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Heredity
I. How Organisms get their Traits
A. Traits
- specific ________________ of living things
ex.: ___________ and _____ (_____ or ______)
___________
- traits are __________ from one generation of
organisms to the next through _____________
B. Family Pedigrees
- shows the ________ (history) of the ________
of a trait from one generation to the next in a
family
C. Randomness of traits
- inheritance of traits occurs by ________
- when sex cells are made, _________ occur in
the ____________ composition from cell to cell
probability: how _____ an event is to occur (___)
ex.: coins - ___:___ chance of ______ or _____
parents having children have a ___:___
chance of having a ____ or _____
- may only see _________ of probability with a
__________ amount of data
- __________ causes one trait to appear more
frequently than another
- the fact that those traits show up in that
frequency is purely due to _________
D. Mendel's Work with Pea Plants
- Gregor Mendel - ______________ monk
- “_____________________________”
- traced the transfer of traits from one generation
of _____________ to the next
- observed patterns of variation of the following
traits:
1. _______________ (_______ or _________)
2. _______________ (______ or _________)
3. _______________ (_______ or ________)
4. _______________ (_______ or ________)
5. _______________
- hypothesized that something _________ was
controlling these traits
- noted specific ______________ and recorded
them
- analyzed data for any ___________ of
inheritance
- constructed ___________
- determined and defined ____ characteristics of
inheritance:
1. Genotype - __________ make-up of an
organism
- represented by ________ or _________
ex.: ___ = tall plants
___ = short plants
- the _______________ trait, or gene (the trait
which is ________ seen when its gene is
____________) is always represented with a
___________ letter
ex.: ___ = tall (____________ trait)
- the _____________ trait, or gene, is
represented with the _____________ letter that
represents the ____________ trait
- recessive traits are only seen when the
organism is _______ (_____________)
recessive- has _____ recessive genes
ex.: ___ = short plant (____________)
TT = ______ (_____ or __________
dominant)
Tt= _____ (_______ or _______________
dominant)
tt = _______ (_____ or _____________
recessive)
2. Phenotype - the _________ characteristics
created by the ___________
ex.: _____ or ________ plants are phenotypes
Tt (_____________) = tall (______________)
II. Mendel's Work Explained
A. Dominant v. Recessive Traits
1. Homozygous (pure)- when an organism has
_____ of the same _________ (_______) of the
same ________ in the same _______
- genes (alleles) are either both __________ or
________________
ex.: ____ or ____
2. Heterozygous (hybrid) - when an organism
has two _____________ alleles
- one gene is ___________, the other is
__________
ex.: ____
***REMEMBER*** - if the dominant allele (gene)
is present, its trait will _________ be expressed
B. Punnett Squares and Test Crosses
- used to ________ the ____________ of traits
appearing in offspring
REMEMBER - chromosomes occur in ________
These pairs split during _________
- each parent donates _____ allele to the
offspring
- ___________ (or _________) the new
___________ to help you determine the
__________ (physical characteristics)
- always remember to _________ the offspring's
genotypes
ex.: TT x tt
C. Genotypic and Phenotypic Ratios
- not always the ________
ex.: B = brown eyes b = blue eyes
BB x bb
100 % of the offspring have brown eyes
100 % of the offspring are Bb
(hybrid dominant)
Bb
Bb
Bb
Bb
Bb x Bb
75 % have brown eyes
25 % have blue eyes
BB
Bb
Bb
bb
(3: 1 __________ ratio)
25 % BB (pure dominant)
50 % Bb (hybrid dominant)
25 % bb (pure recessive)
(1:2:1 ___________ ratio)
III. Incomplete Dominance and Sex-Linked
Traits
A. Incomplete Dominance
- when there are ___________ genes that are
dominant for a trait
ex.: __________________, ________________
A = normal trait A' = sickle trait
Two parents, both carrying the sickle cell trait
visit a genetic counselor to determine what risks
they run of having a child with sickle cell anemia.
AA' x AA'
AA
AA’
AA’
A’A’
These parents have a 25 % chance that one of
their children will have sickle cell anemia (A'A')
B. Sex-Linked Traits
- some traits are carried on the _____ pair of
chromosomes (_________________)
- females = ____
males = _____
- Y chromosome usually does not control the
______________ of any traits
- males need only one ________ X chromosome
to express a ____________ trait
- females need ___ _________ X chromosomes
to express a __________ trait
- females with one X chromosome carrying a
sex-linked trait and one normal X chromosome
are called _________, since they _______ the
trait, but do not _________ it, and have the
potential to ________ it on to their offspring
ex.: pattern baldness
X = normal X chromosome
XB (carrier X chromosome)
Y = no traits expressed
A woman who is a carrier for pattern baldness
marries a man who does not have the trait for
pattern baldness. What is the probability that one
of their children will have pattern baldness? What
sex will that child be?
XBX x XY
XBY = baldness (male)
XX = normal female
XY = normal male
XBX = carrier female
XBX
XY
XX
XBY
25% chance of a child having pattern baldness
The child with pattern balness will be male (XY)
IV. How Genes Control Traits
A. DNA
- ________________________
- biological __________
- in shape of a ____________ (twisted ladder)
- can have four possible nucleic bases
1. _____________
2. _____________
3. _____________
4. _____________
- pattern of bases determines what _________
are synthesized
- each base bonds with only ______ other base
- __________ bonds with _________,
___________ bonds with __________
- groups of three bases are called a ________
ex.: _____, _____
- each codon makes a different ____________
- sequences of ___________ make _________
1. Structure of DNA
- double helix (twisted ladder)
- current model was proposed by ____________
and ________________
- DNA controls _______, proteins control
_______