[[G11 Pre-AP Biology]]

Human body cells have 46 chromosomes.

Chromosome 23 is a sex chromosomes.
First 22 chromosomes are autosomes.

First chromatid of first pair is taken in metaphase, organised picture of chromosomes.

DNA is the molecule that holds information.
Chromosomes are structures that consist of DNA and associated proteins.

DNA wraps around histones and forms nucleosomes.
Nucleotide has 1 phosphate, base, and deoxyribose sugar.

4 different bases.
Adenine compliments thymine.
Cytosine compliments guanine.

Genes are sections of DNA that instructs cells to make proteins.
Chromosomes are chromatins but more curly to be more condense and sturdy.

Sperm and egg should have 23 chromosomes, zygote (fertilized egg) should have 46.

Interphase is when all cell functions occur, DNA replicates, and the cell goes through G1, synthesis, and G2.
Prophase is when chromatin condenses, nuclear membrane disappears, centrioles move, and spindle fibers form.
Metaphase is when spindle fibers pull double stranded chromosomes to center of cells.
Anaphase is when spindle fibers contract and pull sister chromatids apart. Single stranded chomosomes start migrating to opposite sides.
Telophase is when single stranded chromosomes arrive at opposite sides, nuclear membrane and nucleolus reappear, and spindle fibers disappear.
Cytokinesis is when cell splits into 2 identical daughter cells.

Homologous chromosomes have the same gene but aren't identical. Same length, centromere location, and banding pattern. One from each parent.

Allele are different version of a gene.

Haploids (n) are one set of chromosomes.
Diploids (2n) are two sets of chromosomes.
One set from sperm, one from egg.
Humans have 46 chromosomes, 23 chromosomes per set.

Meiosis is the process of producing cells with half the number chromosomes of parent cells. Increases genetic variation, different combinations of alleles.

Process of meiosis:
Interphase involves growth of cell and replication of chromosomes.

Prophase I.
Synapsis is when the homologous chromosomes pair up.
Crossover occurs. Non sister chromatids exchange information (homologous chromosome).
Centrosomes move to opposite sides, spindle forms (nuclear membrane disappears, chromosomes coil).
Tetrad is a pair of homologous chromosomes/bivalent.

Metaphase I.
Homologous pairs (tetrad) line up along equator of cells.
![[Pasted image 20261013105105.png|496]]
Cross over has already occured in prophase I.
In mitosis they aren't lined up accross from their pair.
Spindle fibers attach to centromeres of each homologous chromosome.

Anaphase I.
Homologous chromosomes separate from each other, homologues of each bivalent separate. Sister chromatids are still attached unlike mitosis.
Double stranded chromosomes start moving to opposite sides.

Telephase I.
Double stranded chromosomes arrive at opposite ends.
Spindle fibers disappear.
Chromosomes uncoil.
Nuclear membrane reforms.

Meiosis part 2 is just like mitosis.