AP Biology Unit 5: Heredity

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Questions and Answers

What happens during prophase one of meiosis?

  • Sister chromatids move apart to opposite poles
  • Homologous chromosomes condense and line up (correct)
  • Nuclear envelopes form around haploid cells
  • Replication of DNA occurs for the first time

What is the main consequence if meiosis does not occur during gamete formation?

  • The genetic variation among offspring increases.
  • The chromosome number doubles with each generation. (correct)
  • The chromosome number remains stable.
  • All offspring will exhibit dominant traits.

Which process introduces genetic variation during meiosis?

  • Crossing over during prophase one (correct)
  • Separation of sister chromatids in meiosis two
  • Independent assortment during anaphase one
  • Replication of chromatids before meiosis

In terms of susceptibility to malaria, how does CLE cell disease affect an individual?

<p>It provides complete resistance to malaria. (A)</p> Signup and view all the answers

How do the daughter cells produced by meiosis compare to those produced by mitosis?

<p>Daughter cells from meiosis are haploid and genetically distinct (D)</p> Signup and view all the answers

What genetic condition is associated with the presence of three copies of chromosome 21?

<p>Down syndrome (B)</p> Signup and view all the answers

What effect does phenotypic plasticity have on individuals with the same genotype?

<p>They show varying phenotypes due to environmental factors. (C)</p> Signup and view all the answers

What is a key difference between the metaphase of mitosis and the metaphase of meiosis?

<p>In mitosis, sister chromatids are present while in meiosis, homologous chromosomes are present (B)</p> Signup and view all the answers

Which statement accurately describes telophase in meiosis?

<p>Nuclear envelopes reform around two new haploid nuclei (C)</p> Signup and view all the answers

Which disease has an autosomal dominant inheritance pattern and is neurodegenerative?

<p>Huntington's disease (D)</p> Signup and view all the answers

What type of inheritance is characterized by the mother passing the trait to all offspring if she has the trait?

<p>Maternal inheritance (C)</p> Signup and view all the answers

What does the presence of two unaffected parents and one affected child indicate about the child's inheritance pattern?

<p>Autosomal recessive inheritance (C)</p> Signup and view all the answers

Which statement best describes the law of independent assortment?

<p>Alleles segregate into different gametes independently of one another. (D)</p> Signup and view all the answers

Which type of inheritance would likely produce an affected offspring when both parents are unaffected?

<p>Autosomal recessive inheritance (D)</p> Signup and view all the answers

What characteristic defines linked genes?

<p>They are located closely together on the same chromosome. (A)</p> Signup and view all the answers

What ratio is observed in complete dominance for a monohybrid cross?

<p>3:1 (D)</p> Signup and view all the answers

Which scenario describes co-dominance?

<p>AB blood type where both A and B traits are expressed. (A)</p> Signup and view all the answers

How does incomplete dominance differ from co-dominance?

<p>Incomplete dominance results in a third phenotype that mixes the two traits. (C)</p> Signup and view all the answers

Which of the following traits result from autosomal inheritance?

<p>Blood type variations determined by ABO alleles. (D)</p> Signup and view all the answers

What is a key characteristic of dihybrid inheritance?

<p>Requires analysis of two traits simultaneously. (D)</p> Signup and view all the answers

What is the significance of crossing over during prophase one of meiosis?

<p>It allows for the exchange of genetic information between chromatids. (A)</p> Signup and view all the answers

During which phase of meiosis are homologous chromosomes arranged on the metaphase plate?

<p>Metaphase I (C)</p> Signup and view all the answers

How does meiosis differ from mitosis in terms of daughter cells produced?

<p>Meiosis produces four genetically distinct haploid cells. (A)</p> Signup and view all the answers

What role do independent assortment and crossing over play during meiosis?

<p>They contribute to genetic diversity among gametes. (A)</p> Signup and view all the answers

Which of the following accurately characterizes the end products of meiosis?

<p>Meiosis results in four haploid cells that are genetically distinct. (C)</p> Signup and view all the answers

What is the primary effect of being homozygous recessive for CLE cell disease with respect to malaria susceptibility?

<p>Complete resistance to malaria (A)</p> Signup and view all the answers

Which of the following conditions is an example of non-disjunction leading to the presence of an extra chromosome?

<p>Down syndrome (B)</p> Signup and view all the answers

How does phenotypic plasticity influence individuals with the same genotype?

<p>Their phenotype may differ based on environmental conditions (D)</p> Signup and view all the answers

What determines whether an individual with Huntington's disease expresses symptoms?

<p>Symptoms do not emerge until later in life with one dominant allele (B)</p> Signup and view all the answers

What is the effect of an acidic versus alkaline environment on hydrangea flowers?

