Genetics and Chromosomes: Autosomes, Sex Linkage, and Nondisjunction

What are the chromosome pairs that make up autosomes?

Chromosome pairs 1-22.

What are the sex chromosomes for females and males?

Females have XX and males have XY.

Which chromosome determines the sex of the offspring?

The male chromosome (Y) determines the sex.

Why is the X chromosome significant for survival?

You need the X chromosome to survive, but you do not need the Y chromosome.

What are X-linked genes?

Genes located on the X chromosome.

What is dosage compensation in females?

One of the female X chromosomes becomes a Barr body, inactivating and condensing randomly.

What is a genetic mosaic?

A female heterozygote for an X-linked trait, such as a calico cat.

What are linked genes?

Genes found on the same chromosome that are close together.

How does independent assortment relate to linked genes?

Linked genes break independent assortment; if two genes are linked, they will be passed on together.

What disrupts gene linkage?

Crossing over during meiosis.

What is an autosomal dominant trait?

A trait where an individual must be homozygous dominant or heterozygous to be affected.

How does an autosomal recessive trait manifest?

An affected individual has to be homozygous recessive, and heterozygotes are carriers.

What is a characteristic of X-linked recessive traits?

They are more likely to affect males, as they only need one recessive allele.

How do sons and daughters inherit X-linked traits?

Sons inherit the X chromosome from their mother; daughters need one X from each parent.

What is nondisjunction?

The failure of homologous pairs or sister chromatids to separate properly during meiosis.

What is aneuploidy?

The gain or loss of a chromosome.

What is monosomy?

The loss of one copy of a chromosome.

What is trisomy?

The gain of three copies of one chromosome.

What is trisomy 21?

Down syndrome, caused by an extra copy of chromosome 21.

What impact does nondisjunction have on individuals?

It can affect chromosome number, influencing whether individuals survive or not.

Why is the white-eye phenotype always observed in males carrying the white-eye allele?

Because the allele is located on the X chromosome and males have only one X chromosome

In an organism's genome, autosomes are

In an organism's genome, autosomes are sex chromosomes

What cellular process is responsible for genetic recombination?

Crossing over between homologs

Genetic mapping and GWAS

are examples of forward genetics

How does maternal inheritance of mitochondrial genes differ from sex linkage?

Because mitochondria are inherited from the mother, females and males are equally affected.

Which of the following genotypes due to nondisjunction of sex chromosomes is lethal?

OY

A recessive sex-linked gene in humans leads to a loss of sweat glands. A woman heterozygous for this will

have patches of skin with and without sweat glands.

Bipolar disorder is a complex trait that shows high heritability in twin studies. The best way to analyze the genetics of this would be to use

GWAS to look for associations of genetic variants with bipolar disorder.

Down syndrome is the result of trisomy for chromosome 21. Why is this trisomy viable whereas trisomy for most other chromosomes is not?

Chromosome 21 is a small chromosome with few genes, so this does less to disrupt the genome.

Genes that are on the same chromosome can show independent assortment

when they are far enough apart that odd numbers of crossovers are about equal to even.

During the process of spermatogenesis, a nondisjunction event that occurs during the second division would

be better than the one during first division because only two of the four meiotic products would be aneuploid.

How do male fruit flies express genes from their X chromosome?

Males double the gene expression from their single X chromosome.

What happens to one of the X chromosomes in female mammals during development?

One of the X chromosomes is randomly inactivated.

What is the result of X inactivation in heterozygous female mammals?

It produces a mosaic pattern, as seen in the coat color of calico cats.

How do mitochondria and chloroplasts differ in terms of inheritance?

Mitochondria are passed to offspring in the cytoplasm of the egg cell, while chloroplasts are usually inherited maternally.

What is crossing over in homologous chromosomes?

It is the exchange of alleles that occurs by breakage and rejoining of chromosomes.

In which sex are recessive traits on the X chromosome visible?

Recessive traits are visible in males, inherited from their mother.

What is aneuploidy and how does it occur?

Aneuploidy is the result of nondisjunction during meiosis, leading to monosomy or trisomy of a chromosome.

What is the most common outcome of nondisjunction?

Most cases are lethal, but some, like trisomy 21, can result in viable offspring.

Which sex is more likely to experience nondisjunction and how does age affect it?

Nondisjunction is more common on the female's side, with frequency increasing with age.

What methods can be used to determine genetic defects in humans?

Methods include pedigree analysis, amniocentesis, chorionic villus sampling, and noninvasive prenatal testing.

Why was genetic mapping in humans slow to develop?

It required multiple disease-causing alleles segregating in a family.

How can genetic maps be used in identifying genetic disorders?

By following the segregation of disease alleles in multiple families.

What is the purpose of Genome-Wide Association Studies (GWAS)?

GWAS find associations between traits and genetic variants.

How do common and rare genetic variants contribute to phenotype?

Common variants make small contributions, while rare variants make large contributions.

What is reverse genetics and its initial focus in humans?

Reverse genetics involves studying loss-of-function alleles, focusing on nonessential homozygous LOF alleles.

What is binary fission?

A simple form of cell division in prokaryotes resulting in two identical cells.

