Genetics in HumansGenetics in Humans

Marie ČernáMarie Černá

Monogenic inheritance Monogenic inheritance (Mendelian genetics) – 1%(Mendelian genetics) – 1%

– single gene

For each gene, an organism inherits two alleles, one from each parent

• Homozygous – having two identical alleles for a gene• Heterozygous – having two different alleles for a gene

in the phenotype of a heterozygote:• dominant allele – is fully expressed• recessive allele – is completely masked

Monogenic inheritance Monogenic inheritance (Mendelian genetics) – 1%(Mendelian genetics) – 1%

• complete dominance: phenotype # genotype

• incomplete dominance: phenotype = genotype

• codominance (blood group):phenotype = genotype

Polygenic inheritance Polygenic inheritance (multifactorial) – 99 %(multifactorial) – 99 %

– many genes– environmental effect on phenotype

• quantitative characters• Gaussian distribution

Gaussian distributionGaussian distribution

ABABOO blood group blood groupss

ABABOO blood group blood groupss

ABO blood groupABO blood groupss

Frequencies (%) of blood group system Frequencies (%) of blood group system in the U.S.A. populationin the U.S.A. population

Blood group

Blood antigen

Antibody in serum

White Caucasians

Blacks Asians American Indians

O H anti-A,B 45 49 40 79

A A anti-B 40 27 28 16

B B anti-A 11 20 27 4

AB AB - 4 4 5 1

Rh blood groupRh blood group

Rh blood groupRh blood group

Rh blood groupRh blood group

Blood group donors and recipientsBlood group donors and recipients

LiteratureLiteratureBiology, eighth edition,Campbell, Reece

Unit three: GeneticsChapter 14: Mendel and the Gene IdeaConcept 14.3: Inheritance patterns are

often more complex than predicted by simple Mendelian genetics

Pages 271 – 275