DNA, Replication, Sex Chromosomes

Chromatin

DNA+protein.

Nucleosome

DNA around histones.

Chromosome

Condensed DNA.

Centromere

Holds chromatids.

Two strands of DNA are held together by

Hydrogen bonds between complementary bases

Eukaryotic DNA increasing structural organization

DNA, nucleosome, chromatin fiber, chromosome

Karyotype

A display of an individual's chromosomes arranged by size and type.

Aneuploidy

Abnormal chromosome number.

Polyploidy

Extra sets of chromosomes.

Common Aneuploidies

Trisomy 21: Down syndrome; XXY: Klinefelter; XO: Turner; XYY: Jacob's; triploidy: 3 sets of chromosomes.

Chromosomal Rearrangements

Changes like duplications, deletions (Cri du chat), inversions, translocations, rings, and repeats (Fragile X).

Homologous Chromosomes

Same genes, different parents.

Sister Chromatids

Identical copies of one chromosome.

Anatomy of a Chromosome

Includes centromere, kinetochore, p and q arms, autosomes, and sex chromosomes.

Symptoms of Trisomy 21 (Down Syndrome)

Upward slanting palpebral fissures

Brush field spots

Protruding tongue

Small and dysplastic ears

Generous nuchal skin

symptoms of Kleinfelter's syndrome (men)

-rounder abdomen like a woman, small testes, breast tissue

-cannot reproduce

Symptoms of Turner's Syndrome (women)

-early loss of ovarian function

-short stature

-neck webbing

Triploidy Syndrome

either miscarriage or death within the first year of life

Cri du chat Syndrome

A deletion of the short arm of chromosome 5 associated with an array of congenital malformations, the most characteristic of which is an infant cry that resembles a meowing cat.

Fragile X Syndrome

a disorder produced by injury to a gene on the X chromosome, producing mild to moderate intellectual disability and behavioral issues

Asexually produced daughter cells are identical to

To each other, and to the parent cell

How does DNA replicate itself and in what direction?

DNA replicates via semi-conservative replication, where each strand serves as a template. DNA is synthesized in the 5' → 3' direction.

What is the origin of replication?

A specific sequence where replication begins; proteins bind here to open the double helix.

What is the role of DNA polymerase?

DNA polymerase adds nucleotides to the 3' end, synthesizing DNA in the 5' → 3' direction and proofreading for errors.

What is the role of helicase?

Helicase unwinds and separates the DNA strands at the replication fork.

What does topoisomerase (gyrase) do?

It relieves twisting tension ahead of the replication fork by cutting and rejoining DNA strands.

What is the function of primase?

Primase synthesizes short RNA primers to provide starting points for DNA polymerase.

What do single-stranded binding proteins (SSBs) do?

SSBs stabilize separated DNA strands and prevent them from re-annealing or forming secondary structures.

What is the role of ligase?

Ligase joins Okazaki fragments on the lagging strand, creating a continuous DNA strand.

What is the step-by-step process of DNA replication and the role of each enzyme/protein?

1. Origin of replication: replication begins. 2. Helicase: unwinds DNA. 3. Topoisomerase: relieves supercoiling. 4. SSBs: stabilize strands. 5. Primase: makes RNA primers. 6. DNA polymerase: synthesizes DNA 5' → 3'. 7. Ligase: joins Okazaki fragments. Leading strand is continuous; lagging strand is fragmented.

How is the capital Y chromosome different from the capital X chromosome?

The Y chromosome is smaller and carries fewer genes. It contains the SRY gene for male sex determination, while the X chromosome carries many essential genes for general development.

What is the SRY gene?

SRY (Sex-determining Region Y) is a gene on the Y chromosome that triggers male sex determination by initiating testes development.

What happens at the PAR (Pseudoautosomal Regions) of sex chromosomes?

PARs are homologous regions at the ends of X and Y chromosomes that allow them to pair and recombine during meiosis.

When can a chromosomally male develop female reproductive parts, and vice versa (intersex)?

Intersex conditions occur when there is a mismatch between chromosomal sex (XX or XY) and the development of reproductive organs, often due to variations in genes like SRY, hormone production, or hormone receptor function.

What is X inactivation?

X inactivation is the process in females where one of the two X chromosomes is randomly silenced in each cell to balance gene expression with males.

What is a Barr body?

A Barr body is the condensed, inactivated X chromosome visible in the nucleus of female cells after X inactivation.