Download MendelGenetics - Ms. Nakamura`s Biology Class Wiki

D.N.A
AP Biology
When meiosis goes wrong!
 The most common malfunction in
meiosis is called nondisjunction
 This is when the chromosomes DO
NOT come apart in anaphase
AP Biology
Nondisjunction
 This can result in some gametes with
too many chromosomes
AP Biology
EXAMPLE: DOWN SYNDROME
•When nondisjunction occurs on the 21st
chromosomes
AP Biology
•2 of our 46 chromosomes are sex
chromosomes
•Males have the combination XY
•Females have the combination XX
AP Biology
EXAMPLE: TURNER AND
KLINEFELTER’S SYNDROME
•Males with Klinefelter’s Syndrome have XXY
AP Biology
EXAMPLE: TURNER AND
KLINEFELTER’S SYNDROME
•Individuals with Turner Syndrome have XO
AP Biology
CHECK FOR UNDERSTANDING
What is nondisjunction?
When the chromosomes don’t
separate correctly in meiosis
AP Biology
CHECK FOR UNDERSTANDING
What are the sex chromosomes for
females?
XX
What are the sex chromosomes for males?
XY
AP Biology
CHECK FOR UNDERSTANDING
What might be the chromosomes in a male
if nondisjunction occurred?
XXY
What might be the chromosomes in a
female if nondisjunction occured?
XO
AP Biology
Looking at Chromosomes
 A Karyotype is a picture of human
chromosomes
 It shows all 46 chromosomes
matched up with their homologous
pairs
 A karyotype can allow a doctor or
scientist to spot any chromosome
abnormalities.
AP Biology
KARYOTYPES
Normal Human Karyotype
AP Biology
Is this a male or female?
Karyotyping Chromosomal Mutations
Stations!
 Read the descriptions of abnormalities on



your worksheet
5 -6 people at each station
You will spend 5 minutes at each station
After the 5 minutes are up, you will rotate
to the next station
AP Biology
Warm Up
 All of the following are true about the karyotype above except:
A. The karyotype is of a female
B. The karyotype is of a female with 47 chromosomes
C. The karyotype is of a normal human
D. The karyotype is of an abnormal human
AP Biology
D.N.A
Objective: SWBAT explain how Mendel’s particulate
mechanism differed from the blending theory of inheritance.
 Quarter 2 Reflection Questions
1. How did you perform academically in
Ms. Nakamura’s class for 2nd quarter?
 2. How did you perform behaviorally in
Ms. Nakamura’s class for 2nd quarter?
rd quarter?
 3. How can you improve for 3
 4. How can Ms. Nakamura improve for
3rd quarter to help you have a better
learning environment?

AP Biology
Genetics
&
The Work of Mendel
AP Biology
2006-2007
Gregor Mendel
 Modern genetics began in the
mid-1800s in an abbey garden,
where a monk named Gregor
Mendel documented inheritance
in peas
used experimental method
 used quantitative analysis

 collected data & counted them

AP Biology
excellent example of scientific
method
Mendel’s work
 Bred pea plants

Pollen transferred from white
flower to stigma of purple flower
P
cross-pollinate
true breeding parents (P)
 P = parental

raised seed & then
observed traits (F1)
 F = filial

allowed offspring
to self-pollinate
& observed next
generation (F2)
AP Biology
anthers
removed
all purple flowers result
F1
self-pollinate
F2
Mendel collected data for 7 pea traits
AP Biology
Looking closer at Mendel’s work
P
F1
true-breeding
true-breeding
X
purple-flower peas
white-flower peas
100%
purple-flower peas
Where did
the white
flowers go?
100%
generation
(hybrids)
self-pollinate
F2
generation
AP Biology
75%
purple-flower peas
White
flowers came
back!
25%
white-flower peas
3:1
What did Mendel’s findings mean?
 Traits come in alternative versions
purple vs. white flower color
 alleles

