Meisos Flashcards
Chromosome
Rod shaped filamentous bodies present in nucleas & cytoplasm of prokaryotic cell which carries genes
Difference between somatic & gamete
Somatic cells are human body cells with:
46 chromosomes, diploid number
Gametes are sex cells with 23 chromosomes and only n
Zygote
Fusion of female gamete and male gamete
Chromosome components
Centromere : holds 2 chromostids
Gene: segment of DNA that codes for a trait
Chromotids : identical copies making up a chromosome
Homologous chromosomes
Chromosomes that are identical in shape, size & which code genes for same set of characteristics
Karyotype
Image which depicts an organisms chromosomes which determines gender & whether a person has down syndrome
Loci
Genes in same position
Importance of mitosis
Growth (allows zygote to produce more cell in order to grow)
Repair & replacement : allow multicellular organism maintain its tissues.
Cytokinesis definition
Process of cytoplasmic division to form two daughter cells
Karyokinesis
Division of nucleas
Meisos definition
Cell division whereby a diploid cell undergoes 2 cell divisions & divides to form 4 dissimilar haploid cells (sex)
Prophase 1
Homologous Chromosomes shorten, visible
Nuclear membrane & Nucleolus dissappear
Spindle starts to form
Chiasma from pairing of homologous pairs
Metaphase 1
Homologous chromosomes line up at equator
Centromere of chromosome attaches to extended spindle fibres
Random arrangement at equator
Anaphase 1
Spindles contract, shorten & pull chromosomes to opp sides of cell
Creating random assortment
Telophase 1
Nuclear membrane and Nucleolus reform
Each pole has half no. of chromosomes present in original cell
Invagination of cleavage furrow deepens till cytokinesis & karyokinesis occurs to form 2 different daughter cells
Meiosis significance
Process reduces diploid to haploid
Produces Gametes for fertilisation
Ensures no. of chromosomes in species stays constant over generations
Genetic variation
Autosomes
22 pairs of Chromosomes which aren’t sex cells in diploid cell
Bivalent
Homologous chromosomes held together by DNA cross over
Centriole
Organelle in cytoplasm giving rise to spindle fibres during mitosis and meisos
Chiasma
Point where crossing over takes place between chromatids of homologous pair during prophase 1
Mitosis
Process of cell division where resulting daughter cells have same diploid chromosomal no. as original parent cell
Non disjunction
Failure of homologous chromosome to divide leading to extra chromosome or one less chromosome in another gamete
Spindle fibres
Micros tubules that form during cell division
Gonosomes
Last Single pair of sex chromosomes (XX or XY)
Significance of meoisis
Genetic variation
Reduced genetic content by half
Gametes produced for fertilisation
Ensures no. of chromosomes in species remains constant
How Genetic variation occurs
Crossing over
Random arrangement at equator
(metaphase 1 & 2)
Random fertilisation
Where does Meiosis in animals occur
Female: ovary
Male: testis
Where does Meiosis occur in cell
In animal cell:
Centrosome consisting of centriole form spindle fibres that attach to chromosome during meiosis
Fertilisation
Fusion of a sperm and ovum to form a diploid zygote
Interphase
Phase in cell cycle where DNA replicates
Importance of DNA replication
Helps double genetic material to be shared equally during cell division
Tetrads
Homologous pairs carrying genes controlling same inherited traits
Prophase 2
Centriole move to opp sides
Nuclear membrane & Nucleolus disintegrate.
Spindle fibre forms
Metaphase 2
Centromeres attach to spindle fibres
Single chromosomes now like Up at equator
Random arrangement
Anaphase 2
Centromeres split up
Chromatids move to opp sides
Random arrangement
Spindle fibres shorten & contract & pull chromotids to opp poles
Telophase 2
Nuclear membrane & Nucleolus reforms
Cytokinesis occurs.
4 haploid daughter cells produced.
Genetically different
Difference in prophase 1 & 2
No crossing over ring prophase 2, no bivalent
Chromosome have a patched appearance in prophase 2
Metaphase 1 & 2 differences
1: pairs of chromosomes align at equator but 2: single pairs align
Anaphase 1 & 2 differences
2: split centromeres
Telophase 1 & 2 differences
2: unreplicated chromosome / single stranded
2: 4 haploid daughter cells that are genetically different but 1: 2 identical daughter cells
Difference between meiosis and mitosis
Mitosis is for somatic cells and meiosis is for gametes (site)
Mitosis is for growth meiosis is for formation of haploid Gametes
Mitosis makes 2 identical cells and meiosis makes 4 genetically different haploid cells
Mitosis have 1 division and meiosis has 2
Variation importance
Forms raw material for natural selection
Increases survival chance
Creates favorable features and conditions
Causes & consequences of non - dysjunction
Spindle fibres fail to separate during meiosis
One pair of homologous chromosome fail to separate in anaphase 1 or replicated chromosome does not separate & move into different cells in anaphase 3
2 of 4 gametes receive extra copy of affected dna
2 of 4 chromosomes lack dna
Trisomy
Non dysjunction in meiosis 1 resulting in 21 down syndrome
Characteristics of someone with down syndrome
Small eyes
Flattened nasal bridge
Protuding tongue
Broad neck
Epicanthic fold
Cause of abnormal chromosome count
Homologous pairs fail to separate in meiosis 1
Or replicated chromosomes fail to separate in meiosis 2
Types of nondisjunction
Trisomy (3 chromosomes on set 21)
Monomy 23 (has 1 chromosome in set 23)
