Genetics: Chromosomes and Traits

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Questions and Answers

What is the primary function of a chromosome in an organism?

A chromosome serves as a DNA molecule that contains part or all of the genetic material of an organism.

How does a sister chromatid differ from a homologous chromosome?

A sister chromatid is an identical copy of a single chromosome connected by a centromere, while a homologous chromosome is a pair of chromosomes from each parent that are similar but not identical.

Define the terms locus, gene, and allele, and explain their relationships.

A locus is a specific location on a chromosome, a gene is a DNA sequence coding for a trait, and an allele is a variation of a gene found at a locus.

Why can't all traits be represented in a Punnett square?

<p>Not all traits can be modeled with a Punnett square because it is designed for simple Mendelian traits, while complex or polygenic traits cannot be accurately depicted.</p> Signup and view all the answers

What is a lethal allele and how does it affect genetic cross results?

<p>A lethal allele is one that causes the death of an organism, influencing genetic cross results by skewing expected ratios of offspring.</p> Signup and view all the answers

Describe the processes by which sex is determined in animals.

<p>In many animals, sex is determined by sex chromosomes, like the XY system in humans, while in others, environmental factors can play a role.</p> Signup and view all the answers

Give an example of a polygenic trait and explain why it cannot be accurately predicted by a Punnett square.

<p>Height is a polygenic trait influenced by multiple genes, making it complex and unsuitable for prediction with a Punnett square.</p> Signup and view all the answers

How do the characteristics of homologous chromosomes assist in genetic diversity?

<p>Homologous chromosomes carry genes in the same order but may have different alleles, contributing to genetic variation when inherited from each parent.</p> Signup and view all the answers

What is temperature-dependent sex determination, and which group of animals exhibits this trait?

<p>Temperature-dependent sex determination is a phenomenon where the sex of an organism is determined by the temperature during a critical period of development, seen in some reptiles.</p> Signup and view all the answers

How do X-linked traits differ in their inheritance patterns compared to autosomal traits?

<p>X-linked traits are more commonly expressed in males due to them having only one X chromosome, while autosomal traits do not show such sex-based inheritance.</p> Signup and view all the answers

Contrast haploid and diploid cells, and explain how each type is produced.

<p>Haploid cells have one set of chromosomes (n) and are produced by meiosis, while diploid cells have two sets (2n) and are produced by mitosis.</p> Signup and view all the answers

What does incomplete penetrance mean, and what might cause it?

<p>Incomplete penetrance refers to situations where not all individuals with a dominant allele express the expected phenotype, often due to environmental factors or gene interactions.</p> Signup and view all the answers

How many alleles of a single gene can exist in a given population, and how many can a diploid individual possess?

<p>A population can possess many alleles of a single gene due to genetic diversity, while a diploid individual carries only two alleles for that gene.</p> Signup and view all the answers

Define polygenic traits and provide an example, along with some challenges in their study.

<p>Polygenic traits are influenced by multiple genes, resulting in continuous variation; an example is human height. Challenges include the interaction of numerous genes, environmental impacts, and difficulty isolating specific gene effects.</p> Signup and view all the answers

What is the XO chromosomal system, and in which organisms is it typically found?

<p>The XO chromosomal system involves females having one X chromosome (XO) and males having two (XX), and it is typically found in some insects, such as grasshoppers.</p> Signup and view all the answers

Explain how sex determination in clownfish is influenced by social hierarchy.

<p>In clownfish, social hierarchy can lead to sex change, where dominant females can change their sex to male if the male partner is removed or absent.</p> Signup and view all the answers

Males in the XY chromosome system have two X chromosomes.

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

All organisms exist primarily in a diploid stage.

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

Incomplete penetrance means that every individual with a dominant allele will express the trait.

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

A diploid individual can carry two alleles of a single gene, one from each parent.

<p>True (A)</p> Signup and view all the answers

Environmental factors have no effect on the expression of X-linked traits.

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

Polygenic traits only involve a single gene and show distinct categories of variation.

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

Temperature-dependent sex determination occurs in some reptiles.

<p>True (A)</p> Signup and view all the answers

Haploid cells are produced through mitosis.

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

Humans have 46 chromosomes that come in 23 pairs.

<p>True (A)</p> Signup and view all the answers

A homologous chromosome is an identical copy of another chromosome.

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

A Punnett square can be used to predict the outcomes of any genetically inherited traits.

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

In reptiles, sex determination can be influenced by temperature factors.

<p>True (A)</p> Signup and view all the answers

Lethal alleles can only affect individuals in the homozygous form.

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

An allele is a specific location on a chromosome where a gene is found.

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

Complex traits, such as height, can be represented accurately using a Punnett square.

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

Sister chromatids are formed during DNA replication and are identical copies of a chromosome.

<p>True (A)</p> Signup and view all the answers

Flashcards

Chromosome

A DNA molecule carrying genetic material.

Sister Chromatid

Two identical copies of a chromosome joined at a centromere.

Homologous Chromosome

Similar chromosomes with the same genes, but potentially different alleles.

Lethal Allele

An allele causing death, often early in development.

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Punnett Square

A diagram showing possible genetic outcomes of a cross.

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Gene

A DNA sequence coding for a protein and determining a trait.

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Allele

Different versions of a gene at a specific location (locus).

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Sex Determination

The biological process of determining the sex of an individual.

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X-linked inheritance

Genes located on the X chromosome. Males (XY) are more likely to express X-linked recessive traits than females (XX).

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Haploid/Diploid Cells

Haploid (n) cells have one set of chromosomes, while diploid (2n) cells have two sets. Haploid cells are gametes.

