Topic 13 - Patterns of Inheritance

Question 1

What was the significance of Mendel’s work?

Answer 1

Mendel’s experiments demonstrated that traits are transmitted from parents to offspring independently of other traits and in dominant/recessive patterns

Question 2

Trait

Answer 2

Variation in the physical appearance of a heritable characteristic

Question 3

Dominant trait

Answer 3

Trait which confers the same physical appearance whether an individual has 2 copies of the trait or one copy of the dominant trait and one copy of the recessive trait

Question 4

Recessive trait

Answer 4

Trait that appears “latent” or non-expressed when the individual also carries a dominant trait for that characteristic; when present as two identical copies, the recessive trait is expressed

Question 5

Allele

Answer 5

Gene variations that arise by mutation and exist at the same relative locations (loci) on homologous chromosomes

Question 6

Phenotype

Answer 6

The observable traits expressed by an organism

Question 7

Genotype

Answer 7

Underlying genetic makeup, consisting of both physically visible and non-expressed alleles, of an organism

Question 8

Homozygous

Answer 8

Having two identical alleles for a given gene on the homologous chromosome

Question 9

Heterozygous

Answer 9

Having two different alleles for a given gene on the homologous chromosome

Question 10

True or false: each parent can donate one of two different alleles, which segregate randomly into gametes

Answer 10

True

Question 11

Law of Dominance

Answer 11

In a heterozygote, one trait will conceal the presence of another for the same characteristic

Question 12

Law of Segregation

Answer 12

Two alleles for a gene segregate during gamete formation and are rejoined at random, one from each parent, during fertilization
- Occurs during anaphase I of meiosis

Question 13

Law of Independent Assortment

Answer 13

Each pair of alleles segregates into gametes independently of the other pairs, and every possible combination of alleles is equally likely to occur
- Occurs during metaphase I of meiosis
- Only true if pairs of alleles are on separate chromosomes

Question 14

Product rule

Answer 14

The probability of two independent events occurring simultaneously can be calculated by multiplying the individual probabilities of each event occurring alone
- Compound event: when 2 or more independent events happen at the same time
- “and” = product rule

Question 15

Sum rule

Answer 15

The probability of the occurrence of one event or the other event, or two mutually exclusive events, is the sum of their individual probabilities
- “or” = sum rule

Question 16

Under what circumstances is the Law of Independent Assortment NOT true?

Answer 16

This principle only holds true when genes are located far away from one another on the same chromosome or when they are on different chromosomes entirely. Once genes are close to one another on the same chromosome, they become linked together and can no longer be independently inherited.

Question 17

Explain the significance of linked genes.

Answer 17

While genes that are located on separate chromosomes will always sort independently, linked genes are more likely to be inherited as a pair because they are physically close together on the same chromosome

Question 18

Incomplete dominance

Answer 18

In a heterozygote, expression of two contrasting alleles such that the individual displays an intermediate phenotype
Ex. some flowers (red + white = pink)

Question 19

Codominance

Answer 19

In a heterozygote, complete and simultaneous expression of both alleles for the same characteristic
Ex. human blood types (AB)

Question 20

Pleiotropic gene

Answer 20

Single gene that affects multiple characteristics
Ex. sickle-cell anemia

Question 21

Epistasis

Answer 21

Gene at one locus alters gene at a second locus
Ex. coat color

Question 22

Polygenic inheritance

Answer 22

Non-epistatic genes interact additively to influence a phenotypic trait
Ex. skin color