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WorksheetsTVMSC Biology--Mendelian genetics
Total questions: 47
Worksheet time: 24mins
Mendel lived and worked during
the 1500s
the 1600s
the 1700s
the 1800s
Luckily for us, Mendel had some schooling in
metallurgy (black-smithing, etc)
math and probability
physics
chemistry
A diploid organism like Mendel's peas has how many copies of "each chromosome" in each of its body cells
two
one
four
an unpredictable number
Each pollen grain and each egg of the pea plant has how many copies of "each chromosome"?
one
two
four
this is highly variable
That is to say, a diploid organism produces_______gametes
haploid
diploid
triploid
tetraploid
A diploid organism producing haploid gametes is an example of Mendel's "Principle of ___________"
independent assortment
segregation
The traits Mendel worked with (mark all that are true)
were determined by one gene or locus each
had a simple dominant vs recessive pattern of phenotypic expression
had only two alleles that he examined, of each gene
Thus, a "classical Mendelian trait"
is determined by a single gene or locus
has a simple dominant vs recessive pattern of expression in the phenotype
is "polygenic", that is, influenced by many separate genes or loci
"red flower times white flower yields pink flower" sounds like
a simple Mendelian trait
codominance
a polygenic trait
incomplete dominance
"red flower times white flower yields flowers partly red, partly white" sounds like
a simple Mendelian trait
incomplete dominance
codominance
a polygenic trait
the A, B, O blood type system, in which you can be type AB, is a case of
simple Mendelian traits
incomplete dominance
codominance
a polygenic trait
A dominant allele is defined as
the "best" (most advantageous) allele
an allele that will be expressed even if only one copy is present
the commonest allele in a population
an allele that will be expressed only when 2 copies are present
Truly harmful alleles are
usually recessive
usually dominant
equally often dominant or recessive
Why are truly harmful alleles rarely dominant?
that's just the biochemistry of alleles--it can't easily be otherwise
because dominant alleles are more easily removed by natural selection, because they are always expressed when present
What does it mean that a harmful recessive allele can sometimes "hide" from natural selection? Check all that are true:
selection can only act on the phenotype, not directly on the genotype
in the heterozygous state, a recessive allele is not expressed in the phenotype
in the heterozygous state, a recessive allele is effectively "invisible" to natural selection
all of the above make it easier for a harmful recessive allele to persist in a population.
What is a "polygenic" trait?
a trait for which there are multiple alleles of one gene
a trait affected by several different genes or loci
a single gene that affects several different aspects of the phenotype
Polygenic traits are also referred to as
quantitative traits
qualitative traits
categorical traits
discrete traits
Quantitative (polygenic) traits show
discontinuous or categorical variation, like apples & oranges
continuous variation, often expressed by a smooth curve
Which of the following are well known as polygenic traits?
tongue rolling ability vs no such ability
freckles vs no freckles
body height
skin color
Huntington's Disease is a lethal (deadly) dominant allele, yet persists in the population. Why is it not eliminated by natural selection?
the answer is not known
because it's dominant--it's more difficult for natural selection to remove dominant than recessive alleles
because it is not expressed until middle-age, when many folks have already reproduced
What is it called when one gene (one locus) affects multiple aspects of the phenotype?
a polygenic trait
pleiotropy
a dominant allele
codominance
What is a sex-linked gene?
One that is on the Y chromosome
One that is only expressed in males or in females
One that makes an individual male or female
One that is on the X chromosome
Since female humans have 2 X chromosomes, and sex-linked genes are on the X chromosome, sex-linked recessive traits are expressed phenotypically more often in females, right?
wrong
right
Why are rare, recessive sex-linked alleles expressed more often in males than in females?
it is easier for a male to acquire one such allele than it is for a female
a male will express such an allele even if only one copy is present
in a female, the trait will only be expressed if 2 copies of the recessive are present
for a rare allele, the probability of getting 2 copies is far less than the probability of getting one copy
What process during meiosis rearranges chromosomes that will be put into a gamete?
crossing over
mitsosis
metaphase
anaphase
Crossing over is thought to be advantageous by carrying out
genetic recombilnation
natural selection
increased mutation rates
A special advantage of crossing over can sometimes be
putting together a random assortment of alleles
creating mutations
putting on one chromosome alleles at different loci that work especially well together
From the standpoint of evolution, the key aspect of sexual reproduction is
making more individuals
combining DNA from two different individuals
Many kinds of organisms reproduce asexually, that is, without sex
true
false
Thus, it is not always essential for sex to be involved in reproduction
true
false
Why does it puzzle evolutionary biologists that sex evolved at all?
no good reason
they are easily puzzled--not that bright, really
all of the above may well be true, but yet...
without sex, your offspring contain ONLY your own genes; WITH sex your offspring contain only HALF your genes, and half somebody else's genes! Why would you pass on someone else's genes? Huh?
The benefit of sexual reproduction is believed to be
keeps life interesting...no, scratch that!
more offspring can be produced, faster, through sex
it gives your offspring access to genetic variation, for example, possibly useful mutations, that has appeared elsewhere in the population (not in your direct family tree)
nobody has any idea
"which allele a gamete receives at THIS locus is independent of which allele it receives at this OTHER locus" describes:
Mendel's Law of Segregation
Mendel's Law of Independent Assortment
Independent assortment is strictly true ONLY when
the genes involved are on different chromosomes
one gene is dominant and the other recessive
the genes are sex-linked
When two or more genes are on the same chromosome, we call this
genetic linkage
sex linkage
polygenic inheritance
pleiotropy
Being genetically linked means two genes will tend to be
inherited separately
inherited together
degree of separateness vs togetherness is unrelated to the concept of linkage
The closer together two genes are on one chromosome the more:
loosely they are linked
tightly they are linked
Do chromosomes evolve over time? like interchange pieces, with genes possibly moving from, say Chromosome #1 to #3?
no way
sure
virtually EVERY aspect of organisms evolves over time--why not chromosomes?
Which is true about sex determination in different kinds of animals?
all animals use an "X-Y" system of sex chromosomes like humans do
several different systems of sex determination are used in different animal groups
Haplodiploid sex determination occurs in:
reptiles and fishes
ants, bees, and wasps
butterflies, birds, and certain fishes
mammals and amphibians
In haplodiploid sex determination (check all that are true)
a fertilized egg gives rise to a diploid female
an unfertilized egg gives rise to a haploid male
a female ant, bee, or wasp has two parents, but a male has no father
there are no sex chromosomes
You cross true-breeding purple flowers with true-breeding white flowers. You get all purple-flowered offspring. This tells you (check all that are true):
purple is dominant over white
the "white allele" is gone from these offspring
the offspring are all heterozygotes
the offspring are a mix of homozygotes and heterozygotes
You cross orange-flowered plants and get a ratio close to 3 to 1, orange to yellow flowers. This tells you:
orange is recessive, yellow dominant
both parents were heterozygotes
orange is dominant over yellow
one parent was homozygous dominant, the other homozygous recessive
In a generation of mice you see a phenotypic ratio, involving two separate traits, of 9:3:3:1. This makes you think of:
a dihybrid cross
a monohybrid cross
a cross involving one locus, with four alleles
a cross involving two loci with two alleles each
All genetic novelty is ultimately created through
mutation
natural selection
Mutation is
a "directed" process, such that a mutation is most likely to occur when it would be most useful
a random process
Darwin was able to figure out natural selection
because he knew, from Mendel's work, about the mechanism of heredity
even though he did not know the mechanism of heredity
