Mendel’s Laws of Inheritance “The Father of Genetics”

Background Vocab Genetics = The scientific study of heredity Heredity = the passing of traits from parents to offspring Traits = characteristics controlled by our genes Genetic Expression= converting the genetic code into physical traits

Gregor Mendel Austrian monk in the 1800s Grew pea plants with various traits: flower color, pod color, pod shape, stem length, etc. Kept decades of records of traits of parent peas and traits of their offspring, which allowed him to develop the “laws” of inheritance Controlled which flowers were crossed by removing stamens from some and physically pollinating others using a paintbrush

Law of Dominance Part One: Each organism has two alleles for a trait – one allele is inherited from the father, the other from the mother Part Two: An allele that is always expressed (even if only one was inherited) is called dominant. An allele that can be hidden by the dominant allele is called recessive (the recessive trait will only be expressed if two recessive alleles are inherited). Common misunderstandings about dominant alleles: they are NOT always better than recessive alleles and they are NOT always more common than recessive alleles!

Modern Understandings of the Law of Dominance Part One: The alleles Mendel described are actually genes found on chromosomes, and the chromosomes occur in pairs in our cells. During fertilization, a chromosome from the father combines with a chromosome from the mother. Part Two: The genes can either be dominant (always expressed) or recessive (may be masked).

Law of Segregation “Segregation” = Separation! The two alleles that code for a trait separate during meiosis, so that a new organism only gets one allele from each parent. “Segregation” = Separation!

Modern Understandings of the Law of Segregation The homologous pairs of chromosomes carry the pairs of genes for each trait. These pairs separate during meiosis when sperm and egg cells are formed (this is called disjunction). This means that the zygote only receives one of each chromosome from the two gametes, resulting in homologous pairs again.

Law of Independent Assortment Each pair of alleles separates independently of every other pair – in other words, the pairs are sorted randomly. This means that all combinations of traits are possible in the offspring – just because they have one dominant trait, it does not mean that their other traits will also be dominant.

Modern Understandings of the Law of Independent Assortment The separation of chromosomes during meiosis occurs randomly, creating many possible combinations of traits.

1_____ The kinds of genes in an organism 1_____ The kinds of genes in an organism.* 2_____ The first cell of a new organism.* 3_____ A specific version of a gene.* 4_____ A gene that is always expressed.* 5_____ An organism with two of the same alleles. 6_____ A piece of DNA with the code for a trait.* 7_____ The original organisms in a family. 8_____ An organism with two different alleles. 9_____ A haploid sex cell.* 10_____ The offspring of the original organisms. 11_____ The kinds of traits shown in an organism.* 12_____ The grandoffspring of the original organisms. 13_____ The common name for an organism with 2 different alleles. 14_____ An organism with 2 different alleles for 2 different traits. 15_____ A gene that is only expressed if 2 copies are inherited.*