CYTOGENETICS FINALS
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Questions and Answers

What does the term 'proband' refer to in a family genetic study?

  • The first individual diagnosed with a genetic disorder (correct)
  • An individual who is the latest to exhibit symptoms
  • The family member with the most severe symptoms
  • A relative who carries the genetic disorder

Which genotype represents an affected male with an X-linked recessive trait?

  • XX
  • XXY
  • xY (correct)
  • XY

How is an affected female identified genetically in an X-linked dominant trait?

  • Xx
  • Both XX and Xx (correct)
  • XX
  • xY

Which of the following describes a characteristic of autosomal dominant traits?

<p>Affected individuals must have at least one affected parent (A)</p> Signup and view all the answers

Which option correctly identifies the carrier status of a female with an X-linked recessive trait?

<p>XX or Xx (C)</p> Signup and view all the answers

What does Mendel's concept of 'Dominance/Recessiveness' state regarding unit factors?

<p>One unit factor can overshadow the expression of another unit factor. (D)</p> Signup and view all the answers

In Mendel's experiments, what were the resulting plants from the F1 generation cross between tall and dwarf plants?

<p>All were tall plants. (A)</p> Signup and view all the answers

What is the term used for the original parent plants in Mendel's breeding experiments?

<p>P1 generation (C)</p> Signup and view all the answers

How did Mendel classify the visible traits he observed in pea plants?

<p>As unit characters with two contrasting forms. (D)</p> Signup and view all the answers

What was significant about Mendel's use of garden peas in his genetic experiments?

<p>They were self-fertilizing and easy to hybridize. (A)</p> Signup and view all the answers

What did Mendel mean by 'Unit Factors in Pairs'?

<p>Genetic characters exist in pairs, leading to combinations. (B)</p> Signup and view all the answers

In Mendel's experiments, what ratio of tall to dwarf plants did he observe in the F2 generation?

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

Which statement best describes the nature of alleles in Mendel's work?

<p>Each trait is determined by a pair of alleles. (C)</p> Signup and view all the answers

What does a pedigree chart primarily indicate?

<p>The presence or absence of traits in family members (D)</p> Signup and view all the answers

Which of the following best describes an autosomal recessive trait?

<p>It can skip generations and typically appears in individuals with unaffected parents (B)</p> Signup and view all the answers

In pedigree analysis, what does the term 'consanguineous' refer to?

<p>Marriages between individuals who share a common ancestor (B)</p> Signup and view all the answers

What is indicated by a shaded dot within an individual’s symbol on a pedigree?

<p>The individual is heterozygous for the trait (A)</p> Signup and view all the answers

Which characteristic distinguishes monozygotic twins from dizygotic twins?

<p>Monozygotic twins are genetically identical (B)</p> Signup and view all the answers

What method is used to ascertain the mode of inheritance by studying multiple pedigrees for the same trait?

<p>Forked-Line Method (C)</p> Signup and view all the answers

How is an autosomal dominant trait described?

<p>It can be expressed even when only one dominant allele is present (C)</p> Signup and view all the answers

What does a horizontal sibship line indicate in a pedigree chart?

<p>Connection between siblings (D)</p> Signup and view all the answers

What is the primary purpose of a testcross in genetics?

<p>To determine an individual’s genotype with a dominant phenotype (A)</p> Signup and view all the answers

What results from Mendel’s F2 generation when the F1 generation is allowed to self-fertilize?

<p>A unique phenotypic ratio indicating inheritance patterns (B)</p> Signup and view all the answers

What does Mendel's fourth postulate state about gamete formation?

<p>Pairs of unit factors assort independently during gamete formation (A)</p> Signup and view all the answers

What is a dominant phenotype?

<p>Phenotype expressed when two different alleles are present (C)</p> Signup and view all the answers

What type of cross is a trihybrid cross?

<p>A genetic cross involving three pairs of contrasting traits (C)</p> Signup and view all the answers

How many different gametes can F1 individuals produce in a trihybrid cross?

<p>8 different gametes (A)</p> Signup and view all the answers

What does the term 'segregation' refer to in genetics?

<p>The random separation of paired unit factors during gamete formation (B)</p> Signup and view all the answers

In Mendel’s experiments, what did true-breeding parental plants indicate?

