Cell Bio: Chapter 19 Flashcards
(22 cards)
What type of cells are the vast majority in your body?
Somatic cells.
What form of cell division do somatic cells undergo?
Mitosis.
What form of cell division to germ line cells ungero?
Meiosis.
What is a diploid cell?
(2n). 2 copies of each chromosome. Carry the same genes on both copies.
What are haploid cells?
(1n). 1 copy of each chromosomes.
What happens just before meiosis begins?
Each chromosome in the diploid 2n parent cell is replicated.
What happens when replication is complete?
Each chromosome consists of two identical sister chromatids attached at the centromere.
How many chromosomes do diploid organisms have from each parent?
1 from the male and 1 from the female parent.
What happens in meiosis 1?
Homologous chromosomes of each chromosome pair separate and go to different daughter cells (each daughter cell still has 2 identical sister chromatids).
What happens in meiosis 2?
Sister chromatids separate and go to each of two daughter cells. Results in four haploid gametes with one copy of a chromosome.
What happens in prophase 1?
Replicated maternal and paternal chromosomes pair to form a bivalent.
When does crossing over occur between non-sister chromatids?
During late prohpase 1; a chiasma forms at the crossover point.
How often does crossing over occur?
At least once in each pair of chromosomes in most organisms.
What happens in metaphase 1?
Bivalents align on the metaphase plate; helt together by chiasmata.
What happens during anaphase 1?
Homologous chromosomes separate and move to the two poles of the cell.
What are the two sources of genetic diversity?
Independent assortment of homologs during meiosis 1, and crossing over.
How does independent assortment lead to genetic diversity?
An individual inprinciple could produce 2^n different gametes. Humans could produce 8.4x10^6 different gametes in one individual.
How does crossing over lead to genetic diversity?
Mixing up of maternal and paternal chromosomes, some DNA from both on each chromosome. Leads to new combination of alleles.
What is nondisjunction?
When homologs or sister chromatids fail to separate properly in anaphase 1 or 2.
What can lead to miscarriages?
Gametes forming abnormal embryos that fail to develop and die.
Can children with Down syndrome still survive?
Yes; since chromosome 21 is the smallest somatic chromosome.
How often does nondisjunction occur?
10% of meioses of human cells.
