Sexual Reproduction and Inherited Traits
Homework
Background
In sexual reproduction offspring are inherit a mixture of traits from both parents. How
are these traits inherited? You can investigate this question by considering an imaginary
animal called the unimonster. Suppose this animal has only one pair of chromosomes.
Chromosomes carry genes, which control different genetic traits, such as hair color,
height, and other physical characteristics.
Different forms of a gene are called alleles.
The presence of different alleles on the
chromosomes of unimonsters determines
whether they have one horn or two horns.
During reproduction, parent unimonsters
pass on alleles to their offspring. In this
investigation, you will determine the
different allele combinations for the
offspring of two unimonsters and figure out
the number of horns the young unimonsters
will have.
Questions – you should be able to answer these questions before going on.
1. What are dominant and recessive alleles?
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2. Define genotype and phenotype.
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3. What does it mean to say that an organism is homozygous for a trait? Heterozygous for
a trait?
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4. How do the numbers of chromosomes in normal body cells compare with the number
of chromosomes in sex cells?
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5. During sexual reproduction, what fraction of chromosomes does each parent
contribute to its offspring?
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Procedure
1. Page one shows a mother and a father unimonster,
each with different genetic traits. The allele for two
horns is dominant over the allele for one horn.
2. The mother unimonster is heterozygous(Hh). This
means that she has one allele for two horns and one
allele for one horn. Each of her sex cells will have
either a chromosome with the two-horn allele or a
chromosome with the one-horn allele.
3. The father unimonster is homozygous (hh).
4. Fill in the Punnett square to the right, showing the
possible genetic combinations
5.. During sexual reproduction, the sex cells produced by the mother and father
unimonsters combine to form a fertilized egg. The fertilized egg will grow into a
young unimonster. Whether the young unimonster has one or two horns depends on
the alleles on the chromosome contributed by each parent during reproduction. Use
your Punnett square to draw horns on the unimonsters below. Remember that the
allele for two horns is dominant. Anytime the dominant allele (H) is present, the
unimonster will have two horns.
Questions:
1. Which young unimonster(s) are homozygous and have one horn?
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2. Which young unimonster(s) are heterozygous?
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3. Are any young unimonster(s) homozygous with two horns? Explain.
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4. If a mother unimonster is homozygous and has two horns, and a father unimonster is
homozygous and has one horn, what are the phenotypes and genotypes of the possible
offspring? Remember that the two-horn allele is dominant.
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5. Predict the phenotypes and genotypes of the offspring of a mother unimonster and a father
unimonster that are both heterozygous.
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