Download Genetics Class Notes 2017

Research Biology
Genetics
Genetics Class Notes 2017
Heredity- The passage of traits from one generation to another.
Gregor Mendel-Father of genetics, conducted breeding experiments with pea plants,
university education, was a monk.
Why pea plants? (5)
1) Short generation span
2) Easy to grow
3) Easily distinguishable traits
4) Large number of offspring (sample number)
5) Carry out both self and cross pollination
Why Mendel? (5)
1) Kept accurate written records
2) Studied one trait at a time
3) Conducted controlled experiments
4) used a large sample number
5) First to use statistics and probability
Key Concepts Terminology (7)
1) Dominant- A trait which expresses itself if even one dose of the gene is present
2) Recessive- A trait which expresses itself only if two dose of the gene is present
3) Homozygous- Both genes for the trait are the same (BB, bb)
4) Heterozygous- The two genes for the trait are different (Bb)
Homo- Same Hetero- Different Zygote- Fertilized Egg
5) Phenotype- External appearance of a trait
6) Genotype- Actual gene combination for a trait
7) Allele- one form of a gene
Types of Cells
1) Somatic Cells(Body cells)- Cells which are not directly involved in reproduction
46 individual chromosomes per cell.
23 pairs, 2(23) = 46
2) Gametes(sex cells; sperm & egg)- Cells which are directly involved in reproduction
23 Chromosomes per gametes ( sperm & egg)
1 single set of chromosomes
Mr. Luis A. Velázquez
Research Biology
Genetics
Mendel’s Experiments-Height (T=Tall t =Short)
Mendel used the term “Factor” instead of “Gene”
P1-Parental Generation AKA First Generation
F1-First Filial AKA second generation
F2-Second Filial AKA third generation
P1 TT x tt (Homozygous Tall~TT~Crossed with Homozygous Short~tt)
F1 Tt-100% (All of the offspring was Tall)
F2 3:1, Tall: Short, 75% Tall 25% Short (25% Homozygous Tall~TT,50%
Heterozygous Tall~Tt, 25% Homozygous Short~tt)
Punnit Square
Gametes
T
t
T
TT
Tall
Tt
Tall
t
Tt
Tall
tt
Short
1:2:1 Genotypic Ratio TT:Tt:tt
3:1 Phenotypic Ratio Tall:Short
Law of Segregation
When F1 hybrids (heterozygous) are crossed with each other that that did not appear in
the F1 appears in 1/4 of the F2 (3/4 are Tall 1/4 are Short; all the F1 where Tall)
Mr. Luis A. Velázquez
Research Biology
Genetics
Multi-Trait Crossing-Height(T=Tall t =Short)& Seed Color(Y=Yellow y =Green)
P1 TTYY x ttyy (Pure Tall & Yellow crossed with Pure Short & Green)
F1 TtYy x TtYy (100% Tall & Yellow)
F2 9:3:3:1, Tall & Yellow: Tall & Green: Short & Yellow: Short & Green
Alleles
(Gametes)
Gametes
TY
Ty
tY
ty
TY
TTYY
Tall
Yellow
TTYy
Tall
Yellow
TtYY
Tall
Yellow
TtYy
Tall
Yellow
Ty
TTYy
Tall
Yellow
TTyy
Tall
Green
TtYy
Tall
Yellow
Ttyy
Tall
Green
tY
TtYY
Tall
Yellow
TtYy
Tall
Yellow
ttYY
Short
Yellow
ttYy
Short
Yellow
ty
TtYy
Tall
Yellow
Ttyy
Tall
Green
ttYy
Short
Yellow
ttyy
Short
Green
Law of Independent Assortment
When two traits are studied at the same time, the inheritance of one trait is
independent of the second trait Exception-When genes for different traits are found
on the same chromosome they tend to be inherited together
Linked Genes
Incomplete Dominance-AKA Blending Inheritance-The hybrid does not resemble