 different alleles vary in the sequence of
nucleotides at the specific locus of a gene
 some difference in sequence of A, T, C, G
purple-flower allele &
white-flower allele are two DNA
variations at flower-color locus
different versions of gene at
same location on homologous
chromosomes
AP
Biology
Traits are inherited as discrete units
 For each characteristic, an organism
inherits 2 alleles, 1 from each parent

diploid organism
 inherits 2 sets of chromosomes,
1 from each parent
 homologous chromosomes
 like having 2 editions of encyclopedia
 Encyclopedia Britannica
 Encyclopedia Americana
AP Biology
What are the
advantages of
being diploid?
What did Mendel’s findings mean?
 Some traits mask others

purple & white flower colors are
separate traits that do not blend
I’ll speak for
both of us!
 purple x white ≠ light purple
 purple masked white

dominant allele
 functional protein
 masks other alleles

mutant
allele producing
malfunctioning
protein
recessive allele
 allele makes a
malfunctioning protein
AP Biology
wild type
allele producing
functional protein
homologous
chromosomes
Genotype vs. phenotype
 Difference between how an organism
“looks” & its genetics

phenotype
 description of an organism’s trait
 the “physical”

genotype
 description of an organism’s genetic
makeup
X
P
Explain Mendel’s results using
…dominant & recessive
…phenotype & genotype
AP Biology
purple
white
F1
all purple
Making crosses
 Can represent alleles as letters
flower color alleles  P or p
 true-breeding purple-flower peas  PP
 true-breeding white-flower peas  pp

PP x pp
X
P
purple
white
F1
AP Biology
all purple
Pp
Looking closer at Mendel’s work
P
true-breeding
true-breeding
X
purple-flower peas
white-flower peas phenotype
PP
pp
100%
purple-flower peas
F1
genotype
100%
generation
(hybrids)
Pp Pp Pp Pp
self-pollinate
F2
75%
purple-flower peas
25%
white-flower peas
generation
AP Biology
?
?
?
?
3:1
Punnett squares
Pp x Pp
F1
Aaaaah,
phenotype & genotype
can have different
ratios
generation
(hybrids)
%
genotype
male / sperm
female / eggs
P
p
PP
25%
75%
Pp
P
PP
%
phenotype
50%
Pp
Pp
p
AP Biology
Pp
pp
pp
25% 25%
1:2:1
3:1
Phenotype vs. genotype
 2 organisms can have the same
phenotype but have different genotypes
purple
PP
purple
Pp heterozygous
homozygous dominant
How do you determine the
genotype of an individual with
with a dominant phenotype?
AP Biology
Can’t tell
by lookin’
at ya!
Test cross
 Breed the dominant phenotype —
the unknown genotype — with a
homozygous recessive (pp) to
determine the identity of the unknown
allele
How does
that work?
x
is it
PP or Pp?
AP Biology
pp
How does a Test cross work?
Am I
this?
Or am I
this?
x
PP
pp
x
Pp
p
p
P
Pp
Pp
P
Pp
Pp
P
Pp
Pp
p
pp
pp
AP Biology
100% purple
p
pp
p
50% purple:50% white or 1:1
D.N.A
Objective: SWBAT to apply mathematical routines to determine
Mendelian patterns of inheritance.
In humans the allele for albinism is recessive to the
allele for normal skin pigmentation. If two
heterozygtoes have children, what is the chance that a
child will have normal skin pigment? What is the
chance that a child will be albino?
A
a
Normal Pigment chance: AA or Aa
(75%)
Albino chance: 25% aa
Aa
AA
A
If the child is normal,
what is the chance that 2/3 or 67%
Aa
aa
a
it is a carrier
(heterozygous) for the
AP Biology
albino allele?
Mendel’s 1st law of heredity
PP
 Law of segregation

during meiosis, alleles segregate
P
P
 homologous chromosomes separate

each allele for a trait is packaged into
a separate gamete
p
pp
p
P
Pp
AP Biology
p
Law of Segregation
 Which stage of
meiosis creates the
law of segregation?
Metaphase 1
Whoa!
And Mendel
didn’t even know
DNA or genes
existed!
AP Biology
Monohybrid cross
 Some of Mendel’s experiments followed
the inheritance of single characters
flower color
 seed color
 monohybrid crosses

