Inheritance of chromosomes (DNA)
� egg + sperm →→→→ zygote
egg
sperm
zygote
Inheritance of genes
� on the chromosomes passed from Mom & Dad to offspring are genes for a trait
�may be same information
�may be different information
eye color
(blue or
brown?)
eye color
(blue or
brown?)
Effect of genes
� _____________________________________
� ex. brown vs. blue eyes
� ex. brown vs. blonde hair
� different forms of genes are called _______
What will we find out?
� genes come in “versions”
� brown (B) vs. blue (b) eye color
� __________________________________
� alleles are inherited separately from each parenteach parent
� brown (B) & blue (b) eye colors are
separate & do not blend
� either have brown or blue eyes, not brue
� Some alleles mask others
� brown (B) eye color masks blue (b)
� that’s why we capitalized brown!
Genes affect what you look like…
X
BBbb
Bb Bb Bb Bb
X
Bbbb
Bb Bb bb bb
X
BbBb
BB or Bb BB or Bb BB or Bb bb
How does this work?
eye
color
(brown?)
eye
color
(blue?)
� paired chromosomes have same kind of genes
� but may be different alleles
hair
color
hair
color
(brown?)(blue?)
Making gametes
BB = brown eyes
bb = blues eyes
Bb = brown eyes
BB
B
B
b
bb
Bb
→→→→ brown is ________ over blue
→→→→ blue is ________ to brown
b
B
b
BB = brown eyes
bb = blues eyes
2 of the same alleles
____________ BB
B
B
bhomozygous dominant (brown)
Bb = brown eyes
2 different alleles
____________
bb
b
Bb
B
b
homozygous dominant (brown)
homozygous recessive (blue)
Genetics vs. appearance
� There can be a difference between how an organism looks & its
genetics
�_________________ = phenotype�_________________ = phenotype
� brown eyes vs. blue eyes
�_________________ = genotype
�BB, Bb, bb
2 people can have the same appearance but
have different genetics: BB vs Bb
� Modern genetics began in the mid-1800s in an abbey garden, where a
monk named Gregor Mendel
genetics: __________________
___________________________
___________________________
___________________________
monk named Gregor Mendel
documented inheritance in peas
� used good experimental design
� used mathematical analysis
� collected data & counted them
� excellent example of scientific
method
Mendel chose peas wisely
� Pea plants are good for genetic research
� ______________________ with distinct
heritable features with different variations
� flower color, seed color, seed shape, etc.
____________________________________� ____________________________________
____________________________________
� each pea plant has male & female 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
� ____________________________________
� most characters are controlled by
a single gene
� each gene has only 2 alleles, � each gene has only 2 alleles,
(forms of a gene) one of which
is completely “dominant” over
the other
Pollen transferred from white flower to stigma of purple flower
� he bred easy-to-grow pea plants
� cross-pollinate
true breeding
parents
� raised seed and
white X white
white X white
white X white
purple X purple
purple X purple
purple X purple
all purple flowers result
?
self-pollinate
� raised seed and
then observed
easy-to-see traits
� allowed offspring
to self-pollinate
& observed next
generation
Looking closer at Mendel’s work…
Parentsgeneration
(P)
1st
Xtrue-breeding
purple-flower peastrue-breeding
white-flower peas
2ndgeneration
(F2)
1stgeneration(F1 hybrids)
self-pollinate
What did Mendel’s findings mean?
I. Mendel’s Principal of Dominance
� purple & white flower colors are separate traits that do not blend � purple x white ≠ light purple
I’ll speak for both of us!
� purple x white ≠ light purple
� purple masked white
� dominant allele� masks other alleles
� __________________________________________________________
� recessive allele� not expressed when dominant allele is present
homologous
chromosomes
What did Mendel’s findings mean?
� traits come in alternative versions that can be passed down
� purple vs. white flower color
� alleles = different forms of a gene� different alleles vary in the sequence of � different alleles vary in the sequence of nucleotides (DNA letters) in the code
purple-flower allele &
white-flower allele are
2 DNA variations at
flower-color spot
different versions of
gene on homologous
chromosomes
Dominant ≠ most common allele
� Because an allele is dominant does not mean…
� it is better, or
� it is more common
Polydactyly
dominant allele
Polydactyly
the allele for >5 fingers/toes
is DOMINANT & the allele for
5 digits is recessive
individuals are born with
extra fingers or toes
recessive allele far morecommon than dominant→→→→only 1 individual out of 500
has more than 5 fingers/toes
→→→→so 499 out of 500 people are homozygous recessive (aa)
� homologous (similar) chromosomes have the same order of genes…however…
� these chromosomes might not have the exact ________________ of a gene!
