Inherited Traits The Law of Dominance

Questions to Ponder… Why do some people look like their parents or grandparents? How is it possible for a blond-haired child to have two brown-haired parents? Why do brothers in one family resemble each other and in one family have no resemblance?

Gregor Mendel –1860s Grew up on a farm in Austria and became a monk Observed pea plants and wondered why generations passed on traits he observed Experimented with pea plants and learned many things related to heredity Father of Modern Genetics

Dominant and Recessive Traits Handout

Dominant & Recessive Traits Dominant traits are “stronger” and more likely to be visible Recessive traits are “weaker” and less likely to be visible Law of Dominance: dominant traits “trump” recessive traits

Dominant & Recessive Traits Genes occur in pairs (alleles) The combination of gene pairs determines the offspring’s phenotype (physical trait) One gene comes from the mother and the other comes from the father

Dominant & Recessive Traits Offspring receives… – dominant trait from mother – dominant trait from father Offspring phenotype is… – dominant trait Curly hair is dominant & straight hair is recessive A boy inherits the gene for curly hair from both his mother and father, and he has curly hair

Dominant & Recessive Traits Offspring receives… – dominant trait from mother – recessive trait from father Offspring phenotype is… – dominant trait Curly hair is dominant & straight hair is recessive A girl inherits curly hair from her mother but straight hair from her father, and she has curly hair

Dominant & Recessive Traits Offspring receives… – recessive trait from mother – recessive trait from father Offspring phenotype is… – recessive trait Curly hair is dominant & straight hair is recessive A boy inherits straight hair from both his mother and father, and he has straight hair

Dominant & Recessive Traits dominant + dominant = dominant – homozygous: gene pairs (alleles) are the same dominant + recessive = dominant – heterozygous: gene pairs (alleles) are different recessive + recessive = recessive – homozygous

Dominant & Recessive Traits Genes occur in pairs, alleles The combination of gene pairs (genotype) determines the offspring’s phenotype One gene comes from the mother and the other comes from the father

Dominant & Recessive Traits dominant + dominant = dominant – homozygous: gene pairs (alleles) are the same – Height in Pea Plants: TT genotype dominant + recessive = dominant – heterozygous: gene pairs (alleles) are different – Height in Pea Plants: Tt genotype recessive + recessive = recessive – homozygous – Height in Pea Plants: tt genotype

Application Charlie cannot roll his tongue. His mother cannot roll her tongue. – Can you determine his father’s phenotype? – Can you determine any of their genotypes?

Application Maria has unattached ear lobes. Her father has attached ear lobes. – Can you determine any of their phenotypes? – Can you determine any of their genotypes? – Can you determine if Maria could have a child with attached ear lobes?

Application Mr. Henderson has a bent little finger, and so does his wife, Mrs. Henderson. – Can you determine any of their phenotypes? – Is it possible for their son and daughter to have different phenotypes? – Can you determine any of their genotypes?