F1 phenotype. One gene incompletely masks the
other in the heterozygote.
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Complete the following Punnett squares using the information. Since dominance is not
operating, a slight modification of gene symbols is used. We will use the letter C to represent
color in snapdragons. CR will represent the allele for red color and CW will represent the allele
for white color. The hybrid of a red and a white snapdragon is pink, so would be represented
as CR CW.
Use this Punnett square to reveal the genotype of the F1 generation, where the parent plants
consist of a red and a white snapdragon plant.
Parent (CR CR)
Parent (CW CW)
F1 Generation
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•
What is the expected genotype of the F1 generation? ______________
Describe the expected phenotype(s) of the F1 generation: ___________
Genetics and Health Science Worksheet
Incomplete Dominance
Parental Generation F2
p. 5
Next, cross two of these F1 snapdragon plants to obtain the theoretical or expected phenotypic
and genotypic rations of the F2 generation.
Parent (CR CW)
Parent (CW CR)
F2 Generation
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What is the expected genotype of the F2 generation? ______________
Describe the expected phenotype(s) of the F2 generation: ___________
Genetics and Health Science Worksheet
Probability:
The likelihood of occurrence of a given event.
•
p.6
In humans, the fusion of gametes at fertilization results in 46 chromosomes for the
developing fetus. Twenty two of those are homologous autosomes plus the sex chromosomes
that determine the sex of the offspring. The mother can only contribute an X chromosome.
The father can contribute an X or a Y, depending on which was independently assorted to
the particular sperm that fertilized the egg.
Father (XY)
Mother (XX)
Sex Chromosomes of Offspring
What’s the probability of any sperm cell containing a Y-chromosome? _______
An X-chromosome? ______
What is the probability of fertilization resulting in a female child? _____________
Genetics and Health Science Worksheet
Accuracy of Actual Ratio
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p.6
In the table below, record data concerning the number of males and number of
females in your family. Then record the same data for the entire class. Your
instructor will facilitate the gathering of these data.)
# Males # Females Ratio
Your natal family (you and your siblings) >>>>>
Class members’ natal families >>>>>>>>>>>>>>>>>>
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Is the ratio in your family the same the expected ratio? _________________
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Is the ratio for the whole class closer to the expected ratio than was the ratio
for your family? __________
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Why do you think this is?________________________________________
Genetics and Health Science Worksheet