Biology Chapter 4: Genetic Inheritance and Evolution

Question 1

Directional selection

Answer 1

where a more extreme phenotype is favored

Question 2

Allopatric speciation

Answer 2

occurs because of physical barriers. Geographic isolation, separating the Asian and European samples, is a common cause of allopatric speciation

Question 3

Sympatric speciation

Answer 3

describes reproductive isolation that emerges when no physical barrier separates a population (ie behavioural and ecological differences)

Question 4

If one parent is homozygous recessive, what is the probability that an offspring will carry one or more recessive alleles?

Answer 4

100%

Question 5

Genetic bottleneck occurs when

Answer 5

A population experiences a sharp reduction in size, leading to a loss of genetic diversity, increased genetic drift, potential inbreeding

Question 6

Allele

Answer 6

Variation of a gene

Question 7

Law of independent assortment

Answer 7

Inheritance of various genes are not correlated with each other

Question 8

Linkage is an exception to

Answer 8

Independent assortment because genes that are physically close to each other on the same chromosome tend to have alleles inherited together

Question 9

What is hemizygousity?

Answer 9

Only 1 allele (like on x Y chromosomes in males)

Question 10

Why perform a test cross? And how?

Answer 10

To find the genotype of dominant allele (either AA or Aa). Cross the unknown dominant with a known recessive

Question 11

What is a back cross and why perform it?

Answer 11

To obtain offspring more similar to the parent. Cross a hybrid from F1 with a parent

Question 12

Penetrance

Answer 12

Probability that genotype actually manifests

Question 13

Expressivity

Answer 13

The extent of the intensity of the gene expression

Question 14

On a pedigree analysis, circles, squares and shaded shapes refer to what?

Answer 14

Circles = females, squares = males, shaded = manifest a certain phenotype. Half shaded means that the person is a carrier

Question 15

Chiasmata

Answer 15

The point of crossing over. Occurs at random

Question 16

Recombination frequency

Answer 16

Describes how often a single crossover will occur between 2 genes during meiosis

Question 17

If the recombination frequency of two genes is exactly 50% then the genes? Less than 50%? Greater than 50%?

Answer 17

Obey the law of independent assortment at exactly 50%.

Less than 50% - genes are linked, meaning that the genes are close enough together that they don’t assort independently. Closer the genes, lower the rf

Not possible to have rf greater than 50%

Question 18

Distance associated with 1% increment in the recombination frequency

Answer 18

Centimorgan (cM)

Question 19

Difference in inheritance between autosomal mutations and somatic mutations

Answer 19

Autosomal mutations are found on chromosomes 1-22 and ARE inheritable if in germ line cells like egg and sperm (such as cystic fibrosis, Huntington’s disease)

Somatic mutations are located in body cells, NOT germline cells and therefore aren’t inherited. Ie cancer mutations, UV-induced skin damage etc

Question 20

Autosomal dominant inheritance patterns

Answer 20

Do not skip generations

Question 21

Autosomal recessive inheritance pattern

Answer 21

Can skip generations

Question 22

X-linked inheritance patterns

Answer 22

More males affected

Question 23

Dihybrid cross ratio

Answer 23

9:3:3:1

Question 24

Fitness

Answer 24

Chance of reproduction associated with a certain phenotype. Must be defined by specific environment constraints

Question 25

Inclusive fitness

Answer 25

Chance of reproductive success of an entire group of organisms (not just the individual)

Question 26

Gene pool

Answer 26

All the genotypes in a population

Question 27

Hardy-Weinberg equilibrium definition

Answer 27

Determines the genotype and allele frequency in a population. AND can use to predict the phenotypes in the population and vice versa

Question 28

Hardy-Weinberg equilibrium criteria

Answer 28

Question 29

Hardy-Weinberg equations

Answer 29

And p + q = 1

Question 30

Polygenic

Answer 30

Multiple genes collective contribute to a trait. Often involved with traits that show variation along a spectrum such as height

Question 31

Stabilizing selection

Answer 31

Extreme phenotypes selected against

Question 32

Disruptive selection

Answer 32

Extreme phenotypes selected for, median phenotype selected against

Question 33

Directional selection

Answer 33

Occurs only if one extreme phenotype is selected against and the other is favoured

Question 34

Genetic drift

Answer 34

Role of CHANCE in determining the reproductive fitness of various alleles

Question 35

Polymorphism

Answer 35

Phenotypic variations can exist in a single species ie ABO blood group systems

Question 36

Example of post zygotic barrier

Answer 36

Hybrid sterility

Question 37

Leakage

Answer 37

On the level of the gene pool, genes can sometimes travel between species

Question 38

Accumulation of random changes in genome over time

Answer 38

Molecular clock. Can be used as a method for dating divergence from last common ancestor

Question 39

Differential reproduction

Answer 39

means individuals with traits better suited to their environment are more likely to survive, reproduce, and pass on their genes to the next generation. “Survival of the fittest, through reproduction”

Question 40

parsimony

Answer 40

which seeks the simplest explanation for the observed data—i.e., the phylotree that minimizes the number of evolutionary events (such as gene gains or losses)

Question 41

Which phylums share the most genes?

Answer 41

simpsoni, mascarensis and aegypti

Question 42

Convergent vs divergent evolution

Answer 42

🔹 Convergent Evolution → Different species evolve similar traits due to similar environments (e.g., wings in birds & bats 🦅🦇). 🔹 Divergent Evolution → A common ancestor gives rise to different traits in species adapting to different environments (e.g., Darwin’s finches 🐦). 💡 Key Mnemonic: Convergent = Come Together (similar traits, different ancestors). Divergent = Divide (different traits, shared ancestor).

Question 43

Why is one X chromosome in females inactivated, and how does it happen?

Answer 43

🔹 X-Inactivation (Lyonization) ensures equal gene expression between males (XY) and females (XX). 🔹 One X chromosome is randomly inactivated early in development. 🔹 The inactivated X forms a Barr body (highly condensed, inactive). 🔹 XIST gene coats the inactive X, silencing transcription. 🔹 Creates a genetic mosaic (some cells express the maternal X, others the paternal X). 💡 MCAT Tip: Explains patchy fur in calico cats 🐱. Influences X-linked disease severity in females.

Question 44

If X-inactivation failed completely

Answer 44

females (XX) would have double the gene expression from the X chromosome, causing major developmental problems.

Question 45

Adaptive radiation

Answer 45

involves the divergence of one species into multiple species over time, which can occur when subgroups of the original species are separated or isolated in different environments so that these subgroups evolve independently of one another.