Why we look the way we look... Laws of Heredity Why we look the way we look...

What is heredity? Heredity: passing of characteristics (traits) from parents to offspring Genetics: the study of heredity

Important Terms ALLELES = alternative forms of the same gene: F-f, E-E, D-d, etc. Make up the genotype. alleles for a trait are located at corresponding positions on homologous chromosomes HOMOLOGOUS CHROMOSOMES genes as “bands” iin in chromosomes A b C D E f B d

Important Terms GENOTYPE = the genes present in the DNA of an organism; GG, Bb, tt Homozygous = both alleles are identical  GG & tt Heterozygous = the two alleles (found on homologous chromosomes) are different  Bb PHENOTYPE = how the trait physically shows-up in the organism; green seed coat, curly hair

Gregor Mendel The first person to predict how traits are transferred from parents to offspring. Called the “Law of Inheritance.” Studied pea plants extensively

Why Study Pea Plants? Reproduce sexually 2. They have both male and female sex cells (gametes) on the same flower. 3. Their traits are easy to isolate.

Mendel crossed pea plants… Fertilization: the uniting of male and female gametes Cross: combining gametes from parents with different traits Mendel’s cross: transferred pollen from plant to plant and studied the resulting offspring pea plants. PUNNETT SQUARE P: Parent Generation F1 First Offspring Generation

1. Law of Independent Assortment Alleles for different traits are distributed to sex cells (& offspring) independently of one another 2. Law of Segregation During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other.  Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring.

Some alleles are dominant, others are recessive. 3. Law of Dominance Some alleles are dominant, others are recessive. Recessive traits: hidden whenever dominant allele is present; lower case letters Dominant traits: cover or mask recessive traits; capital letters G = green = dominant allele g = white = recessive allele Gg = green gg = white

NON-MENDELIAN INHERITANCE Does NOT follow Mendel’s Laws of Inheritance: Incomplete Codominance Multiple-Allele Sex-Linked

Incomplete Dominance genotype: heterozygous (hybrid) phenotype: the mix or “in between” of the two parents example: white flower x red flower  pink flowers

Codominance genotype: heterozygous (hybrid) phenotype: both alleles in the offspring are dominant; parent traits show separately in same individual example: black cow x white cow  checkered (roan) cow

Blood Type Inheritance Multiple Alleles Traits that are controlled by more than 2 alleles example: height, skin color, hair color, eye color, blood type Blood Type Inheritance blood type determined by the presence or absence of proteins on the surface of red blood cells types: A, B, AB, O Note: AB blood type is also codominant!

Antigen on red blood cell (UNIVERSAL RECIPIENT) BLOOD TYPES Phenotype (blood type) Genotype Antigen on red blood cell Safe Transfusions To From A AA or AO A, AB A,O B BB or BO B, AB B, O AB only AB A and B (UNIVERSAL RECIPIENT) A, B, AB, O O only O none (UNIVERSAL DONOR)

SEX-LINKED INHERITANCE controlled by genes located on sex chromosomes usually found on the X (female) chromosome female are usually carriers because they have XX for X-linked traits, males pass the trait to their daughters not their sons…why? examples: colorblindness, hemophilia

H = does not have hemophilia h = hemophilia Xh Y XH Xh