+ Intro to Genetics Mrs. MacWilliams Biology

+ Objectives 1. Describe how homologous chromosomes carry the same genes, but may be different alleles. 2. Define the terms dominant, recessive, genotype, phetotype homozygous, and heterozygous. 3. Compare Mendel’s three laws of heredity.

+ Key Terms Genetics The study of heredity Heredity The study of HOW parents pass certain traits to offspring. Chromosome Rod shaped structures within the nucleus of the cell that contain genes

+ Key Terms continued Genes Units of heredity information located on chromosomes Gametes Reproductive cell Human: sperm & eggs; Flowers: pollen (sperm) & pistil (eggs) Alleles Either member of a pair of GENES that determines a single trait Ex: gene pair Yy

+ Two factors involved in development 1. Heredity 2. Environment

+ Relationship of Genes to Each Other 1. DOMINANT - trait that hides the recessive 2. RECESSIVE - trait that is hidden by the dominant

+ Homozygous vs. Heterozygous Homozygous (PUREBRED) (homo=same) Two genes in a pair are identical Homozygous Dominant – both genes in the pair are the dominant trait Example: AA Homozygous Recessive – both genes in the pair are the recessive trait Example: aa Heterozygous (HYBRID) (hetero=different) There is one dominant gene and one recessive gene Example: Aa **ZYGOUS = ZYGOTE

+ Ha Ha Just kidding… this is not what they would look like!!!!

+ Two Ways to Designate Organisms 1. GENotype (GENes) a. Actual genetic info on the chromosome b. Uses DOUBLE LETTERS to signify double letters because each parent “sends” a trait double letters because each parent “sends” a trait double letters due to HOMOLOGUS nature of chromosomes double letters due to HOMOLOGUS nature of chromosomes HOMO = SAMELOGOUS = LOCATION HOMO = SAMELOGOUS = LOCATION c. Use only one letter per TRAIT uppercase letters for dominant traits uppercase letters for dominant traits lower case letters for recessive traits lower case letters for recessive traits i.e. AA, Aa, aa (NOT AB) i.e. AA, Aa, aa (NOT AB)

+ 2. PHenotype (PHoto) a. Outward appearance of organism Example: brown eyes, blonde hair Example: brown eyes, blonde hair

+ GREGOR MENDEL “The Father of Genetics” Mendel was a pioneer in genetics, born 1822, lived in a monastery, plant breeding experiments. Used pea plants. WHY? 1. Easy to grow 2. short gestation time 3. produced many offspring at a time. Studied traits that had 2 contrasting forms: Ex. Tall vs. short; yellow vs. green Kept meticulous records and calculated ratios. Did this through many generations several times for each trait.

+ Mendel’s 1st Law of Heredity DEALS WITH ONE GENE 1. Law of Segregation -In a pair of alleles (e.g. blue and brown eye color) only ONE of the two are represented in a gamete. **Alleles SEGREGATE into different gametes during meiosis

+ Mendel’s 2nd Law of Heredity DEALS WITH 2 OR MORE GENES 2. Law of Independent Assortment Alleles of different genes separate independently of one another during gamete formation (ex. Alleles for eye color separate independently from hair type) The combination of alleles in any one gamete is totally random Mother donates blue eyes allele and straight hair allele Father donates brown eyes allele an curly hair allele Offspring can get any combo Blue eyes straight hair Blue eyes curly hair Brown eyes straight hair Brown eyes curly hair

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+ 3. Law of Dominance One gene in a pair may prevent the other gene in the pair from being expressed. ALWAYS REPRESENTED BY A CAPITAL LETTER Recessive- the gene that is hidden by the dominant gene ALWAYS REPRESENTED BY lower case letters Example Yellow (A) Dominant Green (a) recessive Mendel’s 3rd Law of Heredity