Basic Genetics Chapter 11

I. HEREDITY the passing on of traits from PARENTS to OFFSPRING.

II. TRAIT a. any CHARACTERISTIC of an organism. EX: hair color, eye color, spots on a cheetah, skin color, freckles, DIMPLED CHIN, *breast cancer susceptibility, *ALCOHOLISM SUSCEPTIBILITY b. all traits are located on CHROMOSOMES, IN PAIRS c. each trait has a certain SEGMENT OF DNA: this segment is a GENE. d. the chromosomes that are passed on are located in the SEX CELLS (sperm and egg).

III. HISTORY OF GENETICS a.GREGOR MENDEL is the father of genetics. He worked with PEA PLANTS. b.Mendel concluded that genes are inherited in a PREDICTABLE PATTERN.

IV. DOMINANT AND RECESSIVE ALLELES a. An ALLELE is a particular form of a gene. Alleles arise due to mutations in DNA. b. alleles are in pairs on the chromosomes c. each allele is given one letter. d. capital letters are dominant alleles, and always show through e. lower case letters are recessive alleles, and are masked by the dominant allele f. Examples: Dominant Recessive R, D, T, Z, Wr, d, t, z, w

IV. DOMINANT AND RECESSIVE ALLELES g. in sperm and egg, only one allele for a trait is passed on Gg GgGg

GENETIC DEFINITIONS Genotype, 2 alleles make up one genotype  the genotype is the allele sequence for the trait  EX: BB—two dominant alleles Bb—one dominant and one recessive allele bb—two recessive alleles

GENETIC DEFINITIONS Phenotype, what the genotype says. What is expressed or seen.  putting the genotype into words  EX: BB = Brown eyes Bb = Brown eyes bb = Blue eyes

ALLELE MEANINGS a) B (brown fur) is dominant to b (white fur) in a rabbit. b) R (tongue rolling) is dominant to r (non-roller) c) T (tallness in peas) is dominant to t (short height) d) I (indented chin) is dominant to i (normal chin)

TYPES OF GENOTYPES 1. Homozygous dominant : 2 dominant alleles GenotypePhenotype BBBrown RRTongue roller TTTall IIIndented chin

TYPES OF GENOTYPES 2. Homozygous recessive : 2 recessive alleles GenotypePhenotype bbwhite rrnon-roller ttshort iinon-indented chin

TYPES OF GENOTYPES 3. Heterozygous : one dominant allele and one recessive allele GenotypePhenotype BbBrown RrTongue roller TtTall IiIndented chin

STEPS FOR COMPLETING A PUNNETT SQUARE: MONOHYBRID CROSS Purpose of the Punnet Square: To visually see the possible genotypic offspring outcomes from two parents

STEPS FOR COMPLETING A PUNNETT SQUARE: MONOHYBRID CROSS 1. Determine the parent genotypes from the information given. Example: The father is heterozygous and the mother is homozygous recessive  Dad: Tt  Mom: tt

STEPS FOR COMPLETING A PUNNETT SQUARE: MONOHYBRID CROSS 2. Draw the square with one allele over each column or in each row. Tt t t

STEPS FOR COMPLETING A PUNNETT SQUARE: MONOHYBRID CROSS 3. Complete the cross by bringing each allele down and over until you have a pair in each box. Tt tTttt tTttt

STEPS FOR COMPLETING A PUNNETT SQUARE: MONOHYBRID CROSS 4. Determine the phenotypic ration by writing out the meanings of each genotype, and write the number as a fraction or %. TT = Tall 0/4 or 0% Tt = Tall 2/4 = ½ or 50% tt = short 2/4 = ½ or 50% Phenotypic ratio  50% or ½ tall 50% or ½ short

STEPS FOR COMPLETING A PUNNETT SQUARE: MONOHYBRID CROSS 5. Determine the genotypic ratio by counting how many of each genotype (Tt, tt, or TT) are in the boxes. Write the number as a fraction or a %. TT = 0/4 or 0% Tt = 2/4 = ½ or 50% tt = 2/4 = ½ or 50% Genotypic ratio  0% TT 50% or ½ Tt 50% or ½ tt