Chapter 12: Genetics and Evolution

Question 1

What does it mean for an allele to be

• Dominant:
• Recessive:

Answer 1

• Dominant: A dominat allele is one that requires one copy of expression.
• Recessive: A recessive allele requires two copies of expression.

Question 2

What does it mean for a genotype to be

• Homozygous:
• Heterozygous:
• Hemizygous:

Answer 2

• Homozygous:
  
  • A homozygous gentotype is when two alleles are the same (RR, rr).
• Heterozygous:
  
  • A heterozygous genotype is when two alleles are different (Rr)
• Hemizygous
  
  • A hemizygous genotype is one in which only one allele is present for a given genotype (such as parts of the X chromosome in males). (XY)

Question 3

Complete Dominance

Define

Answer 3

• Complete dominance:
  
  • occurs in one alle (the dominant one) completely masks the expression od the other (recessive one)

Question 4

Codominace

Define

Answer 4

Occurs when a gene has more than one dominant allele, and two different dominant alleles can be expressed simultaneously.

Question 5

Incomplete Dominance

Define

Answer 5

Occurs when a gene has no dominant alleles, and heterozygotes have phenotypes that are intermediate between homozygotes.

Question 6

What is the difference between Penetrance and expressivity?

• Penetrance:
• Expressivity:

Answer 6

• Penetrance:
  
  • The probability, given a particular genotype, a person will express the phenotype
    
    • Ex: Huntingtons disease is caused by an expansion of repetive sequences in the huntingtin gene. individuals with more than 40 sequence repeats will express full penetrance (having it). Vice versa
• Expressivity:
  
  • Describes the differences in expression (severity, location, and so on) of a phenotype in individuals.
    
    • A disease that many different phenotypes can carry.

Question 7

With which phase of meiosis does each of Mendel’s laws most closely correlate?

• Mendels First Law:
• Mendels Second Law:

Answer 7

• Mendels First Law: Law of Segregation
  
  • Aligns with Anaphase I of Meiosis.
• Mendels Second Law: Law of Independent Assortment
  
  • Aligns with Prophase I of Meiosis

Question 8

Natural Selection

Answer 8

States that certain traits that arise from chance are more favorbale for reproductive success in a given environment, and that those traits will be passed on to future generations.

Question 9

Modern Synthesis Model

Answer 9

Takes natural selection and explains that selection is for specific alleles, which are passed on to future generations through formation of gametes; the alleles for these favorable traits arise from mutations.

Question 10

Inclusive Fitness

Answer 10

Explains that the reproductive success of an organism is not only due to the number of offspring it creates, but also the ability to care for young (that can then care for others); it explains changes not only at the individual level, but changes based on the survival of species(and that individuals alleles within the species, including in other related individuals).

Question 11

Punctuated Equilibrium

Answer 11

States that for some species, little evolution occurs for a long period, which is interrupted by rapid burst of evolutionary change.

Question 12

What is the biological definition of a species?

Answer 12

A species is defined as the largest group of organisms capable of breeding to form fertile offspring.

Question 13

Answer 13

Question 14

Answer 14

Question 15

Crossing two heterozygotes for a trait with complete dominance results in a _____ ratio of gentotypes and a ____ ratio of phenotypes.

Answer 15

• 1:2:1
• 3:1

Question 16

Dihybrid crosses between two heteozygotes with complete dominance has a ratio of ___.

Answer 16

• 9:3:3:1

Question 17

What are the three main types of point mutations?

Answer 17

1. Silent Point Mutations
2. Missense Mutations
3. Nonsense Mutations

Question 18

Silent Point Mutations

Answer 18

Occur when one nucleotide is changed for another, but there is no change in the protein coded for by this DNA sequence (due to the redundancy in the genetic code).

Question 19

Missense Mutations

Answer 19

Occurs when one nucleotide is changed for another, and one amino acid, and one amino acid is substituted for another in the final protein.

Question 20

Nonsense Mutations

Answer 20

Occurs when one nucleotide is changed for another, and a stop codon substitutes for an amino acid in the final protein.

Question 21

What are the two types of frameshift mutations?

Answer 21

1. Insertion
2. Deletion

Question 22

Why is genetic drift more common in small populations? What relationship does this have to the founder effect?

Answer 22

Genetic drift occurs due to chance, so its effects will be more pronounced with a smaller sample size (in small populations). The founder effect occurs when a small group is reproductively isolated from the larger population, allowing certain alleles to take on a higher prevalence in the group than in the rest of the population.