AP Biology
Dihybrid cross
 Other of Mendel’s
experiments followed
the inheritance of 2
different characters
seed color and
seed shape
 dihybrid crosses

AP Biology
Mendel
was working out
many of the
genetic rules!
Dihybrid cross
P
true-breeding
yellow, round peas
Y = yellow
R = round
true-breeding
green, wrinkled peas
x
YYRR
yyrr
y = green
r = wrinkled
yellow, round peas
F1
100%
generation
(hybrids)
YyRr
self-pollinate
F2
generation
AP Biology
9:3:3:1
9/16
yellow
round
peas
3/16
green
round
peas
3/16
yellow
wrinkled
peas
1/16
green
wrinkled
peas
What’s going on here?
 If genes are on different chromosomes…
how do they assort in the gametes?
 together or independently?

YyRr
YR
AP Biology
yr
Is it this?
Or this?
YR
YyRr
Yr
Which system
explains the
data?
yR
yr
YyRr
Dihybrid cross
YR
YyRr x YyRr
YR
Yr
yR
yr
or
YR Yr
yr
YyRr
Yyrr
yR YyRR YyRr yyRR
yyRr
yr
AP Biology
YYRr
YyRr
YYrr
Yyrr
yyRr
yyrr
yR
yr
9/16
yellow
round
3/16
green
round
YR YYRR YYRr YyRR YyRr
Yr
YyRr
BINGO!
3/16
yellow
wrinkled
1/16
green
wrinkled
Mendel’s 2nd law of heredity
Can you think
of an exception
to this?
 Law of independent assortment

different loci (genes) separate into gametes
independently
green
 non-homologous chromosomes align independently
 classes of gametes produced in equal amounts
round
 only true for genes on separate chromosomes or
yellow
 YR = Yr = yR = yr
wrinkled
on same chromosome but so far apart that crossing
over happens frequently
YyRr
Yr
Yr
1
AP Biology
yR
:
yR
1
YR
:
YR
1
yr
:
yr
1
Law of Independent Assortment
 Which stage of meiosis
creates the law of
independent assortment?
Remember
Mendel didn’t
even know DNA
—or genes—
existed!
AP Biology
Metaphase 1
EXCEPTION
 If genes are on same
chromosome & close together
 will usually be inherited
together
 rarely crossover separately
 “linked”
The
chromosomal
basis of Mendel’s
laws…
Trace the genetic
events through
meiosis, gamete
formation &
fertilization to
offspring
AP Biology
Review: Mendel’s laws of heredity
 Law of segregation

monohybrid cross
 single trait

each allele segregates into separate gametes
 established by Metaphase 1
 Law of independent assortment

dihybrid (or more) cross
 2 or more traits

genes on separate chromosomes
assort into gametes independently
 established by Metaphase 1
AP Biology
EXCEPTION
 linked genes
metaphase1
Mendel chose peas wisely
 Pea plants are good for genetic research

available in many varieties with distinct
heritable features with different variations
 flower color, seed color, seed shape, etc.

Mendel had strict control over
which plants mated with which
 each pea plant has male & female
AP Biology
structures
 pea plants can self-fertilize
 Mendel could also cross-pollinate
plants: moving pollen from one plant
to another
Mendel chose peas luckily
 Pea plants are good for genetic research

relatively simple genetically
 most characters are controlled by a single gene
with each gene having only 2 alleles,
 one completely dominant over
the other
AP Biology
Any Questions??
AP Biology
2006-2007