Inheritance: the way genes are passed down. If a father doesn’t have a leg does that mean his children will be born with out a leg????
Hundreds of years ago people knew that somehow certain traits would be passed on to their children.
Gregor Mendel was the first to predict the outcome of inheritance. The study of inheritance is Genetics.
Genes and Alleles A gene is a specific piece of DNA. You have two genes that code for the same thing (ex. Height). Each of those two genes is called an allele. So if something had the genes Aa one allele would be “A” the other would be “a”).
Why two alleles for every gene? Because organisms get 2 sets of chromosomes ……….one from the mother and one from the father.
Phenotype Is the physical characteristics of the trait. In most cases it is what we can “see”. Example: Freckles, dimples, attached earlobes etc.
Genotype Is the actual alleles that make up the trait. In most all cases this is represented by 2 letters. Example: AA, Aa, aa
Dominant –A dominant trait is a trait that covers or hides the other trait of an allele. For example, dark colors in hair usually overshadow the other allele. In this class Dominant will always be represented with a capital letter. Example: Say “D” is the allele for black hair and “d” is the allele for blond. The if an animal had Dd then it would have black hair.
Recessive A recessive trait is the trait that is hidden by the dominant trait. In an animal with Dd for hair color the recessive allele is “d”. The animal carries a gene for blond hair but you can’t tell by looking at it.
Heterozygous This is the term given two different alleles. For example, Aa is heterozygous. It may contain one gene for brown eyes(A) from the mother and one gene for blue(a) eyes from the father.
Homozygous This is the term given to the two same alleles. For example, AA or aa A person may contain 2 genes for -brown eyes – one from each parent (AA) or 2 for blue (aa).
Common traits in animals Polled-horned Normal-double muscled Normal size- dwarf
Exceptions to Simple inheritance Polygenic traits-controlled by additive gene Intermediate expression- –Incomplete dominance –Co-dominance Multiple allele Modifying and regulator genes Incomplete penetrance
Sex-related gene effects Sex-limited-expressed in one but not the other sex-controlled- expressed in both sexes differently genetic imprinting- expressed differently depending on parent received from.