1. Pick up your plickers card
Bell Work
BEFORE the bell rings
Pick up your plickers card
Pick up the sex linked traits worksheet (homework)

2. Genetic crosses & practice for different inheritance patterns
Mrs. Stewart
Honors Biology

3. Review: Plickers Question
What is the genotype of the F1 generation?
Homozygous Dominant
Heterozygous
Homozygous Recessive
Cannot be determined

4. Standards
CLE Predict the outcome of monohybrid and dihybrid crosses.

5. Lesson Objectives
Correctly create and analyze the punnett square results from monohybrid and dihybrid crosses
Know how to use a test cross to determine a genotype
Can identify scenarios of complete dominance, incomplete dominance and codominance successfully

6. Mendel proposed two laws
These laws explain how the homologous chromosome pairs for each parent will separate into the gametes during meiosis.
Law of segregation
Law of Independent Assortment

7. Law of segregation
Homologous chromosomes separate during the formation of gametes
The alleles for a characteristic will segregate into a different gamete during meiosis

8. Law of Independent Assortment
Homologous chromosomes can line up in a different way each time meiosis happens – which can lead to different allele combinations for each set of gametes produced

9. Siblings
Since parents contribute chromosomes randomly, every child inherits a “unique” combination of traits.
Some may resemble mom; some may resemble dad; others will be completely unique
They may resemble each other or be totally different.

10. Think – pair – share
What do we use to predict the inheritance of traits?
Punnett Squares

11. Monohybrid Cross
Monohybrid = a cross between two organisms that predicts the inheritance pattern/probability of only one characteristic at a time
Punnett squares for these crosses only work on single-gene traits

12. Monohybrid Cross Review
A homozygous one-eyed purple people eater is crossed with a homozygous two-eyed purple people eater. All of their offspring have two eyes. Which trait is dominant?
Use E = two eyed and e = one. What is the genotypic ratio for the offspring if you cross a purebred one-eyed purple people eater with a heterozygous two-eyed purple people eater?
If you crossed two heterozygous two-eyed purple people eaters with each other, how many of the resulting offspring would have two eyes?
Two-eyed
1:1
3 out of 4 or 75 %

13. Monohybrid Heterozygous x Heterozygous
B b
Complete this cross - Bb x Bb
Genotypic ratio:
BB : Bb: bb = 1:2:1 Always!
Phenotypic ratio:
Dominant trait shown: Recessive Trait shown = 3:1 Always! BB Bb B b Bb bb

14. Real World Examples D = dwarf height d = normal height
DD = fatal combination – spontaneous abortion of pregnancy
Dd = dwarfism (achondroplasia)
dd = normal height
What are the genotypic ratios possible when two dwarves cross?

15. 25% Would you risk it? Real World Examples
Cystic Fibrosis – a single gene recessive disorder that causes a build-up of thick mucus in the lungs, pancreas and other digestive organs.
What are the chances of having an offspring with CF when two heterozygous parents cross?
25%
Would you risk it?

16. Determine Genotype of Dominant Trait
A guinea pig breeder has had many requests for black hair guinea pigs babies lately.
The breeder has 3 different black hair guinea pig males
B = black and b = brown
What are the possible genotypes for the black guinea pigs?
BB and Bb

17. Test Cross
A guinea pig breeder has 3 black hair males that she can breed with her brown hair females.
How can the breeder determine which of her black guinea pig males are homozygous dominant, so she can maximize the number of offspring that will have black fur?
Test Cross = cross an individual that expresses the dominant phenotype with one that shows the homozygous recessive phenotype to determine the unknown genotype.

18. Test Crosses
If any of the offspring come out with the recessive phenotype, then we know the parent must be heterozygous.
If all of the offspring show the dominant phenotype, the parent is most likely homozygous dominant.

19. Test Cross b b b b B Bb Bb B b Bb Bb bb Bb Bb bb
If a black guinea pig is crossed with a homozgous recessive white guinea pig and even one of the offspring is white, what is the only possible genotype for the black guinea pig?
b b
b b B Bb Bb B b Bb Bb bb Bb Bb bb

20. Bb Plickers question B = black b = brown
What is the genotype of the black dog? BB Bb bb
Cannot determine Bb

21. Bell Work BEFORE the bell rings Pick up your plickers card
Pick up the sex linked traits worksheets
Get out your statistics of inheritance pogil

22. Sex Linked Traits
Traits that are coded for on the X chromosomes but not the Y
Females: XX – have two alleles for the trait
Males: XY – have only one allele for the trait

23. Real World Examples – Sex Linked Traits
Red – Green Colorblindness: Xc XC
Baldness: Xb XB
Hemophilia: Xh XH
Complete Sex Linked traits practice worksheet

24. Plickers Question
More males exhibit sex linked disorders than women. Why?

25. Dihybrid Crosses
A cross in which TWO characteristics are predicted for offspring
Color hair: B = black, b = white
Length of hair: L = long, l = short

26. Remember: Law of Independent Assortment
Homologous chromosomes can line up in a different way each time meiosis happens – which can lead to different allele combinations for each set of gametes produced

27. Use f.o.i.l. method to determine gametes

28. What are the four possible gamete combinations for a guinea pig with the genotype BbLl?
BL Bl bL bl
F – pair the first two alleles of each characteristic
O – pair the outer two alleles for each characteristic
I – pair the inner two alleles for each characteristic
L – Pair the last two alleles for each characteristic

29. Pick up your plickers card Get out the dihybrid cross worksheet
Bell Work
BEFORE the bell rings
Pick up your plickers card
Get out the dihybrid cross worksheet

30. Shortcut: Heterozygous x Heterozygous
What are the gamete combinations for each guinea pig?
Offspring Shortcut: 9:3:3:1 phenotypic ratio
9 – Two dominant traits
3 – One dominant one recessive trait
3 – The other dominant and recessive combo
1 – both recessive traits

31. Practice
Fill in your guinea pig worksheet