either parent but instead is a blend of parental traits
1)Four O’ Clocks(R=Red Flowers W=White Flowers)
P1 RR x WW
F1 RW- 100% Pink
F2 1:2:1, Red: Pink: White, 25% Red 50% Pink 25% White
Gametes R
R
RR
Red
W
RW
Pink
Mr. Luis A. Velázquez
W
RW
Pink
WW
White
Research Biology
Genetics
2) Andalusian Fowl (B=Black Feathers W=White Feathers)
Incomplete dominance
P1 BB x WW
F1 BW-100% Blue
F2 1:2:1, Black: Blue: White,25% Black 50% Blue 2% White
Gametes B
B
BB
Black
W
BW
Blue
W
BW
Blue
WW
White
Sickle Cell Disease (HbA-HemoglobinA=Normal HbS-HemoglobinS=Abnormal
Gametes
HbA
HbA
Normal
HbS
Sickle Cell
Trait
HbS
Sickle Cell
Trait
Sickle Cell
Anemia
Sickle Cell Trait- Both types of cells, greater resistance to Malaria
Sickle Cell Anemia- Shortened Life span by approximately 50%
Multiple Alleles
There are 3 or more different genes in the population but any individual has only 2
genes/trait
Alleles for Blood -IA; group A, IB; group B, i; Group O
Blood Groups
Phenotype: A
Genotype:
IA IA, IAi
Antigen:
A
Antibody:
anti-b
Mr. Luis A. Velázquez
B
IB IB, IBi
B
anti-a
AB
IA I B
A&B
none
O
ii
None
anti-a/anti-b
Research Biology
Genetics
Antigen- A foreign substance which stimulates the formation of antibodies (Red
blood cells)
Antibodies- A substance formed in response to an antigen (plasma-liquid part of
blood)
Blood groups are an exception to these definitions
‘O’ blood is known as the universal donor
‘AB’ blood is known as the universal recipient
Agglutination Reaction-Caused by transfusions when the antibodies attack the
transfused blood
RH Factor(RH=Positive(+) = Negative(-)
Blood types
A+,A-,B+,B-,AB+,AB-,O+,ORH Disease
Mother’s RH Factor Negative
Father’s Positive
Fetus/Baby’s Positive
Antibodies from the mother attack the fetus if any blood from the baby leaked into the
mother, the second Fetus with Positive blood will be attacked if blood is leaked from
the second fetus, the mother’s body remembers the foreign RH and antibodies are
already pre-created from first fetus, the second fetus may be injured or killed by the
antibodies. After the first Baby is born a vaccine may be created to prevent the
creation of antibodies that may injure or kill the second fetus.
Placenta- Provides O2 and nutrients to the fetus, carries away fetal waste
Sex Determination
Somatic Cells-46 chromosomes/cell (23 Pairs)
44 Autosomes (22 Pairs)
2 Sex Chromosomes (1 Pair)
X chromosome-Female, Y Chromosome-Male
XX-Normal Female, XY-Normal Male
Mr. Luis A. Velázquez
X
Y
X
XX
XY
X
XX
XY
Research Biology
Genetics
Female to Male ratio should be the same however it is not; 106 Males:100 FemalesThe Y chromosome is smaller and lighter in weight then the X chromosome. Y sperm
can swim slightly faster then the X sperm so more Y sperm will reach the egg. There
is a somewhat better chance that the Y sperm will fertilize the egg.
Twins
1) Fraternal-Two eggs each of which is fertilized by its own sperm
2) Identical-One egg is fertilized by one sperm then the zygote divides and each
zygote matures by itself.
Variations in Sex Chromosomes
Sexual Syndromes Pair 23 Males or Females only
1)XO-Female-45 chromosomes per somatic cell; 44 autosomes 1 sex chromosome
AKATurners Syndrome-sexually immature Female.
