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Questions and Answers
What phenotypic ratio is expected in the offspring from a cross between a homozygous solid-winged dad and a homozygous polka-dotted mom?
Which of the following best describes the principle of incomplete dominance?
How many alleles can an individual inherit for a single gene that has multiple alleles?
In which genetic phenomenon do multiple genes influence a single trait?
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Which of the following statements is true regarding the inheritance of traits with multiple alleles?
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What is the expected outcome for daughters when a colorblind dad mates with a mom with normal vision?
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How does inbreeding primarily affect a population genetically?
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What is a consequence of inbreeding in dog breeds?
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What might be a safeguard against inbreeding in human populations?
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What type of inheritance pattern is observed when a red carnation and a white carnation produce all pink offspring?
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In a TT x Tt cross, what is the expected ratio of tall to short plants?
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What requirement must be met for expressing an autosomal recessive disease?
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What led to the genetic problems associated with the Hapsburg family and Queen Victoria's lineage?
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What does a diploid organism possess in terms of chromosomes?
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Which of the following best describes the function of a gene?
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What characterizes a recessive allele?
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How are homozygous and heterozygous individuals differentiated?
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What role do mutations play in the formation of different alleles?
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What is a characteristic trait of dominant alleles?
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What is the phenotype of an individual primarily determined by?
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In a genetic cross, what is the purpose of the controlled mating experiment?
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What does Mendel's Law of Segregation state about alleles during gamete formation?
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In a cross between true-breeding plants with purple flowers (YY) and white flowers (yy), which generation will be heterozygous?
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Which of the following describes the concept of dominant alleles as stated by Mendel?
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What ratio of dominant to recessive phenotypes is typically expected in the F2 generation?
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What is indicated by the term 'filial' in genetics as used by Mendel?
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Which principle states that genes do not influence each other's sorting into gametes?
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When crossing two heterozygous plants (Pp), what are the possible genotypes for their offspring?
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If a trait is controlled by alleles that show complete dominance, how would an organism with two recessive alleles appear?
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How does a Punnett square help in genetic crosses?
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Which blood type combination would indicate a child has an AB blood type?
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What is the main difference between codominance and incomplete dominance in genetic traits?
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In the context of epistasis, what is the primary role of Gene C as described?
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Which of the following describes pleiotropy correctly?
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Which of the following traits is considered polygenic?
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How would a parent with a whole chromosome defect, such as Down Syndrome, affect their child's genetic inheritance?
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Which statement regarding the influence of environment on polygenic traits is true?
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What characterizes the blood type of an individual with genotype IBi?
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What genetic disorder is caused by a mutation in the Fibrillin 1 gene?
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What could lead to a person with Type O blood having a child with Type AB blood?
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Study Notes
Mendel's Principles of Inheritance
- Mendel proposed that offspring inherit two "units" of genetic information - one from each parent, called alleles.
- One allele is inherited from the egg (mother), and one from the sperm (father).
- These units combine to form the offspring's genotype.
Genetic Crosses
- A true-breeding plant is one that produces offspring with the same phenotype as the parent.
- The P generation refers to the true-breeding parental plants.
- The F1 generation is the first filial generation.
- The F2 generation is the second filial generation.
- The F2 generation demonstrates a predictable ratio of dominant to recessive phenotypes (3:1).
Summary of Mendel's Concepts
- Alternative versions of genes cause variation in inherited traits.
- Offspring inherit one copy of a gene from each parent.
- A dominant allele has exclusive control over the phenotype when paired with a different allele (Law of Dominance).
- Two copies of a gene segregate during meiosis and end up in different gametes (Law of Segregation).
- Genes do not influence each other regarding the sorting of alleles into gametes (Law of Independent Assortment).
- Gametes fuse during fertilization without regard to the alleles they carry.
Law of Segregation
- The Law of Segregation can be illustrated using a Punnett square.
- The genotypes of each parent are listed, and alleles are segregated to represent the gametes.
- A Punnett square shows the probability of genotypes and phenotypes in the offspring.
