Cell Division and Genetic Diversity

These flashcards cover key vocabulary related to cell division, genetics, and associated concepts, as outlined in the lecture notes.

Chromosome

A structure made of DNA and proteins that carries genetic information.

Chromatin

A complex of DNA and protein that condenses during cell division.

Centromere

The region where sister chromatids are joined and spindle fibers attach during cell division.

Sister Chromatids

Identical copies of a chromosome connected by a centromere.

Homologous Chromosomes

Chromosomes that are the same size, shape, and carry the same genes (one from each parent).

Diploid (2n)

A cell with two sets of chromosomes (one set from each parent).

Haploid (n)

A cell with only one set of chromosomes (gametes).

Crossing Over

Exchange of genetic material between homologous chromosomes during Prophase I of meiosis.

Independent Assortment

Random distribution of maternal and paternal chromosomes into gametes during Metaphase I, leading to different allele combinations.

Cytokinesis

The process by which the cytoplasm divides, creating two new cells.

Mitosis

Process of cell division resulting in two genetically identical diploid somatic cells.

Meiosis

Type of cell division that results in gametes with half the number of chromosomes.

Aneuploidy

Abnormal number of chromosomes, often resulting from nondisjunction during meiosis. Examples include Trisomy 21 (Down syndrome), Turner syndrome (XO), and Klinefelter syndrome (XXY).

Translocation

A segment of one chromosome becomes attached to another chromosome. Types include Reciprocal translocation (segments exchanged) and Robertsonian translocation (whole-arm fusion, often causing familial Down syndrome).

Deletion

Chromosome loses a segment. Examples include Cri-du-chat syndrome (5p deletion) and Williams syndrome (7q11.23 deletion).

Genotype

The genetic makeup of an organism (e.g., Aa).

Phenotype

The observable traits of an organism (e.g., purple flowers).

Stages and product of Mitosis

Prophase → Metaphase → Anaphase → Telophase; product = two genetically identical diploid somatic cells.

When does crossing over occur?

Prophase I of meiosis.

Separation of homologous chromosomes in Meiosis

Anaphase I; homologous chromosomes separate, reducing chromosome number (cells become haploid with sister chromatids).

Contribution of crossing over to genetic diversity

It produces recombinant chromosomes by exchanging alleles between homologs, creating new allele combinations.

Difference between homologous chromosomes and sister chromatids

Homologous chromosomes have the same gene set but different parental origin; sister chromatids are identical copies of one chromosome joined at the centromere.

Importance of Meiosis

Halves chromosome number to maintain species chromosome count across generations and increases genetic diversity.

Nondisjunction and resulting disorders

Chromosomes fail to separate during meiosis, leading to gametes with the wrong chromosome number; e.g., Trisomy 21 (Down syndrome).

Main stages of the cell cycle

G₁ (growth), S (DNA replication), G₂ (growth and checkpoint), M (mitosis) + cytokinesis.

When does DNA replication occur and why?

S phase — to copy the genome so each daughter cell receives a full set.

Difference between G₁ and G₂ phases

G₁ = cell growth and normal function before DNA replication; G₂ = growth and preparation after replication, checking for DNA damage/complete replication.

Three major cell-cycle checkpoints and their functions

1. G₁/S: checks cell size, nutrients, DNA damage. 2. G₂/M: checks DNA replication completion, DNA damage. 3. Spindle (M): checks chromosome attachment to spindle and proper alignment.

Consequences of cell-cycle checkpoint failure

Cells may divide with DNA damage or incorrect chromosome numbers, leading to mutations or aneuploidy; can result in cancer or cell death.

Relationship between cancer and cell-cycle regulation

Cancer arises when cell-cycle regulation fails (e.g., oncogenes activated, tumor suppressors lost), causing uncontrolled cell division.

Mechanisms contributing to genetic diversity

1. Crossing over: exchange of alleles between homologous chromosomes in Prophase I. 2. Independent assortment: random segregation of different chromosome pairs in Metaphase I. 3. Random fertilization: any sperm can fuse with any egg, multiplying possible combinations. (Mutation also introduces new alleles).

Define allele, homozygous, and heterozygous

Allele: a variant form of a gene. Homozygous: having two identical alleles for a trait (e.g., AA or aa). Heterozygous: having two different alleles for a trait (e.g., Aa).

