1 Mendelian Inheritance BIO 2215 Oklahoma City Community College Dennis Anderson.
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Transcript of 1 Mendelian Inheritance BIO 2215 Oklahoma City Community College Dennis Anderson.
4
Mendel’s Hypotheses
• Each parent has two factors (alleles)
• Each parent gives one of those factors to the offspring
• Tall has TT
• Short has tt
• Tall is dominant
• Short is recessive
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Law of Segregation
• Alleles separate during gamete production
• Gametes have one allele for each trait
• During fertilization gametes combine at random to form individuals of the next generation
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Discovery of Chromosomes in 1900 Confirmed Law of Segregation
• Chromosomes are in pairs
• Each chromosome has one of the allele pair
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Chromosomes line up in a double row.
Meiosis Metaphase
Assume a T allele on each red chromatid and a t allele on each blue chromatid
T T t t
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Allele
• Member of a paired gene– One allele comes from each parent
• Represented by a single letter
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Dominant & Recessive Alleles
• Dominant alleles are expressed
• Recessive alleles are not expressed in the presence of a dominant allele– Recessive alleles are only expressed if both
recessive alleles are present
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Gene
• A unit of heredity that controls the development of one trait
• Made of DNA
• Most genes are composed of two alleles
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Homologous Chromosomes
• Chromosomes of the same pair
• Each homologue will have one allele for a paired gene
• Homologous chromosomes pair up during meiosis
• Only one of each homologue will be in each gamete
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Sickle Cell Anemia
• RBCs sickle shaped• Anemia• Pain• Stroke• Leg ulcers• Jaundice• Gall stones• Spleen, kidney & lungs
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Sickle Cell Anemia
• Recessive allele s, codes for hemoglobin S – Long rod-like molecules– Stretches RBC into sickle shape
• Homozygous recessive ss, have sickle cell anemia
• Heterozygous Ss, are carriers
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Amino Acids Melanin PigmentEnzyme
A a
AA = Normal pigmentation
Aa = Normal pigmentation
aa = Albino
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A man & woman are both carriers (heterozygous) for albinism. What is the chance their children will inherit albinism?
Monohybrid Cross or One Trait
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AA = Normal pigmentation
Aa = Normal pigmentation (carrier)
aa = Albino
Man = Aa Woman = Aa
A
a a
A
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A man & woman are both carriers (heterozygous) for PKU disease. What is the chance their children will inherit PKU disease?
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PP
Pp
Pp
pp
Genotypes1 PP, 2Pp, 1pp
Phenotypes
3 Normal
1 PKU disease
Probability
25% for PKU disease
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A man with sickle cell anemia marries a woman who is a carrier. What is the chance their children will inherit sickle cell anemia?
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Ss
Ss
ss
ss
Genotypes2 Ss, 2ss
Phenotypes
2 Normal (carriers)
2 Sickle cell
Probability
50% for Sickle cell
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Dwarfism = D
Normal height = d
DD = Dwarfism
Dd = Dwarfism
dd = Normal height
Dwarfism
Dwarf Band
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A man with heterozygous dwarfism marries a woman who has normal height. What is the chance their children will inherit dwarfism? Dwarfism is dominant.
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Law of Independent Assortment
• The inheritance of one gene does not influence the inheritance of another gene if they are on separate chromosomes.
• The gene for albinism does not affect the gene for dwarfism
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Dihybrid Cross or Two Traits
• A heterozygous tall plant that is also heterozygous for yellow seeds is crossed with another plant with the same genotype
• Tall and yellow seeds are dominant to short and green seeds.
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9 Tall-Yellow
Match gametes on a Punnent Square
TY
Ty
tY
ty
TY Ty tY ty
TtYy
TtYy
TTYY TTYy TtYY
TTYy TTyy Ttyy
TtYY TtYy ttYY ttYy
TtYy Ttyy ttYy ttyy
3 Tall-Green
3 Short-Yellow
1 Short-Green
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A man with blue eyes and normal height marries a woman with heterozygous brown eyes and heterozygous dwarfism. What are the possible phenotypes of their children? Dwarfism & brown eyes are dominant.
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DB
Db
dB
db
Match gametes on Punnent Square
db
DdBb
Ddbb
ddBb
ddbb
Dwarf-Brown eyes
Dwarf-blue eyes
Normal height-Brown eyes
Normal height-Blue eyes