� these different forms are called ________
What did Mendel’s findings mean?
� these different forms are called ________
� ex. eye colors: brown, hazel, green, blue
eye
color
eye
color
� in simple patterns of inheritance, there are two different forms of a gene (alleles),
where one is __________ and one is
__________
� DOMINANT IS SHOWN WITH CAPITALS
What did Mendel’s findings mean?
� DOMINANT IS SHOWN WITH CAPITALS
� recessive is shown with lowercase
R – round seeds
r – wrinkled
Q – six fingers
q – five fingers
A – not-albino
a – albino
B – brown eyes
b – blue eyes
T – tall plants
t – short plants
P – purple
p – white
Y – yellow seeds
y – green seeds
Genotype vs. phenotype
� difference between how an organism “looks” & its genetics
� ____________
� “physical” description of an organism’s trait
____________� ____________
� description of an organism’s genetic
makeup
� shown by letters!
Explain Mendel’s results using
dominant & recessive
phenotype & genotype F1
P X
purple white
all purple
Making crosses
� can represent genotypes alleles as letters
� flower color alleles →→→→
� true-breeding purple-flower peas →→→→
� true-breeding white-flower peas →→→→
x
F1
P X
purple white
all purple
Describing Genotypes
� the 2 copies of the gene can be the same � homozygous = same alleles = PP, pp
� the 2 copies of the gene can be the different� heterozygous = different alleles = Pp
What did Mendel’s findings mean?
II. Mendel’s Principal of Segregation and Recombination
� when gametes are formed during meiosis (DIPLOID ���� HAPLOID), the homologous chromosomes (which may contain the different allelic forms of a gene) separate randomlyallelic forms of a gene) separate randomly
� this is called ____________________
What did Mendel’s findings mean?
II. Mendel’s Principal of Segregation and Recombination
� if the organism has a ______________ (the same alleles) genotype for a given trait, then all gametes will also have that allele for that trait
PP
P
P
pp
p
p
What did Mendel’s findings mean?
II. Mendel’s Principal of Segregation and Recombination
� if the organism has a ________________ (NOT the same alleles) genotype for a given trait, then halfof the gametes will have one allele and the other half will have the other allele
Pp
P
p
half will have the other allele
What did Mendel’s findings mean?
II. Mendel’s Principal of Segregation and Recombination
� when the haploid gametes fuse during fertilization, the diploid number of chromosomes is restored
this can result in a new combination of alleles!� this can result in a new combination of alleles!
� this is called ____________________
Parentsgeneration
(P)
1st
Xtrue-breeding
purple-flower peastrue-breeding
white-flower peas
PP pp
Looking even closer at Mendel’s work…
2ndgeneration
(F2)
1stgeneration(F1 hybrids)
self-pollinate
Pp Pp Pp Pp
????
P p
male / sperm
PP
75%
25%
50%
% genotype % phenotype
Pp
1stgeneration(hybrids)
To show segregation and recombination, we use
Punnett squares!
Pp x Pp
P
p
female / eggs
25%
50%
25%
PP Pp
Pp pppp
Pp
Punnett squares
Bb x Bb
male / sperm
X
female / eggs
Goldberg’s Punnett Square MethodFollow these 4 steps when solving Punnett squares
and you will not get the answer wrong!
Problem:
A homozygous tall pea plant is crossed with a short pea
plant. In pea plants, tall is dominant over short. What
would the expected phenotypes (phenotypic ratio) and
genotypes (genotypic ratio) of their offspring?genotypes (genotypic ratio) of their offspring?
STEP #1set up the key that
will show how each
haploid allele and
each diploid
combination will be
represented
Goldberg’s Punnett Square MethodFollow these 4 steps when solving Punnett squares
and you will not get the answer wrong!
Problem:
A homozygous tall pea plant is crossed with a short pea
plant. In pea plants, tall is dominant over short. What
would the expected phenotypes (phenotypic ratio) and
genotypes (genotypic ratio) of their offspring?genotypes (genotypic ratio) of their offspring?
