Questions from last week You have a mouse with red eyes and a mouse with blue eyes. How could you determine which is the dominant trait?
Mouse Eyes Without knowing anything about the parents you ll need to do a test cross This can result in two possible situations X X EE ee Ee or ee Ee or ee Red is dominant
Mouse Eyes If situation number two occurs you need to do a second test cross, again with two possible situations. X X ee ee Ee Ee Red is recessive Red is dominant
Questions from last week In fruit flies clear wings are dominant over orange wings. A generation has 35 flies with clear wings and 12 with orange wings. What is the genotype of both members of the P generation.
Fly Wings Time for MATH! The total number of flies is 35 clear wings + 12 orange wings = 47 total flies If we then look at the ratios: 35/47 = ~0.75 so 75% of our flies have clear wings 12/47 = ~0.25 so 25% of our flies have orange wings
Fly Wings What does this information tell us about the parents? Can either of the parents be homozygous for clear wings? (WW) No! Then all the offspring would have clear wings. Let s try the other possible combinations using Punnett Squares
Fly Wings Ww ww w W Ww w ww w Ww ww 50% of the offspring have clear wings 50% of the offspring have orange wings
Fly Wings Ww Ww W W WW w Ww w Ww ww 75% of the offspring have clear wings 25% of the offspring have orange wings
SPECIAL CASES IN MONOHYBRID CROSSES
Cow Colours In a specific type of cow it has been shown that when red cows breed with red cows only red cows are found When white cows breed with white cows only white cows are found X?
Co-Dominance Neither the red or the white allele is more dominant than the other The phenotype is clear, but what does the genotype look like in these cases? RR WW RW
Punnett Squares in Codominance With both homozygous parents RR WW W R WR R WR W WR WR 100 % Roan Offspring
Punnett Squares in Codominance With both heterozygous parents RW RW R W R RR WR W WR WW 50% Roan, 25% Red, and 25% White
50% Roan, and 50% White Punnett Squares in Codominance With a heterozygous and a homozygous parent RW WW W R RW W WW W RW WW
Practice A red cow and a roan cow are used to produce calves for a new farm. What will be the mix of calf colours on this farm? A green and a yellow parrot reproduce. Their offspring are 50% green and 50% yellow. What are the genotypes of the parents? How can we know if ratio is due to dominant and recessive traits or co-dominant traits?
Multiple Alleles In some cases there can be more than two different forms of one gene A gene for hair colour for example may have a black, brown, and red form Sometimes two of the genes can combine as in codominant, with the other gene either more dominant or recessive to the other genes.
Challenge Question Rats possessing alleles for both grey and white colours have a spotted pattern of both. Rats with a brown fur allele however are always brown. Give a possible genotype for all four different colours.
In Humans An example of this is the four possible blood types possible for people Blood types Type A Type B Type AB Type O These represent the antigens present on your red blood cells
Human Blood types Can you identify any possible information about the genotype from the phenotype? CLUE: Two people with AB blood types cannot have a child with blood type O
Genotype in Human Blood Type Three different possible alleles I A A Antigen I B B Antigen i No antigen Type can be determined through the mixing of the alleles Type A Type B Type AB Type O Genotype I A I A or I A i Genotype I B I B or I B i Genotype I A I B Genotype ii
Determining Offspring s Blood Type Alleles I A and I B are codominant with allele i being recessive to both Predict the possible blood types when someone heterozygous for type A has a child with someone heterozygous for type B
Punnett Squares with Multiple Alleles I A i I B i I B i I A I A I B I A i i I B i ii 25% Type AB, 25% Type A, 25% Type B, 25% Type O
Practice A person homozygous for blood type A (Joe) has a child with someone with blood type O. If this child reproduces with someone with the blood type AB, predict the possible blood types of Joe s grandchildren. A scandal has gripped town. A woman with blood type A had fraternal triplets with the blood types A, A, and O. Her husband, blood type B, is furious and insists that the children are not his. Is it possible that her husband is the father? Is it likely? Show the genotypic ratios to improve your point.