<p>Acidic conditions yield blue flowers (A)</p> Signup and view all the answers

What is the expected phenotypic ratio resulting from a dihybrid cross demonstrating complete dominance?

<p>9:3:3:1 (C)</p> Signup and view all the answers

In the context of genetics, how does maternal inheritance differ from standard inheritance patterns?

<p>Traits are inherited through mitochondrial DNA. (A)</p> Signup and view all the answers

What pattern of inheritance is associated with blending traits, as seen when two colors create a third?

<p>Incomplete dominance (B)</p> Signup and view all the answers

What does the term 'autosomal inheritance' refer to?

<p>Traits inherited on one of the non-sex chromosomes. (C)</p> Signup and view all the answers

Which of the following statements best describes co-dominance?

<p>Both alleles in the heterozygote are fully expressed. (C)</p> Signup and view all the answers

What type of inheritance is indicated when offspring inherit a trait exclusively from their mother, regardless of the father's status?

<p>Mitochondrial inheritance (C)</p> Signup and view all the answers

Which scenario would most likely indicate an autosomal recessive inheritance pattern?

<p>Two unaffected parents have an affected child (B)</p> Signup and view all the answers

In the context of genetic linkage, what does a higher recombination percentage between two genes indicate?

<p>The genes are located far apart on the same chromosome (B)</p> Signup and view all the answers

What does the law of segregation state regarding allele inheritance?

<p>Alleles for a trait will separate into different gametes (D)</p> Signup and view all the answers

Which inheritance pattern is suggested by observing an equal number of affected males and females in a pedigree?

<p>Autosomal recessive inheritance (C)</p> Signup and view all the answers

Flashcards

Crossing Over

The process of homologous chromosomes exchanging genetic information during prophase I of meiosis.

Anaphase II

Sister chromatids are pulled apart to opposite poles of the cell, resulting in four haploid daughter cells. This occurs during meiosis II.

Prophase I

The first stage of meiosis where homologous chromosomes pair up and exchange genetic information.

Independent Assortment

The random alignment of homologous chromosomes on the metaphase plate during meiosis I.

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Meiosis

A type of cell division that produces four haploid daughter cells, each with half the number of chromosomes as the parent cell. It occurs in gametes.

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Codominance

A type of inheritance where the heterozygous genotype expresses both alleles' phenotypes separately. Both traits appear, not blended.

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Incomplete Dominance

A type of inheritance where the heterozygous genotype expresses a blended phenotype, a mix of both alleles' traits.

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Autosomal Inheritance

Describes genes located on autosomes, the non-sex chromosomes. Autosomes are numbered from 1 to 22.

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Sex-linked Inheritance

Describes genes located on the sex chromosomes (X or Y). These genes influence sex-linked traits.

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Maternal Inheritance

A type of inheritance where the mitochondria's DNA, passed solely from the mother, influences traits.

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Linkage

A type of inheritance where genes are located on the same chromosome and are inherited together.

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Law of Segregation

The separation of homologous chromosomes during meiosis, ensuring each gamete receives one copy of each chromosome.

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Law of Independent Assortment

The independent assortment of chromosomes during meiosis, resulting in diverse combinations of maternal and paternal chromosomes in gametes.

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Sickle Cell Trait

A condition where an individual carries one copy of the sickle cell allele (HbS) and one copy of the normal allele (HbA). This results in a milder form of the disease and also provides resistance to malaria.

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Tay-Sachs Disease

A rare genetic disorder that affects the nervous system due to a buildup of fatty substances in the brain. Individuals lack the necessary enzymes to break down these fats effectively.

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Huntington's Disease

A genetic disorder that causes a progressive breakdown of nerve cells in the brain. It's an autosomal dominant disorder, meaning that having just one copy of the mutated gene is enough to cause the disease.

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Down Syndrome

A genetic condition characterized by the presence of an extra copy of chromosome 21. It can lead to a range of physical and developmental challenges.

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Phenotypic Plasticity

A genetic disorder caused by changes in gene expression due to environmental factors. Individuals with the same genotype can exhibit different phenotypes depending on their environment.

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Meiosis II

The division of sister chromatids during meiosis II, resulting in four daughter cells, each with half the number of chromosomes as the parent cell.

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Linked Genes

Traits controlled by genes located on the same chromosome tend to be inherited together.

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Sickle Cell Disease

A condition where a person inherits two copies of the sickle cell allele, leading to severe symptoms like chronic pain, fatigue, and organ damage. This trait is also linked to resistance to malaria.

