Chromosomes and Karyotypes: Key Points from Amoeba Sisters Lecture

Introduction to Chromosomes

Chromosomes are often mistakenly visualized as always being in an X shape due to common diagram representations.
Human chromosomes can be represented as single components or duplicated (e.g., during interphase).
Chromosomes made of chromatin, which consists of DNA and protein.
DNA is wound around proteins called histones to form nucleosomes and further condenses into chromosomes.
Purpose of chromosome packaging:
- Fits DNA inside the cell nucleus.
- Facilitates DNA movement during cell division (e.g., mitosis).

Humans have 46 chromosomes that can duplicate into chromatids.
During interphase, 46 chromosomes duplicate but are counted as 46 chromosomes with 92 chromatids.
Chromatids are separated during mitosis so each new cell receives 46 chromosomes.
Genes on chromosomes can be turned on/off depending on cell type (e.g., eye cells vs. stomach cells).

Karyotype: an image of all chromosomes in a cell, often used in medical screenings.
Chromosomes in karyotypes are typically stained and visible during the metaphase stage of mitosis.
Karyotypes are arranged in homologous pairs:
- 23 pairs in total, with 22 pairs known as autosomes.
- The last pair is the sex chromosomes (XX for females, XY for males).
- The name of X and Y chromosomes does not relate to their shape.

Each parent contributes 23 chromosomes:
- Sperm and egg cells (gametes) are haploid, containing 1 set of chromosomes.
- Upon fertilization, the zygote becomes diploid, with 2 sets of chromosomes, forming more diploid cells.
Fathers determine the biological sex of offspring (XY or XX).

Karyotypes help identify genetic disorders through revealing missing or extra chromosomes.
Genetics is a rapidly expanding field; careers such as genetic counseling are recommended for further study.

Understanding chromosomes and karyotypes is crucial for genetic research and medicine.
Encouragement to remain curious about the field of genetics.