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 parent each 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!
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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
� 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