Genetics and Chromosomes: DNA Structure, Chromosome Basics, Meiosis, and Gametogenesis

Flashcards covering DNA structure, chromosome basics, and the meiosis/gametogenesis topics from Pages 1–9.

What does DNA stand for and what type of molecule is it?

DNA stands for deoxyribonucleic acid; it is a nucleic acid macromolecule that forms a double helix.

What proteins does DNA wind around to form chromatin?

Histones; DNA wraps around histones to form chromatin and further condenses into chromosomes.

What are the three components of a nucleotide?

A phosphate group, a sugar (deoxyribose), and a nitrogenous base.

What does each phosphate group in DNA contain?

1 phosphorus atom and 4 oxygen atoms.

What is the sugar in DNA called and how many carbons does it have?

Deoxyribose, a five‑carbon (pentose) sugar.

Which bases are purines and which are pyrimidines in DNA?

Purines: adenine (A) and guanine (G) with two rings; Pyrimidines: cytosine (C) and thymine (T) (uracil in RNA) with one ring.

Which base pairs form hydrogen bonds in DNA and how many bonds does each pair have?

A pairs with T via 2 hydrogen bonds; G pairs with C via 3 hydrogen bonds.

How many strands make up DNA and what is its overall shape?

Two strands forming a double helix.

What is the term for DNA bound with proteins to form higher order structure?

Chromatin.

What is the difference between coding DNA and non‑coding DNA?

Coding DNA codes for proteins; non‑coding DNA does not code for proteins but has other functions (e.g., packing, replication signals, regulation).

What is the genome?

All of the DNA found in the cells of an organism.

How long is one DNA molecule before condensing?

About 2 metres long.

What is a karyotype?

A display of the number and appearance of chromosomes observed at late prophase and metaphase.

What are autosomes and what is the 23rd chromosome pair?

Autosomes are the first 22 pairs; the 23rd pair consists of the sex chromosomes (XX in females, XY in males).

What are the female and male sex chromosome compositions?

Females: XX; Males: XY.

What is Turner syndrome?

Monosomy X in females; one X chromosome is missing or partially missing.

What is Down syndrome?

Trisomy 21; developmental changes and physical features.

What is aneuploidy?

Addition or loss of one chromosome from a cell.

What is trisomy?

Three copies of an autosome.

What is monosomy?

Missing a copy of an autosome.

What is monoploidy and polyploidy?

Monoploidy (1n) = one set of chromosomes; Polyploidy (3n, 4n, etc.) = three or more copies of each chromosome.

Name a few chromosomal disorders mentioned and their chromosomal alterations.

Trisomy 13 (Patau syndrome); Trisomy 18 (Edwards syndrome); Trisomy 21 (Down syndrome); Turner syndrome (monosomy X); Williams syndrome (deletion on chromosome 7); Klinefelter syndrome (XXY).

What is a locus?

The location of a specific gene on a chromosome.

What are homologous chromosomes?

A pair of chromosomes that have the same size, shape, and genes at the same loci.

What is the purpose of a karyotype besides identifying abnormalities?

To determine gender and detect chromosomal abnormalities.

What is the function of non‑coding DNA elements?

They can help DNA packaging, initiate replication, align chromosomes during mitosis/meiosis, stabilize chromosome ends, and regulate gene expression.

Where are mitochondrial DNA (mtDNA) and chloroplast DNA (cpDNA) located and what are their characteristics?

mtDNA is in mitochondria and cpDNA in chloroplasts; both are circular and lack histones; mtDNA codes for some mitochondrial proteins; cpDNA codes for photosynthesis proteins.

What is supercoiling in DNA organization?

A process by which DNA is folded/condensed by proteins to compact the molecule.

What are plasmids?

Small circular DNA rings in the cytoplasm of prokaryotes that code for non‑essential genes.

Where does meiosis Prophase 1 occur and what are key events?

In the nucleus; chromatin condenses into X‑shaped chromosomes, synapsis occurs, crossing over happens, nuclear membrane disappears, centrioles move to poles with spindle fibers.

What happens in Metaphase 1 of meiosis?

Homologous chromosomes line up at the equator and attach to spindle fibers.

What happens in Anaphase 1 of meiosis?

Homologous chromosomes are separated and pulled to opposite ends of the cell.

What happens in Telophase 1 of meiosis?

Spindle fibers disappear; nuclear membrane reforms; two genetically different haploid daughter cells are formed; sister chromatids may be non-identical due to crossing over.

What happens in Prophase 2 of meiosis?

Nuclear membrane disappears and spindle fibers form from centrioles.

What happens in Metaphase 2 of meiosis?

Chromosomes line up at the equator and attach to spindle fibers from both poles.

What happens in Anaphase 2 of meiosis?

Sister chromatids separate and move to opposite poles.

What happens in Telophase 2 of meiosis?

Spindle fibers disappear; nuclear membranes reform; four genetically different haploid daughter cells are produced.

What is fertilisation and its relation to meiosis?

The fusion of male and female haploid gametes to form a diploid zygote; meiosis halves the DNA and fertilisation restores the species’ DNA amount, creating genetic variation.

What are spermatogenesis and oogenesis and where do they occur?

Spermatogenesis: formation of haploid sperm in the seminiferous tubules of the testis; Oogenesis: formation of eggs (ova) in the ovaries; spermatogenesis yields motile gametes, oogenesis yields non‑motile gametes (ovum with polar bodies).