Chapter 11

Gregor Mendel Father of Genetics Born in 1822 in the Czech Republic Priest in monastery Fertilization by testing pea plants

Cross pollination

Cross Pollination

Genes and Dominance Gene: a specific characteristic that varies

from one individual to another. Alleles: different forms of a gene.

Principle of Dominance Dominant trait: overshadows the recessive

trait Recessive trait: only can be seen when with

another recessive trait

Homozygous: organisms that have two identical alleles for a particular trait.(TT) True breeding

Heterozygous: organisms that have two different alleles for a particular trait. (Tt) Hybrid

Terms for Genetic Crosses Phenotype: physical characteristics Genotype: genetic makeup P group: parental group F1: First offspring or generation F2: second generation

Rules for Punnett Squares1. Determine the symbols for the traits

2. Determine the genotype of the parents.

3. Make the cross

4. Answer the questions

Practice Problem #1 Mendel found that the allele for tall (T) pea

plants is dominant to the allele for short (t). What offspring phenotypes would be expected from the following parents:

Male: TT Female: tt Male: Tt Female: tt Male: Tt Female: Tt

Practice Problem #2 The allele for axial flowers (A) in peas is

dominant to the allele for flowers borne terminally (a). What phenotypic ratios would you expect among the offspring of a cross between a known heterozygous axial-flowered plant and one whose flowers are terminal?

Practice Problem #3 Two drosophilas (fruit flies) with normal

wings are crossed. Among 123 progeny, 91 have normal wings and 32 have dumpy wings. A. which trait is dominant? B. what were the genotypes of the parents?

Practice Problem #4 Black fur in guinea pigs is a dominant trait

and white is the recessive trait. When a homozygous black (BB) guinea pig is crossed with a homozygous white one (bb), what is the phenotype and genotype of the F1 generation?

Law of Segregation Alleles segregate from each other during the

formation of gametes EX: allele for tall separates from allele for

short

Incomplete Dominance Cases in which one allele is not completely

dominant over another Heterozygous phenotype is somewhere

between the two homozygous phenotypes.

Incomplete Problem A homozygous red flower is crossed with a

homozygous white flower. This produces pink flowers in their offspring. What would the offspring look like if a pink flower cross-pollinated with a red flower?

Codominance Both alleles contribute to the phenotype. Both show

Codominance Problem In certain varieties of chickens, the allele for

black feathers is codominant with the allele for white feathers. Offspring are speckled with white and black. What would happen if a chicken who is homozygous black feathers is crossed with a chicken who is speckled.

Multiple Alleles Genes that have more than two alleles EX: coat color in rabbits. Determined by a

single gene that has at least four different alleles.

Polygenic Traits Traits controlled by two or more genes EX: wide range in skin color in humans

comes about because more than four different genes control this trait.