Download Genetics Study Guide - Norwell Public Schools

Name__________________________________________________ Class___________ Date_______________
Review Guide
Genetics
The fundamental principles of genetics were first discovered by ________________________.
What type of plant did he breed? ___________________.
True-breeding parental plants are called the ______ generation. Their hybrid offspring are
called the _______ generation.
What is the F2 generation?
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A monohybrid cross is the mating of two parents that differ in
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Define the following terms:
Gene:
Allele:
Homozygous:
Heterozygous:
Dominant Allele:
Recessive Allele:
Co-dominance:
Incomplete Dominance:
Polygenic:
Sex-linked gene:
Carrier:
What does the Law of Segregation state?
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Describe the difference between an individual’s genotype and their phenotype:
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How can two plants with different genotypes for a particular gene be identical in phenotype?
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If an individual is heterozygous (Gg) for a gene, then according to the law of segregation, each
gamete formed by this individual will have either the ______ allele or the ______ allele.
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What is the name of the process that cells go through to form gametes? _____________________
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Set up a Punnett square for this monohybrid cross: Pea plant that is homozygous recessive for
flower color crossed with a pea plant that is heterozygous for flower color.
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• What are the possible phenotypes that this mating could produce?
• In what ratio would these phenotypes occur?
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What is a dihybrid cross?
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What does the Law of Independent Assortment state?
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Dihybrid cross problem: You are observing the inheritance of two different genes in Labrador
retrievers—the gene for coat color and the gene for vision. A black coat color is dominant over a
brown coat color, and normal vision is dominant over blindness. You breed two dogs that are
heterozygous for both genes.
• Assign alleles to:
black coat: ____
brown coat: ____
normal vision: ____
blindness: ____
• Assign genotypes to each parent in your cross: ____________ x _____________
• What are the allele combinations in the gametes of each parent? ______ ______ ______
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• Create a Punnett square that shows the possible genotypes of the offspring:
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• What is the phenotypic ratio of the offspring? _____________________
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If a mother is a carrier of Tay-Sachs disease, an autosomal recessive disorder, and her husband
is healthy and not a carrier…
• What are the genotypes of the parents?
• What are the chances that their children will have the disease?
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• Draw a pedigree of this family if they have two boys and two girls.
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How can a child inherit a recessive disorder if both parents are not affected by the disease?
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An example of incomplete dominance is humans: Hypercholestemia
• A recessive allele can cause hypercholestemia—dangerously high blood cholesterol levels.
• What kind of cholesterol levels would be found in an individual who…
o Is homozygous dominant (HH)? ___________________
o Is heterozygous (Hh)? ___________________________
o Is homozygous recessive (hh)? ________________________
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The ABO blood group phenotype in humans involves three alleles of a single gene.
• How do we symbolize these three different alleles? _______ _______ _______
• Both the _____ allele and the ______ allele are dominant to the ______ allele.
• The A and B alleles are ______________________, because both alleles are expressed in
heterozygous individuals.
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How is codominance different from incomplete dominance?
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What are the names of the human sex chromosomes? ____________________
• Females have __________ while males have __________.
A human female’s gametes all contain one _______ chromosome, while a human male’s gametes
all contain either _________ or ________ chromosome.
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A gene located on either sex chromosome is called a ____________________________, although
the term refers specifically to a gene on the ________ chromosome.
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White eye color in fruit flies is an X-linked recessive trait.
• If a female fruit fly homozygous for red eyes is mated with a white-eyed male, will
any of their offspring have white eyes? Explain.
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• A female, red-eyed fruit fly that is a carrier of the recessive allele is mated with a
red-eyed male. Draw a Punnett square to show the potential genotypes of their
offspring.
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▪ In what ratio do the phenotypes occur?
▪ Why is that only male offspring produced from this cross could
possibly have white eyes?
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▪ In order for a female with white eyes to be produced, it would have
to inherit
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Why do sex-linked recessive disorders affect males more often than females?
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Why is it that only females can be considered carriers of a sex-linked disorder?
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Name two sex-linked recessive disorders in humans:
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Practice Problems
1. A couple are both phenotypically normal, but their son suffers from hemophilia (sexlinked recessive!). What fraction of their potential children are likely to suffer from
hemophilia? What fraction are likely to be carriers?