STEP #2set up the parents
that will be crossed;
use the information
from the word
problem itself!
Goldberg’s Punnett Square MethodFollow these 4 steps when solving Punnett squares
and you will not get the answer wrong!
Problem:
A homozygous tall pea plant is crossed with a short pea
plant. In pea plants, tall is dominant over short. What
would the expected phenotypes (phenotypic ratio) and
genotypes (genotypic ratio) of their offspring?genotypes (genotypic ratio) of their offspring?
STEP #3carry out the Punnett
square; that is, put
one parent’s
segregated alleles on
top, and the other on
the left…then fill in
Goldberg’s Punnett Square MethodFollow these 4 steps when solving Punnett squares
and you will not get the answer wrong!
Problem:
A homozygous tall pea plant is crossed with a short pea
plant. In pea plants, tall is dominant over short. What
would the expected phenotypes (phenotypic ratio) and
genotypes (genotypic ratio) of their offspring?genotypes (genotypic ratio) of their offspring?
STEP #4determine the ratios
of the cross;
phenotypes describe
their appearance,
genotypes describe
their alleles
Goldberg’s Punnett Square MethodFollow these 4 steps when solving Punnett squares
and you will not get the answer wrong!
Problem:
A homozygous tall pea plant is crossed with a short pea
plant. In pea plants, tall is dominant over short. What
would the expected phenotypes (phenotypic ratio) and
genotypes (genotypic ratio) of their offspring?
Tt Tt
Tt Tt
tall tall
tall tall
hetero-
zygous
hetero-
zygous
hetero-
zygous
hetero-
zygous
genotypes (genotypic ratio) of their offspring?
t
t
T Tphenotypic ratio
genotypic ratio
Problem #1:
Use a Punnett square to show the offspring of a
cross between two pea plants that are heterozygous
for height (Tt). Give the expected phenotypic and
genotypic ratios of the offspring
phenotypic ratio genotypic ratio
Problem #2:
Use a Punnett square to show the offspring of a
cross between a pea plant that is homozygous tall
and one that is heterozygous. Give the expected
phenotypes and genotypes of the offspring.
phenotypic ratio genotypic ratio
Problem #3:
In pea plants, yellow seeds are dominant over green
seeds. What would the phenotypic and genotypic
ratios be from a cross between a homozygous green
seeded plant and a pea plant that is a hybrid for
seed color?
phenotypic ratio genotypic ratio
Test cross
PP?
If an organism has the dominant phenotype, how
can we tell if it is homozygous dominant (AA) or
heterozygous (Aa)
PP?
Pp?
x
PP pp
Test cross
p p p p
x
Pp pp
p p
P
P
Pp
Pp Pp
Pp
p p
P
p
Pp
pp pp
Pp
Intermediate Patterns of Inheritance
� Mendel worked with a simple system
� peas are genetically simple
�most traits are controlled by single gene
� each gene has only 2 version
� 1 completely dominant (A)� 1 completely dominant (A)
� 1 recessive (a)
� But its usually not that simple!
A) Incomplete dominance
� __________________________________________________________________________
� hybrids have “in-between/blended” appearance
�RR = red flowers
� rr = white flowers
→→→→
→→→→� rr = white flowers
�Rr = pink flowers� make 50% less color
RR Rr rr
→→→→
→→→→
100% pink flowers
X
1st
Parentgeneration
(P)true-breedingred flowers
true-breeding white flowers
RR R′R′
4 O’clock
flowersA) Incomplete dominance
2ndgeneration
(F2)
1stgeneration(F1 hybrids)
RR′RR′RR′RR′
self-pollinate
25%white
25%red
50%pink
R R′male / sperm
25%
%
genotype
%
phenotype
RR 25%
RR′ x RR′
A) Incomplete dominance
R R′
R
R′
female / eggs RR
RR′ R′R′
RR′
25%
1:2:1
50%
25%
1:2:1
RR′
RR′
R′R′
50%
Problem #4:
Use a Punnett square to show the offspring of a
cross between a red Four O’clock flower and one
that is heterozygous. State the phenotypic and
genotypic ratio of the offspring of the cross.
phenotypic ratio genotypic ratio
Problem #5:
What would the phenotypic and genotypic ratios be
of the offspring produced from a cross bewteen a
white Four O’clock flower and one that is pink?
phenotypic ratio genotypic ratio
B) Codominance
� __________________________________________________________________________
�RR = red coat color
� rr = white coat color
�Rr = pink coat color?
