GENETICS
GENETICS
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Gregor Mendel considered the
father of genetics
Studied Pea Plants to learn
about the transmission of traits
from parents to offspring
Trait = Genetically determined
characteristic
Characteristic = a heritable
feature ( fur/hair color, eye color,
height ect..)
Mendelian Genetics
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Mendel started with plants that were
True-Bred (when self pollinate)
 True-bred =all offspring of same
variety
Hybridization – Cross-Pollinated
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(crossing of 2 different true-breds)
P generation (parents)
F1 generation (first filial generation)
Leading to the Law of Segregation
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Alleles: Alternative versions of genes that
account for variations in inherited
characteristics
 For each character, an organism
inherits 2 alleles, one from each parent
 Dominant – the allele that is fully
expressed when carried by only one of
a pair of homologous chromosomes
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Recessive- an allele that is expressed
only when two recessive alleles for the
same characteristic are inherited
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( designated by a capital letter P)
Designated by a lower case p
The alleles for each character segregate
(separate) during gamete production
(meiosis).
Genetic vocabulary…….
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Punnett square: predicts the
results of a genetic cross between
individuals of known genotype
Homozygous: pair of identical
alleles for a character
Heterozygous: two different
alleles for a gene
Phenotype: an organism’s traits,
what is physically shown
Genotype: an organism’s genetic
makeup
Testcross: breeding of a recessive
homozygote X dominate phenotype
(but unknown genotype)
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Codominance-both alleles for a gene are
expressed in a heterozygous offspring;
neither allele is dominant or recessive and
there is no blending;
 Ex.
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Monohybrid cross-a genetic cross in which
only one characteristic is tracked
 Ex;
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Blood Types
Fur Color in guinea pigs
Di hybrid cross- a genetic cross in which
two different characteristics are tracked
 Ex.
Fur color and length of fur in guinea pigs
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Probability is the likelihood that a
particular event will occur
It can be written as a:
Fraction 1/4
Percent 25%
Ratio 1:3
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If we flip a coin we have a
two outcomes
 Heads
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or tails
We can express this as
 50%
½
 1:1
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Alleles segregate randomly
just like a coin flip. . . So can
use probability to predict
outcomes of genetic crosses.
Punnett Squares
 Used
to predict the probability
of offspring.
 Show how both parents’ alleles
might combine in their
offspring.
Start by drawing your punnett square.
Place the genotype of the parents alleles
above and beside the box
Fill in the box by carrying the letters
down and across
B
rabbit heterozygous for
Black fur (dominant B)
Bb
Rabbit homozygous for
Black fur - BB
B
B
b
Did you get it?
B
b
B
BB
Bb
B
BB
Bb
Now Practice with Bikini Bottom Genetics Page One!
Agenda
How is the phenotypic outcome in a incomplete dominance cross
different than a dominant cross?
What process must you complete to determine what gametes a
parent will produce in a dihybrid genetic cross?
Go over Genetic Cross Worksheet
 Introduce:Incomplete Dominance and
Dihybrid Crosses
 Complete Genetic Cross Worksheet #2
and go over
 Notes: Dihybrid Cross
 Worksheet
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Dihybrid-Two Factor Crosses
A dihybrid cross involves two alleles per trait for
two traits, for a total of four alleles.
 Due to independent assortment an allele for a
particular trait has an equal chance of being in
the gamete.
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 For
example, a guinea pig's alleles for a dihybrid
cross are BbSs.
 Using foiling the possible allele combinations in the
guinea pig's gametes are:
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BS, Bs, bS, bs,
P- parent
 F1- first generation
 F2-second generation
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Incomplete dominance-phenotype of a
heterozygote is intermediate between the
phenotypes determined by the dominant and
recessive traits – Ex. Red flowers crossed with
white flowers produce pink flowers
Red – AA
White – aa
Pink - Aa
Review
How is the phenotypic outcome in a
incomplete dominance cross different
than a dominant cross?
What process must you complete to
determine what gametes a parent will
produce in a dihybrid genetic cross?
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Complete Dihybrid Cross Worksheet
Agenda
Why are more sex linked traits expressed in males?
What is a woman called if she carries a sex-linked
trait on only one of her chromosomes?
Notes: Sex-linked crosses
 Guided Practice
 Worksheet
 Genetic Disorder Project
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Sex-linked Traits
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X and Y chromosomes not only carry the
genes that determine male and female
traits but also those for some other
characteristics as well. Genes that are
carried by either sex chromosome are said
to be sex linked.
Baldness is a sex-linked trait carried on the x chromosome
•Expressed more often in males because they only have one x
chromosome
•Females with the gene present on one chromosome called
“carriers” for the trait.
X
XB
Y
XBX
XBY
XX
XY
X
http://www.ksu.edu/biology/pob/genetics/xlinked.htm
Review
Why are more sex linked traits expressed in
males?
What is a woman called if she carries a sexlinked trait on only one of her chromosomes?
Complete Sex-linked Cross Worksheet
and hand in
 Work on Genetic Disorder Research
Project
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Agenda
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Notes: Multiple Alleles or Codominance
Multiple Alleles or Codominance
Two alleles in a gene pair are each as
sociated with different substances.
 When both substances appear together in
heterozygotes, codominance occurs.
 The two alleles of a pair at a specific locus
are not identical but the expression of both
is observed.
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An example is blood types
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Cross a heterozygous B with an
heterozygous A
IB
i
IA
IAIB
IAi
i
IBi
ii
Agenda
What are two ways we may use the information provided on
a pedigree?
Genetics Quiz
 Notes: Pedigrees
 Worksheet: Pedigree Problems & Family
Tree Project Sheets
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A
pedigree chart is a diagram of
family relationships that include
two or more generations.
Example of Pedigree Charts
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The Shaded means that person has that
trait
Interpreting a Pedigree Chart
2.
Determine whether the trait is dominant or
recessive. (remember: the dominant traits
shows if there is one or two, the recessive shows
only if there are two)
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If the trait is dominant, one of the parents must
have the trait.
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If the trait is recessive, neither parent has to
have the trait because they can be
heterozygous.
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Circle= female
Solid or colored in= express the trait
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Square=male
Dot or line inside= carrier of trait
ee
EE
Ee
Ee
ee
Ee
ee
Ee
Lung cancer is a recessive disease. what are the genotypes of
a, b, c, d.
AA
Aa
aa
aa
Aa
Aa
Aa
Aa
Aa, AA
aa Aa
Aa
Aa, AA
Aa
aa
aa
Pedigrees can be drawn up to trace any
trait through a family tree.
 They are used to trace genetic traits
through several generations and determine
the probability that a trait will be passed
from one set of parents to their parents.
 The applications of Mendel’s Laws provide
opportunities for treatment and prevention
of genetic disorders.
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Review
What are two ways we may use the
information provided on a pedigree?
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Worksheet: Pedigree Problems & Family
Tree Project Sheets