Transcript Ch 26 Inheritance of Traits

Standard Biology
Chapter 26 Inheritance of
Traits
Section 1 Genetics, How and Why
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Genetics

Genetics: the study
of how traits are
passed from parent
to offspring
– Mystery for a long
time
– Now know traits
are passed in sex
cells
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Chromosomes
Nucleus found in
center of cell which
directs the cell’s
activities
 Chromosomes are
found in nucleus
 Chromosomes are
thickened and easy to
see
 Remember,
chromosomes are
duplicated before cell
reproduction

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Chromosomes
Two kinds of cells
 Body cellschromosomes in
pairs (diploid)
 Sex cells- single
chromosomes (so
½ the number of
chromosomes as
body cells)

(haploid)
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Genes on Chromosomes

Gene
– Small section of
chromosome that
determines a
specific trait;
examples
 Eye color
 Wing shape
 Chemical process
– Humans have about
23,000 genes
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Genes on Chromosomes
Genes are arranged
on a chromosome
like beads on a
necklace
 Chromosomes are
paired, so genes
are paired (except
sex cells)

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Passing Traits to Offspring
Traits are passes
from parent to
offspring in sex
cells
 Example: Ear Lobe
Shape p. 548

Female
egg
A
A
F
F
Male
sperm
AF
Child will
have
free ear
lobes
A= attached
ear lobes
F= free ear
lobes
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Dominant and Recessive Genes

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One trait dominates another like free
dominates attached
Free=dominate and Attached=recessive
Mother is pure attached (AA) or
homozygous recessive (homo means
same)
Father is pure dominate (FF) or
homozygous dominate
Child is one Free and one Attached (FA) or
heterozygous (hetero means different)
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Traits of Plants and Animals
Trait found in Dominant
Trait
Flies
Long wings
Recessive
Trait
Short wings
Pea plants
Purple flowers
White flowers
Humans
Corn plants
Can roll tongue Can’t roll
tongue
Normal height Dwarf
Dogs
Short hair
Long hair
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When Both Parents are
Heterozygous
If mother is heterozygous (FA), she
can make F eggs and A eggs
 If father is Heterozygous (FA), he can
make F sperm and A sperm
 How many combinations of traits in
children as possible? Table 26-2 p.
551

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When Both Parents are
Heterozygous

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Mother’s eggs: F and A
Father’s sperm: F and A
Child: FF, FA, AF or AA
So four combinations of genes possible
(although FA and AF are the same)
Child will have free ear lobes if FF, FA or
AF
Child will have attached ear lobes if AA
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Standard Biology
Chapter 26 Inheritance of
Traits
Section 2 Expected and Observed
Results
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Punnett Square

Easy way to look at
combinations of traits
is with a Punnett
Square
– Letters used represent
genes
– Capital letters dominant
– Lower case letters
recessive
– Trait’s letter based on
dominant
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Punnett Square
Mother’s genes
Example:
 Free ear lobes
dominant F
 Attached ear lobes
recessive f
 Homozygous
recessive mother ff
 Homozygous
dominant father FF
F
F
f
f
Ff
Ff
Ff
Ff
Father’s genes
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Punnett Square
Mother’s genes
Example when
parents are
heterozygous:
F
F
f
FF
Ff
Father’s genes
f
Ff
ff
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Directions for Punnett Square
1.
2.
3.
4.
5.
6.
Draw a Punnett Square (4 boxes). Each box
shows possible combination of genes in
offspring.
Decide what genes will be in the sex cells of
each parent.
Write mother’s genes on top; write father’s
genes on side.
Copy the letters that appear at the top of the
square into the boxes below each letter.
Copy the letters that appear at the side into the
boxes next to each letter.
Look at the 4 small boxes in the Punnett
Square, these are possible combinations in the
offspring.
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Expected Results
Get from Punnett
Square
 What you expect to
happen
 Probability

Expected Results
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Observed Results
Expected Results

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Observed results
when you count the
pods of this one
cross:
71 yellow pods and
24 green pods

The numbers you
actually get
They don’t match up
exactly with what you
expect
The greater the
number of offspring,
the closer you should
get to the expected
results.
Table 26-3 p. 557
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Mendel’s Work

Gregor Mendel
– Father of Genetics
– 1865 Austrian
monk/teacher in Czech
– Grew garden peas,
came up with ideas
about how traits are
inherited
– Counted 1000’s of traits
in pea plants and
conducted scientific
investigations (applied
math to science)
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Mendel’s Work
– Traits he studied:
 Plant height
 Pod color
Pod shape
 Seed color
 Seed shape
 Flower color
 Flower position

Always found 3 dominate to 1
recessive when heterozygous parents
were crossed
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