14 Mendel and the Gene

Question 1

What is genetics?

Answer 1

The branch of biology that focuses on inheritance

Question 2

Who worked out the rules of inheritance through a series of brilliant experiments on garden peas?

Answer 2

Gregor Mendel

Question 3

What is heredity?

Answer 3

Is the transmission of traits from parents to their offspring

Question 4

What is a trait?

Answer 4

Is any characteristic of an individual?

Question 5

What basic questions was Mendel trying to address?

Answer 5

• why offspring resemble their parents?

- how does transmission of traits occurs?

Question 6

What two hypothesis had been formulated to try to answer these two question?

Answer 6

1) blending inheritance
- parental traits blend
- such that their offsprings have intermediate traits
2) inheritance of acquired characteristics
- parental traits are modified
- then passed on to their offspring

Question 7

Why did Mendel choose the common garden pea?

Answer 7

• it is easy to grow
• its reproductive cycle is short
• it produces large number of seeds
• its matings are easy to control
• its traits are easily recognizable

Question 8

How did Mendel arrange mating?

Answer 8

• peas normally pollinate themselves through self-fertilization
• Mendel could prevent self-pollination by removing stamen containing pollen from each flower
• he then used this pollen to fertilize the female reproductive organ on different plants
• thus performing cross-pollination

Question 9

What traits did Mendel study?

Answer 9

• seed shape
• seed color
• pod shape
• flower color
• flower position
• pod position
• stem length

Question 10

What is phenotype?

Answer 10

And individuals observable features

-Mendel pea population had two distinct phenotype for each of the seven traits

Question 11

What does F indicate in F generation?

Answer 11

F indicates first filial

Question 12

How did Mendels first experiment contradict blending hypothesis?

Answer 12

Mendel crossed plants with only one differing trait: round seeds and plants with wrinkled seed

• all F1 generation had round seeds
• contradicted blending inheritance because genetic determinant for wrinkled seeds seemed to have disappeared
• Mendel allowed F1 to self pollinate and wrinkled seeds reappeared in F2 generation

Question 13

What are the principles of segregation?

Answer 13

• two members of each gene pair must segregate
• they separate into different gamete cells
• during the formation of eggs and sperm in parents

Question 14

What is the principle of independent assortment?

Answer 14

Alleles of different genes are transmitted independently of each other.

Question 15

Chromosome theory of inheritance

Answer 15

Arose out of Sutton and Boveri’s careful observations of meiosis

States:

• chromosomes compose of Mendel’s hereditary determinants (what are now called genes)
• separation of alleles during anaphase of meiosis 1 is responsible for Mendel’s principle of segregation

Question 16

What is the wild type?

Answer 16

The most common phenotype for each trait

Question 17

Mutations

Answer 17

• phenotypes that differed from the wild type

- resulted from a change in a gene

Question 18

Mutants

Answer 18

Individuals with traits attributable to mutation

Question 19

Sex-linked inheritance

Answer 19

The various inheritance patterns that can occur when genes are carried on the sex chromosomes

Question 20

Non-sex chromosomes are called

Answer 20

Autosomes

Question 21

Autosomal inheritance

Answer 21

Genes on autosomes

Question 22

Linked genes

Answer 22

• are genes predicted to always be transmitted together during gamete formation
• should violate the principle of independent assortment
• are inherited together unless crossing over occurs

Question 23

Recombinant

Answer 23

-the combination of alleles in offsprings is different from the combination of alleles in parents

Question 24

Recombinant genotypes occur

Answer 24

During the crossing over of prophase in meiosis I

Question 25

Multiple allelism

Answer 25

Genes have more than two alleles

Question 26

Polymorphic

Answer 26

When more than two distinct phenotypes are present in a population due to multiple allelism

Question 27

What is incomplete dominance?

Answer 27

When alleles of a gene don’t show a clear dominant or recessive but have an intermediate phenotype

Question 28

Codominance

Answer 28

Neither allele is dominican nor recessive to the other

Question 29

Genes that influence many traits

Answer 29

Pleiotropic

Eg Marfan syndrome Abe Lincoln

Question 30

The combined effect of gene and environment (example)

Answer 30

Gene-by-environment interaction
Eg phenylketonuria (PKU) - causes mental retardation

Question 31

Gene-by-gene interaction

Answer 31

The expression of genes that depend on the presence of other genes.

Chicken comb

Question 32

Discrete traits

Answer 32

Characteristics that are qualitatively different

Garden peas are either yellow or green, no intermediate exists

Question 33

Quantitative traits

Answer 33

Traits that are not discrete

Question 34

Polygenic inheritance

Answer 34

Many genes are involved in specifying traits that exhibit continuous variation.

Each allele adds a small amount of phenotype
Creates normal distribution curve

Question 35

Pedigree

Answer 35

Family tree that shows the genetic relationships among the individual, each persons sex and the phenotype for the trait being studied

Question 36

What two scientist formulated the chromosome theory of inheritance?

Answer 36

Walter Sutton and Theodor Boveri

Proposes that meiosis causes the patterns of inheritance that Mendel observed