Chromosomes Flashcards
(12 cards)
When are chromosomes visible during the cell cycle?
During metaphase as chromosomes are highly condensed
DNA has already been copied so there is twice as much DNA as there is at interphase
What is a chromosome?
Very continuous piece of DNA
How many chromosomes are in human somatic cells?
46 chromosomes in 23 pairs
Chromosomes pairs 1 to 22 are autosomes
23rd pair are sex chromosomes (XX and XY)
What are nubbins?
At the top of some chromosomes, contain highly repetitive DNA coding for ribosomal DNA
What are telomeres?
Tips of chromosome that tether to nuclear membrane
What is centromere?
Joins sister chromatids, essential for segregation at cell division
What is a chromatin?
DNA + protein
What is heterochromatid?
Region of highly condensed DNA not coding for anything
What is acrocentric?
Centromere near top
Anatomy of metaphase chromosomes - light bands
- DNA less packed so takes up less dye
- Active genes here
- Replicate early in S phase
Anatomy of metaphase chromosomes - dark bands
- DNA packed tightly here so takes up more dye
- Replicate late
What is a karyotype?
Number and visual appearance of chromosomes in cell nuclei
