Genetic Traits, Genes and Alleles

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Questions and Answers

In genetics, what distinguishes alleles from genes?

  • Alleles are the genetic makeup and genes are the physical expression of genetic traits.
  • Genes are the physical expression of genetic traits, while alleles are the genetic makeup.
  • Genes contain the information for a particular genetic trait, while alleles are slightly different versions of that gene. (correct)
  • Alleles are basic units that affect genetic traits, while genes are slightly different versions of a trait.

If a plant has a genotype of 'Aa' for a particular trait, and 'A' is dominant, how would you describe the plant?

  • Homozygous dominant, displaying the 'A' trait.
  • Homozygous recessive, displaying the 'a' trait
  • Heterozygous, displaying a blend of 'A' and 'a' traits.
  • Heterozygous, displaying the 'A' trait. (correct)

If a certain trait is X-linked recessive, which statement is most accurate?

  • Males and females are equally likely to express the trait.
  • Females are more likely to express the trait.
  • Males are more likely to express the trait. (correct)
  • The trait will only be expressed in homozygous individuals, regardless of sex.

Which of Mendel's principles explains that the two alleles for a trait separate during gamete formation?

<p>Law of Segregation (D)</p> Signup and view all the answers

How does the Law of Independent Assortment relate to the inheritance of different traits?

<p>It indicates genes for different traits are inherited independently if they are on different chromosomes. (B)</p> Signup and view all the answers

In genetic terms, what does the term homozygous mean?

<p>Having two identical alleles for a particular gene. (C)</p> Signup and view all the answers

Which of the following best describes the relationship between genotype and phenotype?

<p>Genotype determines the phenotype. (D)</p> Signup and view all the answers

What is the significance of the 'P generation' in Mendel's genetic crosses?

<p>It represents the parental generation. (B)</p> Signup and view all the answers

How does a dominant allele affect the phenotype when paired with a recessive allele in a heterozygous individual?

<p>The recessive allele is masked by the dominant allele. (A)</p> Signup and view all the answers

Which of the following is the most accurate definition of 'invariant trait'?

<p>A trait that is the same in all individuals of a species. (D)</p> Signup and view all the answers

Flashcards

Genetic Trait

Any inherited characteristic of an organism.

Invariant Traits

Traits that are the same in all individuals of a species.

Variable Traits

Traits that vary among individuals.

Gene

Basic unit of information that affects genetic traits.

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Alleles

Slightly different versions of a gene.

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Genotype

The genetic makeup of an individual (not visible).

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Phenotype

The physical expression of a genetic trait (what you see).

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Dominant Allele

An allele that prevents another allele from affecting the phenotype.

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Recessive Allele

An allele that has no effect on the phenotype when paired with a dominant allele. Requires two copies to show.

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Homozygous

Having two identical alleles for a gene.

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Heterozygous

Having two different alleles for a gene.

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Study Notes

Genetic Traits

  • Genetic traits are inherited characteristics of an organism.
  • Invariant traits are the same in all individuals of a species.
    • Examples include having two eyes, two legs, and two arms.
  • Variable traits differ among individuals.
    • Examples include curly hair and eye color changes.

Genes and Alleles

  • A gene is the basic unit of information that affects genetic traits.
    • Genes contain the information or code for a particular genetic trait.
  • Alleles are slightly different versions of a given gene.
  • Genotype refers to the genetic makeup of an individual for a given trait and cannot be seen.
  • Phenotype is the physical expression of a trait's genetic makeup and can be seen.

Dominant vs. Recessive Alleles

  • A dominant allele prevents a second allele from affecting the phenotype when the two alleles are together.
    • If a child gets one dominant gene from either parent, they will show that trait.
  • A recessive allele has no effect on the phenotype when paired with a dominant allele.
    • A child needs two copies of the recessive gene, one from each parent, to show that trait.

Homozygous vs. Heterozygous

  • Homozygous refers to a genotype consisting of two copies of the same allele.
    • Homo=same.
    • Example: BB or bb
  • Heterozygous individuals have two different versions of a gene, one inherited from each parent.
    • Hetero=Different.
    • Example: Bb
    • The individual will show the phenotype of the dominant allele.

X-Linked (Sex-Linked)

  • The gene is found on the X chromosome.
  • Males, having only one X chromosome, are more likely to show these traits, even if the gene is recessive.

Gregor Mendel's Principles of Genetics

  • Law of Segregation: During gamete formation (sperm and egg cells), the two alleles for a given trait separate (segregate) so that each gamete carries only one allele for each gene.
    • The two alleles of a gene are separated during meiosis 1 and end up in different gametes.
  • Law of Dominance: When two different alleles for a trait are present in an organism, the dominant allele is expressed, while the recessive allele is masked.
  • Law of Independent Assortment: Genes for different traits are inherited independently of each other, provided they are located on different chromosomes or are far apart on the same chromosome.
  • Chromosome Theory of Inheritance: Genes are located on chromosomes, and the inheritance of traits is determined by the movement of chromosomes during meiosis.
  • Codominance: When the effects of two alleles are equally visible in the phenotype.
  • Pleiotropy: When a single gene influences a number of genetic traits.
  • Polytrophy:

Mendel's Genetic Crosses

  • Genetic crosses were performed as controlled mating experiments to examine how a particular trait is inherited.
  • P generation: Parental offspring.
  • F1 Generation: First generation of offspring.
  • F2 Generation: Results of crossing the F1 generation.
  • Crossing the P1 generation results in the F1 generation, and crossing the F1 generation results in the F2 generation.

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