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.