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Incomplete Penetrance

Not all individuals with a dominant allele express the associated trait.

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Number of alleles per gene in a population vs. individual

Many alleles of a single gene can exist in a population, but a diploid individual only carries two alleles per gene.

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Polygenic traits

Traits influenced by multiple genes, leading to continuous variation.

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XY sex determination

Sex determination system common in mammals, with males having XY chromosomes and females XX chromosomes.

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ZW sex determination

Sex determination system common in birds and some reptiles, with males having ZZ chromosomes and females ZW chromosomes.

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XO sex determination

Sex determination system found in some insects, like grasshoppers, with females XO and males XX chromosomes.

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Sister Chromatid

Identical chromosome copies, joined at a centromere, formed during DNA replication.

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Homologous Chromosomes

Similar chromosomes (same genes), inherited from each parent.

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Lethal Allele

An allele causing death, often early in development.

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Punnett Square Limitations

Simplistic genetic cross predication, only useful for single-gene, two-allele traits.

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Sex Determination (Animals)

The biological process of determining sex, often specified by sex chromosomes (XY or ZW systems) or other factors (like temperature).

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Locus

Specific location of a gene or genetic marker on a chromosome.

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Gene and Allele Relationship

Genes code for traits, while alleles are different versions of a gene at the same locus.

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Complex Traits and Punnett Squares

Punnett squares don't accurately depict complex traits like polygenic traits or those influenced by environment; they're limited to single-gene traits.

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X-linked Inheritance

Genes located on the X chromosome; in males (XY), it's more likely to express recessive traits than in females (XX) because they have one X chromosome.

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Haploid/Diploid Cells

Haploid cells (n) have one set of chromosomes, diploid cells (2n) have two. Haploid cells are typically for reproduction.

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Incomplete Penetrance

Not all individuals with a dominant allele show the associated trait.

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Alleles per gene (population vs. individual)

Many alleles of a gene exist in a population; a diploid individual only carries two.

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Polygenic Trait

A trait influenced by multiple genes, often showing continuous variation in a population, like human height.

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XY Sex Determination

Sex determination system, common in mammals; XY chromosomes determine male, XX for female.

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Temperature-dependent sex determination

A mechanism for which the sex of an offspring is determined by the temperature during embryonic development.

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Social Sex Determination

Sex is determined by social factors, like hierarchy.

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Study Notes

Chromosome, Sister Chromatid, and Homologous Chromosome

  • Chromosome: A DNA molecule containing an organism's genetic material. Humans have 46 chromosomes in 23 pairs.
  • Sister Chromatid: Two identical copies of a single chromosome, connected by a centromere, created during DNA replication.
  • Homologous Chromosome: Chromosomes similar in size, shape, and genetic content, one inherited from each parent. They share the same genes but may have different alleles.

Locus, Gene, and Allele

  • Locus: A specific location on a chromosome where a gene is found.
  • Gene: A DNA sequence that codes for a protein and determines a trait. Each gene has a specific locus.
  • Allele: Different versions of a gene at a given locus. For example, eye color genes have alleles for blue or brown eyes.

Punnett Squares and Traits

  • Punnett squares are best for simple Mendelian traits (one gene, two alleles).
  • Complex traits (e.g., polygenic, environmental influences) cannot be accurately predicted using Punnett squares.
  • Examples of traits that can be represented by Punnett squares are blood types (ABO). Height and skin color, however, are polygenic traits.

Lethal Alleles

  • Lethal Allele: An allele causing an organism's death, often early in development (homozygous or heterozygous).
  • Impact on Genetic Crosses: Lethal alleles skew expected ratios in genetic crosses. For example, if a recessive condition is lethal, only heterozygous and homozygous dominant individuals survive.

Sex Determination

  • Methods of Sex Determination: Sex in animals varies with environmental, social, or chromosomal factors.
  • Environmental Factors: Temperature (reptiles) or social status (certain fish).
  • Chromosomal Factors (XY System): Males have XY; females have XX chromosomes—common in mammals.
  • Chromosomal Factors (ZW System): Males have ZZ; females have ZW chromosomes—common in birds, some reptiles, and some fish.
  • Chromosomal Factors (XO System): Females have XO; males have XX chromosomes—common in some insects like grasshoppers.

X-linked Inheritance

  • X-linked Inheritance: Genes located on the X chromosome.
  • Difference from Autosomal Genes: X-linked traits show different inheritance patterns, often affecting males more frequently. Autosomal genes are not sex-linked.

Haploid and Diploid Cells

  • Haploid (n): Cells with one set of chromosomes (gametes).
  • Diploid (2n): Cells with two sets of chromosomes, one from each parent (body cells).
  • Production Methods: Haploid cells are produced by meiosis; diploid cells are produced by mitosis.
  • Presence in Organisms: Not all organisms have both. Many plants and some fungi alternate between haploid and diploid phases; animals are primarily diploid.

Incomplete Penetrance

  • Incomplete Penetrance: Not all individuals with a dominant allele express the trait.
  • Reasons: Environmental factors, interactions with other genes, or developmental processes.

Alleles in Populations and Individuals

  • Population Alleles: Many alleles of a single gene can exist in a population.
  • Diploid Individual Alleles: A diploid individual has only two alleles for a given gene.

Polygenic Traits

  • Polygenic Trait: Traits influenced by multiple genes.
  • Examples: Human height, skin color.
  • Challenges: Studying polygenic traits is complex due to multiple genes, environmental factors, and isolating individual gene effects.

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