Lecture 11: Genetics I: Mendel’s Laws of Dominance and Segregation

Question 1

our longest-running genetic experiment: dogs

Answer 1

• people have selected and mated dogs with preferred traits for more than 15,000 years
• such genetic tinkering has led to the incredible variety of body types and behaviors in dogs today
• all domestic dogs were derived originally from a wolf ancestor

Question 2

heredity

Answer 2

the transmission of traits from one generation to the next

Question 3

genetics

Answer 3

the scientific study of heredity

Question 4

Gregor Mendel

Answer 4

• first person to clearly explain the patterns of inheritance
• deduced the fundamental principles of genetics in the 1860s

Question 5

what Mendel studied and why

Answer 5

garden peas
* easy to grow
* came in many readily distinguishable varieties
* easily manipulated
* can self-fertilize
* had years of experience studying these plants and knowledge from the University of Vienna to prepare him

Question 6

cross-fertilization in Mendel’s study

Answer 6

• Mendel emasculated the purple plant by taking the stamens off, then used a brush to take the pollen from the white plant off and brushed it on the purple plant
• the resulting flowers would be purple

Question 7

reciprocal cross in Mendel’s study

Answer 7

• if Mendel emasculated the white plant, the flowers would be purple
• discovered that purple is the dominant color trait

Question 8

character

Answer 8

a heritable feature that varies among individuals
* e.g. flower color

Question 9

trait

Answer 9

a variant of a character
* e.g. white flower color vs. purple flower color

Question 10

characters and traits in Mendel’s study

Answer 10

each of the characters Mendel studied occurred in 2 distinct traits, either dominant (visible) or recessive (not visible)

character: traits (dominant - recessive)
* flower color: purple - white
* flower position: axial - terminal
* seed color: yellow - green
* seed shape: round - wrinkled
* pod shape: inflated - constricted
* pod color: green - yellow
* stem length: tall - dwarf

Question 11

hybrids

Answer 11

the offspring of 2 different purebred varieties
* P generation: parental plants
* F1 generation: hybrid offspring (“F” stands for filial, so F# denotes the number of generations after the parental generation)
* F2 generation: cross of the F1 plants

Question 12

monohybrid cross

Answer 12

a cross between purebred plants that differ in only 1 character

Question 13

law of dominance

Answer 13

when an organism inherits two different alleles for a trait, the dominant allele will be expressed, while the recessive allele will be masked, meaning the offspring will only exhibit the dominant trait in their phenotype

Question 14

allele

Answer 14

alternative versions of genes
* the dominant allele for flower is represented as a capital letter “P” (purple), while the recessive allele is a lowercase letter “p” (white)

Question 15

for each inherited character, an organism inherits _____ alleles, _____ from each parent

Answer 15

2; 1

Question 16

homozygous

Answer 16

an organism is homozygous for a gene if both alleles are identical
* e.g. PP and pp

Question 17

heterozygous

Answer 17

an organism is heterozygous for a gene if the alleles are different
* e.g. Pp

Question 18

dominant allele

Answer 18

if 2 alleles of an inherited pair differ, one determines the organism’s appearance, which is called the dominant allele

Question 19

recessive allele

Answer 19

if 2 alleles of an inherited pair differ, one has no noticeable effect on the organism’s appearance, which is called the recessive allele

Question 20

law of segregation

Answer 20

gametes only carry one allele for each inherited character. the 2 alleles for a character segregate from each other during the production of gametes.

Question 21

punnet square

Answer 21

• highlights the four possible combinations of gametes and
• four possible offspring in the F2 generation

Question 22

phenotype

Answer 22

an organism’s physical appearance

Question 23

genotype

Answer 23

an organism’s genetic makeup

Question 24

locus

Answer 24

• a gene locus is a specific location of a gene along a chromosome
• homologous chromosomes have alleles (alternate versions of a gene) at the same locus