Agenda 12/10- Mendelian Genetics
• Bellwork (next slide)
• New information: Mendelian Genetics
• Finish/discuss “Should this dog be called
spot?” worksheet (blocks 1 and 2)
• Punnett Square practice
• HW- finish Punnett Squares, if needed,
and vocabulary
Bellwork
Genetics
The scientific study of heredity.
Some vocab
• Trait –
– specific characteristic that varies from one individual to another
• Gene –
– sequence of DNA that codes for a protein and thus determines a
trait
• Allele –
– one of a number of different forms of a gene
More Vocab!
• The principle of dominance: some alleles are
dominant and others are recessive.
– dominant- expressed even if there’s only one; hides other alleles
– recessive- only shows up if there are two of them (homozygous
recessive)
• Law of Segregation: alleles separate during
gamete formation so each gamete carries only a
single copy of each gene (MEIOSIS).
Gregor Mendel –
Father of Modern Genetics
• Mendel had true- breeding pea
plants.
• He asked the question: What
would happen if he bred pea
plants with different traits?
Dominant and Recessive Traits &
Gregor Mendel’s Peas
• P – Parent generation (homozygous)
• F1 – first generation of offspring (F – filial from latin
filius “son”)
Parent Genotypes- Yellow vs. Green Peas
• The allele gets a letter representing the name of the
DOMINANT allele (ex. Y for yellow, y for green)
• Homozygous = two of the same alleles- ex. YY=
homozygous dominant; yy = homozygous recessive
• Heterozygous – two different alleles- ex. Yy
Punnett Square
• Diagram showing the gene combinations
that might result from a genetic cross
• Cross YY (female, yellow peas)and yy
(male-green peas)
• Meiosis produces gametes with only one
copy of each chromosome, and therefore only
one copy of each gene. (Law of segregation)
Probability and Genetics
•Probability - likelihood that a particular event
will occur
Y
Y
Yy
Yy
Yy
Yy
y
y
Genotypes and Phenotypes
• Phenotypes and
Genotypes- these plants
have different genotypes
(TT and Tt), but they have
the same phenotype (tall).
– Genotype = genetic makeup
– Phenotype = physical
appearance
Crossing true-breeding parent generation
•Trait
P Generation
•Trait
–Yellow pea
–dominant
–Green pea
–recessive
•Genes (alleles)
–yy
•Gametes
formed
Cross
YY and
yy
Y
y
Y
•Genes (alleles)
–YY
•Gametes
formed
y
–y and y
F1 Generation
–Y and Y
Crossing the F1 generation
•Trait
F1 Gen.
–Yellow pea
–Yellow pea
•Genes
(alleles)
•Trait
•Genes
(alleles)
Cross
Yy and
Yy
–Yy
–Yy
•Gametes
formed
F2 Generation
•Gametes
formed
5-minute Write- Punnett Square Practice
• Set up the square for each of the crosses listed below.
The trait being studied is seed shape: round seeds
(dominant) and wrinkled seeds (recessive).
• Rr x rr
– What percentage of the offspring are expected to
have round seeds? Wrinkled seeds?
• A homozygous round seeded plant is crossed with a
homozygous wrinkled seeded plant.
– What are the genotypes of the parents?
– What percentage of the offspring will also be
homozygous?
• Rr x rr
• What percentage of
the offspring will
have round seeds?
• Wrinkled seeds?
• A homozygous round
seeded plant is crossed
with a homozygous
wrinkled seeded plant.
• What are the genotypes of
the parents?
__________ x __________
• What percentage of the
offspring will also be
homozygous?
____________
Agenda 12/11/14- Mendelian Genetics
• Bellwork (next slide)
• Dihybrid Crosses
– Practice worksheet
• Homework- Punnett Square practice
packet; vocabulary mini-quiz tomorrow
Agenda 12/11/14- Mendelian Genetics
• Bellwork (next slide)
• New information: Principle of
Independent Assortment; Punnett
Square practice;
• Homework- vocabulary; vocabulary
mini-quiz tomorrow
Punnett Square
Diagram showing the gene
combinations that might result from
a genetic cross
•
• Meiosis produces gametes with only
one copy of each chromosome, and
therefore only one copy of each gene.
(Law of segregation)
Probability and Genetics
•Probability - likelihood that a particular event
will occur
Y
Y
Yy
Yy
Yy
Yy
y
y
Genotypes and Phenotypes
• Phenotypes and
Genotypes- these plants
have different genotypes
(TT and Tt), but they have
the same phenotype (tall).
