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

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

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

Standards CLE 3210.4.3 Predict the outcome of monohybrid and dihybrid crosses.

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

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

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

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

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.

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

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

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 %

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

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?

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?

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

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.

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.

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

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

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

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

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

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

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

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

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

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

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

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

Practice Fill in your guinea pig worksheet