What is a test cross?

Crossing an individual with an unknown genotype to a homozygous recessive individual to determine the unknown genotype.

Completion: Sperm and ovum

A sperm and ovum are able to fuse; the resulting product is called a zygote which is a diploid organism.

Three degrees of dominance

1. Complete dominance: one allele completely masks the other. 2. Incomplete dominance: the heterozygote shows an intermediate phenotype between the two homozygotes. 3. Codominance: both alleles are expressed equally and distinctly in the heterozygote.

Sickle cell anemia: genetics and heterozygote advantage

caused by a mutation in the hemoglobin gene. Heterozygotes (with sickle trait) are resistant to malaria, offering a selective advantage in malaria-prone regions.

Law of Independent Assortment and its exception

States that alleles of different genes segregate independently into gametes. Exception: genes that are linked (located close together on the same chromosome) tend to be inherited together.

Law of Segregation

States that the two alleles for a heritable character segregate (separate) from each other during gamete formation, so each gamete receives only one allele.

Probability rules for monohybrid crosses

1. Use Punnett squares. 2. Multiply probabilities for independent events (AND). 3. Sum probabilities for mutually exclusive events (OR).

Epistasis and its effect on phenotypic ratios

when one gene masks or modifies the expression of another gene. It changes the classic 9:3:3:1 dihybrid F₂ phenotypic ratio into other ratios (e.g., 12:3:1, 9:3:4), depending on the type of epistasis.

Nonreciprocal translocation

A type of translocation where a segment of one chromosome (e.g., a gene on Chr8) attaches to another chromosome (e.g., Chr14) without an equivalent exchange occurring.

What is a karyotype? Components of human karyotype

a visual display of an organism’s chromosomes arranged by size and shape. The human karyotype contains 22 pairs of autosomes and 1 pair of sex chromosomes.

Phase of crossing over and its product

Crossing over occurs in Prophase I of meiosis and produces recombinant chromosomes (chromosomes with mixed parental alleles).

Process leading to aneuploidy

Nondisjunction during meiosis.

Description of incomplete dominance

The heterozygote shows a blended phenotype intermediate between both homozygotes.

gamete

A male or female reproductive cell that contains half the genetic material of the parent organism, contributing to genetic diversity during sexual reproduction.

huntingtons disease

A genetic disorder caused by a mutation in the HTT gene, leading to progressive neurological degeneration. - fatal

marfans syndrom

A genetic disorder affecting connective tissue, characterized by tall stature, long limbs, and cardiovascular complications.

neurofibromatosis

A genetic disorder characterized by the growth of tumors along nerves, skin changes, and bone deformities.

hereditary breast cancer

A genetic predisposition to breast cancer, often associated with mutations in the BRCA1 and BRCA2 genes.

cystic fibrosis

A genetic disorder affecting the lungs and digestive system, caused by mutations in the CFTR gene, leading to thick mucus production. - reduced life span 40 years

tay sachs

primarily affects those of jewish asnkenazi descent,causing progressive damage to the nervous system due to a deficiency in the hexosaminidase A enzyme. death in 4-5 years

trisomy 21

a genetic condition caused by the presence of an extra copy of chromosome 21, leading to Down syndrome.

trisomy 18

edwards syndrom - a genetic condition caused by the presence of an extra copy of chromosome 18, leading to severe developmental issues and often resulting in shortened lifespan.

turners syndrom

a genetic condition resulting from the partial or complete absence of one X chromosome in females, leading to various developmental and medical challenges.

klinefelter syndrom

a genetic condition in males resulting from the presence of an extra X chromosome, leading to physical and reproductive development issues.

chronic myelogenous luekemia

a type of cancer that affects the blood and bone marrow, characterized by the overproduction of myeloid cells.

di george syndrome

a genetic disorder caused by the deletion of a small segment of chromosome 22, leading to heart defects, immune deficiencies, and other developmental issues.

prader willi

syndrome is a genetic disorder caused by the loss of function of specific genes on chromosome 15, leading to excessive hunger, obesity, and cognitive impairments.

cru du chat

syndrome is a genetic disorder caused by the deletion of a portion of chromosome 5, leading to cat-like cry, developmental delays, and intellectual disabilities.