<p>They have a fixed genotype that produces consistent traits (C)</p> Signup and view all the answers

Which of the following accurately describes a homozygous individual?

<p>An individual with two identical alleles (D)</p> Signup and view all the answers

What does a Punnett square with 64 boxes represent?

<p>The possible outcomes of a trihybrid cross (A)</p> Signup and view all the answers

Which statement is true regarding recessive alleles?

<p>They can only be expressed in homozygous conditions. (C)</p> Signup and view all the answers

In a Punnett square, what does the vertical column represent?

<p>The alleles of the female parent in a genetic cross (A)</p> Signup and view all the answers

Which of the following statements about the testcross is true?

<p>It can be applied to individuals expressing two dominant traits (C)</p> Signup and view all the answers

Which best defines the term 'genotype'?

<p>The genetic makeup including specific combinations of alleles (B)</p> Signup and view all the answers

What is true about the trait expressed in the F1 generation?

<p>It is controlled by a dominant unit factor. (A)</p> Signup and view all the answers

Which of the following correctly describes an allele?

<p>One of the variants of a gene at a specific locus (C)</p> Signup and view all the answers

What does the term 'wild-type allele' refer to?

<p>The form of a gene that appears most frequently in a population (B)</p> Signup and view all the answers

Which of Mendel’s postulates does NOT hold true for other types of inheritance?

<p>Unit factors come in pairs (C), Unit factors have either a dominant or recessive form (D)</p> Signup and view all the answers

Which of the following best describes 'partial dominance'?

<p>Neither allele is completely dominant over the other (A)</p> Signup and view all the answers

What can alter Mendelian inheritance patterns through maternal transmission?

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

What does a 'null allele' signify?

<p>A mutation resulting in loss of function in proteins (B)</p> Signup and view all the answers

How does the environment influence phenotypes in genetics?

<p>By affecting the expression of genes (B)</p> Signup and view all the answers

Which of the following statements is true about multiple genes?

<p>They may affect phenotypes in a polygenic inheritance model (D)</p> Signup and view all the answers

What is indicated by Mendel's fourth postulate regarding gametes?

<p>Gametes assort independently of one another (D)</p> Signup and view all the answers

What do both alleles in a heterozygous individual exhibit in the case of codominance?

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

Which blood type is characterized as having both A and B antigens present?

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

What is the primary purpose of forward blood typing?

<p>To identify the recipient’s blood type (B)</p> Signup and view all the answers

When Rh typing is performed, what does agglutination indicate?

<p>The blood type is Rh-positive (A)</p> Signup and view all the answers

Which of the following is NOT a step in forward blood typing?

<p>Identification of Rh antibodies (A)</p> Signup and view all the answers

What is a characteristic of multiple alleles?

<p>More than two alleles can influence a single trait (B)</p> Signup and view all the answers

Which procedure separates blood components in forward blood typing?

<p>Centrifugation (D)</p> Signup and view all the answers

Who identified the ABO blood group system?

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

What does a karyotype provide information about?

<p>Chromosomal abnormalities and structure (D)</p> Signup and view all the answers

Which of the following is a step in the karyotyping analysis process?

<p>Staining to visualize banding patterns (A)</p> Signup and view all the answers

What do cytogeneticists analyze to identify chromosomal abnormalities?

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

Which type of sample is typically used for karyotyping analysis?

<p>Blood or amniotic fluid (A)</p> Signup and view all the answers

How many chromosomes are typically found in a human karyotype?

<p>46 (D)</p> Signup and view all the answers

What is examined under a microscope during the karyotyping process?

<p>Stained chromosomes (D)</p> Signup and view all the answers

Which aspect of chromosomes is NOT typically focused on in karyotyping?

<p>Function of genes (B)</p> Signup and view all the answers

What is a primary purpose of karyotyping in genetic counseling?

<p>To assess potential chromosomal disorders in offspring (C)</p> Signup and view all the answers

What is a karyogram or idiogram primarily used to represent?

<p>A visual representation of an individual's chromosomes (D)</p> Signup and view all the answers

Which type of deletion refers to the loss occurring at the end of a chromosome?

<p>Terminal Deletion (D)</p> Signup and view all the answers

In which type of inversion does the inversion segment include the centromere?

