Transcript Inheritance of Traits

Inheritance of Traits
Anatomy & Physiology 2
How Genetics Work

Genetics is the
study of how traits
are passed for
parents to offspring
 We learned about
chromosomes:
– They are found in the
nucleus
– They are made of DNA
– Humans have 46
chromosomes, but only 23
in the sex cells
How Genetics Work

More about chromosomes:
– All chromosomes contain
genes
– Genes are small sections
that determine specific traits
– Traits could be eye color,
hair color, skin color, etc
– In the body cells, the
chromosomes are pair – so
there are 23 pairs or 46 total
– In the sex cells, the
chromosomes are single –
so there are only 23 total
Chromosomes
How Genetics Work
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Traits are passed from
parents to offspring
Genotype vs. Phenotype
– Genotype is the genetic
make of the organism
– Phenotype is what the
organism looks like
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How can an offspring have
characteristics that neither
parent has?
Because not all genes are
expressed – some are
“carried” by the parents and
expressed in the offspring
How Genetics Work
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Dominant Traits
– Genes that keep other
genes from showing
– An organism with two
dominant genes is
homozygous dominant &
the trait is expressed
– An organism with one
dominant trait and one
recessive trait is
heterozygous & the trait
is still expressed
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Recessive Traits
– Genes that do not show
when dominant traits are
present
– The only way for these
traits to be expressed is
when 2 recessive genes
are present
– This is called
homozygous recessive
Dominant Traits
Recessive Traits
Punnett Squares

Punnett Squares are
used to predict the
phenotype based off the
genotype
 Uppercase letters will
be used for all dominant
genes are lowercase
letters will be used for
all recessive genes
 Remember: each gene
has a pair and the pair
is either going to be
homozygous or
heterozygous
Punnett Squares

Setting up Punnett Squares – Step 1:
draw a box with 4 squares
Punnett Squares
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Step 2 – on the top and side of the box
write the parents’ genotype
f
F
f
f
Punnett Squares
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Step 3 – match up the top and side in
each box inside the square
f
F
f
Ff
ff
f
Ff
ff
Punnett Square
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Step 4 – Analyze the results
Let’s say the “F” stands for
freckles
The father has a genotype Ff
– What is his phenotype?
The mother has a genotype
ff – what is her phenotype?
The possible combinations
of the offspring are Ff or ff –
what could their phenotypes
be?
Punnett Squares
Punnett Squares
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Punnett Squares were
developed by Gregor
Mendel
He is said to be the
father of genetics
He noticed that pea
plants had a variety of
features and when he
crossed them he got
different results
He developed the
concept of dominant
and recessive genes
Human Genetics
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There are a total of 46
chromosomes in each
human body cell
23 pairs – 23 from the
mother and 23 from the
father
1 pair determines the
sex of the offspring –
these are called sex
chromosomes
The other 22 pairs are
called autosomes
Human Genetics
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Determining sex using Punnett squares:
Human Genetics
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Blood type is also
determined by
genetics
 OO is recessive
 A & B are dominant
 Combinations: AO,
AA, BO, BB, AB, OO
Genetic Disorders
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What happens when
something goes
wrong in the genes?
 A genetic disorder
can occur
 Some disorders are
minor and can easily
be lived with;
however, others are
fatal
Genetic Disorders
http://www.noah-health.org/en/genetic/
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Disorders of the Sex Chromosomes:
– Hemophilia: blood disorder where the
blood won’t clot
– XXX syndrome: many don’t have signs or
symptoms, but some can include delayed
puberty, infertility, mental retardation
(extreme cases) – occurs only in females
– XXY syndrome: learning disablities, lower
IQ’s – occurs only in boys
Genetic Disorders
http://www.noah-health.org/en/genetic/
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Disorders of the Sex Chromosomes:
– Turner’s Syndrome: girls born without the
other X chromosome – without treatment
girls will not grow to full height or reach
puberty
Genetic Disorders
http://www.noah-health.org/en/genetic/
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Other Disorders:
– Albinism
– Color-blindness
– Cystic Fibrosis
– Down Syndrome
– Fragile X Syndrome
– Huntington’s Disease
– Klinefelter Syndrome