→→→→
→→→→
→→→→
Problem #6:
What would the phenotypic and genotypic ratios be
from the cross between two roan cattle?
phenotypic ratio genotypic ratio
C) Multiple Alleles
� when there are more than just 2 alleles for a given trait
� human blood types are an example with ____________ ________________________________________________________________________
� alleles are A, B, i and code for ‘marker’ on red blood cells
� _________________________________, but…
� ______________________ each other (that means are equally expressed)
pheno-
typegenotype
antigen
on RBC
antibodies
in blood
donation
status
A AA orA itype A antigens
on surface anti-B antibodies __
A allele codes for the ________
B allele codes for the ________
i allele codes for ________
A AA orA i on surface
of RBC
anti-B antibodies __
B BB or B itype B antigens
on surface
of RBC
anti-A antibodies __
AB ABboth type A &
type B antigens
on surface
of RBC
no antibodiesuniversal recipient
O i ino antigens
on surface
of RBC
anti-A & anti-B
antibodies
universal
donor
Blood donation
clotting clotting
clotting clotting
clotting clotting clotting
Problem #7:
If a heterozygous A person and a homozygous B
person have children, can they have a baby with A
type blood?
Problem #8:
Four newborn babies in the delivery room were
accidentally mixed up by the nurse who attached the
wrong wristbands to each child. The blood types of the
four babies were known to be AB, O, A, and B. The blood
types of each set of parents are also known. Using your
knowledge of genetics, carry out all possible crosses to
determine which baby belongs to which set of parents.
(HINT: You may have to do two crosses for certain (HINT: You may have to do two crosses for certain
parents!)
Parental Set #1 : O and AB
Parental Set #2 : AB and B
Parental Set #3 : O and O
Parental Set #4 : O and A
A or B
AB or
A or B
O and AB
parents
AB and B
parentsor
only O
A or O
O and O
parents
O and A
parents or
D) Sex-Linked Traits
� most diploid organisms have two different types of chromosomes
1) autosomes: _________________________ ___________________________________• a.k.a. somatic chromosomes
2) sex chromosomes: ___________________ 2) sex chromosomes: ___________________ ____________________________________
� humans have 22 pair (44 total) of autosomes and 1 pair (2 total) of sex chromosomes
46 chromosomes
23 pairsdiploid (2n) = 2 copies
XX
diploid (2n) = 2 copies 46 chromosomes
23 pairs
XY
D) Sex-Linked Traits
� __________________________________________________________________________
� _____________________________________ (50%-50% chance!)
� this occurs along with the segregation of all homologous autosomes during the homologous autosomes during the production of gametes—meiosis
� besides the genes for sex determination, other genes are found on these chromosomes too!
XX XY
Thomas Hunt Morgan
� embryologist at Columbia University
� 1st to associate a specific gene with a
specific chromosome
�Drosophila breeding
� 2 week generations� 2 week generations
� 4 pairs of chromosomes
� XX=female, XY=male
Thomas Hunt Morgan
� he noticed that some traits were inherited more frequently in males than
females
� ______________________________________________________________________________________________________
Thomas Hunt Morgan
� because the Y chromosome is actually smaller than the X chromosome, men
only have one copy of certain genes…
� so… if the X chromosome has a
recessive allele, that has to be recessive allele, that has to be
expressed because that is all that is
there!
YX
D) Sex-Linked Traits
� for Punnett squares, there are different ways to
set up a key for a sex-linked recessive allele…
X = normal X
Y = normal Y
X = recessive X
XA= normal X
Y = normal Y
Xa= recessive X
XH Ymale / sperm
XHY
XH
HH HhxXHY XHXh
D) Sex-Linked Traits
XH
Xh
female / eggs
XHXH
XHXh
XHY
XhYXHXh
XH
Xh
XHY
Y XHXH XHY
XHXh XhY
Problem #9:
Use a Punnett square to show the offspring of a
cross between a woman with normal (not a carrier)
vision and a color-blind male. What percentage of
each sex would you expect this condition to occur?
Problem #10:
Use a Punnett square to show the offspring of a
cross between a woman who carries the hemophilia
gene and a man who is a hemophiliac. What
percentage of each sex would you expect this
condition to occur?
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