BIOLOGY 1M03 Lecture Notes - Lecture 20: Birth Weight, Stabilizing Selection, Genetic Variation

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2 Aug 2018

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Types of natural selection: occurs when individuals with certain phenotypes produce more offspring than individuals with other phenotypes do. Environmental change is severe enough, population may fact extinction. In chapter 24, according to data, natural selection ahs increased frequency of drug-resistant strains of the tb bacterium and caused changes in beak shape and body size in medium ground finches. If directional selection continues over time favored alleles will eventually approach a frequency of 1. 0, while disadvantageous alleles will approach a frequency of 0. In 1996, a population of cliff swallows native to north america endured a 6-day period of extreme cold and rainy weather: they feed by catching mosquitoes and other insects. If difference in body size among individuals were due to variation their genotypes. If directional selection of this type continued then the alleles that contribute to small body size would quickly decline in frequency. This is evidence that birth weight was under strong stabilizing selection in humans.

Related Questions

Which of the following provides evidence for evolution?

All of these answers are correct

Comparing DNA sequences between species

Looking at the geographic distribution of similar species

Analyzing transitional fossils

Which one of the following statements is true?

Natural selection works on non-heritable traits.

Mutations only give rise to harmful traits.

Natural selection works on variation already present in a population.

Individuals evolve through natural selection.

Which one of the following can create new alleles?

Which of the following is true concerning evolution?

An individual can evolve

Genetic drift is a non-random part of natural selection

An organism's fitness is determined by how long it survives

Natural selection occurs through a change in allele frequency

All living things need carbon. How does carbon enter the living portion of an ecosystem?

Atmospheric carbon dioxide taken in by photosynthesis.

Atmospheric carbon dioxide taken in by soil bacteria.

Elemental carbon taken in by plant roots.

Elemental carbon taken in by cellular respiration.

Elemental carbon taken in by cellular transpiration.

The burning of fossil fuels:

Releases excess carbon dioxide into the atmosphere.

Removes pollutants from the atmosphere.

Was developed by scientists to combat global climate change.

Has no effect on the carbon cycle.

Is good for the environment

__________ conducts water and dissolved minerals from the __________ to the ___________.

Phloem; roots; shoots

Xylem; roots; shoots

Phloem; shoots; roots

Xylem; shoots; roots

What is a disadvantage of growing traditional crops such as corn, soy or sugar cane for making biofuel?

they require lots of land and fresh water

they take carbon dioxide out of the atmosphere

they release oxygen into the atmosphere

they release water through their stomata

______ is the source of the oxygen gas released by a photosystem.

Through what structure(s) do plants obtain most of their water?

Need help with evolution questions:

1.) A haplotype is best defined as the ________________.

	haploid genotypes of all the gametes produced by a diploid individual

ABO blood type conferred by an individual gamete

genotype of either the paternal or maternal chromosomal complement

multilocus genotype of a chromosome or gamete

2.) Which of the following statements regarding linkage disequilibrium is true?

Exists when D is less than zero, but not when it is greater than zero.

Is reduced by sexual reproduction.

Is increased by crossing-over during meiosis.

Is increased by any random sampling error that happens to create or destroy certain chromosome genotypes but not others.

Is reduced by selection that favors certain combinations of genotypes.

3.) Selection on multilocus genotypes in random-mating populations leads to linkage disequilibrium when _______________.

it reduces mutation rates

it eliminates all haplotypes from the population

it prevents crossing-over during meiosis

some allele combinations confer greater fitness than do others

4.) When two loci are in linkage equilibrium, the allele carried on a chromosome at one locus is independent of the allele carried on the chromosome at another locus. When this is the case, _________________.

allele frequencies will not change over time

the two loci (or, more specifically, their protein products) do not interact

the frequency of each haplotype can be calculated by multiplying the frequency of its two alleles

all possible haplotypes occur at equal frequency

5.) Which of the following accurately characterize(s) Muller's ratchet model for the selective advantage of sexual reproduction?

Drift establishes linkage disequilibrium because multilocus genotypes with few mutations are eliminated by chance events.

In populations without sexual reproduction, deleterious mutations accumulate, eventually imposing such a burden that the population goes extinct.

Sex is favored selectively because it recreates the zero-mutation genotypes lost due to drift.

All of the above correctly characterize Muller's ratchet model for the evolution of sexual reproduction.

6.) The genetic signature of recent positive selection on a locus is _______________.

high frequency and low linkage disequilibrium

low frequency and low linkage disequilibrium

low frequency and high linkage disequilibrium

high frequency and high linkage disequilibrium

7.) Sexual reproduction is advantageous both in changing environments and in constant environments, compared to asexual reproduction.

True

False

8.) Sexual reproduction causes genetic recombination via crossing-over, which combines genotypes from different parents.

True

False

9.) One reason sex may be maintained in natural populations is proposed by the "Red Queen Hypothesis", which states that.....

genotypes created by sex are created by natural selection over and over

recombination creating novel genotypes that can resist infection by parasites

mutation load is reduced by novel adaptive mutations

the ability of sex to fix multiple

BIOLOGY 1M03 Lecture Notes - Lecture 20: Birth Weight, Stabilizing Selection, Genetic Variation

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