Genetic Basis of Evolution

Question 1

Gregor Mendel (1822-1884)

Answer 1

Considered to be the father of genetics

Conducted groundbreaking work on theories of heredity

The understanding of heredity is vital for the understanding of evolution

Question 2

Heredity

Answer 2

The transmission of “traits” from parents to offspring

Question 3

Genes

Answer 3

any portion of chromosomal material that potentially last for enough generations to serve as a unit of natural selection
Particular units of inheritance that are passed from parents to offspring

Question 4

Locus / Loci

Answer 4

a place on a chromosome where genes affecting a particular trait occur

Question 5

Homozygous

Answer 5

when the mother and father contribute identical genes for the locus in question

Question 6

Heterozygous

Answer 6

When the mother and father contribute different genes for the locus in question

Question 7

Genotype

Answer 7

the genetic code carried by a particular individual- metaphor- a recipe. You have the genotype and the environment which creates phenotype

Question 8

Phenotype

Answer 8

the expression of a particular genotype
The result of the interaction between the environment and the genotype

Question 9

Dominant gene

Answer 9

a gene that is expressed in the phenotype regardless of whether it is homozygous or heterozygous

Question 10

Recessive gene

Answer 10

a gene that is expressed in the phenotype only when it is homozygous
Eye color is classic example

Question 11

Genes / Heredity

Answer 11

Genes are particular

Particles retain their integrity and are not diluted or reduced when combined with the particles of the mate

Question 12

Discrete trait

Answer 12

a trait with a small number of clearly separate phenotypes (e.g. eye color)

Question 13

Continuous trait

Answer 13

a trait with a large number of alternative phenotypes (e.g. height)

Question 14

Normal Adult Genes

Answer 14

Each normal adult carries a pair of genes for each trait

One gene comes from the mother, one gene comes from the father

When these genes are identical, they are homozygous

When these genes are different, they are heterozygous

Question 15

Diploid

Answer 15

the condition of having two sets of chromosomes. Normal body cells are diploid

Question 16

Haploid

Answer 16

the condition of having one set of chromosomes. Sex cells (eggs and sperm) are haploid

Question 17

Genes / Particles

Answer 17

Although pairs of genes do not dilute or change each other permanently, they can influence each others expression

Some genes can overshadow the effects of other genes (dominance effects)

The dominant gene is expressed in the heterozygous and homozygous conditions

The recessive gene is only expressed in the homozygous condition

The effects on one gene have an effect on another.

Question 18

Deoxyribonucleic acid (DNA)

Answer 18

the molecule that contains the information needed to build cells and control inheritance

Question 19

Chromosome

Answer 19

structures in the nucleus cell that house DNA. Chromosomes contain DNA and proteins bind to it
Can be thought of as “a long string of genes”

Question 20

Alleles

Answer 20

variant forms of a single gene. Alternatives at a particular locus
Two thirds of all loci have only a single allele

Question 21

Mutation

Answer 21

a heritable change in the base sequence of the DNA genome

A mistake in gene copying
The ultimate source of all new alleles. How novelty enters the equation
Occurs when sex cells are coming together.

Question 22

DNA: A Chemical Code for Proteins

Answer 22

DNA contains 2 strands of complimentary pairs
Adenine (A) always pairs with Thymine (T)
Guanine (G) pairs with Cytosine (C)

These are called base pairs
This allows DNA to separate and replicate, forming exact copies

Question 23

Codon

Answer 23

a set of three nucleotides (base pairs) along the DNA sequence that specify one amino acid

Question 24

Alleles may be selectively neutral

(Reasons for Genetic Variation)

Answer 24

Alternative alleles at a particular locus may produce equally fit phenotypes

Blood types??? Remains a topic of debate

Question 25

Environmental Variation
(Reasons for Genetic Variation)

Answer 25

Changing or fluctuating environments may select different alleles

Question 26

Heterozygote superiority
(Reasons for Genetic Variation)

Answer 26

In some cases, heterozygotes are fitter than homozygotes
i.e. sickle cell anemia

Question 27

Frequency-dependent selection (Reasons for Genetic Variation)

Answer 27

When natural selection favors an allele when it is rare, but disfavors it when it becomes more common

Question 28

Mutation (Reasons for Genetic Variation)

Answer 28

Gene copying errors; the ultimate source of all genetic variation

Most mutations decrease fitness and are quickly eliminated from the population

Rarely, but often enough, mutations increase fitness and are spread throughout the population

Random gene copying errors

Natural selection cannot choose which mutations to make

Selection evaluates these alternatives once they exist, eliminating the harmful ones and spreading the beneficial ones

Question 29

Common Mistakes in Evolutionary Thinking

“Evolution has a goal”

Answer 29

Natural selection is a description of a process that lacks consciousness, intentions, morals, and goals

Why tigers have stripes
Not because evolution wanted them to blend in against a forested background

Because at some point in their past, striped tigers out-reproduced other tigers

Question 30

Common Mistakes in Evolutionary Thinking
“Evolution works for the good of the species”

Answer 30

DNA can develop any type of mechanism that assists in its own replication, even when the mechanisms involve inhibiting other conspecifics from reproducing

Copulatory plugs in some insects and reptiles
After a male mates with a female, he secretes a thick “glue” preventing other males from having successful intercourse with the female

This clearly works against the good of the species

Question 31

Common Mistakes in Evolutionary Thinking
“Evolution and optimization”

Answer 31

Evolution does not find the global optimum. Instead, it finds solutions, some of which may be local maxima
Herons, pelicans, osprey, and loons all catch fish for a living, but they do so in different ways.

There is more than one way to get your genes into the next generation
Each species provides a different example