– Genotype = genetic makeup
– Phenotype = physical
appearance
Mendel’s Principles
• Principle of Dominance
– Some alleles are dominant, some are recessive.
• Principle/Law of Segregation:
– During meiosis, alleles separate so each gamete carries
only a single copy of each gene
• Principle of Independent Assortment
Law of Independent Assortment
• The principle of independent assortment: genes
for different traits can segregate independently
during gamete formation.
• In other words, genes (alleles) of one trait do not
affect the inheritance of genes of another trait
(unless they’re on the same chromosome, when they
MIGHT be linked).
• This allows us to cross genes for different traits at
the same time.
Cross of heterozygous yellow and round peas.
• Dihybrid Crosses (2
traits)
• First, what is the
genotype of the
parents?
• Second, how many RY
different gametes
can be formed?
• Third, what are the
different gametes?
Parent:
RrYy
Ry
rY
ry
Cross of heterozygous yellow and round peas.
• How many
different
phenotypes do
we expect?
–4
• What are the
expected
phenotype
ratios?
– 9:3:3:1
Agenda 12/12- Mendelian Genetics
• Bellwork- vocabulary quiz (next slide)
• Dihybrid crosses, incomplete and codominance, multiple alleles, polygenic
traits- notes
• Punnett square practice
• HW- finish worksheets, if needed
• Unit test next Thursday (Mendelian
Genetics, Meiosis)
Beyond dominant and recessive alleles.
• Most genes do not follow the simple patterns of
dominant and recessive alleles.
• Some alleles are neither dominant nor recessive,
and many traits are controlled by multiple alleles
or multiple genes.
Beyond dominant and recessive alleles
• Incomplete dominance
- one allele is not
completely dominant
over another
• New phenotype:
blending of the two
alleles
• Ex. Red flower, White flower,
produce pink flowers
Beyond dominant and recessive alleles
FRFR
• Incomplete dominance
- one allele is not
completely dominant
over another
• New phenotype: pink
(blending of the two
alleles)
FR
FR
FRFW
FRFW
FRFW
FRFW
FW
FWFW
FW
Beyond dominant and recessive alleles
• Codominance - both alleles of a gene
contribute to the phenotype of the organism
FB = black feathers
FW = white feathers
FBFW = both show
equally (black and
white feathers)
No blending, as in
incomplete
dominance.
Beyond dominant and recessive alleles
• polygenic trait - trait
controlled by two or
more genes
• Ex. Height
Beyond dominant and recessive alleles
• multiple alleles - three or more alleles of
the same gene
• Example- human blood type
Alleles
Present
A A
I I
IA i
IB IB
B
I i
ii
IA IB
Genotype
Homozygous Dominant
Heterozygous
Homozygous Dominant
Heterozygous
Homozygous Recessive
Heterozygous Dominant
Phenotype
A-Glycoprotein
A-Glycoprotein
B-Glycoprotein
B-Glycoprotein
No Glycoproteins
A & B-Glycoproteins
Blood Type
A
A
B
B
O
AB
Blood Type Inheritance
Multiple alleles and Codominance
Alleles
Present
A A
I I
IA i
IB IB
B
I i
ii
IA IB
Genotype
Homozygous Dominant
Heterozygous
Homozygous Dominant
Heterozygous
Homozygous Recessive
Heterozygous Dominant
Phenotype
A-Glycoprotein
A-Glycoprotein
B-Glycoprotein
B-Glycoprotein
No Glycoproteins
A & B-Glycoproteins
Blood Type
A
A
B
B
O
AB
The Human Karyotype
Agenda 12/15- Autosomal and Sex-linked Traits
• Bellwork
• New information: karyotypes, autosomal
vs. sex-linked traits
• Sex-linked traits worksheet
• Build-a-Kid Lab
Bellwork 12/15/14
• Determine the possible genotypes of the parents
and offspring. Brown fur is dominant.
1. Two brown dogs are bred and produce 5
puppies, 3 brown and 2 yellow.
2. Two brown dogs are bred, producing 7 brown
puppies.
3. A brown and a yellow dog are bred, producing
a litter of 3 brown and 2 yellow puppies.
Question about the HW?
• How many chromosomes do humans
have?
• How many different pairs of
chromosomes do humans have?
The Human Karyotype
Homologous Pairs
Autosomal Dominant and Recessive
• A gene is autosomal if it is
on a non-sex chromosome.
