Genetic variation and chromosomal changes

What is genetic variation?

Differences between members of the same species or those of different species.

What are the two main types of chromosomal changes?

Changes in chromosome structure and changes in chromosome number.

What are deletions in chromosome structure?

Loss of segments of chromosomes, which can lead to phenotypic effects.

What are duplications in chromosome structure?

When a segment of a chromosome is copied, potentially leading to gene families.

What is an inversion in chromosome structure?

A segment of a chromosome is flipped to the opposite orientation.

What is a translocation in chromosome structure?

A segment of one chromosome is transferred to another chromosome.

What is aneuploidy?

A condition where the number of chromosomes is not an exact multiple of the haploid number.

What is polyploidy?

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

What is karyotyping?

A microscopic examination of chromosomes to identify and classify them.

What three features do cytogeneticists use to classify chromosomes?

Location of the centromere, size, and banding patterns.

Why are banding patterns useful in cytogenetics?

They help distinguish individual chromosomes, detect large-scale changes, and reveal evolutionary relationships.

What is heterochromatin?

Areas of tightly packed DNA that often contain long stretches of AT repeats and fewer genes.

What genetic disease is caused by a deletion in chromosome 5?

Cri-du-chat syndrome.

What is the typical cause of chromosomal duplications?

Abnormal events during recombination leading to misalignment between homologous chromosomes.

What is Copy Number Variation (CNV)?

A segment of DNA that varies in copy number among members of the same species.

What is the breakpoint effect in inversions?

An inversion breakpoint occurs within a vital gene, separating it into two nonfunctional parts.

What is the position effect in inversions?

A gene is repositioned in a way that alters its expression, potentially affecting its function.

What is the incidence of detectable inversions in the human population?

About 2% of the population carries detectable inversions.

What is Prader-Willi syndrome caused by?

A deletion in the father's chromosome 15, affecting gene expression due to imprinting.

How do duplications contribute to evolution?

They provide raw material for the addition of genes based on modifications of existing genes.

What are the phenotypic consequences of deletions?

They depend on the size of the deletion and whether vital genes are lost, often resulting in detrimental effects.

Why do duplications tend to have less harmful effects than deletions?

Duplicated genes can mutate without severe consequences, allowing for beneficial mutations to accumulate.

What is the expected outcome of a chromosome with a duplication?

It may lead to the formation of gene families and can have modest phenotypic effects.

What is the typical range of Copy Number Variation in genomes?

0.1-10% of a genome may show CNV, with a human rate of approximately 0.4%.

What are inversion heterozygotes?

Individuals with one normal chromosome and one inverted chromosome, who may be phenotypically normal but have a high probability of producing abnormal gametes.

What is the significance of an inversion loop during meiosis?

An inversion loop forms to allow proper synapsis of homologous chromosomes, but crossover within this loop can lead to abnormal chromosomes.

What are reciprocal translocations?

A type of chromosomal translocation where segments of two non-homologous chromosomes exchange genetic material, usually without major phenotypic consequences.

What are unbalanced translocations?

Translocations that alter the total amount of genetic material, leading to duplications or deletions, and are often associated with phenotypic abnormalities.

What is Familial Down Syndrome?

A condition resulting from a Robertsonian translocation where a large segment of chromosome 21 is attached to chromosome 14, leading to three copies of genes on chromosome 21.

What is a Robertsonian translocation?

A type of translocation that occurs when breaks near the centromeres of two non-homologous acrocentric chromosomes lead to the fusion of larger fragments and loss of smaller acentric fragments.

What are the two main ways chromosome numbers can vary?

Euploidy, which is the variation in complete sets of chromosomes, and aneuploidy, which is the variation in the number of particular chromosomes within a set.

What is trisomy?

A condition where an organism has three copies of a chromosome instead of the usual two.

What is monosomy?

A condition where an organism has only one copy of a chromosome instead of the usual two.

What is the impact of aneuploidy on phenotype?

Aneuploidy can cause an abnormal phenotype due to an imbalance in gene product levels, often leading to developmental issues.

What is the frequency of Trisomy 21 (Down syndrome)?

1 in 800 live births.

What are the characteristics of Trisomy 13 (Patau syndrome)?

Mental and physical deficiencies, a variety of organ defects, and early death.

What is the frequency of Trisomy 18 (Edward syndrome)?

1 in 6000 live births.

What are the characteristics of Klinefelter syndrome (XXY)?

Sexual immaturity in males, including lack of sperm and possible breast swelling.

What is the frequency of Turner syndrome (X0)?

1 in 5000 live births.

What is the significance of meiotic nondisjunction?

It refers to the failure of chromosomes to segregate properly during anaphase, leading to gametes with abnormal chromosome numbers.

What happens during nondisjunction in Meiosis I?

Homologous chromosomes fail to separate, resulting in two gametes with an extra chromosome and two gametes missing a chromosome.

What happens during nondisjunction in Meiosis II?

Sister chromatids fail to separate, resulting in two normal gametes, one gamete with an extra chromosome, and one gamete missing a chromosome.

What percentage of ferns and flowering plants are polyploid?

30 to 35%.

What are the agricultural benefits of polyploid plants?

Polyploid strains often exhibit larger size and robustness, leading to improved agricultural characteristics.

What is the role of sterility in polyploid plants?

Sterility can be beneficial for agriculture, leading to seedless fruits and flowers, which can be more desirable for consumption.