1. Basic Genetics
Chapter 11

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

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

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

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

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

7. 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

8. 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

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

10. TYPES OF GENOTYPES Homozygous dominant : 2 dominant alleles
Genotype Phenotype
BB Brown
RR Tongue roller
TT Tall
II Indented chin

11. TYPES OF GENOTYPES Homozygous recessive : 2 recessive alleles
Genotype Phenotype
bb white
rr non-roller
tt short
ii non-indented chin

12. TYPES OF GENOTYPES
Heterozygous : one dominant allele and one recessive allele
Genotype Phenotype
Bb Brown
Rr Tongue roller
Tt Tall
Ii Indented chin

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

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

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

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

17. STEPS FOR COMPLETING A PUNNETT SQUARE: MONOHYBRID CROSS
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

18. STEPS FOR COMPLETING A PUNNETT SQUARE: MONOHYBRID CROSS
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