• A gene is sex-linked if it is
found on a sex chromosome
• What are the two sex
chromosomes?
Autosomal Disorders
• Autosomal Dominant
– Polydactyly
– Huntington’s Disease
• Brain cells die, nervous system deteriorates; onset usually
between 35-44
• Can a parent be unaffected but pass on the
allele for the trait to their offspring?
Autosomal Disorders
• Autosomal Recessive
– Sickle Cell Disease
• Point mutation- affects hemoglobin
• Red blood cells shaped like a sickle (instead of a smooth
round shape- get stuck in capillaries)
• What’s the advantage?
– Heterozygous individuals have some protection from
malaria, common in Africa
Sex-linked Disorders
• Sex-linked disorders are found on sex
chromosomes
• Sex-linked recessive traits– Females can be carriers- have one allele for
the trait but do not express it.
– Males either have the disorder or don’t.
They can’t be carriers.
Sex-linked Disorders
• Red-Green Colorblindness
– Sex-linked recessive
– 5-10% of males affected
– Cross a heterozygous female with a
homozygous dominant male
– Cross a heterozygous female with a
homozygous dominant male.
-Probability that a child will
be female?
- Probability that a child
will be male?
-Probability that a female
child will be color-blind?
-Probability that a male
child will be color-blind?
-Why are males more likely
to be color-blind?
Sex-linked Traits Practice
• Complete the worksheet in pairs.
• When you’re done, check in with me and
get the “Build a Kid” Lab
Bellwork 12/16
Agenda 12/16- Nondisjuction; Pedigrees
• Bellwork
• Review sex-linked traits worksheet
• New information: nondisjunction;
pedigrees
• Build a Kid Lab
• HW- finish review worksheet, study for
test Thursday
The Human Karyotype
Homologous Pairs
Chromosomal Abnormalitites
• Sometimes there are errors during meiosis, and
chromosomes don’t divide correctly
(nondisjunction).
• Karyotyping can be used to predict genetic
disorders.
– Trisomy 21- Down’s Syndrome
• 3 copies of chromosome # 21
Other Chromosomal Disorders
• Sex Chromosomes (#23)- X, Y
– XX or XY
• Turner Syndrome:
– monosomy (one copy) 23
– XO
• Klinefelter Syndrome:
– Trisomy 23
– XXY
Pedigrees
• Pedigree = family tree
= Affected male
= Affected female
Pedigree
• Draw a pedigree for the following family.
• Jane and Pete are married. They have 2
children: one boy and one girl.
• Their daughter, Joan, is married to Dale, and
they have one daughter.
• Jane and Pete’s son is married to Debbie, and
they have 4 children: 3 boys and one girl.
• Pete, Joan, and the Dale’s daughter all have an
autosomal recessive disease.
Hemophilia A: the Royal Disease
X-Linked Cross:
• Hemophilia A: a hereditary blood disorder,
primarily affecting males (1 in 10,000) and rarely
affecting females (1 in 100,000,000).
• Characterized by a deficiency of the blood
clotting protein that results in abnormal bleeding.
• Hemophilia is a recessive genetic disorder
located on the X chromosome (sex-linked trait).
Hemophilia A: the Royal Disease
Alice of Athlone, had one
hemophilic son (Rupert) and two
other children—a boy and a girl—
whose status is unknown. a) What
is the probability that her other son
was hemophilic? b) What is the
probability that her daughter was a
carrier? A hemophiliac? c) What is
the probability that both children
were normal?
Summary of Mendel’s Principles
• Genes code for proteins, and therefore traits, and
are passed from parents to their offspring
(heritable).
• Principle of Dominance: When two or more
forms of the gene for a single trait exist, some
forms of the gene may be dominant and others may
be recessive.
• In most sexually reproducing organisms, each
adult has two copies of each gene—one from each
parent. These genes are segregated (usually
independently) from each other when gametes are
formed. (Independent Assortment, Law of
Segregation)
Linkage and Gene Maps
•Which law states that genes located on
different chromosomes separate independently?
•But what about genes located on the same
chromosome?
Wouldn’t they generally be inherited together?
• Thomas Hunt Morgan’s studies back in 1910
helped us to answer this question.
Linkage and Gene Maps
• Just because two genes are
located on the same
chromosome does not mean
that they are linked together
forever.
• Crossing-over (metaphase I of
meiosis I)
• The further apart the genes
are the more likely they are
to separate. The closer they
are the less likely they are to
separate.