1. Chapter 8
Section 3 Studying Heredity
Objectives
Predict the results of monohybrid genetic crosses by using Punnett squares.
Apply a test cross to determine the genotype of an organism with a dominant phenotype.
Predict the results of monohybrid genetic crosses by using probabilities.
Analyze a simple pedigree.

2. New Vocabulary Punnett square Test cross Probability pedigree
Sex-linked gene

3. To predict the genotypes and phenotypes of offspring, Mendel ___________ his crosses and analyzed ________ amounts of data
In 1905, a mathematician named Reginald ___________ devised a _______________ method, called a punnett square, for predicting the outcome of ________________ crosses
controlled
vast
short hand
Punnett
individual

4. Chapter 8 Punnett Squares
Section 3 Studying Heredity
Punnett Squares
A Punnett square is a diagram that predicts the outcome of a ______________ cross by considering all possible ___________ combinations of gametes in the cross.
single
allele

5. segregate Female Y Y top Male y left y
Remember, the two alleles in a gene _________________ during gamete formation
The possible gametes that the female can produce are written along the _________ of the square.
The possible gametes that the male can produce are written along the _________ side of the square.
segregate
Female Y Y
top
Male y
left y

6. Each box inside the square is filled in with two letters obtained by ___________ the allele along the ______ of the box with the allele along the _________ of the box.
Female
combining
top
Male Yy Yy
side Yy Yy

7. What process is occurring in each box when the gametes combine?
fertilization

8. What genotype will all of the possible offspring have?
And the phenotype? Yy
yellow

9. Practice! T t T TT Tt t Tt tt 1TT : 2Tt : 1tt 3 tall : 1 short
Cross a two pea plants heterozygous for height…
T = tall and t = short
Genotype ratio?
Phenotype ratio? T t T TT Tt t Tt tt
1TT : 2Tt : 1tt
3 tall : 1 short

10. Practice! Y y y Yy yy y Yy yy 2Yy : 2yy 2 yellow : 2 green
Cross a “female” pea plant heterozygous for seed color and a “male” recessive for seed color…
Y = yellow and y = green
Genotype ratio?
Phenotype ratio? Y y y Yy yy y Yy yy
2Yy : 2yy
2 yellow : 2 green

11. Reduce the ratio 2:2
Convert this ratio to a fraction
What percent does the fraction represent?
1 : 1
50%

12. The previous crosses were for genes on _________________ chromosomes
Review…what are autosomes?
Punnett squares can also be created for ________ chromosomes
In this case, the alleles must be linked on the _______ or _______ chromosome
autosomal
Your 1st 22 homologous pairs of chromosomes
sex X Y

13. Morgan
In 1910, Thomas Hunt __________ discovered sex-linked inheritance while studying _______ ________.
In fruit flies, the gene for eye color is linked on the ______ chromosome
If R = red and r = white, determine the eye color and sex for the following genotypes
XRXR = ________________
XRXr = _________________
XrXr = __________________
XRY = __________________
XrY = __________________
fruit
flies X
Red female
Red female
White female
Red male
White male

14. In humans, red green color blindness is a _____________ trait linked on the _____ chromosome
Determine the following phenotypes…
XCXc = _______________
XcY = ________________
XCY = ________________
The female above does not have color blindness but ____________ the recessive allele
recessive X
Color vision female
Color blind male
Color vision male
carries

15. Practice! XC Xc Xc XCXc XcXc XCY XcY Y 1 XCXc : 1 XcXc : 1 XCY : 1 XcY
Cross a female who is a carrier for colorblindness with a male recessive for color blindness
C = normal vision and
c = colorblind
Genotype ratio?
Phenotype ratio?
Does a male offspring inherit colorbindness from his mom or dad? Xc
XCXc
XcXc
XCY
XcY Y
1 XCXc
: 1 XcXc
: 1 XCY
: 1 XcY
1 c.v. female : 1 c.b. female : 1 c.v. male : 1 c.b. male
Mom!...inherits Y from dad

16. Review? What genotype(s) may a purple pea plant have?
Animal breeders, horticulturists, and others involved in breeding organisms often need to know whether an organism with a dominant phenotype is _______________ or ________________ for a trait.
To determine the genotype, breeders cross the organism with an individual that is _____________ for the trait in a cross called a ________ cross
PP or Pp
homozygous
heterozygous
recessive
test

17. Test cross P P P p p p p p Pp pp Pp Pp Pp Pp Pp pp
If the unknown genotype is PP, what color flowers will all of the offspring have?
If the unknown genotype is Pp, what color flowers may the offspring have?
Purple
Purple and white

