Transcript Chapter 4: Patterns of Heredity

Chapter 4: Patterns
of Heredity
Section 1: Living things
inherit traits in patterns.
Inherited Traits
 Traits
passed down from
your parents
 Genetically
linked
Acquired Traits
 Something
gained or learn
during your lifetime
 Not
genetically linked
Acquired
traits
Inherited
Traits
Combination
of Both
Learning to Snap
Eye color
Diabetes
Heredity

is the passing of genes from parents
to offspring
These genes code for the expression of
traits.
 an organism does not inherit the traits
ONLY the genes for the traits
 Some characteristics are affected by
many genes in complicated ways.

Homologs


Most eukaryotic cells
contain pairs of
chromosomes, with
one chromosome of
each pair coming from
each of two parents.
The chromosomes in a
pair are called
homologs.

They resemble each
other, having the same
size and shape, and
carrying genetic
information for
particular traits.
alleles
a gene
Alleles
alleles

An alternate form of
a gene for a specific
trait or gene product.

a gene

Ex) in the picture A
or a are different
alleles for the same
gene
Ex) Tongue roller
and non-tongue
roller are different
alleles for people
Gene

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The basic unit of
heredity that consists
of a segment of DNA
on a chromosome.
Are sites that code for
particular traits such
as eye color, hair color,
etc.
alleles
a gene
Each species has a characteristic
number of chromosomes.
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Chimpanzees have 24
pairs of chromosomes
(48 total)
Fruit flies have 4 pairs
of chromosomes (8 total)
Humans have 23 pairs
(46 total)
What’s special about the 23rd pair?
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The 23rd pair are the
sex chromosomes.
In humans, the sex
chromosomes are
called the Xchromosome and the
Y-chromosome.

A human female = XX

A human male = XY
Phenotype vs. Genotype
Describes the
actual
characteristics that
can be observed
 P for Picture of
what the genes
“look” like
 Ex.) Brown hair,
Blue eyes

The name for the
genes an organism
has.
 Describe an
organisms specific
alleles
 Ex.) Aa, AA, aa

Dominant vs. Recessive

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More prominent,
more powerful,
stronger alleles
Usually represented
by a capital letter
Only needs 1 allele
to control the
phenotype
Has the power to
mask (hide)
recessive alleles

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Less prominent, less
powerful, weaker
alleles
Usually represented
by a lower case letter
Needs 2 alleles to
control the phenotype
Can not mask
dominant alleles
Homozygous vs. Heterozygous

Having 2 of the
same alleles in the
genotype
BB – Homozygous
Dominant
 bb – Homozygous
recessive




Also known as a
PURE BREED
Having 2 different
alleles in the
genotype

Bb –
Heterozygous
Also known as a
HYBRID
Gregor Mendel

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A monk, trained in science and math,
who lived in Austria during the mid1800s
Performed the first major experiments
investigating heredity
Began investigating the inheritance of
traits among the pea plants in the his
garden
Separately worked with seven different
traits:

plant height flower and pod position, seed
shape, seed color, pod shape, pod color, and
flower color.
Mendel Experiments
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Mendel noticed variations in
the heights of pea plants
So he purposely crossed
(mated) pea plants that
were pure-breed dwarf &
pure-breed regular to see
what their offspring would
become
Regular x Dwarf
TTxtt
First generation (F1 )
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After crossing a truebreeding regular pea
plant with a truebreeding dwarf pea plant
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all regular pea plants were
produced in the first
generation.
Two of these plants were
then crossed to produce
a second generation
F1 generation all
regular (Tt)
Second generation (F2 )
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After allowing the first
generation pea plants
to cross
¾ regular pea plants
(TT & Tt) and ¼
dwarf pea (tt) plants
were produced
1 Regular (TT), 2 Regular (Tt), & 1 Dwarf (tt)
were produced
So What?!?

Mendel drew upon his knowledge of
mathematics while analyzing his data in
order to suggest a hypothesis that would
explain the patterns he observed.Mendel
realized that each plant must have two
“factors” for each possible trait, one factor
from each parent. Some traits, such as
dwarf height, could be masked—dwarf
height could be seen in the
Chapter 4: Patterns
of Heredity
Section 2: Patterns of
heredity can be predicted
Punnett Square
 Illustrates
how the parent’s
genes can possibly combine
 Compare
Ratio
2 different
quantities (numbers)
 Ex)
Ratio of boys to girls =
10 to 7 or 10:7
#
order depends on the
wording
Probability
The
chance or likelihood
of an event or something
happening
Percentage
Compares
the probability
of something to 100
Ex)
93% of the questions
on a test were correct
Incomplete dominance
 Also
known as “Codominance”
 Is when there are 2
different dominant alleles
which share power
 Ex)
RW = pink in poinsettias
Dihybrid Crosses
 Deals
once
with 2 genotypes at
 Includes
Brown
4 alleles
Hair = B
Blonde Hair = b
Brown eyes = Q
Blue eyes q
Geno
BBQQ
BBQq
Pheno
Br
Br hair
hair & & eyes
eyes
p
BbQQ
BbQq
BBqq
Bbqq
bbQQ
bbQq
bbqq
Br hair
& eyes
Br hair
& eyes
Br hair
& blue
eyes
Br hair
& blue
eyes
Blonde
& br
eyes
Blonde
& br
eyes
Blonde
& blue
eyes
BQ
Bq
bQ
bq
BBQQ
BBQq
BbQQ
BbQq
BBQq
BBqq
BbQq
Bbqq
BbQq
bbQQ
bbQq
Bbqq
bbQq
bbqq
Br &
br
9/16
BQ
Br &
bl
3/16
Bq
Bl &
br
3/16
bQ
BbQQ
Bl &
bl
1/16
bq
BbQq
Chapter 4: Patterns
of Heredity
Section 4.3: Meiosis is a special
form of cell division
Gamete
Special cells that contain only half the
number of chromosomes in a normal
cell of that organism
 Also known as “1n” cells, haploid or
sex cells

In a female their gametes are referred
to as eggs
 In males, gametes are referred to as
sperm

Body Cells
 Are
normal typical cells
 Ex)
skin, or muscle cells
 Also known as “2n cells” or
diploid cells
Fertilization

The process that
takes place when
the egg and the
sperm combine
to form one new
“2n cell”
Meiosis
 Special
kind of cell division
that produces haploid cells
 Involves a single cell going
through 2 divisions
 Meiosis
I & Meiosis II
How meiosis works…
• At the beginning of meiosis I, the parent cell has
made two copies of each chromosome pair.
• During meiosis I, the homologs of the
chromosome pair separate; there are two
cells, each with two copies of one homolog
from each pair.
• During meiosis II, the two copies of each
homolog separate; each daughter cell has one
homolog.
1n
Meiosis I
Meiosis II
1n
1n
1n
Mitosis
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Produces 2
daughter cells
Splits once
Parent and
daughter cells
genetically
identical
Produces 2n
cell, diploid
cells or body
cells
Has 4 main
stages
Meiosis
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Starts with
a single cell
Are forms of
cell division
Happens in
stages
Chromosomes
(DNA) only
copied 1
time
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Produces 4
daughter cells
Splits twice
Daughter cells
have ½ the
parents
genetic info
(DNA)
Produces 1n
cell, haploid
cells, gamete
or sex cells
Has 8 main
stages