Download GENETICS = Scientific study of inheritance

GENETICS & INHERITANCE
GENETICS = Scientific study of ______________
Gregor Mendel (1860) = ____________________________
 Experimented with ______________
 Used _______________(asexual reproduction) and cross-fertilization
methods (sexual reproduction)
 chose simple traits to follow (flower color, height, seed color, seed texture
etc.)
Trait = any ___________that can be passed from parents to their offspring
Gene = genetic material on a ___________that contains the instructions for
creating a particular trait
Allele = one of several _______of a gene, an alternate form of the same gene for
a given trait
example: A or a (same letter, different case)
Locus = the __________on a chromosome where a gene is located
Every ____________(body) cell contains two copies of each chromosome, one
from each parent. This is called a _____________. Each chromosome in the
pair contains a gene for the same trait at exactly the same loci.
See PICTURE OF HOMOLOGOUS PAIRS HERE
Monohybrid Cross = a cross involving only a _______ responsible for a trait;
each parent contributes information for the trait (ex. Aa X AA)
Dominant trait = the trait that gets expressed in a monohybrid cross where the
mode of inheritance is ______________________; shown by a capital letter : A
Recessive trait = the trait that is hidden in a monohybrid cross where the mode
of inheritance is_________________; ______________shown by a lower case
letter : a
Homozygous = the two alleles for a trait that an organism has are
______________ex: Homozygous Dominant = AA , Homozygous Recessive =
aa
Heterozygous = the two alleles coding for a trait are __________________ex:
Aa
Genotype = the actual___________________, all the alleles that an organism
possesses (the actual letters)
Phenotype = ________________________based on alleles
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GENETICS & INHERITANCE
Mendel’s Laws of Heredity
1. Law of__________: When a trait is Completely Dominant over another trait,
then that dominant allele controls the gene pair. In the heterozygous form (Aa)
the dominant trait only gets expressed. The recessive allele gets hidden.
2.
Law of___________: Pairs of alleles separate during the formation of the
gametes (sex cells) during Meiosis I. Therefore each gamete will contain
one allele for each gene.
See picture of meiosis and fertilization here
3. Law of______________________: Gene pairs separate into the gametes
both independently and randomly of each other.
The rules of __________are used to describe how the different chromosomes
and their alleles from parents assemble into ________and ultimately
into__________.
PUNNETT SQUARES
Used to track a trait from parents to offspring.
Shows possible ratios for offspring outcomes.
P Generation = Parents
F1 Generation = Offspring from the cross of the parents
F2 Generation = Offspring produced from crosses among the F1
F = filial, refers to sons and daughters
Rules:
1. Make a key; show dominant and recessive alleles
2. Properly label parents genotypes, place them on the outside of the punnett
square
3. Correctly perform the cross
4. Interpret the results; determine ratios
Monohybrid Cross ratios:
Complete Dominance = 3:1 (Aa X Aa) ; 4:0 (AA X aa); 2:2 (Aa X aa)
TEST CROSSES
Suppose we have two Tall pea plants
T= tall; t = short
What are the possible genotypes for each plant?
__________ or ___________
To find out whether an individual showing a dominant trait is homozygous or
heterozygous, the individual can be crossed with an individual whose genotype is
known for certain.
What type of plant would we know for certain the genotype of?
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GENETICS & INHERITANCE
Test Cross: cross the tall plant (TT or Tt) with a short one (tt)
If any recessive phenotypes show up in the next generation, the unknown
genotype MUST be Heterozygous
Homozygous tall x short
Homozygous Tall x short
TT x tt
Tt x tt
Offspring =
Offspring =
Chromosome Theory of Inheritance: genes that code for various traits are
found on ____________which are made of _____ and found in the
____________of each cell
Thomas Hunt Morgan (1910): Studies Drosophilia melanogaster ;common fruit
fly
 Discovered the gene for eye color and wing size were both located on the
same chromosome (X) = __________
 Linkage = _____________________________________
 The closer the genes are on the chromosome, the _____________the
likelihood of crossing over
 The Law of _______________________does not apply to linked genes!
Barbara McClintock & Harriet Creighton (1950): Studied Zea mays ; corn
 Looked at __________________
 They noticed that 2 copies of it were different sizes
 Conclusion = ______________had occurred, an abnormal event caused a
piece of another chromosome to attach itself to one of the copies of
chromosome #9
 Crossing Over disrupts_________________________!
Chromosomes: Humans have __individual chromosomes in every cell of the
body except the ___________
22 pairs = _____________(regular, information carrying chromosomes)
1 pair = ____Chromosomes, determines gender (XX = female, XY = male)
MODES OF INHERITENCE
Different ways of inheriting genetic traits
1. Complete Dominance: dominant allele completely masks out the recessive
trait (AA, Aa)
 Autosomal Dominant = trait carried on an autosome by a dominant gene (A)
 Autosomal recessive = trait carried by a recessive allele (aa)
Example: flower color in pea plants
P = Purple, p = white
PP x pp
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Pp x Pp
GENETICS & INHERITANCE
2.
Incomplete Dominance: One allele of a gene pair is not fully dominant over
the other; being heterozygous produces an intermediate form, no masking
occurs (AA, Aa, aa)
Example: Flower color in snapdragons
RR = red, rr = white, Rr = pink
RR x rr
Rr x Rr
3. Codominance: both alleles express themselves when heterozygous (Blood
types A, AB, B, O). There is no true recessive trait.
 AB Blood type is an example of Codominance = Both alleles in the
heterozygous form (IAIB ) end up expressing themselves equally. Both traits
show up in the phenotype.
Example: coat color in horses
RR = red , WW = White , RW = roan
(RR = red , R’R’ = White , R R’ = roan)
RR x WW
RW x RW
4. Polygenic Traits: trait is controlled by more than one pair of genes (Eye
color, Skin color, Human Height). This usually results in continuous variation.
Polygenic inheritance is considered the opposite of Pleiotropy.
5.
Pleiotropy = when a single gene has more than one phenotypic expression.
Example: Sickle Cell Anemia = misshapen red blood cells ultimately causes
other problems such as anemia, pneumonia, heart & kidney failure, bone
abnormalities, and impaired mental functioning.
6. Epistasis = one gene affects the phenotypic expression of a second gene.
(Skin pigmentation) One gene codes for color, the other codes for the amount of
pigment.
7. Multiple Alleles: a gene having more than two alleles
(Blood types)
PHENOTYPES
*
A
B
AB
O
% of Population
39%
12%
4%
45%
GENOTYPES
IAIA
IBIB
IAIB
IiIi
, IAIi
, IBIi
 Discovered in 1900 by Dr. Karl Landsteiner
 Based on the presence or absence of specific agglutinogens (clotting
factors) on the surface of red blood cells (RBC’s = Erythrocytes)
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GENETICS & INHERITANCE
 For example: a person with blood type A posseses A-antigens and
Anti-B antibodies
 The blood will clot if a foreign Antigen is present
Universal Donor = Blood type O ; contains no A or B antigens  No Clotting
reaction
Universal Recipient = Blood type AB ; contains both A & B antigens  Will
recognize antigens from any blood type
Rh Factor = (Rhesus monkey) You either have it (+) or you don’t (-)
Sensitization can occur by:
1.)
Rh+ blood transfused into Rh- person
2.) Rh- mother carries a fetus who is Rh+
IAIA
x
IBIB
IAIix IBIi
8. Sex-Linked Inheritance: trait carried on the sex chromosomes; usually the X
(XX = female; XY = male)
a

