Transcript Ch. 10 Mendel`s Genetics

Ch. 10.1 Mendel’s Discoveries
Gregor Mendel (1866)
• “Father of
Modern Genetics”
• Breed pea plant.
(Pre- Mendel:
Blending of traits
hypothesis)
Background Vocab
True-breeds: pure gene lines – offspring
match parent
Self-pollination: pollen from flower
fertilizes the same plant
Cross-fertilization: pollen will fertilize
a different plant
Hybrid: Cross between organisms with
different traits (blonde hair & brown
hair)
Trait: Physical characteristics
Cross pollination
4/2/2016
4
Trait Studied
Dominant
Form
Recessive6
Form
F2 Dominant-toRecessive Ratio
SEED SHAPE
5,474 round
1,850 wrinkled
2.96:1
SEED COLOR
6,022 yellow
2,001 green
3.01:1
POD SHAPE
882 inflated
299 wrinkled
2.95:1
POD COLOR
428 green
152 yellow
2.82:1
FLOWER COLOR
705 purple
224 white
3.15:1
FLOWER POSITION
651 long stem 207 at tip
3.14:1
STEM LENGTH
787 tall
2.84:1
277 dwarf
Mendel’s Experimental design
Parental generation (P)
White X Purple
(truebreed X truebreed)
Offspring: F1 Generation
(Hybrids)
100% purple
F1 Cross
Purple X Purple
(hybrid X hybrid)
Offspring: F2
(3:1 – Purple : White)
75% Dominant: 25% Recessive
4/2/2016
Mendel’s Conclusions:
Inheritance is determined by chemical factors
(genes) passed from one generation to the
next (particulate hypothesis)
Genes can come in more than one form= allele
Example: (white vs purple)
Ch. 10.2 Mendel’s Genetics
More Genetics Vocab
• Homozygous: two identical alleles
(AA or aa)
• Heterozygous: two different alleles
(Aa)
• Phenotype: Physical appearance
• Genotype: Genetic make-up
– Homozygous dominant (AA)
– Homozygous recessive (aa)
– Heterozygous (Aa)
Mendel’s Principles
1. There are alternative forms of genes
(alleles)
2. There are 2 alleles for each trait (BB,Bb, bb)
* we now know there can be more.
3. Some alleles are dominant; some
recessive.
4. Principle of SEGREGATION: Alleles for
each trait segregate (separate) during
gamete formation (Anaphase I of meiosis)
Monohybrid Crosses = Parents differ in only 1 trait
P: Purple X White
F1: all purple (100% dominant)
F1 purples self- fertilize to see if white trait was
lost.
F2: 75% purple; 25% white
(dominant)
(recessive)
Diagram that shows all possible
outcomes of a genetic cross
Standard Mendelian Cross #1:
If purple flower color is dominant, what phenotypes are expected if
a purebred purple flowered plant is crossed with a purebred white
flowered plant?
WW x ww
Phenotypic Ratio:
100% purple
Genotypic ratio:
100% Ww
4/2/2016
15
Standard Mendelian Cross #2:
If purple flower color is dominant, what genotypes are expected if a
heterozygote is crossed with another heterozygote.
Ww x Ww
Phenotypic ratios:
3 purple: 1 white
Genotypic ratios:
1WW:2Ww:1ww
4/2/2016
16
Testcross: Helps determine the genotype of a
dominant phenotype
• Dominant phenotype could be AA or Aa
• Unknown Dominant X Recessive (aa)
- Any recessive offspring, unknown= Aa
- All dominant offspring, unknown= AA
Mendel’s DIHYBRID CROSSES
(2 traits)
Independent Assortment: Alleles for
different traits do not influence each
other’s segregation during meiosis.
List the gamete combinations possible for each of
the genotypes listed below:
RrYY
RY, rY, RY, rY
rrYY
rY, rY, rY, and rY
RrYy
RY, Ry, rY, and ry
4/2/2016
21
Dihybrid Cross
Traits are inherited
separately.
F2: 9:3:3:1 Ratio
Black hair is dominant to white
Short hair is dominant to long
Cross a heterozygous black & short haired
mouse with a white & heterozygous short haired
mouse.
1. What are the genotypes of the parents?
2. What are the genotypic and phenotypic ratios
of the F1 generation?
10.3 Exceptions to Mendel
Incomplete/Intermediate dominance:
blending of phenotypes
neither allele takes a fully dominant role
P1: Red x White flowers
F1: Pink flowers
F2: 1 red: 2 pink: 1 white
Codominance
• BOTH alleles are expressed in heterozygotes.
