GENETICS

Mendel and the Gene Idea

Genetics The study of heredity. The study of heredity. Gregor Mendel (1860’s) discovered the fundamental principles of genetics by breeding garden peas. Gregor Mendel (1860’s) discovered the fundamental principles of genetics by breeding garden peas.

He Used Plants that looked like this: True Breeding Plants: consistently have offspring with same trait as parent.

Genetics Alleles Alleles 1.Alternative forms of genes. 2.Units that determine heritable traits.

Dominant Alleles Dominant alleles (TT - tall pea plants) (TT - tall pea plants) a. homozygous dominant Homozygous = two alleles that are the same.

Recessive Alleles Recessive alleles (tt - dwarf pea plants) (tt - dwarf pea plants) a. homozygous recessive Homozygous = two of the same alleles Recessive = Hidden allele when dominant is present.

Mixed Alleles Heterozygous (Tt - tall pea plants) Mixed set of alleles. Dominant takes over for physical trait (phenotype).

Phenotype Outward appearance Outward appearance Physical characteristics Physical characteristics Examples: Examples: 1.tall pea plant 2.dwarf pea plant

Genotype Arrangement of genes that produces the phenotype Arrangement of genes that produces the phenotype Example: Example: 1.tall pea plant TT = tall (homozygous dominant) 2.dwarf pea plant tt = dwarf (homozygous recessive) 3.tall pea plant Tt = tall (heterozygous)

Punnett square A Punnett square is used to show the possible combinations of gametes. A Punnett square is used to show the possible combinations of gametes.

Showing a cross with Pea Plants tall (TT) vs. dwarf (tt) pea plants tall (TT) vs. dwarf (tt) pea plants t t TT

tall (TT) vs. dwarf (tt) pea plants t t TT Tt All Tt = tall (heterozygous tall) produces the 1 st generation

Cross the 1 st generation tall (Tt) vs. tall (Tt) pea plants tall (Tt) vs. tall (Tt) pea plants T t Tt

tall (Tt) vs. tall (Tt) pea plants TT Tt ttT t Tt produces the 2 nd generation 1/4 (25%) = TT 1/2 (50%) = Tt 1/4 (25%) = tt 1:2:1 genotype 3:1 phenotype 3:1 phenotype

Monohybrid Cross Mendel did A breeding experiment that tracks the inheritance of a single trait. Mendel did A breeding experiment that tracks the inheritance of a single trait.

Principle of Segregation Segregation The principle of segregation is explained by the behavior of homologous chromosomes at meiosis.

Law of Independent Assortment Genes for different traits are separated and distributed to gametes (sex cells) independently of one another Genes for different traits are separated and distributed to gametes (sex cells) independently of one another

Incomplete Dominance This is when both alleles contribute to the phenotype of a heterozygous individual to produce a trait that is not exactly like either parents. This is when both alleles contribute to the phenotype of a heterozygous individual to produce a trait that is not exactly like either parents. Ex: A flower has genes for white petals (W) and red petals (R). When you mix white flowers with red flowers you get pink flowers. Ex: A flower has genes for white petals (W) and red petals (R). When you mix white flowers with red flowers you get pink flowers.

Codominance Two dominant alleles are expressed at the same time. Two dominant alleles are expressed at the same time. The human ABO blood group illustrates another genetic phenomenon – codominance. The human ABO blood group illustrates another genetic phenomenon – codominance. The AB phenotype (genotype I A and I B is an example. The AB phenotype (genotype I A and I B is an example.

Polygenic Inheritance – When a Single Trait is Influenced by Many Genes Height is a polygenic trait

Multiple Alleles Many genes are present in 3 or more versions (alleles) – this is known as multiple alleles. Many genes are present in 3 or more versions (alleles) – this is known as multiple alleles. The human ABO blood group is determined by three alleles (IA, IB, and i) of a single gene. The human ABO blood group is determined by three alleles (IA, IB, and i) of a single gene.

Pleiotropy – When One Allele Influences Many Traits

Sex-Linked Traits Traits carried on sex chromosomes X or Y Traits carried on sex chromosomes X or Y Ex: Red green color blindness, Hemophilia Ex: Red green color blindness, Hemophilia