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Non-Disjunction

The process of homologous chromosomes failing to separate properly during meiosis, resulting in an abnormal number of chromosomes in the daughter cells.

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Study Notes

Meiosis

  • Meiosis is similar to mitosis initially, with prophase I.
  • Chromatin condenses; sister chromatids and homologous chromosomes pair up.
  • Crossing over occurs: Non-sister chromatids from maternal and paternal chromosomes exchange genetic material.
  • Parental chromosomes (outer ones) vs. recombinant chromosomes (inner, with crossing over). Crossing over produces genetically distinct chromatids.
  • Prophase prepares for division.
  • Metaphase I: Homologous chromosomes line up on metaphase plate. This differs from mitosis where sister chromatids line up.
  • Independent assortment: Maternal and paternal chromosomes align independently on metaphase plate, contributing to genetic variation.
  • Anaphase I: Homologous chromosomes move to opposite poles.
  • Two haploid cells result from Meiosis I (cytokinesis).
  • No DNA replication between Meiosis I and II.
  • Meiosis II: Similar steps to Meiosis I (prophase II, metaphase II, anaphase II, telophase II). Sister chromatids separate.
  • Four haploid cells result.
  • Meiosis I deals with homologous chromosomes; Meiosis II with sister chromatids.
  • Mitosis vs. Meiosis:
    • Both start as diploid (2n).
    • Mitosis replicates and divides once (2n → 2n). Daughter cells identical to parent.
    • Meiosis replicates and divides twice (2n → 4n →4 haploid cells). Daughter cells genetically distinct due to crossing over and independent assortment.
  • Crossing over and independent assortment in prophase I and metaphase I are critical for genetic variation.

Inheritance Patterns

  • Complete dominance: Dominant trait masks recessive. Functional vs. nonfunctional proteins. Homozygous dominant and heterozygous are indistinguishable.

  • Codominance: Both traits are expressed independently. AB blood type, example of both A and B glycoproteins.

  • Incomplete dominance: Traits blend. Heterozygous exhibits a blended phenotype (e.g., blue + yellow = green).

  • Monohybrid: Heterozygous for one trait. Ratios can be calculated with Punnett Squares (3:1).

  • Dihybrid: Heterozygous for two traits. 9:3:3:1 ratio (complete dominance).

  • Dominance vs. Prevalence: Dominant doesn't equal common. Five fingers = homozygous recessive example; six fingers = a dominant trait.

  • Autosomal inheritance: On non-sex chromosomes.

  • Sex-linked inheritance: On sex chromosomes (X or Y).

  • Maternal inheritance: Inherited from mitochondria or chloroplasts (passed from mother).

  • Linkage: Genes located on the same chromosome tend to be inherited together.

  • Recombinant frequencies: Used to determine the physical distance between linked genes (map units). The % of recombinant offspring indicates the distance between linked genes.

Pedigree Analysis

  • Autosomal recessive: Two unaffected parents + affected child. Equal frequency of affected males and females.
  • Sex-linked recessive: Affected males only have one X chromosome. More males than females affected. Affected males inherit the trait from heterozygous mothers.
  • Autosomal dominant: Affected individuals present in every generation.
  • Maternal inheritance: All offspring of an affected mother have the trait.

Genetic Disorders

  • Sickle cell disease: Autosomal recessive. Heterozygous: increased resistance to malaria.
  • Tay-Sachs: Autosomal recessive. Lipid buildup in brain.
  • Huntington's disease: Autosomal dominant. Neurodegenerative, symptoms appear later in life.
  • Down syndrome: Trisomy 21 (three copies of chromosome 21), non-disjunction.
  • Cri du chat: Deletion of a portion of chromosome 5.
  • Klinefelter syndrome: XXY (extra X chromosome).
  • Turner syndrome: XO (lack of second sex chromosome).
  • Phenotypic plasticity: Environment influences phenotype. Examples include rabbit fur color, bird plumage, hydrangea flower color.

Meiosis and Inheritance (Specific Examples)

  • Effect of non-occurrence of meiosis: Chromosome number doubles each generation if meiosis does not occur.
  • Independent Assortment and crossing over: Data showing crossing over between genes leads to recombinant phenotypes.
  • Test crosses: Predictions for offspring phenotypes when crossing with homozygous recessive.
  • Pedigree analysis: Determining genotypes and inheritance patterns from family history data.
  • Chi-square test: Statistical analysis to determine if observed data matches predicted ratios. Determines if parent genotypes match the observed phenotypes. Chi-square analysis is used to determine if observed data fits the predicted ratios, considering the role of crossing over or independent assortment (using observed and expected frequencies). A smaller Chi-square value indicates better fit.

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