X-Linked Recessive = X (Colorblindness, Hemophilia)

X-Linked Dominant = X ; Y-Linked (Rare)
Carrier = person not affected by the trait but can pass it on to offspring =
A
A
a
X X Only females can be carriers for sex-linked traits because if a male has
the gene, he will also exhibit the trait!
A
A
X X
x Xa Y
A
a x
X X
XA Y
9. X – inactivation: one of the two X chromosomes in a female does not uncoil
during embryonic development. The chromosome that remains coiled is called a
Barr Body and contains genes that will not get expressed. This could cause a
sex-linked trait to affect a female that would normally be only a carrier.
10. Sex-Influenced Traits: expressed in both sexes, but they are expressed
differently (Pattern Baldness)
B= Normal; b= Bald
female (bb) = bald; male (bb or Bb) =bald
BB x Bb
Bb x Bb
11. Sex-Limited Traits: autosomal traits expressed in only one sex (Lion’s
mane)
12. Dihybrid Crosses: follow 2 traits at a time (AaBb)
Example: A = purple flowers, a = white
B = Tall, b = short
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GENETICS & INHERITANCE
If you cross two parents, where the father is AABB and the mother is aabb: the
possible gametes are AB x ab. This can be determined using the F.O.I.L
method.
F = first
O = outside
I = inside
L = last
Results = 100% AaBb
Suppose we cross AaBb x AaBb:
GENETIC DISORDERS
Disorders or diseases related to a persons genes or chromosomes;
inherited in the same ways as other traits.
2 Mechanisms exist:
1. Inherited on Genes: inherited as a trait (Autosomal, sex-linked, sex
influenced, etc...)
 colorblindness
 hemophilia “bleeder’s disease”
 muscular dystrophy
 albinism
 Progeria
2. Chromosome Abnormalities: not caused by a gene
A.) Extra or Missing Chromosomes. Aneuploidy = abnormal
chromosome number
Non-Disjunction = failure of chromosome pairs to separate properly
during meiosis, end up with daughter cells having either too many
or not enough chromosomes in them.
Ex. Down Syndrome “Trisomy 21”
B.) Mutated Chromosome = damaged DNA, genes located in that section
are damaged
Deletion: missing gene or piece of chromosome
Duplication: extra piece, genes duplicated
Translocation: gene switches chromosomes
Inversion: fragment of gene gets turned around
SCREENING FOR DISORDERS
1. Karyotyping = genetic map of all the chromosomes that an organism
possesses
2. Amniocentesis = test done before birth, take sample of amniotic fluid
(C.V.S.)
3. Genetic Counseling = determine family medical history
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