<p>Pericentric Inversion (C)</p> Signup and view all the answers

Which type of chromosomal alteration involves the movement of a segment of one chromosome to another non-homologous chromosome?

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

What does polyploidy refer to?

<p>Having more than two complete sets of chromosomes (C)</p> Signup and view all the answers

What describes a tandem duplication?

<p>The duplicated segment is adjacent to the original segment (C)</p> Signup and view all the answers

Which type of translocation involves two non-homologous chromosomes exchanging segments?

<p>Reciprocal Translocation (C)</p> Signup and view all the answers

How is an interstitial deletion characterized?

<p>Loss occurs within the chromosome away from the ends (D)</p> Signup and view all the answers

What characterizes aneuploidy?

<p>Presence of an extra chromosome or missing chromosome (A)</p> Signup and view all the answers

What is monosomy?

<p>Having only one copy of a specific chromosome (B)</p> Signup and view all the answers

What does nondisjunction cause during cell division?

<p>Improper separation of chromosomes (B)</p> Signup and view all the answers

Which technique uses Giemsa dye to visualize chromosome banding?

<p>G-Banding (A)</p> Signup and view all the answers

What is the focus of T-Banding in chromosome studies?

<p>Staining telomeric regions (C)</p> Signup and view all the answers

What type of chromosomal condition is trisomy?

<p>Three copies of one chromosome (B)</p> Signup and view all the answers

What is euploidy?

<p>A complete and balanced set of chromosomes (A)</p> Signup and view all the answers

What is the primary purpose of karyotype analysis?

<p>To assess chromosome arrangements and abnormalities (A)</p> Signup and view all the answers

What primary information does a karyotype reveal about chromosomes?

<p>The presence or absence of individual chromosomes and their abnormalities (D)</p> Signup and view all the answers

Which period of a cell's lifecycle is crucial for karyotyping analysis to effectively visualize chromosomes?

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

What is the significance of photographing chromosomes during karyotype analysis?

<p>To document abnormalities and assist in diagnosis (D)</p> Signup and view all the answers

What type of chromosomal abnormalities can karyotype analysis identify?

<p>Numerical and structural abnormalities (D)</p> Signup and view all the answers

During which step of karyotyping are chromosomes stained to reveal banding patterns?

<p>Staining (D)</p> Signup and view all the answers

In karyotype analysis, what is the role of genetic counseling?

<p>To discuss the potential health implications based on the karyotype findings (D)</p> Signup and view all the answers

Which of the following samples can be used for karyotyping analysis?

<p>Blood and amniotic fluid (C)</p> Signup and view all the answers

What observation might indicate a significant chromosomal aberration during karyotyping?

<p>Variation in chromosome size and structure (A)</p> Signup and view all the answers

What term describes the loss or absence of a part of a chromosome?

<p>Deletion (D)</p> Signup and view all the answers

Which type of duplication involves a duplicated segment adjacent to the original segment on the same chromosome?

<p>Tandem Duplication (C)</p> Signup and view all the answers

Which type of translocation involves the exchange of segments between two non-homologous chromosomes?

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

What describes the genetic condition characterized by the presence of more than two complete sets of chromosomes?

<p>Polyploidy (D)</p> Signup and view all the answers

Which type of inversion involves the centromere in its chromosomal segment?

<p>Pericentric Inversion (D)</p> Signup and view all the answers

What describes a visual representation or photograph of an individual's chromosomes arranged in a standard format?

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

What type of deletion occurs at the end of a chromosome?

<p>Terminal Deletion (C)</p> Signup and view all the answers

Which of the following accurately specifies the type of duplication where the duplicated segment is found elsewhere in the genome?

<p>Displaced Duplication (C)</p> Signup and view all the answers

What is the genetic condition called when there is only one copy of a particular chromosome in a diploid cell?

<p>Monosomy (D)</p> Signup and view all the answers

Which type of banding selectively stains areas around the centromeres of chromosomes?

<p>C-Banding (B)</p> Signup and view all the answers

What genetic condition results in three copies of a chromosome instead of the usual two?

<p>Trisomy (D)</p> Signup and view all the answers

Which event during cell division leads to an abnormal number of chromosomes in daughter cells?

