Biology: Chapter 12

Question 1

Genes

Answer 1

DNA sequences that code for heritable traits that can be passed from one generation to the next

Question 2

Genotype

Answer 2

the genetic combination possessed by an individual

Question 3

Phenotype

Answer 3

the manifestation of a given genotype as an observable trait

Question 4

Dominant

Answer 4

if only one copy of an allele is needed to express a given phenotype

Question 5

Recessive

Answer 5

if two copies are needed to express a given phenotype

Question 6

Complete dominance

Answer 6

-when only one dominant and one recessive allele exist for a given gene
-dominant allele will mask the recessive allele

Question 7

Codominance

Answer 7

more than one dominant allele exists for a given gene

Question 8

Incomplete dominance

Answer 8

heterozygote expresses a phenotype that is intermediate between the two homozygous genotypes

Question 9

Penetrance

Answer 9

-population measure defined as the proportion of individuals in the population carrying the allele who actually express the phenotype
-Full penetrance: 100% of the individuals who have the allele show symptoms or the trait

Question 10

Expressivity

Answer 10

-varying phenotypes despite identical genotypes
-Constant expressivity: all individuals with a given genotype express the same phenotype
-Variable expressivity: individuals with the same genotype may have different phenotypes

Question 11

Mendel’s First Law: Law of Segregation

Answer 11

-Genes exist in alternative forms (alleles)
-An organism has two alleles for each gene- one inherited from each parent
-The two alleles segregate during meiosis, resulting in gametes that carry only one allele for any inherited trait
-If two alleles of an organism are different, only one will be fully expressed and the other will be silent. The expressed allele is said to be dominant, while the silent allele is recessive (codominance and incomplete dominance are exceptions to this rule)

Question 12

Mendel’s Second Law: Law of Independent Assortment

Answer 12

-The inheritance of one gene does not affect the inheritance of another gene
-Segregation and independent assortment allow for greater genetic diversity in the offspring

Question 13

Mutations

Answer 13

-a change in DNA sequence, and it results in a mutant allele
-Mutagens: substances that can cause mutations
-Transposons: can insert and remove themselves from the genome; if a transpon inserts in the middle of a coding sequence, the mutation will disrupt the gene

Question 14

Point mutations

Answer 14

occur when one nucleotide in DNA (A, C, T, or G) is swapped with another

Question 15

Silent mutation

Answer 15

-point mutation
-change in nucleotide has no effect on the final protein synthesized from the gene

Question 16

Missense mutation

Answer 16

-point mutation
-the change in nucleotide results in substituting one amino acid for another in the final protein

Question 17

Nonsense mutation

Answer 17

-point mutation
-the change in nucleotide results in substitution a stop codon for an amino acid in the final protein

Question 18

Frameshift mutations

Answer 18

-occur when nucleotides are inserted into or deleted from the genome
-Insertion of deletion of nucleotides can shift the reading frame, resulting in changes in the amino acid sequence or premature truncation of the protein
-Insertion or deletion mutations

Question 19

Deletion mutations

Answer 19

-a large segment of DNA is lost from a chromosome
-small deletion mutations are considered frameshift mutations

Question 20

Duplication mutations

Answer 20

a segment of DNA is copied multiple times in the genome

Question 21

Inversion mutations

Answer 21

a segment of DNA is reversed within the chromosome

Question 22

Insertion mutations

Answer 22

-a segment of DNA is moved from one chromosome to another
-Small insertion mutations are considered frameshift mutations

Question 23

Translocation mutations

Answer 23

a segment of DNA from one chromosome is swapped with a segment of DNA from another chromosome

Question 24

Genetic leakage

Answer 24

-a flow of genes between species
-Individuals from different (but closely related) species can mate to produce hybrid offspring (ex: mule which is a hybrid of a male horse and female donkey)

Question 25

Stabilizing selection

Answer 25

keeps phenotypes within a specific range by selecting against extremes

Question 26

Directional selection

Answer 26

-adaptive pressure can lead to the emergence and dominance of an initially extreme phenotype;
-a new standard phenotype may emerge as a result of differential survivorship

Question 27

Disruptive selection

Answer 27

two extreme phenotypes are selected over the norm

Question 28

Polymorphisms

Answer 28

-naturally occurring differences form between members of the same population
-necessary for disruptive selection

Question 29

Adaptive radiation

Answer 29

related concept in which there is a rapid rise of a number of different species form a common ancestor

Question 30

Speciation

Answer 30

-The formation of a new species through evolution
-Reproductive isolation may occur either prezygotically or postzygotically
-Prezygotic mechanisms: prevent formation of the zygote completely
-Postzygotic mechanisms: allow for gamete fusion but yield either nonviable or sterile offspring

Question 31

Divergent evolution

Answer 31

the independent development of dissimilar characteristics in two or more lineages sharing a common ancestor

Question 32

Parallel evolution

Answer 32

related species evolve in similar ways for a long period of time in response to analogous environmental selection pressures

Question 33

Convergent evolution

Answer 33

independent development of similar characteristics in two or more lineages not sharing a recent common ancestor