Genetics

Question 1

What are the advantages to using pea plants in genetic experiments?

Answer 1

• Many varieties with distinct features
• Mating of plants can be controlled
• Each plant has both a male organ (stamen) and female organ (carpel)
• Short generation time
• Large number of offspring produced

Question 2

What is the definition of “true-breeding”?

Answer 2

A true-breeding plant produces offspring of the same variety when it self-pollinates.

Question 3

How did Mendel achieve cross-pollination in pea plants?

Answer 3

He cut off the stamens of one plant and brush it with the pollen of another plant.

Question 4

What is hybridization?

Answer 4

Breeding two contrasting true-breeding varieties of the same species.

Question 5

The P generation plants cross-pollinate and produce a generation called the…

Answer 5

F1 generation.

Question 6

The F1 generation plants self-pollinate and produce a generation called the…

Answer 6

F2 generation.

Question 7

What is a dominant allele?

Answer 7

The allele that is expressed in the F1 generation.

Question 8

What are Mendel’s laws?

Answer 8

The Law of Dominance, the Law of Independent Assortment, and the Law of Segregation.

Question 9

What does the Law of Segregation state?

Answer 9

The two alleles for a heritable characteristic separate during gamete formation and end up in different gametes, meaning that each gamete of an individual has one version of the gene. (This refers to Meiosis II.)

Question 10

What does the Law of Independent assortment state?

Answer 10

Each pair of alleles segregates independently of each other pair of alleles in gamete formation. (This refers to Meiosis I, and only applies to genes on non-homologous chromosomes.)

Question 11

What does the Law of Dominance state?

Answer 11

If the two inherited genes differ, one will be expressed and the other will have no effect. The one that is expressed is the dominant allele.

Question 12

What is a dihybrid cross?

Answer 12

A cross between individuals that are heterozygous for two traits.

Question 13

What is a monohybrid cross?

Answer 13

A cross between true-breeding homozygotes that are different in two ways (two genes).

Question 14

In Mendel’s experiments, the F1 generation had a 3:1 ratio for the dominant phenotype:recessive phenotype. What is the ratio used to describe the F2 generation?

Answer 14

9:3:3:1

Question 15

What is co-dominance?

Answer 15

It means that both of the alleles inherited by an individual affect its phenotype in separate, distinguishable ways.

Question 16

What is incomplete dominance?

Answer 16

It means that the phenotype of an F1 hybrid is somewhere between the phenotypes of the two opposite alleles inherited.

Question 17

What is complete dominance?

Answer 17

It means that the phenotypes of a individual heterozygous for the trait, and a dominant homozygous individual, are identical.

Question 18

What are some circumstances in which actual genetic patterns deviate from Mendelian genetics?

Answer 18

A gene has more than two possible alleles; a gene produces multiple genotypes; more than one gene has an affect on a trait; the phenotype depends on environment as well as genotype.

Question 19

What is epistasis? Give an example.

Answer 19

The dependence of one gene’s phenotypic expression on the expression of another gene. For example, in mice, coat colour depends on two genes. This causes the phenotypic ratios to differ from Mendelian predictions.

Question 20

What is pleiotropy? Give an example.

Answer 20

Pleiotropy occurs when one gene influences two or more seemingly unrelated traits. For example, sickle cell anemia is caused by a pleiotropic mutation.

Question 21

What are the advantages to using fruit flies for genetic studies?

Answer 21

• They breed at a high rate
• A generation can be bred every two weeks
• They have only four pairs of chromosomes

Question 22

What is a sex-linked gene? How does it affect human males?

Answer 22

A gene that is found on the sex chromosomes, X and/or Y. Human males have an X and a Y chromosome, and the Y does not carry all of the same genes as the X (it is only partially homologous). The result is that a male’s phenotype for sex-linked genes is entirely dependent on one allele.

Question 23

True or false: the ovum is the sex-determining gamete.

Answer 23

False. Only sperm can carry the Y chromosome, therefore it is the determining factor.

Question 24

What are linked genes?

Answer 24

Genes that tend to be inherited together.

Question 25

What is genetic recombination? Who discovered it?

Answer 25

• Another term for crossing-over
• The cause of occurrence of traits in a descendent which are different from either of its parents (refers to Prophase I of meiosis)
• Morgan discovered this.

Question 26

What is a genetic map?

Answer 26

An ordered list of genetic loci along a particular chromosome.

Question 27

True or false: the smaller the distance between two genes on a chromosome, the less likely it is that crossing-over will occur.

Answer 27

True. Genes that are physically far apart can have a recombination frequency of up to 50%.

Question 28

What is a linkage map?

Answer 28

A genetic map, but based on recombination frequencies. Distances between genes are expressed as map units, or centimorgans. One centimorgan represents a 1% recombination frequency.

Question 29

What is nondisjunction? Give examples.

Answer 29

The sticking together of homologues during meiosis that causes one gamete to have multiples of the same type of chromosome, and the other to receive none. Down’s Syndrome is the result of fertilization of such gametes (which is called aneuploidy).

Question 30

What are the four ways by which a chromosome’s structure can be altered?

Answer 30

Insertion, deletion, translocation, and duplication.