Predicting Results of Monohybrid Crosses

1. Predicting Results of Monohybrid Crosses

2. Alec has a white mouse & a black mouse. Black coloration is dominant to white. Over a period of 2 years their offspring number 90 babies. If 48 of the babies were white, what are the genotypes of the parents. 1. (working backwards)

3. In Koalas brown fur is dominant over grey fur. If the pair in the San Diego Zoo produced 25 offspring in their lifetime and 19 were brown 6 were grey. What did the zookeepers determine as the genotype of the parents? 2. (working backwards)

4. Incomplete Dominance- a condition in which both alleles contribute to the phenotype of a heterozygous individual to produce a trait that is not like either parent. **heterozygous form = A BLEND** • (Example) Snapdragons • Petal color determined by by two alleles CR = red CW= white • Phenotypic ratio is 1 red: 2 pink: 1 white • Genotypic ratio 1 CRCR: 2 CRCW: 1 CWCW Incomplete Dominance

6. Capital letters with superscripts are often used to represent genotypes in incomplete dominance. Write alleles in alphabetical order when writing gametes or genotypes F1 generation has a phenotype that is different from that of every parent Andalusion Chickens Pure black x Pure white produces offspring that appear blue Incomplete Dominance Rules

7. Davey Jones from Pirates of the Caribbean has strange facial growth; tentacles instead of whiskers. There are two alleles for facial growth, one that codes for curly tentacles and one that codes for straight tentacles. The heterozygous condition produces wavy tentacles. Davey Jones has wavy tentacles and his wife has curly ones, what are the possible genotypic and phenotypic ratios of their offspring? 1.

8. Lop-eared rabbits have 2 alleles for ear length, one codes for long ears (10 inches) and the other for short ears (4 inches). The heterozygous condition produces a rabbit with medium ears (7 inches). What is the genotypic ratio of a cross between a long eared rabbit and a medium eared rabbit? What is the phenotypic ratio? 2.

9. In cats the absence of a long tail allele results in a manx cat. The presence of a tail allele results in a long tail cat. A cat with both alleles is short tailed. What would be the genotypic & phenotypic ratios of the possible offspring if you cross two short tail cats? 3.

11. Codominance- a condition in which two dominant alleles are expressed at the same time. • Neither allele is dominant or recessive. • The alleles do not blend in the phenotype. • Example: Homozygous red cows crossed with homozygous white cows will generate cows with a roan coat. Roan coats consist of a mixture of all red hairs and all white hairs. • Each hair is either all red or all white therefore it is codominant! Codominance

12. Use capital initial letters for each allele (Since both alleles influence phenotype) • Genotype for homozygous red coat: • Genotype for homozygous white coat: • Genotype for heterozygous animal with roan coat: How to Show Codominance…

14. The alleles for hair texture in Koala bears will produce straight hair if homozygous for the trait, curly hair if homozygous for the trait or straight & curly if heterozygous for the trait. Cross a straight haired koala with a curly haired Koala. What are the genotypic and phenotypic ratios of their offspring? 1.

15. Two lop-eared rabbits are bred. One of the rabbits is black and the other has both black & grey fur. What would be the genotypic ratios and phenotypic ratios of their offspring? 2.

16. 1. Yellow pigs are crossed with white pigs and produce cream offspring. • 2. Radishes can be long, round, or oval. • 3. Birds can be black, white , or black with white feathers. • 4. A grasshopper can have red stripes, yellow stripes, or both red and yellow. • 5. A mouse can be black, white or gray. Incomplete Dominance Or Codominance???

17. Multiple alleles - for some traits there are more than three alternate forms of a gene (alleles) • However, only two of the alleles can be present in a single organism (1 on each homologous chromosome) • Multiple alleles explains why there are four different blood types (A, B, AB, and O) Multiple Alleles

18. Three alleles code for blood type (A, B, O) • O is the recessive allele • A & B are both dominant over O, but neither one is dominant over the other. Multiple Alleles

19. Use capital letter “I” to show a dominant allele • Use a lower case letter “i” to show the recessive allele • Superscript letters stand for each dominant allele • Six possible genotypes! Multiple Alleles

20. Blood Antigens • On the surface of red blood cells are chemical structures (proteins) calledantigens • A person’s blood type depends on the presence/absence of two antigens (A, B) on surface of RBC • Antigens cause an immune response when recognized as foreign • Blood plasma contains antibodies- proteins that bind to/attack specific antigens

21. Blood Typing Blood TypeAntigens on RBCAntibodies Can Receive A A anti-B A, O B B anti-A B, O AB AB none A, B, AB, O O none both A & B O (Rh + blood) contains Rh antigen  85% of human population (Rh – blood) no Rh antigen  15% of human population

22. If blood containing a specific antigen is mixed with blood containing the corresponding antibodies, the blood clots • Universal donor- (type O blood) no antigens (RBC) to be attacked • Universal recipient- (type AB) no antibodies to attack received blood Why is it bad if you receive the wrong blood type?

23. Blood Typing Human serum containing specific antibodies can be purchased Separately mix a drop of unknown blood sample with drop of each anti-serum Reaction between blood and anti-serum No reaction between blood and anti-serum

24. Blood Typing Example A sample of unknown blood is mixed with three anti-sera samples: Tube 1 (Anti-A): No reaction Tube 2 (Anti B): No reaction Tube 3 (Anti Rh): Cloudy reaction In terms of the A-B-O and Rh systems, what type blood is the sample? O positive

25. 1905 Wilson studied insects • In males: 1 homologous pair of chromosomes did not match • In females: all homologous chromosomes matched • Called the female sex chromosome the X chromosome & the unmatched male chromosome the Y chromosome (determines sex) • All the other body chromosomes = autosomes • Male Gametes (X & Y) Female (X & X) Sex Chromosomes & Sex Determination

26. Sex-linked traits- a trait that is controlled by a gene found on the sex chromosome. • Chance of showing trait is affected by the sex of the individual • Most determined by genes found on the X chromosome • 1098 on X • 29 on Y • Accounts for size difference Sex-linked Traits

27. Morgan studied Drosophila melanogaster (fruitflies) • Surprised to see a white-eyed fly (it was male) • Mated white-eyed male with normal red-eyed female resulting in an F1 generation: all red eyes • Conclusion: red eyes is _________ over white • Mated members of F1 generation: Results: ¾ red eyes, ¼ white eyes • BUT all white eyes were male!! • Concluded that this trait is carried on a sex chromosome! (sex-linked) • Gene for red & white eyes carried on the X chromosome… no corresponding allele on the Y chromosome Sex-linked Genes

28. Therefore, males get eye color from 1 gene…on the X chromosome from mom • For a female to have white eyes, must get two white alleles = red allele on X chromosome = white allele on X chromosome Y = male sex chromosome with no allele for eye color Now, cross a normal male & a heterozygous female with red eyes Sex-Linked Genes

29. Genotypes of F1 fruitfly generation

30. Review: video clip ~5:25“DNA”

31. Color-blindness • Hemophilia • Muscular dystrophy Human Sex-linked Traits

32. A: 29, B: 45, C: --, D: 26  Normal vision A: 70, B: --, C: 5, D: --  Red-green color blind A: 70, B: --, C: 5, D: 6  Red color blind A: 70, B: --, C: 5, D: 2  Green color blind Sex-Linked Traits

35. Testcross- the crossing of an individual of unknown genotype with an individual with a homozygous recessive individual to determine the unknown genotype. • Can determine the genotype of any individual Whose phenotype expresses the dominant trait. Testcross