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Genetics Part 1

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Lauren Thompson

on 13 January 2015

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Transcript of Genetics Part 1

Labeling system
Whole of the genetic information of an organism

Chromosome - made of DNA and Protein

Genes - contained in chromosomes

Alleles - different forms of a specific gene
structural units, made of DNA and proteins

DNA is coiled around proteins to condense, allows a large amount of information to be stored in nucleus
4 Genetics Part 1
Gene for tumor preventions

located at 17p13.1
4.1 Chromosomes, genes, alleles and mutations
Gene locus
Specific position of a gene on a chromosome

Homologous - all individuals within a species have same genes and gene location on the same chromosome
Members of a species have the same number of chromosomes, genes, and gene loci

between species, chromosomes count varies
Sickle cell disease
A single base substitution occurs
Gene Mutations
Permanent change to base sequence

Millions of mutations, leading to natural selection and a more 'evolved' speciese
Not all mutations cause disease

can be caused by mutagen exposure

can also include improperly expressed gene
mutagens -chemicals,radiation
May or may result in effect on amino acid in polypeptide

Silent Mutation - No affect on amino acid produced
Missense Mutation
Change has resulted in formation of a different amino acid

(sickle cell)
Nonsense Mutation
Cause a "stop" codon to be produced. polypeptide is shortened

(cystic fibrosis)
Sickle cell disease
Single substitutions - makes valine instead of glutamine

Produces abnormal blood cells

One copy of mutated gene - some abnormal Hb
Two copies - all abnormal Hb
Malaria and Sickle Cells
Malaria - parasitic disease, plasmodium cell
carried by mosquitos, invades red blood cells, causes them to lyse

Symptoms - fever, shivering, vomiting, anemia
death due to kidney failure/animia
Malaria cannot infect sickle cells - people with sickle cells are resistant
sickle is more prominent
in regions where there
are many cases of
Evolution of Sickle Cell Disease
Evolution - the cumulative change in heritable characteristics of a popultion

gradual - over generations

Natural selection
Variation within a species (result of mutation)
may be beneficial to individual, greater reproductive success - mutation will be passed on
How sickle cell is passed on
Stem Cells
Stem cells were used to repare and replace faulty genes in mice

Retroviruses used to insert corrected gene into mouse tails - then inserted into mouce to produce health blood cells
Meiosis - a reduction division of nuclei
form haploid gametes
somatic cell nuclei - body cells, are diploid (contain 2n chromosomes)
23 pairs of chromosomes n=23
A diploid (2n), contains 2*23 - 46 chromosomes
of interphase
Chromosomes replicate - forms pairs of sister chromatids, joined at centromere
meiosis 1 - separates the homologous pairs - reduction division
Meosis is a process of two divisions
meisis 2 - separates the sister chromids
Product: single somatic diplid cell
4 haploid gametes
Homologous Chromosomes
"same structure"
Somatic cells - diploid (2n)

Contain homologous pair of each chromosome.

one pair is paternal - from father
one is maternal - from mother
Homologous chromosomes
same in size and structure
same genes and same loci
alleles carried at each locus
may vary
22 of the human chromosomes
pairs are homologous
last pair - sex
Interphase -
chromosomes replicate for reduction division of meiosis

Synthesis phase (S-Phase) of meiosis, DNA replication

Single Chromosomes duplicate
make sister chromatids
joined with centromere

Prophase I
Homologous chromosomes associate with eachother

the nuclear membrane breaks down and centrioles go to
opposite poles
Exchanges between non-sister chromatids can occur
Recombination of alleles
also source of genetic
variation of gametes
Metaphase I
Bivalent, homologous pairs line up at equator

These and "line up" in random - large genetic variation

2^23 possible orientations
Anaphase I
Spindle fibres contract

Homologous pairs are separated to opposite poles

reduction division
Non-disjunction - will
affect chromosome
number of all four

Telophase I -
Cytokinesis - cytoplasm divides, new nuclei form

No longer diploid

one pair of sister chromatids

if exchange, recombination -
not identical copies
Interphase II -
no synthesis (s phase)
Prophase II -
Nuclei break down -
no crossing over
Metaphase II -
Chromatids align at equator, spindle fibres form and attache to centromeres

Again, random orientation
Anaphase II -
spindle fibres contract, centromere's split
chromatits are pulled to opposite poles
incorrect distribution will result in the wrong number of chromosomes
Telophase II -
new haploid nuclei
Cytokinesis - cell split
four Haploid (1n) gametes
Fertilization - diploid zygote (2n)
Meiosis I
Interphase I -
DNA replication (synsis/s-phase)

Chromosomes replicated, pairs of chromatids
Prophase I -
Homologous pairs associate
cross-over takes place
- exchange of alleles between non-sister chromatids
Metaphase I -
Homologous pairs align at equator
Anaphase I -
Homologous pairs are separated
reductions division
non-disjunction can occur
Telophase I-
New nuclei are formed and cytokinesis begins
each contains pairs of sister chromatids, no homologous pairs
No DNA replication
in this
No crossing-over
sister chromatids align at
centromere is broken and chromatids are separated
non-disjuction can occur
New nuclei are formed and cytokinesis begins

for haploid gamete cells are produced
Meiosis II
Non-Disjunction -
in anaphase I or II
changes in chromosome #
In Anaphase I
In Anaphase II
Trisomy Disorders
Abnormal number of chromosomes
zygotes and somatic
cells with trisomy of one chromosome can be fatal or cause
Down Syndrome -
Trisomy 21 - extra copy of chromosome 21
in gamete (usually egg)
slightly shortened life expectancy, learning difficulties and generally happy nature
Girls are born with all eggs they will ever use in ovaries
at puberty,m these eggs undergo meiosis
continues till menopause

As a mother ages, risk for errors in these eggs increases

after age 40 women who are pregnant are advised to have a karyotype of their fetus analyzed

Lows Governing termination of pregnancy?
Ethical issues regarding pre-natal testing and abortions?

forewarned as forearmed?
pre-natal test, checks for gender and trisomy disorders

1. Extract fetal cells by amniocentesis or chronic villus sampling
2. Culture cells and stimulate mitosis
3. Stop Division in metaphase
4. take a photograph under the light microscope or scan with computer
5. Arrange chromosomes in homologous pairs (based on size, bands, centromere)
6. Check Gender, triosmy disorders
Chorionic Villus Sampling
10-12 weeks, via cervix or abdomen, risk:1:100

after 15 weeks
via abdomen
risk 1:1000

Nuchal Translucency - build up of fluid under babies neck - can indicate trisomy
Theoretical Genetics Continued
One pair of chromosomes -
give XX - female
XY - male

X chromosome is much larger than the Y chromosome

Non-Homologous Region - region where genes are carried on X
chromosome and not Y chromosome
Sex determining region Y -
leads to male development
Sex Determination
Females produce all XX chromosomes
Males produce both X and Y chromosomes

Even chance of male and female
XYY syndrome - fertile males, increased learning difficulties, weakly correlated with violent tendency
XO - monosomy of X, female, short stature
XXX - fertile females, some X carrying gametes can be produced
XXY, Klinefelter Syndrome - males with enhanced female characteristics
Full transcript