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

What is the primary use of the Giemsa dye in the study of karyotypes?

<p>To produce an alternating pattern of dark and light bands on chromosomes (A)</p> Signup and view all the answers

Which type of banding focuses on staining the telomeric regions of chromosomes?

<p>T-Banding (A)</p> Signup and view all the answers

Which term describes a condition where a cell has a complete and balanced set of chromosomes?

<p>Euploidy (D)</p> Signup and view all the answers

What is the main advantage of using white blood cells for karyotype studies?

<p>They readily undergo division in culture (B)</p> Signup and view all the answers

What phenotype describes the expression of alleles in a heterozygous individual exhibiting codominance?

<p>Both alleles are fully expressed independently (D)</p> Signup and view all the answers

Which of the following blood types would show agglutination with anti-A and anti-B sera during forward blood typing?

<p>Blood type AB (C)</p> Signup and view all the answers

What is the main purpose of the centrifugation step in forward blood typing?

<p>To separate the cellular components (A)</p> Signup and view all the answers

Which of the following best defines the concept of multiple alleles in genetics?

<p>More than two alleles contribute to a characteristic (C)</p> Signup and view all the answers

In forward blood typing, what is checked to determine if a blood type is Rh-positive?

<p>The presence of agglutination in anti-Rh serum (C)</p> Signup and view all the answers

What does the Rh factor refer to in human blood typing?

<p>A protein on the surface of red blood cells (D)</p> Signup and view all the answers

Which step in forward blood typing involves mixing the patient's red blood cells with specific anti-serum?

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

When performing forward blood typing, what outcome indicates the absence of a specific antigen in the blood sample?

<p>No agglutination occurs (C)</p> Signup and view all the answers

Which of the following accurately describes a mutant allele?

<p>Specifies an altered gene product due to mutations. (C)</p> Signup and view all the answers

What inheritance pattern is disrupted when multiple genes influence a single phenotype?

<p>Mendelian inheritance patterns. (B)</p> Signup and view all the answers

Which Mendelian postulate holds true for other types of inheritance as well?

<p>Multiple unit factors assort independently. (D)</p> Signup and view all the answers

Which statement best describes the term 'partial dominance'?

<p>One allele is partially dominant, affecting the phenotype less than another dominant allele. (A)</p> Signup and view all the answers

Which type of inheritance pattern is specifically transmitted through the female gamete?

<p>Extranuclear inheritance. (D)</p> Signup and view all the answers

What characterizes a null allele?

<p>It completely inhibits the expression of the gene product. (A)</p> Signup and view all the answers

What role does the environment play in the expression of phenotypes?

<p>It modifies or influences the expression of genetic traits. (B)</p> Signup and view all the answers

What happens to Mendelian ratios in certain inheritance patterns?

<p>They may become distorted due to gene interaction. (D)</p> Signup and view all the answers

Flashcards

Mendel's Experiment

Gregor Mendel's study of pea plants demonstrated how traits are passed from generation to generation.

Unit Factors

Specific factors controlling traits, occurring in pairs.

Dominant Trait

A trait that masks or hides the effect of the recessive trait when both are present.

Recessive Trait

A trait that is masked by a dominant trait.

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F1 generation

The first generation of offspring resulting from a cross between two parent strains.

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F2 generation

The second generation of offspring resulting from self-fertilization of the F1 generation.

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Allele

Different forms of the same gene.

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Garden Pea

A plant used by Mendel in his experiments because of its ease of breeding and visible traits.

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Testcross

A specific type of genetic cross used to determine the genotype of an individual with a dominant phenotype. It involves crossing the individual with a homozygous recessive individual.

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Dihybrid Cross

A genetic cross involving two traits. It helps understand how two pairs of alleles segregate and assort independently during gamete formation.

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Independent Assortment

A principle that suggests that during gamete formation, different pairs of alleles segregate independently of each other, leading to various combinations.

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Trihybrid Cross

A genetic cross involving three pairs of contrasting traits, showcasing the inheritance patterns of three characteristics simultaneously.

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Gamete Formation

The process of producing reproductive cells (sperm or egg) that carry a single allele from each pair, ensuring genetic diversity.

