Transcript Genetics Powerpoint for Bio. I

Genetics
Biology I
Chromosomes
Centromere
↓
Chromatid
Chromatid
database of
genes that are
on each
chromosome
(hax1, fuca1)
Karyotype – spread of human
chromosomes to look for chromosomal
abnormalities
OR
Chromosome Terminology
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Homologous Chromosomes – paired
chromosomes – same size, same
banding pattern, same type of genes but
not necessarily the exact same forms of
each gene

Example – gene on one chromosome for
brown eyes and gene on its homologue
for blue eyes
GGGTCAGTCATTTTAAGAGATC
GGGAAAGTCATTTTAAGAGATC
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Remember – Sister Chromatids are two
halves of the same double chromosome
and are exact copies of one another
Real Karyotype
Down’s Syndrome Karyotype
Cell Types and Chromosome Types
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Diploid – cell with the normal # of
chromosomes (2n)
Haploid – cell with ½ the normal number
of chromosomes (n)
Somatic cell – normal body cell
Sex Cell, gamete – sperm and egg –
haploid cells
Germ cell – 2n cell that is the precursor
to the gametes
Autosomes – chromosomes 1-22
Sex chromosomes – X and Y, necessary
to determine sex, but code for many
proteins not related to sex and found in
all cells
Meiosis – cell division process that
produces the sperm and egg (n)
Purpose of Meiosis
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Egg
n
To make haploid sex cells so that
when they come together, the
zygote has the normal amount of
DNA (2n)
Sperm
n
Fertilization
→
Mitosis
Zygote
2n
Embryo
Steps of Meiosis
Germ Cell (2n) in G1 (46 single chromosomes)
S-Phase – copy all DNA so after have 46 double
chromosomes
When Chromosomes form in meiosis I – 46
doubles
Chromosomes
form and
homologous
pairs come
together
Crossing over in Prophase I
Homologous
Pairs line up
down center
Still 46
doubles or
23 double
pairs
Each daughter cell
has 23 double
chromosomes – no
longer have pairs –
just one of each
pair
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Meiosis I is the reduction
division because the cell
went from 46
chromosomes or 23 pairs
to just 23 chromosomes
The daughter cells are now
haploid but they don’t yet
have ½ of the DNA of the
orginial germ cell, they
must undergo meiosis II
Chromosomes reform in
the two daughter cells
Each individual
chromosome lines
up down the
center and sister
chromatids split
Now that sister chromatids split – we
have 23 single chromosomes – ½ the
DNA of a normal cell – this is the finished
sex cell
Summary
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Meiosis happens only in ovaries
and testes to make sperm and egg
Sperm and egg have only 1 of
each pair of chromosomes and are
haploid
Sex cells come together to make a
zygote that contains a pair of each
chromosomes again and is diploid
Meiosis Animation
Mitosis vs. Meiosis
Egg vs. Sperm
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Each germ cell forms 4
sperm of equal size
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Sperm form everyday
throughout life in a male
Each germ cell forms 1
large egg (cytoplasm
divides unequally and
small cells
disintegrate)
Females are born with all
of the eggs they will
ever have
Sexual Reproduction
Brings about Variation by:
 Crossing Over
 Independent Assortment
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Random Fertilization
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Amount of variation due to IA – 2n
In humans = 2 23 = 8 million
8 million x 8 million = 64 TRILLION
combinations
Crossing Over makes this almost
infinite
Chromosomal Abnormalities
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Trisomy or Monosomy due to
non-disjunction during meiosis
Chromosomal deletions (a
piece of a chromosome breaks
off)
Chromosomal Translocations
(whole or parts of
chromosomes)
Chromosomal Inversions
Non-disjunction causes
trisomy’s, monosomy’s, and
aneuploidy
Chromosomal Abnormalities
Translocation of chromosome 13 and 14 – normal
phenotype
Translocation Abnormality
Philadelphia Chromosome
A piece of chromosome 22 is translocated to chromosome
9 causing Chronic Myelogenous Leukemia
Chromosomal Deletions
Each chromosome 22 on the right of each
pair is missing a piece
Cri-du-chat – have a deletion from chromosome #5
and the babies sound like a cat crying – mental
retardation and heart disease
Mendel
Mendelian Principles
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Alleles – different forms of the
same gene
Dominant – gene that is seen
Recessive – only seen if with
another recessive allele
Homozygous – having 2 like alleles
Heterozygous – having 2 different
alleles
Genotypes – actual gene make-up
for a particular locus or trait
Phenotypes – visible trait
Mendelian Laws
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Law of Segregation - When the
gametes form – each gamete
receives only 1 of each pair of
alleles.
