week 7

Question 1

What led to the evolution of giant insects, and how do insects’ respiratory systems differ from other organisms?

Answer 1

High O2 levels led to the evolution of giant insects. Insects have a respiratory system consisting of tracheae that deliver oxygen directly to tissues and lack a circulatory system.

Question 2

What evidence supports the existence of giant insects in the past?

Answer 2

Fossils show that giant dragonflies with a wingspan of over 70 cm lived around 300 million years ago, during a time when atmospheric O2 levels peaked at about 28%.

Question 3

What does the phylogenetic tree of life suggest about the prevalence of unicellular and multicellular organisms?

Answer 3

What does the phylogenetic tree of life suggest about the prevalence of unicellular and multicellular organisms?

Question 4

Who are the closest known unicellular living relatives of animals?

Answer 4

Choanoflagellates are unicellular eukaryotes and the closest known unicellular living relatives of animals.

Question 5

What supports the close evolutionary link between choanoflagellates and animals?

Answer 5

The close resemblance of choanocytes in sponges with choanoflagellates supports the close evolutionary link between them and animals.

Question 6

How many times has multicellularity arisen, and in which groups?

Answer 6

Multicellularity has arisen independently multiple times, specifically in animals, fungi, and land plants.

Question 7

What does the independent invention of multicellularity suggest about this trait?

Answer 7

The independent rise of multicellularity in different groups suggests that there are selective advantages to being composed of multiple different cells.

Question 8

Which groups are animals more closely related to, choanoflagellates or plants/fungi?

Answer 8

Animals are more closely related to choanoflagellates than they are to plants or fungi.

Question 9

What are the steps in the road to true multicellularity?

Answer 9

1. Colony formation, where cells have the ability to stick together.
2. Development into a true multicellular organism characterized by selective cell adhesion, division of labor, and composition of genetically identical cells.

Question 10

How can predation be a driving force for colony formation?

Answer 10

Organisms like Chlorella vulgaris can develop into stable colonies as a response to predation, significantly increasing their immunity to being eaten by predators.

Question 11

What is the downside of colony life in terms of genetic conflict?

Answer 11

In colonies, the presence of genetically non-identical cells can give rise to “cheater” cells that exploit the collective effort of the colony, as seen in Dictyostelium.

Question 12

How does Volvox demonstrate division of labor among cells?

Answer 12

In Volvox, a species of Volvocaceae, cells become differentiated into distinct cell types where only certain cells can reproduce, while others, the flagellated cells, cannot divide but contribute to locomotion and other functions.

Question 13

Who is Gregor Mendel and what did he contribute to genetics?

Answer 13

Gregor Mendel is known as the father of modern genetics. He crossed hundreds of pea plants and analyzed the traits of their progeny using statistics to formulate the laws of Mendelian inheritance.

Question 14

What is the first law of Mendelian inheritance, also known as the law of segregation?

Answer 14

The law of segregation states that genes exist in variants called alleles, and during gamete production, the two alleles segregate so each gamete receives only one copy. The zygote will have two alleles, one from each parent.

Question 15

How does dominant inheritance of a monogenic condition work?

Answer 15

In dominant inheritance, if an individual possesses one dominant allele (A), they will display the condition, regardless of the second allele. Thus, genotypes AA and Aa are affected, while aa is not.

Question 16

How does recessive inheritance of a monogenic condition work?

Answer 16

in recessive inheritance, an individual must have two recessive alleles (aa) to be affected by the condition. Individuals with genotypes AA or Aa are not affected, but Aa individuals are carriers.

Question 17

What is the second law of Mendelian inheritance, also known as the law of independent assortment?

Answer 17

The law of independent assortment states that alleles of different genes are divided across the gametes independently. This leads to new combinations of traits in the progeny but generally applies only to genes on separate chromosomes.

Question 18

What are multiple alleles, and how can they affect phenotypes?

Answer 18

Multiple alleles refer to the existence of more than two alleles for a gene in a population, producing a range of phenotypes, such as coat color in rabbits.

Question 19

What is incomplete dominance?

Answer 19

incomplete dominance occurs when neither allele is dominant, resulting in heterozygotes displaying an intermediate phenotype, like pink flowers from red and white parents.

Question 20

How does co-dominance differ from incomplete dominance?

Answer 20

Co-dominance is when both alleles in a heterozygote are fully expressed, leading to phenotypes that show both alleles, such as red and white spotted flowers.

Question 21

What is a pleiotropic allele?

Answer 21

A pleiotropic allele has multiple phenotypic effects, such as an allele causing both coat coloration and crossed eyes in Siamese cats.

Question 22

Explain epistasis.

Answer 22

Epistasis occurs when one gene alters the phenotypic expression of another gene, like how coat color in Labradors is determined by genes for pigment deposition and pigment color.

Question 23

What are polygenic traits?

Answer 23

Polygenic traits are controlled by multiple genes and often show a normal distribution within a population, such as human height.