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Punnett Square

A diagram used to predict the possible genotypes and phenotypes of offspring resulting from a genetic cross. It visualizes all possible allele combinations.

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Dominant vs Recessive

The dominant trait masks the recessive trait when both alleles are present. The recessive trait is expressed only when two identical recessive alleles are present.

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Phenotype vs Genotype

Phenotype refers to the observable characteristics of an organism (e.g., purple flower), while genotype refers to the genetic makeup (e.g., PP, Pp, pp) that determines those characteristics.

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Homozygous vs Heterozygous

Homozygous means having two identical alleles (PP or pp), while heterozygous means having two different alleles (Pp).

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What is a Gene?

A gene is the basic unit of heredity, responsible for passing traits from parents to offspring. It's a segment of DNA that provides instructions for building a specific protein.

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What is an Allele?

An allele is a different form of a gene, like variations on a theme. For example, a gene for flower color might have alleles for purple or white.

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What is Segregation?

During gamete formation, the paired alleles separate, so each gamete receives only one allele. This ensures genetic diversity.

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Purpose of Punnett Squares

Punnett squares are a graphical tool used to predict the possible combinations of alleles in offspring resulting from a genetic cross.

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How does a Punnett Square work?

The rows and columns of a Punnett square represent the possible gametes from the mother and father. Each square represents a unique combination of alleles.

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Pedigree

A family tree diagram used to trace the inheritance of a specific trait or disorder through generations.

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Autosomal Recessive Trait

A genetic trait that is masked by a dominant allele and only appears in individuals who inherit two copies of the recessive allele, one from each parent.

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Autosomal Dominant Trait

A genetic trait that is expressed in individuals who inherit at least one copy of the dominant allele.

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Consanguineous

A relationship between individuals who are related by blood, often referring to marriage or union between relatives.

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Sibs

Siblings, or brothers and sisters, who share the same parents.

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Monozygotic Twins

Identical twins that develop from a single fertilized egg that splits into two embryos.

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Dizygotic Twins

Fraternal twins that develop from two separate fertilized eggs.

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Pedigree Analysis

A method of studying a family tree to determine the inheritance patterns of genetic traits or disorders.

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Proband

The individual in a family whose phenotype first brings attention to a genetic disorder. They're the first one in the family to be diagnosed with a specific condition.

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X-Linked Dominant Trait

A trait on the X chromosome where having one copy of the dominant allele is enough for expression. Affected females pass it on to half their children, while affected males pass it to all their daughters.

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Wild-Type Allele

The most frequent allele in a population, considered the 'normal' allele. Often dominant and used as a reference for comparing mutations.

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Mutant Allele

An allele that has undergone a change in genetic information leading to an altered gene product.

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Null Allele

A mutation that completely disrupts the function of a gene, resulting in a non-functional protein.

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Partial Dominance

A pattern of inheritance where neither allele completely masks the other, resulting in a blended phenotype.

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Extranuclear Inheritance

Inheritance patterns influenced by DNA found outside the nucleus, specifically in mitochondria and chloroplasts, often transmitted through the female gamete.

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Mendel's Postulates: Exceptions?

Mendel's principles of inheritance, while foundational, have exceptions, leading to unexpected phenotypes.

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Allele Function: What's the Difference?

Alleles are alternative forms of a gene, with wild-type being the common form, mutant being a changed form, and null completely inactivating the gene.

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Mendel's Postulates That Always Hold True?

Two of Mendel's postulates always hold true: Alleles segregate during gamete formation and multiple alleles assort independently.

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Incomplete Dominance

A pattern of inheritance where the heterozygous phenotype is a blend of the two homozygous phenotypes. Neither allele is fully dominant.

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Codominance

A pattern of inheritance where both alleles are fully expressed in heterozygotes, contributing independently to the phenotype.

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Multiple Alleles

When more than two alleles exist for a single gene, leading to more diverse phenotypes.

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ABO Blood Group System

A system for classifying human blood based on the presence or absence of specific antigens (A, B, or both) on red blood cells.

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Rhesus Factor (Rh Factor)

A protein found on the surface of red blood cells that can be present (Rh+) or absent (Rh-).

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Forward Blood Typing

The initial step in blood typing, where a lab determines a person's blood type by testing their blood for specific antigens.

