Cell ReproductionCell Reproduction

Chromosome Structure & FunctionChromosome Structure & Function

ReviewNucleus:

Control center of eukaryotic cells

Contains genetic information

Contains DNA in Chromosomes

Chromosome/ChromatinChromosome/Chromatin When a eukaryotic cell is not

dividing, the DNA and associated proteins is a tangled mass of thin threads called chromatin.

At the time of cell division, the chromatin condenses to form highly compacted structures called chromosomes.

Chromatin

chromosome

HistonesHistones

DNA wraps tightly DNA wraps tightly around histone proteins around histone proteins when coiling.when coiling.

DNA Supercoil

Chromosome/ChromatidChromosome/Chromatid Just prior to mitosis, each chromosome duplicates to

form sister chromatids Sister chromatids are genetically identical. A duplicated chromosome is made of two sister

chromatids held together in a region called the centromere.

When the cells divide sister chromatids separate from one another.

At the end of mitosis, each chromosome consists of a single chromatid.

Chromosome NumberChromosome Number

Each species has a characteristic number of Chromosomes in their body cells:

Humans: 46 Cat: 38Fruit fly: 8 Catfish: 58Broccoli: 18 Dog: 78Goldfish: 94 Black Mulberry: 308

Mosquito: 6 King Crab: 208

Note: prokaryotes usually have only 1 chromosome

Sex chromosomesSex chromosomes

Chromosomes that Chromosomes that determine sex.determine sex.

Humans: X or YHumans: X or Y– Females: XXFemales: XX– Male: XYMale: XY

AutosomesAutosomes

Chromosomes that do not determine sex

Homologous ChromosomesHomologous Chromosomes

Every organism made by Every organism made by sexual reproduction haS 2 sexual reproduction haS 2 copies of each autosome.copies of each autosome.

Same size and shape.Same size and shape.

Carry genes for the same Carry genes for the same trait. trait.

KaryotypesKaryotypes

A “picture” of a person’s 46 chromosomes. A “picture” of a person’s 46 chromosomes.

KaryotypesKaryotypes

Chromosomes are arranged in Chromosomes are arranged in homologous pairs.homologous pairs.

Why use karyotypes?Why use karyotypes?

To determine sex:To determine sex:» Male- XYMale- XY» Female- XXFemale- XX

To see abnormalities in chromosomesTo see abnormalities in chromosomes» Extra chromosomesExtra chromosomes» Missing chromosomesMissing chromosomes» Extra/missing pieces of chromosomesExtra/missing pieces of chromosomes

DiploidDiploid

Cells with two sets of chromosomes (both Cells with two sets of chromosomes (both chromosomes for each homologous pair) & chromosomes for each homologous pair) & 2 sex chromosomes2 sex chromosomes

2n2n

HaploidHaploid

1 set of chromosomes (1/2 as many as the 1 set of chromosomes (1/2 as many as the diploid cell).diploid cell).

1n1n

Sex cellsSex cells