Lecture 15: Meiosis and heredity Flashcards
Mitosis and Meiosis
Germ cells
- Meiosis
Somatic cells
- Mitosis
Mitosis and Meiosis
Germ cells
- Meiosis
Somatic cells
- Mitosis
Where does meiosis occur in each life cycle?
The transmission of cytoplasm differs between sex cells
Male contribution: Sperm or pollen transfer little or no cytoplasm to the egg
•Female contribution: Egg contributes almost all of the cytoplasm to the zygote
Gametogenesis
sperm cells (haploid) - 200,000,000 per day ovum (haploid) - 1 per cycle
Gametogenesis in Females
Mitosis in Fetal Ovary
Meiosis I, Asymmetrical division completed at ovulation
Meiosis II: Asymmetrical division (occurs only after fertilization)
Gametogenesis in Males
Mitosis occurs in adult testis
Meiosis I
Meiosis II
Differentiation
Meiosis I
Condensation of chromosomes
synapsis
recombination
prometaphase I
metaphase I - alignment at spindle midpoint
anaphase I - homologous chromosomes move to opposite poles
telophase - two haploid (n) nuclei form
Interkinesis
Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II
What are the differences between mitosis and meiosis?
Mitosis
•One division
•Two genetically identical daughter cells
•Chromosome number of the daughter cells is the same as the parent (i.e. 2n)
•Occurs in the cells of the body as the organism grows
Meiosis
•Two divisions
•Four daughter cells that are genetically different
•Chromosome number of daughter cells is half that of the parent cell (i.e. 1n haploid)
•Occurs in the production of gamete cells
Non-disjunction
MITOSIS: failure of sister chromatids to separate during and after mitosis
MEIOSIS: failure of homologous chromosomes to segregate during and after meiosis
Dosage compensation
Humans
Barr bodies: condensed genetically inactive X-chromosomes found in the nuclei of XX individuals (but not XY individuals)
•Inactivated X-chromosome is cell independent: some cells have inactivated maternal chromosomes others have inactivated paternal chromosomes
•Epigenetic silencing of one X-chromosome
Calico cats
Genetic mosaic: Inactivated X-chromosome is cell independent: some cells have inactivated maternal chromosomes, others have inactivated paternal chromosomes
Variation
Independent assortment
Chromosomes and chiasma
Chiasma
Bacteria sex: The F factor
F-factor: fertility plasmid Plasmid: small circle of DNA in a bacterial cell containing a larger circular chromosome
Transfer of bacterial genes:
Transformation occurs when bacteria take up DNA from disintegrated bacteria
•Linear fragments recombine by double crossovers
Transduction occurs when bacterial phages transfer DNA from one bacteria to another
- Virus incorporates DNA fragments from one cell
- If DNA fragments are homologous, new bacteria become partial diploids
- Recombination by double crossovers
Corn genetics
Corn is often purple or yellow
•In Coloured purple (C) kernels the pigment is produced but no pigment is produced in colourless (c) kernels
•But how could there be mottled kernels?
Transposable Elements
Transposable elements (TEs)
•Segments of DNA that move around cell genome
•Transposition is movement of TEs, jumping gene
•Target site of TE is not homologous with TE
•No crossing-over
TEs can move in two ways
•Cut-and-paste, original TE leaves
•Copy-and-paste, original TE stays in place
Transposition mutation
Bacterial Transposable Elements
Insertion sequences
•Contain only genes for tranposition
•Transposase catalyzes insertion or removal
•Inverted repeats mark insertion sequence
Transposon
•Multiple genes within inverted repeat sequences
•Antibiotic resistance genes within transposons
•Transposons can move to plasmi
Transposons
Eukaryotic transposons are similar in structure and function to prokarytotic
•Use transposase and inverted repeat sequences
•Use cut-and-paste or copy-and-paste
Retrotransposons
Retrotransposons transpose by copy-and-paste but transposition occurs via intermediate RNA
•Retrotransposon transcribed into RNA
•Reverse transcriptase uses RNA to make DNA
•DNA copy inserted into DNA at new location
Retroviruses
RNA genome replicates with DNA intermediate
•Uses reverse transcriptase
•Provirus similar to prophage
Common in vertebrates
•Retrovirus genomes common in humans
•HIV and carcinogenic retroviruses
Where does meiosis occur in each life cycle?
