Class Notes (837,836)
Canada (510,504)
Biology (2,437)
BIOLOGY 2C03 (138)
Joe Kim (16)
Lecture 5

Lecture 5 - February 5, 2013.docx

10 Pages
Unlock Document

Joe Kim

Course Code Year Lecture 5 – Feb 5, 2013 Chromosomal Theory of Inheritance  A collection of studies revealed that genes are on chromosomes – in fact multiple genes are present on each chromosome  Homologous Chromosomes – a pair of matching chromosomes; one homolog from each parents  Ploidy – the number of complete chromosome sets  Most eukaryotes – diploid adults, haploid gametes Classification of eukaryotic chromosomes by structure:  Position of the centromere – constriction along length of chromosome; attaches to spindle fibers during mitosis and meiosis  Length of chromosome  Human chromosome set: 23 chromosomes  Figure – two copies of the set (diploid)  Chromosomes can be distinguished as: o Autosomes: present in the same copy number in both males and females; number and morphology of autosomes is species- specific o Sex-chromosomes – present in different copies in males vs. females; single pair of sex chromosomes or a single sex chromosome 1 Course Code Year  Questions we need to answer: o How do we know that genes are on chromosomes? o What is the structure of a chromosome? o How does the structure of a chromosome affect gene expression?  Chromosomal basis of hereditary o Review of mitosis and meiosis – connection between chromosome dynamics and Mendelian principles o Development of the chromosomal theory of inheritance – connecting Cytology and Genetics  The chromosome theory of inheritance – the union of cytology and genetics o Cytology – the study of cells (chromosomes that we can see) o Genetics – the study of heritable factors (genes) o 1902: Sutton and Boveri - genes are on chromosomes  What is the accumulated proof for this theory?  Much evidence that suggested that heritable information is found on chromosomes: 1) Chromosomes number is species specific o But, Sable Antelope: 46 o Karyotypes differ – structures differ not just number 2) Blakeslee: Jimsonweed (Datura) plants with different chromosome sets display different phenotypes o 12 chromosomes in Datura stramonium o 12 variant phenotypes, each associated with a single extra chromosome (each showing trisomy for a different chromosome) o Observation – extra chromosome; changes phenotype o Mendel – phenotypes determined by genes o Hypothesis – genes must be located on chromosomes 2 Course Code Year 3) Sex chromosomes – chromosomes represented differently in the two sexes o Different chromosomes set in males and females o How does this provide proof for chromosomal theory of inheritances? o See different phenotype in males vs. females (morphological behavioural; at the cellular level have a different chromosomal set o The difference between males and females must lie in the chromosome 4) Elinor Carothers – meiosis in grasshoppers, independent assortment of chromosomes o Homologous pair of autosomes that look slightly different o Equal likely that the longer autosome segregated with X or Y o Pair of homologous chromosomes were similar along most of their length, but one partner had a little extra at the end o Still partnered together and segregated in meiosis o Followed 2 sets of chromosomes that have different characteristics o Watched X and Y chromosomes o Watched autosomal chromosomes too 5) Patterns of chromosome movements in meiosis parallel Mendel’s patterns of inheritance (Walter Sutton) o Follow chromosome in meiosis o Show how they are consistent with pattern of behaviour o 2 divisions occur  Homologs segregate  Sister chromatids segregate o Segregation of pairs – consistent of segregation of alleles Cell Division Mitosis  Mitosis – replication of identical cells; one cell produces two cells that are genetically identical to one another and to the original mother cell  One diploid cell (2n)  two diploid cells (2 x 2n)  All cells of the body reproduce and multiply by mitosis 3 Course Code Year  Non-disjunction – chromosomes fail to separate  Homologues – two chromosomes carrying the same gene sequence o Paternal and maternal copies of the same chromosome are homologues  Centromere – point of attachment of sister chromatids and attachment of microtubules  Replicated chromosome – after DNA replication, a chromosome contains two sister chromatids  Chromosome – DNA and proteins Meiosis  Meiosis – germ line cells undergo meiosis in order to produce haploid gametes  Take diploid (2n) and produce collection of haploid cells (n)  Can be divided into two stages – two distinct cell divisions  Meiosis-specific events help to explain many observations in genetics  Meiosis I – first division; increase DNA molecules (2n4n) o Interphase I to Prophase I – replicated chromosomes o Prophase I – potentially tetraploid cell that can go on to produce 4 haploid cells o Metaphase I – homologous chromosome pair o Anaphase I – reduction division (2n  n)  Homologues separate and therefore alleles separate  Meiotic spindle attach to homologous chromosome o Telophase – divide; one homologous chromosome in each cell o Mendel’s First Law: Principle of Equal Segregation  Meiosis II – second division o Each cell ends up with one replicated sister chromatid o End of meiosis 2 we have 4 haploid cells o Anaphase II – equational division  Now replicated, paired sister chromatids separate  Metaphase I – assembly of spindle is completed; each chromosome pair (bivalent) aligns across the equatorial plane of the spindle o homologous chromosome pair o Paired centromeres of homologues assemble on spindle 4 Course Code Year  Metaphase-Ana
More Less

Related notes for BIOLOGY 2C03

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.