18. Chapter 8 Outcomes of Crosses # of outcomes # of outcomes
Section 3 Studying Heredity
Outcomes of Crosses
Like Punnett squares, ______________ calculations can be used to predict the results of genetic crosses.
Probability is the _________________ that a specific event will occur.
Probability =
probability
likelihood
# of outcomes
desired
# of outcomes
total

19. So if there are five marbles in a jar, and only one is red, what is the probability that you pull a red marble out of the jar?
If you flip a coin, what is the probability that it will land heads up?
If you flip a coin again, what is the probability that it will lands head up?
1/5
1/2
1/2

20. future X X X XX XX Y XY XY 1/2 1/2
So prior events do not affect the outcome of ____________ events
In the following cross…
What is the probability that two
parents will have a girl?
What is the probability that their next child will be a girl? X X X XX XX Y XY XY
1/2
1/2

21. The outcomes predicted by Punnett squares are most often seen in ______________ populations….
Is everyone’s family made up of exactly half girls and half boys?
But a larger population, like the entire _________, is roughly 50:50 or 1:1
large no
planet

22. multiple
To determine the probability of ____________ events or events occurring at the _________ time, the probability for each event is _________________ by eachother.
What is the probability that a coin will land heads up four times consecutively?
same
multiplied
½ x ½ x ½ x ½
= 1/16

23. P p P PP Pp p Pp pp T t T TT Tt t Tt tt 3/4 3/4 ¾ x ¾ = 9/16
What is the probability that a pea plant offspring will have purple flowers?
What is the probability that a pea plant offspring will be tall?
What is the probability that a pea plant offspring will have purple flowers and tall height? P PP Pp
3/4 p Pp pp
3/4 T t T TT Tt t Tt tt
¾ x ¾
= 9/16

24. Chapter 8 Inheritance of Traits
Section 3 Studying Heredity
Inheritance of Traits
Geneticists often prepare a ________________, a family history that shows how a trait is inherited over _____________ generations.
Pedigrees are particularly helpful if the trait is a genetic _______________ and the family members want to know if they are _____________ or if their _________________ might get the disorder.
By analyzing a pedigree, we can determine if a trait is ______________ or ______ - linked and ____________ or ______________
pedigree
several
disorder
carriers
children
autosomal
sex
dominant
recessive

25. Female = circle
Male = square
Horizontal Line = mating
Vertical line = offspring
Shaded = affected by the trait
Diagonal line = death from trait

26. Autosomal recessive Aa Aa aa recessive two carrier Aa or AA
Most genetic disorders are caused by _____________ alleles
In this situation, an offspring with ______ recessive alleles has the trait, while each parent is a _________________
What allele combinations might have the other two offspring have? Aa Aa
recessive aa
two
carrier
Aa or AA

27. Autosomal Dominant aa aa Aa aa
If a trait is dominant, an affected individual will have at least ______ parent who also has the _____________ trait
Is the female parent homozygous dominant or heterozygous?
How do you know? aa Aa
one aa Aa aa
dominant
heterozygous
Not all of the offspring inherit
a dominant allele

28. Sex-linked XcY XcY XCXc males XCXc Y female
If a trait is sex-linked, it will appear more often in ________ than in females
What genotype must all of the females have?
What chromosome does a male parent pass onto his son?
So is the recessive X-linked gene inherited from the male or female parent?
XcY
XCXc
males
XcY
XCXc Y
female

29. Objective 1 T t t t Tt tt Tt tt 2Tt : 2tt 2 tall : 2 short
Predict the results of monohybrid genetic crosses by using Punnett squares.
If T = tall and t = short…
Genotype ratio?
Phenotype ratio? T t t Tt tt t Tt tt
2Tt : 2tt
2 tall : 2 short

30. Objective 2 t t Tt Tt Dominant Genotype? tt tt T t
Apply a test cross to determine the genotype of an organism with a dominant phenotype. t t Tt Tt T
Dominant
Genotype? tt tt t

31. Objective 3 T t T TT Tt t Tt tt
Predict the results of monohybrid genetic crosses by using probabilities.
If T = tall and t = short,
what is the probability that
an offspring will inherit
short height? T t T TT Tt t Tt tt
1/4

32. Objective 4 Analyze a simple pedigree. Does this pedigree
show an autosomal
dominant, autosomal
recessive, or sex-
linked trait?
Autosomal recessive