BIO 2133 Study Guide - Quiz Guide: Sister Chromatids, Pseudogene, Barr Body
27 Apr 2018
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MODULE 3: HUMAN GENOME AND INHERITANCE
LEARNING OBJECTIVES
•Explain the meaning of ploidy (haploid, diploid, etc) and how it relates to the number of
homologues of each chromosomes.
Ploidy refers to the number of sets of chromosomes in a cell or in cells of an organism
Homologues are chromosome pairs that are similar in length and gene positions
After meiosis one, cells are HAPLOID. !Reduction division because the number of chromosomes /
centromeres are reduced by half
For ploidy, count centromeres
Loci = fixed positions on a chromosome
A variant of the similar gene sequence located at a given locus is called an allele
•Describe how the positions of individual genes on a given chromosome are related to their
positions on the homolog of that chromosome.
The closer 2 loci reside along the axis of a chromosome the less likely that any single crossover event
will occur between them. The position of a gene / loci on a pair of homologs is the same
•Differentiate between a gene and an allele.
!Genes are nucleotide sequences which make up DNA and code for proteins.
Alleles are variant forms of genes on a locus of a chromosomes
Genes code for different traits and different alleles result in a slight variation of that trait. There can be
multiple alleles for a gene but one can only have as many as their ploidy. (humans can only have 2 at a
time while population has 9 possibilities)
everyone may have a gene for something but depending on the allelic makeup, one may not express
the gene.
•Diagram a typical eukaryotic gene and indicate the locations of (i) regions that are genetic but not
coding, (ii) regions that are transcribed but not translated, and (iii) regions that are both transcribed
and translated.
(i) Centromere, telomere, viral elements, Cis and trans regulatory elements, transposons, repeated
sequences(VNTR, SNTR, LINEs, SINES)pseudo genes, Non coding functional RNA, promoter
(ii)!Introns, spliceosomes, transposons, transcription factors .
(iii) Everything else, genes, exons
Non coding DNA do not encode proteins but some are transcribed to functional RNA molecules for
regulatory purposes of transcription or translation
•Describe the general organization, possible function, and frequency of genes and non-gene DNA
sequences in a typical eukaryotic genome.
non coding – Does not code for functional RNA
transposons – sequences that can move from one position on a chromosome to another or even from
one chromosome to another and may disrupt a gene function in the process
introns – non coding sections intersperse with coding regions of a gene or exon.
•Explain the lack of correlation between chromosome number and genetic information content.
Chromosome number does not necessarily mean more genetic information.
Chromosomes contain many non-coding regions such as telomeres, introns, pseudo gene and
repeated sequences. More chromosomes could just mean more non coding DNA and does not
necessarily mean more transcription / protein production.
•Explain how all cells have the same genetic content and yet have different functions in the body.
All cells contain the same hereditary information in their nuclei. This information acts as the instructions
for the production of proteins by each cell.
Cells perform different tasks and thus will translate and transcribe different genes for their individual
tasks
Each cell will have different expression levels of each gene depending on signaling (epigenetics)
Although multiple cells have same genotype, depending on the environment can have different genes
expressed and thus different phenotypes
not all genes are expressed at the same time.
tart of with stem cell, and depending on signal becomes a different cell
serious of signals recognized to turn genes on and off which results in different cells
•Describe the anatomy of a chromosome
sister chromatids: contain identical copies of DNA, formed
by replicating a single chromatid
centromere → Where the sister chromatids attach
Both chromatids are DOUBLE STRANDED.
Barr Bodies
Heterochromatin → system shuts one of 2 X’s off. Other becomes so heterochromatin in nature
becomes a barr body.
Number of X - 1 barr bodies.
Enhancer can be after the gene in the case that DNA can loop on itself.
•Explain the functional significance of packaging DNA into chromosomes.
Histones
Sequence in between histones less packed and more activity than sequences on histones which are
tightly wound and hard to transcribe and
Acetylation and deacetylation happens on histones
Acetylation → loosen genes around histones. Methylation → compact DNA
Mutation on histone influence DNA packaging
•Meiosis
Independent Assortment
Each pair lines up at metaphase I. 50/50 change daughter cell well
one copy or another.
2^23 combinations ~ 8 million
Crossing over
Occur anywhere along autosomes, sex chromosomes only at
certain regions
Document Summary
Learning objectives: explain the meaning of ploidy (haploid, diploid, etc) and how it relates to the number of homologues of each chromosomes. Ploidy refers to the number of sets of chromosomes in a cell or in cells of an organism. Homologues are chromosome pairs that are similar in length and gene positions. Reduction division because the number of chromosomes / centromeres are reduced by half. A variant of the similar gene sequence located at a given locus is called an allele: describe how the positions of individual genes on a given chromosome are related to their positions on the homolog of that chromosome. The closer 2 loci reside along the axis of a chromosome the less likely that any single crossover event will occur between them. The position of a gene / loci on a pair of homologs is the same: differentiate between a gene and an allele. Genes are nucleotide sequences which make up dna and code for proteins.