Incomplete Dominance
- Incomplete dominance occurs when the heterozygote displays an intermediate phenotype.
- Neither allele exerts its full effect on the phenotype.
- If heterozygous offspring are bred, the parental features reappear. (e.g., red + white snapdragons produce pink flowers).
Multiple Alleles
- Multiple alleles exist when there are three or more alleles for a gene (but an individual still inherits only two).
- Example: Human blood groups have three alleles: IA, IB, and i.
- These alleles produce four blood groups: A, B, AB, and O.
Codominance
- Codominance occurs when both parental alleles are equally visible in the heterozygote.
- Both parental phenotypes are expressed together in the offspring.
- Human blood groups show codominance. For example:
- IAIA or IAi = Type A
- IBIB or IBi = Type B
- IAIB = Type AB
- ii = Type O
Epistasis
- Epistasis refers to the interaction of genes where the phenotypic effect of alleles of one gene is dependent on the alleles present for another gene.
- Example: In mice, coat color is determined by Gene B:
- BB or Bb = black
- bb = brown
- Gene C also influences coat color:
- CC or Cc = the color determined by Gene B.
- cc = white, regardless of Gene B alleles.
- Gene C is epistatic to Gene B.
Pleiotropy
- Pleiotropy occurs when a single gene influences multiple traits.
- Example: Albinism affects different traits such as:
- Absence or reduced melanin production
- Skin color
- Vision problems
- Albino mice are white because of epistatic effects of Gene C on Gene B.
Polygenic Traits
- Polygenic traits are determined by two or more genes.
- They result in a continuous distribution of the range of traits (e.g., body size, height, skin color).
- Skin color is influenced by at least three genes that control melanin production and environmental factors.
Human Genetic Disorders
- Human genetic disorders can arise from gene or whole chromosome defects.
- For a disorder to be inherited, the parent can:
- Show and have the disorder.
- Be asymptomatic and a carrier for the disorder.
- Not have the disorder seen in the child because it is a whole chromosome condition and not allele-based.
Genetic Testing
- Genetic testing can be used to determine if an individual carries a gene for a specific disorder.
- For example, a colorblind dad and a mom with normal vision can have offspring with the following outcomes:
- Girls are carriers for the disorder.
- Boys are affected by the disorder.
Inbreeding
- Inbreeding is the mating of closely related organisms by ancestry.
- It increases the risk of recessive alleles remaining in the population.
- This is more likely to occur in small or isolated populations.
- Examples of inbreeding include:
- Dog breeds
- The Habsburg family
- Queen Victoria of England
- Racehorses
Essential Terms in Genetics
- Diploid: having two copies of each chromosome, one paternal and one maternal. In humans, 2n = 46.
- Haploid: reproductive cells have only one copy of each chromosome (in humans, n = 23).
- Gene: portion of DNA that governs one or more genetic traits.
- Allele: an alternative version of a gene.
- Genotype: the allelic makeup responsible for an individual's phenotype.
- Phenotype: the expression of a genetic trait.
Somatic Cells are Diploid
- Somatic cells are body cells that have two sets of chromosomes (one from each parent).
- This makes them diploid.
Alleles in an Individual
- Dominant allele: exerts control over the phenotype.
- Recessive allele: has no effect on the phenotype when paired with a dominant allele.
- Homozygote: an individual with two copies of the same allele.
- Heterozygote/Heterozygous: an individual with two different alleles.
Mutations in Alleles
- Different alleles arise from mutations, changes in the DNA that make up a gene.
- Mutations can be harmful, neutral, or beneficial.
- Harmful mutations tend to be recessive alleles.
- Neutral mutations produce almost identical protein to the original.
- Beneficial mutations improve function.
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Description
Test your knowledge on Mendel's principles of inheritance, including the concepts of alleles, genetic crosses, and the F1 and F2 generations. Understand how traits are inherited and the significance of dominant and recessive alleles. This quiz covers the essential foundations of genetics as proposed by Gregor Mendel.