Law of Independent Assortment
– If genes aren’t on the same
chromosome (linked) they will not
have to remain together in the
gamete
Independent Assortment
Pairs:
 Red and Green
 Yellow and Black
 Brown and White
 Brown String and White String
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Line up you pairs as in Metaphase I
Pick a side to be the gamete
Independent Assortment
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Red = red hair, thin eyebrows, long fingers, and genetic
disease for cystic fibrosis, light skin
Green = brown hair, bushy eyebrows, short fingers, normal,
dark skin
Yellow = big nose, hairy fingers, can’t taste sour things, tall
Black = small nose, no hair on fingers, can taste sour things,
short
Brown = slow metabolism, blue eyes, great cholesterol
receptors, 5 fingers on each hand, dark skin
White = fast metabolism, brown eyes, slightly misshapen
cholesterol receptrs. 6 fingers on each hand, light skin
White String = light skin, unibrow, mishappen clotting
enzyme
Brown String = dark skin, separated brows, normal clotting
enzyme
Punett Squares – Mono
and Di-Hybrid Crosses
Used to calculate the probability of
having certain traits in offspring
 Figure out all possible gametes for
male and females
 Place them on the outside of the
square
 Cross the gametes to come up
with the possible genotypes and
phenotypes of the offspring
Story of Mendel and Punnett Squares
Beyond Mendel
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Incomplete Dominance – the phenotype
in the heterozygous condition is a mix of
the two (white and red snapdragons
make pink)
Co-dominance – both alleles are
expressed in heterozygous condition
(A,B blood types, Roan cattle)
This can become a “gray” area in
diseases – Tay Sachs – make ½ normal
protein and ½ misshapen – do not
exhibit disease so recessive but
moleculary have both expressed so is it
co-dominance or even incomplete if has
a slight effect ????
Multiple Alleles
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More than two allele choices
although always only have 2
alleles at each gene locus
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Example: Human Blood Types
Alleles = A, B, & O (also an
example of co-dominance)
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Paternity Testing?
Blood Types
Blood
Type
A
B
AB
O
Antigens
on blood
cells
Genotype
Body will
make Ab
against
Person can
Donate to:
Person
can
Receive
From:
Sex-Linked
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Located on a sex chromosome
Usually is X-linked (few known
genes on the Y)
X-linked usually show more in
males since only have 1 allele –
only need 1 recessive allele to
show
Pedigrees
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Used to figure out genotypes of
family members to see if someone
is carrying a disease gene
Used to determine the mode of
inheritance
Practice
Higher Genetics
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Pleiotropy – one gene effects
many traits
Polygenic – one trait determined
by many genes – continuous
pattern
Multifactorial – may be multiple
genes and the environment
Chromosomal Inheritance
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Aneuploidy – abnormal
chromosome # (ex. Trisomy)
Polyploidy – 3n, 4n (nondisjunction of all chromosomes)
More normal than aneuploid –
some plants live fine but can only
reproduce with other polyploid
plants
 2n egg and 1n sperm = 3n
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Or
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Zygote replicates DNA but doesn’t
divide = 4n
Sex Chromosomes and
Chromosomal Inheritance
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Non-disjuction of sex chromosomes
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XXY – Klinefelter’s (small testes, sterile, breasts)
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XYY – taller, more aggressive?? Males
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XXX – normal female
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XO – Turner’s Syndrome (no secondary
sex characteristics, sterile, short)