Question 24

What does incomplete penetrance mean?

Answer 24

ncomplete penetrance refers to variable phenotypic expression of a genotype, where not all individuals with a genotype will express the expected phenotype.

Question 25

What determines ABO blood type?

Answer 25

The ABO blood type is determined by three alleles of the ABO gene: I^A, I^B and i (aka I^O) with I^A and I^B being dominant over i

Question 26

How does the FUT1 gene affect ABO blood groups?

Answer 26

The FUT1 gene, with alleles H and h, controls the presence of AB antigens on red blood cells. The H allele adds a fucose to a precursor molecule, while the h allele is inactive.

If it’s left unmodified, it results in blood type O. Additional modifications by other enzymes create A or B blood types.

Question 27

How does the ABO gene demonstrate co-dominance?

Answer 27

The ABO gene encodes for a glycosyltransferase enzyme, with different alleles adding specific sugar molecules to the H antigen, resulting in the A or B antigen.

Question 28

What is the Bombay phenotype in the context of ABO blood groups?

Answer 28

Individuals with the Bombay phenotype are homozygous for the FUT1 h allele, meaning they cannot produce the H antigen and have antibodies against A, B, and H antigens. They can only receive blood from other individuals with the Bombay phenotype.

Question 29

How can the environment influence the penetrance of a trait?

Answer 29

Environmental factors, such as changes in healthcare and wealth distribution, can influence the penetrance of a trait, as seen with the correlation between social changes and average height gain.

Question 30

What are the two main processes that introduce genetic variation?

Answer 30

The two main processes that introduce genetic variation are mutation, a heritable change in genetic information, and recombination, the rearrangement of genetic material during sexual reproduction.

Question 31

What can cause spontaneous mutations?

Answer 31

Spontaneous mutations can be caused by chemical reactions that alter nucleotides, errors in DNA replication, or errors during meiosis.

Question 32

What are induced mutations and what causes them?

Answer 32

Induced mutations are caused by external factors called mutagens, which include damaging chemicals and radiation such as ionizing or UV radiation.

Question 33

What are the different molecular classifications of mutations?

Answer 33

Mutations can be classified by their molecular characteristics: point mutations (synonymous, missense, nonsense, frame-shift) and chromosomal mutations (deletion, duplication, inversion, insertion, translocation).

Question 34

How are mutations classified based on the function of the encoded protein?

Answer 34

Based on the function, mutations can be classified as silent, loss-of-function, or gain-of-function.

Question 35

How are mutations categorized concerning phenotype and fitness?

Answer 35

Concerning phenotype and ‘fitness,’ mutations can be neutral, harmful, or beneficial.

Question 36

What is a point mutation and how does it affect proteins?

Answer 36

A point mutation is a change in one or two nucleotides in DNA. Its effect on the protein depends on the change in the amino acid sequence, which is determined by the genetic code.

Question 37

What is a synonymous (silent) point mutation?

Answer 37

A synonymous point mutation is a change in a nucleotide that does not alter the amino acid sequence of a protein due to redundancy in the genetic code.

Question 38

What is a missense point mutation?

Answer 38

A missense point mutation changes a codon to one that specifies a different amino acid, affecting the amino acid sequence of the encoded protein. It’s denoted by the original amino acid, its position, and the new amino acid, e.g., D5V.

Question 39

What is a silent mutation and when can it occur?

Answer 39

A silent mutation can occur when the amino acid sequence of the protein is unchanged or when a change in the sequence has no effect on the protein’s function.

Question 40

what characterizes a loss-of-function mutation?

Answer 40

A loss-of-function mutation results in a protein that has impaired function. Such mutations often show recessive inheritance because a single wild-type allele may be enough to maintain a normal phenotype.

Question 41

How does a gain-of-function mutation differ from a loss-of-function mutation?

Answer 41

A gain-of-function mutation leads to a protein with abnormally functioning or increased activity. This type of mutation often shows dominant inheritance because the abnormal activity is not countered by the wild-type allele.

Question 42

What is an example of a gain-of-function mutation?

Answer 42

An example of a gain-of-function mutation is a change in the RAS oncogene. A mutation that prevents RAS from hydrolyzing GTP can lead to constitutive activation, promoting tumor cell survival and proliferation.

Question 43

How are mutations classified based on the effect on the organism?

Answer 43

Mutations are classified based on the molecular characteristic (e.g., point or chromosomal mutation), function of the encoded protein (e.g., silent, loss-of-function, gain-of-function), and the phenotype and ‘fitness’ of the organism (e.g., neutral, harmful, beneficial).

Question 44

How can a mutation be both harmful and beneficial? Give an example.

Answer 44

The mutation that causes sickle-cell anemia is harmful because it leads to severe anemia. However, it is also beneficial because heterozygous carriers have resistance to malaria. This dual nature explains why the mutation persists in populations where malaria is prevalent.