Mendel & Genes

Question 1

Genetic Variation

Answer 1

-Contributes to evolution
-mutations= original source of genetic diversity
-Different versions of genes= alleles
-Shuffling of alleles= genetic variation
Mechanisms that contribute to genetic variation
1. Independent assortment of chromosomes
2. crossing over
3. random fertilization

Question 2

Independent Assortment of Chromosomes

Answer 2

• Homologous pairs of chromosomes orient randomly during Metaphase I
• Each pair of chromosomes sort maternal and paternal homologs into daughter cells independently of other pairs

Question 3

Crossing Over

Answer 3

• Produces recombinant chromosomes= combined dna of each parent
• Contributes to genetic variation
• 3 crossovers occur per chromosome

Question 4

Random Fertilization

Answer 4

• Sperm fuse w/ any ovum
• Each zygote has a unique genetic identity
• Adds to genetic variation

Question 5

Alleles

Answer 5

• Alternative versions of genes account for variations in inherited characters
• Ex: pea plants two versions= purple and white

Question 6

Locus

Answer 6

-Specific site one chromosomes where gene resides

Question 7

Homozygote

Answer 7

-Organism w/ two identical alleles for a character

Question 8

Heterozygote

Answer 8

• Organism w/ two different alleles for a gene

- Not true-breeding

Question 9

Phenotype vs. Genotype

Answer 9

• P: trait seen

- G: genetic composition

Question 10

Law of Segregation

Answer 10

• During gamete formation, the alleles for each gene segregate from each other
• Each gamete carries only one allele for each gene

Question 11

Law of Independent Assortment

Answer 11

-Genes for different traits can segregate independently during gamete formation

Question 12

Mendel’s Experiment

Answer 12

• Cross-pollinate purple and white pea plants (p generation)
• Counted offspring in F1 generation= all purple hybrids
• Cross-pollinate purple hybrid w/ purple hybrid
• Counted offspring in F2: 3-1 ratio purple to white

Question 13

Complete Dominance

Answer 13

• Phenotypes of heterozygote and dominant homozygote= identical
• Ex: Pp or PP

Question 14

Incomplete Dominance

Answer 14

• Phenotype of F1 hybrids is somewhere between the two phenotypes of parents
• Ex: Red + white–> pink flower

Question 15

Codominance

Answer 15

• Two dominant alleles affect the phenotype in separate, distinguishable ways
• Ex: bloodtype, where IAIB both creates AB bloodtype

Question 16

Multiple Alleles

Answer 16

• Most genes exist in more than two allelic forms

- The four phenotypes of ABO blood are determined by 3 alleles : IA, IB or i

Question 17

Pleiotropy

Answer 17

• When genes have multiple phenotypic effects

- Diseases such as cysitc fibrosis or sickle-cell

Question 18

Epistasis

Answer 18

• One gene affects the phenotype of another due to interaction of their gene products
• Ex: Coat color in puppies, where one gene determines coat color, and the other inhibits coat color
• Does not follow mendelian principle

Question 19

Polygenetic Inheritance

Answer 19

• Additive effect of two or more genes on a single phenotype

- Ex: 180 genes affect height, skin color

Question 20

Mendel’s Laws

Answer 20

1. Alleles of genes account for variations in inherited characters
2. For each character, an organism inherits two alleles, one from each parent
3. If two alleles at locus differ, dominant determines appearance, recessive has no effect
4. Law of Segregation