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Lecture 7

BIOL 1201 Lecture Notes - Lecture 7: Dihybrid Cross, Mendelian Inheritance, Zygosity


Department
Biological Sciences
Course Code
BIOL 1201
Professor
Bill Wischusen
Lecture
7

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BIOLOGY EXAM 4
Lecture 10/31
Pre-Lecture: Genetic Definitions
o Gene: Information (DNA sequence that codes for a particular protein) leading to a
particular characteristic
o Allele: One form of a gene
o Locust: Location of a gene on a chromosome
o Phenotype: The physical expression of the alleles (purple flowers)
o Genotype: A listing of the alleles for an individual often for just one or two genes
Homozygous: the condition in which both alleles for a gene are the same (AA,
aa)
Heterozygous: The condition in which the alleles for a gene are different (Aa)
Pre- Lecture: Gamete Formation Rules
o An allele can be present in a gamete only if that individual has that allele
o For every pair of alleles an individual gamete only gets one
Homozygous Dominant: [AA] can only give (A) allele
Homozygous recessive: [aa] can only give (a) allele
Heterozygous: [Aa] can give (A) and (a) allele
o Different pairs of alleles assort independently from one another
Life Cycles:
o Alternation if generation
o Organisms w/ multicellular haploid and diploid stages (Fig. 13.6)
Inheritance
o Reproduction:
Asexual, what is the outcome?
Identical offspring (mitosis)
What is the outcome of sexual?
Different offspring (meiosis)
o Key Point:
What is the role of the parent?
Produce gametes
What type of cell division produces gametes?
Meiosis
An individual with the genotype (A/A) can produce gametes containing the following alleles?
o (A), for every pair the daughter cells only get one
An individual with the genotype (a/a) can produce gametes containing the following alleles?
o (a)
An individual with the genotype (A/a) can produce gametes containing the following alleles?
o A and a
Gie this pedigree of a Graes disease fail, is it possile that Graes’ disease is doiat?
o No, recessive
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Two purple flowered pea plants are crossed and the offspring include both purple and white
flowered plants. What are the genotypes of the parents?
o Both heterozygous
Test Cross:
o Cross an individual of unknown genotype with a homozygous recessive individual
Which phenotype has an unknown genotype?
Dominant
If the unknown individual is homozygous dominant we would expect the following ratio of
offspring?
o All purple
o Parental
o F1
o P/P x P/p
If the unknown individual is heterozygous we would expect the following ratio of offspring?
o ½ purple, ½ white
Lecture 11/02
Pre- Lecture:
A/a: B/b: C/c CANNOT produce
o A: b: c
A/a: B/b: C/C: D/d CANNOT produce A: b: c: d
Dihybrid cross (seed form and seed color)
o Phenotype: Round Yellow X wrinkled green
o Genotype: R/R: Y/y ; r/r: y/y
o What will the offspring (F1) look like?
o Genotypically: R/r: Y/y; round yelllow
o R/R:Y/y, r/r: y/y, R:y, r:y,
Medel’s Oseratio
o New non-parental combinations
o 3: 1 ratio for each trait
o Conclusion: This results from 2 separate and independent monohybrid crosses
Product Law:
o The chance that independent events will occur simultaneously is equal to the product of
the chances that they will occur separately.
Lecture 11/04
R/r: Y/y: A/a x R/r: Y/y: A/A
What is the probability of producing an offspring with the genotype:
o R/r: Y/Y: A/A
o 1/16
R/r: Y/y x R/r: Y/y
What is the probability of producing an offspring with the genotype:
o R/-:Y/y
o 3/8
R/R: Y/y: A/a x R/r: Y/y: A/a
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What is the probability of producing an offspring with the genotype:
o R/r: Y/Y: A/A
o 1/32
Linked Genes
o Genes that are on the same chromosome
o Do not assort independently
RY/ry x RY/ry
What is the probability of producing an offspring with the genotype:
o ry/ ry
o ¼
Given that a child of this individual inherits the eye^1 allele, what is the chance that they will
also inherit the eye2 allele from the same parent?
o 0%, since you can only get one allele form each parent and these are linked
Given that a child of this individual inherits the eye1 allele, what is the chance that they will also
inherit the ear3 allele from the same parent?
o , o rossig oer happes sie it’s liked ee liked ith ear3
Given that a child of this individual inherits the nose5 allele, what is the chance that they will
also inherit the throat7 allele from the same parent?
o 100%
Given that a child of this individual inherits the nose5 allele, what is the chance that they will
also inherit the throat8 allele from the same parent?
o 0%
Given that a child of this individual inherits the eye1 allele, what is the chance that they will also
inherit the throat7 allele from the same parent?
o 50%
Given this pedigree of alkaptonuria, is it possible that it is dominant?
o No
Lecture 11/07
Pre-Lecture:
A rooster with gray feathers is mated with a hen of
similar phenotype.
o Among the offspring:
15 are gray
6 are black
8 are white
o What are the phenotypes/genotypes of the
parents?
Variatios o Medel’s Thee
o Incomplete Dominance
o Multiple Alleles
ABO Blood Type
o Co-dominance
o Sex-linkage
o Epistasis/ pleiotropy
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