Eukaryotic Genetics (44-53) Flashcards
What is genomics?
Technology used to generate large data sets of digital information
What is genetics?
Method of experimentation used to understand cause ad effect between genes and phenotypic variation
What is a holobiont?
Host + Microbiome
→ extends our genome
How much DNA does a human cell contain?
Over 2 meters
What are telomeres?
A region of repetitive DNA sequences at the end of a chromosome
→ prevents the ends from becoming tangled and frayed
→ gets shorter each time a cell divides
What is a centromere?
Links sister chromatids together
→ spindle fibres attach via the kinetochore
→ contains satellite DNA - non-coding repeating regions
What is the difference between euchromatin and heterochromatin?
Euchromatin → lightly packed DNA, gene rich, often under active transcription
Heterochromatin → tightly coiled DNA, not good place for genes as too tight for transcription
What is mitosis?
For tissue repair, multiplication and growth
→ generates two identical daughter cells
What is meiosis?
For gametes
→ four genetically distinct daughter cells
→ sexual reproduction ‘shuffles the deck’
What happens during interphase?
Chromosomes and organelles replicate
What happens during prophase?
Nuclear membrane breaks down
→ spindle begins extending from poles and attaches to centromeres
→ centrosome splits to two poles
→ DNA begins to condense
What happens during metaphase?
Centromeres align at the equator (metaphase plate)
→ bipolar attachment
What happens during anaphase?
Chromosomes migrate to opposite poles
(sister chromatids are now chromosomes)
→ chromosomes with two strands of identical information - chromatids
What happens during telophase?
Chromosomes at poles
→ spindle disassembles
→ nuclear membrane reforms
What is cytokinesis?
Chromosomes decondense
→ cell divide
→ same genetic information in both cells
How are sister chromatids joined?
Cohesin
→ cohesion destroyed enzymatically by separase breakdown of cohesin protein
What happens during prophase 1?
Centrosome splits and move to poles
→ DNA condensing begins
→ homologous chromosomes align and synaptonemal complex forms
→ double strand breaks arise and chiasmata form
→ nuclear membrane breaks down
→ spindle begins to form
→ DNA fully condensed, synaptonemal complex breakdowns, monopolar kinetochore attach chromosomes to spindle
What are sister chromatids?
Identical copies of a single chromosome
→ temporarily held together by a centromere during cell devision
What are homologous chromosomes?
Pairs of chromosomes of similar size, shape and gene content
→ inherited from both parents
→ carry same genes at corresponding locations, although alleles differ between the two
→ undergo crossing over - creates genetic diversity
What happens during metaphase 1?
Kinetochores aligned at the equator (metaphase plate)
→ spindle fibres attach to the centromeres of homologous chromosomes
What happens during anaphase 1?
Monopolar attachment pulls homologue chromosomes to the opposite poles
→ pairs in opposite directions
→ sister chromatids remain attached
What happens during telophase 1 and cell devision?
Haploid cells have formed (half the number of chromosome)
→ nuclear envelope reforms
What happens during meiosis II?
Prophase 2 → chromosomes recondense
Metaphase 2 → line up at metaphase plate
Anaphase 2 → sister chromatids separate to opposite poles
Telophase 2 → chromosomes arrive at poles
+ cytokinesis
→ results in 4 genetically unique haploid cells
What is leptotene stage?
1st stage of prophase 1: ‘thin thread’ stage
→ chromosomes start to condense and become visible
→ homolog pairing begins
→ double-stranded DNA breaks are introduced
→ each chromosome consists of two sister chromatids joined by centromere
What is zygotene stage?
2nd stage of prophase 1: ‘paired threads’ stage
→ a synaptonemal complex beings to form - a protein structure that holds homologous chromosomes together
→ paired homologs now referred to as bivalents
→ crossing-over starts to occur at chiasmata
What is pachytene stage?
3rd stage of prophase 1: ‘thick thread’ stage
→ condensing of chromosomes continues
→ synaptonemal complex is complete - homologous chromosomes held together tightly
→ bivalents have 4 sister chromatids
→ crossing-over is completed
What is diplotene stage?
4th stage of prophase 1: ‘two thread’ stage
→ synaptonemal complex dissembles - homologous chromosomes separate slightly but are held at chiasmata
What is diakinesis stage?
5th stage of prophase 1: ‘moving apart’ stage
→ chromosomes repel each other
→ non-sister chromatids remain loosely associated via chiasmata
→ nuclear membrane and nucleolus disappear
→ monopolar attachment of chromosomes to spindle fibres
What is the synaptonemal complex function?
Protein structure formed during meiosis 1 that holds together homologous chromosomes
→ facilitates late stages of recombination
→ prevents different homolog pairs form getting entangled
When does genetic shuffling occur?
During meiosis 1 by:
→ independent assortment of homologous chromosomes
→ crossing-over of chromosomes arms between non-sister chromatids
What are discrete alleles?
Alleles Mendel studies
→ environment doesn’t matter
→ phenotype good prediction
What is Mendel’s First Law of Inheritance?
During the formation of gametes (sex cells), the paired alleles for a trait separate (segregate) from each other, so that each gamete receives only one allele for a particular trait.
Heredity is controlled by paired factors or ALLELES of genes
→ used experimental method to explain 3.15:1 ratio of purple to white flowers
How did Roland Biffen do the first demonstration of applied genetics?
Produced wheat variety that contained resistance to yellow rust disease
→ identified as a simple mendelian trait
What is translational genetics?
Application of genetic research to clinal practice or new therapies
→ from model organisms like:
Arabidopsis thaliana → innate immunity
Drosophila (fruit fly) → multicellular development, innate immunity
Mice → mammalian acquired immunity
What is the chromosome theory?
Chromosomes are the unit of heredity
→ genes are located on chromosomes
→ chromosomes are the carriers of genetic information - DNA
→ not true - genes are unit of heredity
What two things should be true if chromosomes are the unit of heredity?
→ traits on different chromosomes should independently assort
→ traits in the same chromosome should be inherited together
Why was the chromosome theory not holding up with Thomas Hunt-Moragn’s experiments with drosophila?
The ratio of normal and vestigial wings didn’t match predictions (if they were on the same of different chromosomes?
→ recombination
Does the frequency of recombination depend on the physical distance between genes?
Yes
→ genes that are located farther apart on the chromosome have a higher probability of experiencing a crossover event during meiosis
What is the unit of heredity?
Genes are the unit of heredity
→ genes are ‘physically’ locally located in a linear manner along a chromosome
What is map-based cloning?
Molecularly identify a gene that is responsible for a Mendelian trait on the basis of its physical location in the organism genome
Step 1 → identify genes location from a genome-wide search of linkage markers
Step 2 → sequence the DNA across the locus in both wt and mutant variants
Step 3 → verify the function of the causal gene
What is a molecular marker?
A difference in DNA sequence (DNA polymorphism) between two individuals
→ can’t see through karyotyping - need base sequence