• Not incomplete dominance
• EX: Roan cattle and Blood types
Multiple Alleles
More than 2 alleles for an inherited character.
Blood type:
A, B, AB, or
O
Fur color
Eye color
Blood Typing: Multiple
Allelism
a) Human blood type is expressed by 3
alleles: IA, IB and i.
b) IA and IB are Co-dominant
c) i is recessive.
Codominance in blood groups
4/2/2016
33
Blood Type: Codominance & Multiple Alleles
Caucasians
African
American
Hispanic
Asian
O+
37%
47%
53%
39%
O-
8%
4%
4%
1%
A+
33%
24%
29%
27%
A-
7%
2%
2%
0.5%
B+
9%
18%
9%
25%
B-
2%
1%
1%
0.4%
AB +
3%
4%
2%
7%
AB -
1%
0.3%
0.2%
0.1%
• Could a person with Type A blood receive type
O blood? Could they receive Type AB?
• Could a person with AB- blood receive AB+?
• List the blood types that type B+ could receive?
Polygenic Inheritance: Multiple Genes affect a trait
Phenotypes of these traits
demonstrate continuous
variation (bell curve)
Examples: height, weight,
skin color, intelligence.
39
Continuous variation in skin
color
4/2/2016
40
Environmental Influence on
Genes
Temperature, pressure, pH, presence of certain chemical
compounds influence how genes are expressed.
Epigenetics: study of how genes are influenced by
environmental conditions.
Environmental Influence
1.
Some flowers colors are influenced by the
acidity of the soil (Hydrangea).
1.
The color of the arctic fox is influenced
by temperature.
2.
Siamese cats have darker hair at areas that
are cooler than body temperature (ears,
nose and paws).
3.
Human size is influenced by nutrition.
42
10.5: Sex Linked Genes: Genes
located on X or Y chromosome
Do you think the X
chromosome or the
Y chromosome
holds more genes?
Rules
1. Recessive Sex Linked Traits:
- Affect males more than females
- Males only need one copy of the gene (XaY).
- Females can be carries (XAXa)
2. Dominant Sex- Linked Traits:
- More likely to affect females (XA XA or XA Xa)
Recessive Sex-Linked Disorders




Color-blindness
Hemophelia
Baldness
Versions of Muscular
Dystrophy
12.3- Pedigrees
A Pedigree is a family tree that shows the
inheritance of a genetic disorder
Carriers: do not
have the disorder but
can pass it on
(heterozygous)
A pedigree can allow you to determine whether a trait is
autosomal, or sex-linked.
1.
Autosomal disorders affect males and females
equally.
1.
If the trait is autosomal dominant, every individual
who has the disorder will have at least one parent who
has the disorder.
2.
If the trait is autosomal recessive, an individual with
the trait can have one, two or neither parent exhibit the
trait.
1.
Sex-linked traits are carried on the X chromosome, and therefore affect
one gender or the other in disproportionately high numbers.
a)
b)
Sex-linked recessive traits affect males in higher numbers.
•
Since they have only one X chromosome, if males receive a
single copy of this recessive allele, they will show the
phenotype.
•
Females must still receive two recessive versions to show the
phenotype.
Sex-linked dominant traits affect females in higher numbers
•
A female has two X chromosomes, and therefore is twice as
likely to receive the trait
4/2/2016
52
4/2/2016
53
Question:
Is this disorder autosomal or sex-linked?
Is it dominant or recessive?
Parents are
unaffected
Both males and
females are affected
4/2/2016
54
Complete the following pedigrees.
Which is for a sex-linked trait? How do you know?
Is it a dominant or recessive trait?
Royal Family Pedigree
Human genetic disorders
4/2/2016
57
10.4 Gene linkage
Genes located on the same chromosome tend to be
linked
Loci: location of a gene on a chromosome
• Gene Linkage:
• Gene closer together on chromosome have a greater
likelihood of traveling together during crossing over
• Greater likelihood of inheriting genes together
12.1
Genome: the complete set of genetic material
12. 4- Genes and Cancer
• Regulation of Cell Cycle
– Growth factors: Initiate cell division
– Tumor Suppressor Genes: Stop Cell Division
Cancer is ALWAYS a genetic disease due to mutations in DNA
– Mutation in somatic cells= not passed on to offspring
– If mutation occurs in ovaries or testes
• offspring will inherit an abnormal copy of a gene that increases
their likelihood of developing cancer
Epigenetics
NOVA Video