Genetics The Wonder of Heredity

What is Genetics?  Genetics is the study of heredity  Heredity is the passing of traits from parents to offspring  First studied by Gregor Mendel

Gregor Mendel  Lived in a monastery, taught, and tended the gardens  Studied pea plants  Noted that traits of offspring were similar to parents  Considered “Father of Genetics”

 Mendel traced 7 basic characteristics of pea plants

Mendel’s Work  Used garden peas because they were easy to cross, and showed a variety of traits or characters  Pea plants self-pollinate which means the sperm of one plant fertilizes the eggs of the same plant  Mendel worked with true-breeding lines of plants – produce identical offspring to original plant (we know these as “pure”)

 Each of the seven traits had two contrasting characters Ex: green or yellow seeds, purple or white flowers  To prevent self-pollination, Mendel removed the male flower parts Enabled him to cross-pollinate true breeding plants and observe the results

 Mendel crossed plants with different traits for each of the seven traits hybridization Called these the P generation (parental)  Offspring of these crosses are the F1 “first filial” generation All hybrids  He then crossed two of the F1 generation to create the F2 generation “second filial”

Results  The F1 generation always displayed one trait (dominant)  The F2 showed both traits, usually in a 3:1 ratio

Mendel’s Laws  Law of Dominance Some “factors” or alleles can mask over others and are dominant  Law of Segregation The two alleles for a trait separate during gamete formation (meiosis)  Law of Independent Assortment Alleles for a trait separate independently from each other Each trait is independently inherited (refers to those on different chromosomes)

 Work led to the discovery of Genes and alleles Dominant and recessive traits Genotype and phenotype Concept of homozygous and heterozygous

Genes and Alleles  Genes -- factors that control our traits; units of heredity Found on chromosomes; segments of DNA  Alleles -- different forms of a gene Mendel called them “factors” Offspring get one allele from each parent Example: allele for a widow’s peak or an allele for no widow’s peak

Dominant vs. Recessive  Dominant alleles: particular trait will always be seen as long as the dominant allele is present Represented by a capital letter  Recessive alleles: can be masked by dominant allele Particular trait will only be seen if two recessive alleles are present Represented by a lowercase letter

Common Dominant Traits  Widow’s Peak  Rolling your Tongue  Cleft Chin  Polydactyly ( 6 fingers and toes)  Dimples  Freckles  Unattached Ears  Brown Eyes

Genotype and Phenotype  Genotype – describes an organism’s genetic make-up and shows the actual allele combinations Examples: AA, Aa, or aa  Phenotype – describes an organism’s physical appearance or traits Examples – blue or brown eyes, purple or white flowers, cleft chin or no cleft chin

Homozygous vs. Heterozygous  Homozygous – refers to an organism that has two identical alleles for a trait (“homo” means the same) Examples: AA (homozygous dominant) aa (homozygous recessive)  Heterozygous – refers to an organism that has two different alleles for a trait (“hetero” means different) Example: Aa

Examples of Genotype and Phenotype GenotypeHomozygous/ Heterozygous Phenotype WWHomozygous Dominant Widow’s Peak WwHeterozygousWidow’s Peak wwHomozygous Recessive No Widow’s Peak

Other types of expression…  Not all alleles have a simple pattern of dominant and recessive  Majority of genes have more than two alleles  Many traits are controlled by more than one gene

Incomplete Dominance  Dominant allele does not completely mask over recessive  See a blending of traits  Example: Red flower X white flower = pink flowers

Codominance  Both alleles are dominant  See both traits  Ex: Red x white = Red and White

Multiple Alleles  Genes have more than two alleles Individual still only get two, just more variety Increases genotypic and phenotypic possibilities  Ex: coat color in rabbits, human blood types A, B, or O allele

Polygenic Inheritance  Traits controlled by two or more genes  Can show wide range of phenotypes (quantitative characters) Characters vary along a continuum  Ex: eye color, skin tone, height and weight

Polygenic Inheritance

Environment  Many characteristics and traits do not solely depend on genes  Traits are also influenced by environment Nature vs. Nurture  Traits such as height, personality, and weight, are variable due to circumstance and experiences  Multifactorial – describes characters or traits that are influenced by both genotypes and environment