The transmission of cytoplasm differs between sex cells
Male contribution: Sperm or pollen transfer little or no cytoplasm to the egg
•Female contribution: Egg contributes almost all of the cytoplasm to the zygote
Gametogenesis
sperm cells (haploid) - 200,000,000 per day ovum (haploid) - 1 per cycle
Gametogenesis in Females
Mitosis in Fetal Ovary
Meiosis I, Asymmetrical division completed at ovulation
Meiosis II: Asymmetrical division (occurs only after fertilization)
Gametogenesis in Males
Mitosis occurs in adult testis
Meiosis I
Meiosis II
Differentiation
Meiosis I
Condensation of chromosomes
synapsis
recombination
prometaphase I
metaphase I - alignment at spindle midpoint
anaphase I - homologous chromosomes move to opposite poles
telophase - two haploid (n) nuclei form
Interkinesis
Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II
What are the differences between mitosis and meiosis?
Mitosis
•One division
•Two genetically identical daughter cells
•Chromosome number of the daughter cells is the same as the parent (i.e. 2n)
•Occurs in the cells of the body as the organism grows
Meiosis
•Two divisions
•Four daughter cells that are genetically different
•Chromosome number of daughter cells is half that of the parent cell (i.e. 1n haploid)
•Occurs in the production of gamete cells
Non-disjunction
idk
Dosage compensation
Humans
Barr bodies: condensed genetically inactive X-chromosomes found in the nuclei of XX individuals (but not XY individuals)
•Inactivated X-chromosome is cell independent: some cells have inactivated maternal chromosomes others have inactivated paternal chromosomes
•Epigenetic silencing of one X-chromosome
Calico cats
Genetic mosaic: Inactivated X-chromosome is cell independent: some cells have inactivated maternal chromosomes others have inactivated paternal chromosomes
Variation
Independent assortment
Chromosomes and chiasma
Chiasma
Bacteria sex: The F factor
F-factor: fertility plasmid Plasmid: small circle of DNA in a bacterial cell containing a larger circular chromosome
Transfer of bacterial genes:
Transformation occurs when bacteria take up DNA from disintegrated bacteria
•Linear fragments recombine by double crossovers
Transduction occurs when bacterial phages transfer DNA from one bacteria to another
- Virus incorporates DNA fragments from one cell
- If DNA fragments are homologous, new bacteria become partial diploids
- Recombination by double crossovers
Corn genetics
Corn is often purple or yellow
•In Coloured purple (C) kernels the pigment is produced but no pigment is produced in colourless (c) kernels
•But how could there be mottled kernels?
Transposable Elements
Transposable elements (TEs)
•Segments of DNA that move around cell genome
•Transposition is movement of TEs, jumping gene
•Target site of TE is not homologous with TE
•No crossing-over
TEs can move in two ways
•Cut-and-paste, original TE leaves
•Copy-and-paste, original TE stays in place
29
Transposition mutation
Bacterial Transposable Elements
Insertion sequences
•Contain only genes for tranposition
•Transposase catalyzes insertion or removal
•Inverted repeats mark insertion sequence
Transposon
•Multiple genes within inverted repeat sequences
•Antibiotic resistance genes within transposons
•Transposons can move to plasmi
32
Transposons
Eukaryotic transposons are similar in structure and function to prokarytotic
•Use transposase and inverted repeat sequences
•Use cut-and-paste or copy-and-paste
Retrotransposons
Retrotransposons transpose by copy-and-paste but transposition occurs via intermediate RNA
•Retrotransposon transcribed into RNA
•Reverse transcriptase uses RNA to make DNA
•DNA copy inserted into DNA at new location
Retroviruses
RNA genome replicates with DNA intermediate
•Uses reverse transcriptase
•Provirus similar to prophage
Common in vertebrates
•Retrovirus genomes common in humans
•HIV and carcinogenic retroviruses