2)XXY-Male-47 chromosomes per somatic cell; 44 autosomes 3 sex chromosomes
AKA Klinefelter’s Syndrome-sexually immature Male.
3)XXX-Female-47 chromosomes per somatic cell; 44 autosomes 3 sex chromosomes
AKA Super Females.
4)XYY-47 chromosomes per somatic cell; 44 autosomes 3 sex chromosomes
AKASuper Males also known as Jacobs syndrome.
5)XXYY-48 chromosomes per somatic cell; 44 autosomes 4 sex chromosomes.
Autosomal Syndromes seen in both genders Male and Female
6)XX/XY+21 Down 47 chromosomes somatic cell; 45 autosomes 2 sex Trisomy 21
7)XX/XY+18 Edwards 47 chromosomes somatic cell 45 autosomes 2 sex Trisomy 18
8)XX/XY +13 Patau 47 chromosomes somatic cell 45 autosomes 2 sex Trisomy 13
9)XX/XY d-5 Cri du chat 46 chromosomes per somatic cell 44 autosomes 2 sex Pair
5 deletion
Mr. Luis A. Velázquez
Research Biology
Genetics
Normal Gamete Formation
Crossing over is the exchange of genetic material between homologous chromosomes that
results in recombinant chromosomes during sexual reproduction. Happen during prophase I
This will guarantee that all gametes are different.
Abnormal Gamete Formation
Non-Disjunction- Failure of chromosome pairs to separate during Gamete formation
(Same diagram as previous page until the last stage)
Autosomal Non-Disjunction
Down’s Syndrome AKA Trisomy 21 & Mongolism
(incorrectly called Mongolism because of appearance)
47 Chromosomes/ Somatic Cell-45 Autosomes 2 Sex Chromosomes
Mental retardation, Short, Overweight, Round face, Poor muscular coordination, Tip of the
tongue protrudes, Shortened life span, Simian Crease -Line crease across the length of both
hands. Called Trisomy 21 because there are three 21st Chromosomes instead of the normal pair
(2)
Mr. Luis A. Velázquez
Research Biology
Genetics
Amniocentesis-A technique in which amniotic fluid and embryonic cells are retrieved and
analyzed for genetic defects.
Cells are cultured and examined microscopically to find the point of cell division
A photo of the chromosomes is taken which is called a Karyotype-A photo of the chromosomes
arranged in pairs.
Sex Linkage(sex linked traits) - The genes for these traits are found only on the X
chromosome, There are NO genes for this trait on the Y chromosome
Color-blindness (C-Normal color vision c-color blindness)
Females-Has XX therefore 2 genes
Males-Has XY therefore 1 gene (on the X
chromosome)
CC-Normal Color Vision
CY-Normal Color Vision
Cc-Carrier(Normal color vision but has the Cannot be a carrier
gene to pass on)
cc-Color-blind
cY-Color-blind
Gametes
C
c
Mother
CC-Normal Color Vision Cc-Carrier
-Females
C
CY-Normal Color Vision cY-Color-blind
-Males
Y
Father
Hemophilia-A condition in which the blood doesn’t clot and continues to bleed caused by the
body not synthesizing factor VIII(8)-a step in the process of blood clotting
H-Normal Clotting h-Hemophilia
Female
HH-Normal
Hh-Carrier
hh-Hemophilia
Male
HY-Normal
hY-Hemophilia
There have been virtually no cases(but still some) of Hemophilia in a Female because it is a rare
gene and most people die at an early age from it.
Genetics and Environment
1)Green Color in Plants-(C-Chlorophyl production c-No chlorophyl production)
CC- Green
Cc- Green
cc-White (dead)
2)Baldness in Humans-(B-Bald b-Hair)
Female
Genotype Male A minimal level of testosterone
Hair
BB
Bald is needed to activate the dominant
Hair
Bb
Bald gene for baldness in Humans
Hair
bb
Hair
Mr. Luis A. Velázquez