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Agglutination

The clumping of red blood cells in a blood typing test, indicating the presence of the corresponding antigen.

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Rh Typing

The process of determining whether a person is Rh-positive or Rh-negative by testing for the presence of the Rh antigen.

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Karyology

The study of karyotypes and chromosomes.

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Karyogram

A visual representation of an individual's chromosomes arranged in a standard format, based on size, banding patterns, and other characteristics.

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Deletion (Chromosomal)

The loss or absence of a part of a chromosome.

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Duplication (Chromosomal)

The presence of an extra copy of a portion of a chromosome.

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Inversion (Chromosomal)

The reversal of the normal orientation of a chromosome segment.

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Translocation (Chromosomal)

The movement of a segment of one chromosome to another non-homologous chromosome.

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Polyploidy

A genetic condition where an organism has more than two complete sets of chromosomes.

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Robertsonian Translocation

The fusion of the long arms of two acrocentric chromosomes, resulting in a single, larger chromosome.

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Karyotype

A visual representation of all chromosomes in a cell, organized by size and shape, used to detect chromosomal abnormalities.

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What is a Karyotype used for?

Karyotyping is used to determine the number and structure of chromosomes to detect abnormalities such as missing, duplicated, or rearranged chromosomes.

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Autosomes

Chromosomes that are not sex chromosomes (X or Y). Humans have 22 pairs of autosomes.

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Sex Chromosomes

Chromosomes that determine an individual's sex. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).

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Karyotyping Analysis

A laboratory process involving several steps to visualize and study chromosomes to identify any abnormalities.

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What is the purpose of cell culture in karyotyping?

Cell culture is used to grow cells in a controlled environment so there are enough cells for analysis. It allows the cells to divide and reach a suitable stage for chromosome examination.

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Why are chromosomes stained in karyotyping?

Staining helps to make the chromosomes visible under a microscope, revealing banding patterns that aid in identifying different chromosomes.

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What is a karyotype report used for?

A karyotype report provides healthcare professionals with the information about an individual's chromosome structure, helping them understand genetic risks, diagnose conditions, and guide treatment decisions.

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Aneuploidy

A genetic condition where there is an abnormal number of chromosomes in a cell, either an excess or deficiency.

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Monosomy

A type of aneuploidy where a cell only has one copy of a particular chromosome instead of the usual two.

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Trisomy

A type of aneuploidy where a cell has three copies of a particular chromosome instead of the usual two.

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Euploidy

The normal condition in genetics where a cell or organism has a complete and balanced set of chromosomes.

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Nondisjunction

A cellular event during cell division where chromosomes fail to separate properly, leading to an uneven distribution of chromosomes in daughter cells.

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What are chromosomes stained for?

Chromosomes are stained to make them visible under a microscope, revealing banding patterns that aid in identifying different chromosomes.

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Cell Culture (Karyotyping)

The process of growing cells in a controlled environment to obtain a sufficient number for analysis.

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Chromosomal Staining

The process of applying dyes to chromosomes to make them visible under a microscope and reveal banding patterns.

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Karyotype Report

A document that provides information about an individual's chromosome structure, helping healthcare professionals understand genetic risks, diagnose conditions, and guide treatment decisions.

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G-Banding

A technique for staining chromosomes with Giemsa dye, creating alternating dark and light bands along the chromosome.

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R-Banding

A technique for staining chromosomes to create a reverse banding pattern, showing lighter bands where G-banding shows dark bands.

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Study Notes

Mendelian Genetics (Part 1)

  • Gregor Mendel conducted groundbreaking experiments with pea plants (Pisum sativum), establishing foundational understanding of how traits are inherited across generations.
  • Mendel's work revealed distinct units of inheritance, impacting the understanding of gamete formation and transmission genetics.
  • Garden peas were ideal for study due to ease of growth and artificial hybridization, self-fertilization, and seven distinct visible features (unit characters, with contrasting forms or traits). For example, stem height included traits of tall and dwarf.
  • Mendel's experiments involved crossing parent strains with contrasting traits, resulting in the P1 (parental), F1 (first filial), and F2 (second filial) generations.
  • Mendel's experiments revealed characteristic ratios in the F2 generation (e.g., 2.96:1 for seed shape, 3.01:1 for seed color, and 2.84:1 for stem height).