How does bacterial DNA replication occur?

It begins at a specific point, the origin, and proceeds bidirectionally to a termination site.

What is septation in bacterial cell division?

The process of separating new cells by inserting new cell membrane and materials at the midpoint.

What role does FtsZ play in bacterial cell division?

FtsZ forms a ring that contracts radially inward to pinch the cell into two new cells.

What is chromatin?

A complex of DNA and protein that makes up chromosomes.

What distinguishes heterochromatin from euchromatin?

Heterochromatin is not expressed, while euchromatin is expressed.

What is a nucleosome?

A structure formed by DNA wrapped around a core of eight histones.

What is the centromere?

A constricted area of a chromosome where sister chromatids are held together.

What are the phases of the cell cycle?

Gap 1 (G1), synthesis (S), gap 2 (G2), mitosis, and cytokinesis (C).

What is the G0 phase?

A nondividing phase that cells can enter from G1, which can be temporary or permanent.

What occurs during prophase of mitosis?

Chromosomes condense, the spindle forms, and the nuclear envelope disintegrates.

What happens during metaphase?

Chromosomes align at the equator, and sister chromatids are connected to opposite poles by microtubules.

What is anaphase A and B?

Anaphase A is the separation of chromatids to opposite poles, while anaphase B is the movement of poles farther apart.

What is the role of the contractile ring during cytokinesis in animal cells?

It pinches off the daughter cells by contracting under the membrane.

How do plant cells undergo cytokinesis?

By forming a cell plate through the fusion of vesicles in the middle of the cell.

What are the three checkpoints in the cell cycle?

G1/S checkpoint (commitment to divide), G2/M checkpoint (DNA integrity), and spindle checkpoint (chromosome attachment).

What drives the cell cycle?

Cyclin-dependent kinases (Cdks) regulate the progression of the cell cycle.

How does the anaphase-promoting complex/cyclosome (APC/C) function?

It activates a protease that removes cohesins holding sister chromatids together, triggering anaphase.

What is the effect of growth factors like platelet-derived growth factor (PDGF) on cell division?

They stimulate cell division through a MAP kinase cascade that activates cyclins and Cdks.

What types of mutations can lead to cancer?

Mutations in proto-oncogenes (dominant, gain-of-function) and tumor-suppressor genes (recessive, loss of function).

What is the significance of whole-genome sequencing in cancer research?

It helps identify mutations in cancer driver genes that provide a growth advantage to cells.

What is the primary purpose of meiosis?

To reduce the number of chromosomes and produce haploid gametes.

What type of cells are produced by meiosis?

Haploid (1n) cells, specifically egg and sperm.

What occurs during fertilization?

The fusion of two haploid gametes results in a diploid (2n) zygote.

What are germ-line cells?

Cells set aside early in animal development that will form haploid gametes by meiosis.

What is synapsis in meiosis?

The pairing of homologous chromosomes during early prophase I.

What is crossing over?

The exchange of chromosomal material between homologous chromosomes during synapsis.

What happens during anaphase I of meiosis?

Homologs of each pair are pulled to opposite poles, producing two cells with one complete set of chromosomes.

How does meiosis II differ from meiosis I?

Meiosis II is similar to mitosis but occurs without DNA replication.

What is the result of meiosis I and II?

Four haploid cells that are not identical.

What are the four distinct features of meiosis I not found in mitosis?

1. Maternal and paternal homologs pair and exchange genetic information. 2. Kinetochores of sister chromatids function as a unit. 3. Kinetochores of sister chromatids connect to a single pole. 4. DNA replication is suppressed between meiosis I and II.

What is the significance of independent assortment in meiosis?

It contributes to genetic variation in gametes by randomly orienting homologous pairs at the metaphase plate.

What is aneuploidy?

The presence of an abnormal number of chromosomes in a gamete, often due to nondisjunction during meiosis.

What is the role of cohesin proteins during meiosis?

They hold sister chromatids together and are selectively degraded during anaphase I.

What happens during telophase I of meiosis?

The nuclear envelope re-forms around each daughter nucleus, and cytokinesis may or may not occur.

What is the interphase period in meiotic cells similar to?

It is similar to mitosis, consisting of G1, S, and G2 phases.

What is the significance of the synaptonemal complex?

It helps hold homologous chromosomes together during meiosis and facilitates crossing over.

How does meiosis contribute to genetic diversity?

Through independent assortment of chromosomes and crossing over between homologs.

What is the outcome of errors in meiosis?

They can lead to aneuploid gametes, resulting in genetic disorders.

What is the role of kinetochores in meiosis?

They attach to spindle fibers to ensure proper segregation of chromosomes during cell division.

What is the difference between somatic cells and germ-line cells?

Somatic cells divide by mitosis and form the body, while germ-line cells undergo meiosis to produce gametes.

What is the significance of the random orientation of homologous pairs?

It results in the independent assortment of maternal and paternal chromosomes in gametes.

What happens to sister chromatids during anaphase I?

Sister chromatids remain together while homologs are pulled apart.

What is the role of cohesin proteins at the centromeres during meiosis I?

They remain intact to keep sister chromatids connected during the separation of homologs.