I. Meiosis produces four haploid sex cells from one original diploid (2n) cell.
D. Gametes are haploid cells (n)—cells with one of each kind of chromosome.
E. When a sperm fertilizes and egg, the resulting cell is called a zygote.
A. During Prophase I, each pair of homologous chromosomes comes together to form a tetrad.
B. Homologous chromosomes may exchange genetic material in a process known as crossing over.
2. Mendel transferred pollen from one plant to another—this was a cross.
4. Phenotype and Genotype a. Genotype is gene combination (TT)b. Phenotype is physical appearance; expression of the genotype (tall)
c. Two organisms can look alike but have different underlying gene combinations.TT=tallTt=tall
C. Mendel’s Monohybrid Crosses 1. Cross between two parents that differ only by a single trait.
2. Generations a. P1 = parent b. F1 = filial (daughter or son) c. F2 = 2nd filial
Heterozygote (note color) Recessive Homozygote (note color) genotype? genotype? Recessive Homozygote (note color) genotype?
D. Mendel’s Rule of Unit Factor 1. Genes exist in alternative forms called alleles.
E. Mendel’s Rule of Dominance1. Only one trait is observed (phenotype) (either TALL or short)2. The observed trait is dominant.3. The trait that “disappeared” is recessive.
F. Mendel’s Law of Segregation A parent passes on at random only one allele for each trait to its offspring
Dominant Homozygote Recessive Homozygote (note color) Segregation occurs here Heterozygote (note color) Dominant Homozygote Heterozygotes Recessive Homozygote
G. Punnett SquaresMethod used to establish the probabilities of the results of a genetic cross.
H. Uses of Punnett Squares in Monohybrid crosses 1. Example one • Show the cross between a homozygous tall pea plant and a homozygous short pea plant. • TT X tt
T T Tt t Tt t Tt Tt All offspring will be heterozygous Tall
2. Example 2 • Show the cross between a homozygous rough coat guinea pig and a heterozygous guinea pig. • Rough is dominant to smooth • RR X Rr
R R R RR RR r Rr Rr Genotypic Ratio- RR 2: Rr 2 =1:1 Phenotypic ratio- 100% Rough
3. Example 3 • Show the cross between two heterozygous Black coat rabbits. • Black is dominate to brown. • Bb X Bb