mendel and human traits. mendelian inheritance heterozygous and homozygous dominant have the same...
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Mendel and Human Traits
Mendelian Inheritance
• Heterozygous and Homozygous Dominant have the same phenotype
• Homozygous recessive will have a different phenotype
Intermediate Inheritance (Incomplete Inheritance)
• The heterozygote is an intermediate of the two homozygotes
• Red (RR) X White (WW)
• Pink (RW)
RR WW
RW
Pink Flower Ex.
RW RW
RW RW
R R
W
W
• RR - Red• WW - White• RW - Pink• All Offspring are pink
Pink Flower Ex.(cont.)
RR RW
RW WW
R W
W
R
• RR - Red• WW - White• RW - Pink• 1/4 = Red• 1/2 = Pink• 1/4 = White
Codominance
• Sickle Cell Anemia– Blood cells are shaped like
a sickle or half-moon– The sickled cells cause clots
• Heterozygotes have some normal and some sickled cells
• SS = Sickeled cells• RR = Regular cells• SR = Some regular, some
sickled
SR SR
SR SR
S S
R
R
Multiple Alleles
• Sometimes there are more than two alleles for each trait– Ex. Blood types
• A
• B
• O
• AB
• The alleles:– A = IA
– B = IB
– O = i
Multiple Alleles (cont.)
• Blood type is determined by the surface proteins on a blood cell
• Proteins are determined by what alleles the person has
Multiple Alleles (cont.)
A
OB
AB
Multiple Alleles (cont.)Genotypes Surface
ProteinsPhenotype
IA IA, IAi A A
IB IB, IBi B B
IA IB AB AB
ii O
Multiple Alleles (cont.)• Can a man with type A
blood and a woman with type AB blood have a daughter with type B blood?
IA IA IAi
IA IB IBi
IA i
IB
IA
IA IA IAIA
IA IB IAIB
IA IA
IB
IA
Inheritance in Humans
Pedigrees
• A family tree that records and traces traits in a family
Gender
• Gender– Males = Squares
– Females = Circles
• Relationship– A line connecting =
marriage
Relationships
• Vertical lines = parents to children
• Each row = one generation – Roman numerals (I,II,III, etc.)
• Individuals (1,2,3,4, etc.)
• Slash = death
Phenotype
• Shaded circle of square = A person who has the trait being studied
• Unshaded = Does not have trait
• Half-shaded = carrier or heterozygote
Practice
Answers
Parents
Children/Siblings
Death
1 2
2 31
I
II
Used to determine genotypeShaded = attached earlobes (recessive trait) Label the genotypes!F = free earlobes, f = attached earlobes
Used to determine genotypeShaded = attached earlobes (recessive trait) Label the genotypes!F = free earlobes, f = attached earlobes
Ff
Ff
F ?
FfffF?
Ff
F ?Ff
Can predict offspring Genotype
• What is the percent chance that the next child in generation III will have attached earlobes?
Ff
Ff
F ?
FfffF?
Ff
F ?Ff
Use a Punnett Square
FF Ff
Ff ff
F f
f
F25% chance for attached earlobes
Diseases caused by recessive alleles
• Cystic Fibrosis– Defect in cell membrane protein– Develop a thick mucus in lungs and digestive
tract
• Tay-Sachs– No enzyme that breaks down lipids– Lipids build up nervous tissue => Brain damage
• Phenylketonuria (PKU)– No enzyme to change phenylalanine into tyrosine– Build up of phenylalanine => Brain Damage
Dominant Allele diseases
• Huntington’s Disease– Braek down of brain tissue
• Achondroplasia– A form of dwarfism
• Some forms of blindness
Dominant Disorders
• Most of the diseases caused by dominant alleles are lethal in Heterozygotes
• The individuals die before they can reproduce
• Low frequency of these alleles (<99.99%)
Recessive Disorders
• Recessive alleles are not lethal in heterozygotes
• Will be passed on from generation to generation
• Only homozygous recessive individuals are affected.