Meiosis Flashcards
Mitosis
Growth and repair
One division
Two daughters cells
Chromosome number same as parent (diploid)
Genetically identical cells
Meiosis
Formation of gametes
Two divisions
4 daughter cells
Half chromosome number (haploid)
Genetically diverse cells
Importance of meiosis
Formation of gametes for sexual reproduction
Genetic diversity for adaptation and survival
Maintaining chromosome number
Evidence that cell is in first division of meiosis
Chromosomes are in homologous pairs
Bivalnet have formed
Chromatids wrapped around el (crossing over)
How does meiosis result in genetic variation
Homologous chromosomes pair up
Crossing over occurs through formation of chiasma
This produces new combination of alleles
Chromosomes line up at centre of cell randomly
Producing varying combination of chromosomes
What do species have in common
Capable of breeding to produce living fertile offspring
Similar physical and biochemical makeup
Occupy same ecological niche
Challenges with defining species
Theory of evolution
Some species rarely reproduce sexually
Members of diff populations may be isolated so couldn’t interbreed
Define classification
Organising living organisms into groups based on their physical and biochemical similarities and difference
2 types of classification
Arificial : observable feature and analogous characteristics
Phylogeny classification:
based on evolutionary relationships
hierarchy of groups formed
Features taken from ancestors
Phylogeny
Basing classification on evolutionary relationships between organisms
Taxonomy
Study and practice of grouping organisms based on their biological classification by placing them in hierarchical order
Hierarchy
Smaller groups within larger groups with no overlap
DNA sequencing
Determines the order of nucleotides on strand of DNA
Adavathges of using AI classification
Easy to carry out less time consuming
Each characteristic determined by genes
Disadvantage of AI classification
Large number of characteristics can be polyegenic
Characteristics can be modified by environment
Advantages of DNA sequencing
Accurate method to show close and distant relationships
Easy to carry out
Disadvantages of DNA sequencing
Expensive and can be time consuming
Difficult to link extinct species
DNA contains lots of information
Interphase
DNA replicates = chromatids joined by centromere
End of chromatids sealed by telomeres
Prophase
Chromosomes condense
In homologous pairs
Crossing over happens
Nuclear envelope breaks down
Stages of meiosis 1 (after prophase)
Metaphase : bivalents Line up the equator randomly
Anaphase : bivalents separate and pulled apart opposite poles
Telophase : nuclear envelope reforms around 2 groups of chromosomes
Cytokinesis 1
Division of cytoplasm = 2 haploid cells
Meiosis 2
No interphase = No DNA replication
P = nuclear envelope breaks down and chromosomes condense
M = chromosomes line up equator randomly
A = centromeres divide and indivisible chromosomes pulled apart = 4 groups
T = nuclear membrane forms around 2 groups
Cytokinesis 2
Cytoplasm divides = 4 haploid cells
Same number of centromeres but diff chromosomes