Modern Genetic Terminology

  • Phenotype: Observable physical or biochemical characteristics of an organism.
    • Dominant phenotype: seen when alternate alleles are present together (e.g., Pp: purple).
    • Recessive phenotype: seen only when identical alleles are present together (e.g., pp: white).
  • Gene: The fundamental unit of heredity, responsible for passing traits from one generation to the next.
  • Allele: Variant forms of a gene, located at a specific locus on a chromosome.
    • Dominant allele: expressed when paired with a different allele (e.g., P>p).
    • Recessive allele: not expressed when paired with a dominant allele.
    • Homozygous: having two identical alleles (e.g., PP or pp).
    • Heterozygous: having different alleles (e.g., Pp).
  • Genotype: The genetic makeup of an organism, including the specific combination of alleles for a set of genes (e.g., PP, Pp, pp).

Punnett Squares

  • Punnett squares are graphical tools used in genetics to predict allele combinations resulting from a cross between two individuals. Using a Punnett square shows the possible genotypes and phenotypes of the offspring.
  • The vertical column represents the female parent's alleles and the horizontal row represents the male parent's alleles.

Testcross Method

  • The testcross method is a genetic cross used to determine the genotype of an individual of unknown genotype that expresses a dominant phenotype.
  • The unknown individual is crossed with a known homozygous recessive individual.
  • The results of the testcross determine the genotype of the unknown individual.

Mendel's First Three Postulates

  • Unit factors in pairs: Genetic characters are controlled by unit factors existing in pairs in individual organisms. Three combinations are possible (e.g., (TT), (tt), (Tt))
  • Dominance/Recessiveness: One unit factor (dominant) masks the other (recessive) to determine the expressed trait in the F1 generation.
  • Segregation: During gamete formation, paired unit factors separate or segregate randomly so each gamete receives one or the other with equal likelihood.

Mendel's Dihybrid Cross

  • Mendel's dihybrid cross involved crossing parent strains with two contrasting traits each
  • Results of the F2 generation showed a characteristic 9:3:3:1 phenotypic ratio for the traits involved.
  • This confirmed the concept of independent assortment, meaning segregating pairs of unit factors during gamete formation assort independently of each other.

The Trihybrid Cross

  • Mendel's trihybrid cross confirmed his principles applied to inheriting multiple traits.
  • F1 individuals produces eight different gametes with equal frequencies, which are used to construct a Punnett square for determining resultant phenotypes.

Pedigrees

  • Pedigrees are family trees used to study inheritance patterns of traits/disorders.
  • Analyzing pedigrees often reveals characteristic inheritance patterns (e.g., if the trait is dominant or recessive, X-linked or Autosomal).
  • Modern pedigrees also note if the parents are related as a result of consanguineous marriage.
  • Specialized techniques like Forked-Line method or Branch Diagrams are employed to ascertain the inheritance pattern as well.

Key Terms in Pedigree Analysis

  • Proband: The first affected individual in a family that came to the attention of healthcare professionals. Often designated by a 'p'.
  • Affected/unaffected individuals and male/female: Individuals designated by symbols based on their sex and whether or not they exhibit the trait.
  • Consanguineous parents: Parents who are related. Designation typically a "double line" between parents.
  • Siblings: Horizontal sibling line displays the family members
  • Monozygotic/Dizygotic twins: Identical/Fraternal.
  • Carrier: An individual carrying a recessive allele but not displaying the associated trait.
  • Parents (Unrelated/Related): Designates if parents are not related or are related as a result of consanguineous marriage.
  • X-Linked/Y-linked traits: Traits encoded on X or Y chromosomes.
  • Different modes of inheritance (e.g., dominant, recessive, X-linked, autosomal).
  • Disease/trait examples.

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Related Documents

Lesson 6 Mendelian Genetics (Part 1 & 2) PDF
Lesson 7 Modification of Mendelian Ratios PDF
Lesson 8 Introduction To Karyotyping PDF

Description

Explore the pioneering work of Gregor Mendel in his experiments with pea plants. This quiz covers fundamental concepts of inheritance, including gamete formation and the significance of distinct traits. Test your knowledge on Mendel's generations and the ratios observed in his experiments.

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