Cell cycle & Cell division Flashcards
Describe the appearance and behaviour of chromosomes during mitosis: (5 marks)
- Prophase - chromosomes supercoil and condense and become visible.
- Chromosomes appear as 2 identical sister chromatids joined by a centromere.
- During Metaphase, chromosomes line up to the equator of the cell
4.Chromosomes attach to the spindle fibres - By their centromeres
- Anaphase, centromere splits
- sister chromatids are pulled to opposite poles of the cell making a v-shape
- telophase chromatids uncoil and become thinner
What are a homologous pair of chromosomes
Two chromosomes that carry the same genes in the same Loci/location
Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. Explain how. (7 points)
- Homologous chromosomes pair up
- Maternal and paternal chromosomes are arranged in any order
- independent segregation
- crossing over
- equal portions of chromatids are swapped between chromosomes
- produces new combination of alleles
- chromosomes separated at meiosis 2 later
Describe the process of crossing over and explain how it increases genetic diversity.
- Homologous pairs of chromosomes form a bivalent
- Chiasmata form
- equal lengths of chromatids/alleles are exchanged
- producing new combinations of alleles.
Give two differences between mitosis and meiosis.
- One division in Mitosis WHEREAS there are 2 divisions in meiosis
- Daughter cells genetically identical in mitosis WHEREAS daughter cells are genetically different in meiosis
- two cells are formed in mitosis WHEREAS four produced in meiosis
- Diploid->diploid/haploid->haploid in mitosis WHEREAS diploid ->haploid in meiosis
- separation of homologous pairs in meiosis only
- crossing over only in meiosis
- independent segregation only in meiosis
Describe binary fission in bacteria
- replication of circular DNA
- replication of plasmids
- division of cytoplasm to produce daughter cells
Describe and explain the processes that occur during meiosis that increase genetic variation (5 marks)
- Homologous chromosomes pair up/ bivalent form
- independent segregation
- maternal and paternal chromosomes are reshuffled in any combination
- crossing over leads to exchange of parts of alleles between homologous chromosomes
- both create a new combination of alleles.
Name the type of cell division that occurs in the meristem of plants of for growth
Mitosis
Before a cell divides what must happen to its genetic material
chromosomes are replicated
Explain how the chromosome number is halved during meiosis. (2 marks)
- Homologous chromosomes (pair);
- One of each (pair) goes to each (daughter)
cell / to opposite poles;
Define “allele”
allele is an alternative form of a gene and the locus is the specific position of the gene on the chromosome
Define “gene”
base sequence of DNA that codes for: the amino acid sequence of a polypeptide. a functional RNA (including ribosomal RNA and tRNAs).
