Review Sheet answers

1. Garden peas are a great visible example of heredity. The plants have many characteristics (pea color, pea shape, pod color and flower color) which are all determined by a single gene and assort independently.
   
2. Only dominant phenotypes can be heterozygous. In order to show a recessive phenotype the genotype MUST be homozygous because with even one dominant allele, the phenotype will be dominant.
   
3. No. you must possess two recessive alleles to show the allele phenotype.
   
4. A test cross is a cross done in order to determine the genotype of a parent. It is used when the parent displays the dominant trait, but it is unknown whether or not the genotype is homozygous or heterozygous. If the unknown parent is crossed with a recessive phenotype parent and all progeny display the dominant genotype, the unknown parent is homozygous dominant. If the cross results with half of the offspring with the recessive phenotype and half with the dominant, then the unknown parent is heterozygous.
   
5. The gene for the flower color is showing incomplete dominance. In this situation the two flowers are both homozygous (one for blue phenotype and the other for yellow phenotype). When the grower crosses both flowers all of the offspring are heterozygous and are thus green.
   
6. Mendel's law of independent assortment
   
7. Each offspring will receive one allele, this follows mendel's law of segregation.
   
8. When you cut one plant and replant it, you are not changing any genetic material. A seed may yield a plant that varies from the parent because of crossing over. During meiosis homologous chromosomes align and genetic material exchanges between chromosomes. Ultimately at the end of meiosis, all sister chromatids separate and you end up with four daughter cells which genetically different material.
   
9. No, genes assort independently. Normally, the expression of one gene does not determine the expression of another.
   
10. The F1 generation would yield all heterozygous offspring, and so the F2 generation would be determined by crossing two heterozygous plants. When you cross two heterozygous parents, the offspring will have the phenotypic ratio of 3(dominant) to 1(recessive). Therefore, 25% of the offspring will show the recessive trait which is 8/32.
    
11. This varies, but typically one.
    
12. Seed color – Yy, Seed shape – Rr
    

    
    

    	YR	Yr	yR	yr
    YR	YYRR	YYRr	YyRR	YyRr
    Yr	YYRr	YYrr	YyRr	Yyrr
    yR	YyRR	YyRr	yyRR	yyRr
    yr	YyRr	Yyrr	yyRr	yyrr

    Yellow, round: 9, Green, round: 3, Yellow, wrinkled: 3, Green, wrinkled: 1
    

    
     

    Two heterozygous parents crossed in a dihybrid cross is always 9:3:3:1
    

     

13. Gametes produced are:
    
    1. E,F
       
    2. E,e,F
       
    3. e, f
       
    4. E,e,F,f
       
14. Grandparents = ¼, great grandparents 1/8
    
15. No. Hand cells are autosomal cells (non sex cells). Changes in cells in your hand will only affect future hand cells. Offspring are only affected by daughter cells produced in meiosis, which takes place in sex cells.
    
16. 50% chance. Each time you conceive you have a 50/50 chance of having a boy or a girl. The sex of previous children do not affect the sex of future children.
    
17. A roans genotype is heterozygous, Rr. Two roans cannot produce all roan colored offspring, the offspring have a 25% chance of being red, 50% chance of being roan and 25% chance. Roan cows are displaying codominance, when the cow has one allele for red, and another for white, both are expressed resulting in roan color. Since only 50% of the offspring will be heterozygous, only 50% will be roan.
    
18. For some traits, there are more than two possible alleles. An example of this is blood types and fruit fly eye color.
    
19. Don't answer this question.
    
20. Some blood types express co-dominance, and other complete dominance. There are multiple alleles, and blood type is made up of two genes (one for ABO, the other Rh- or +).
    
21. Both parents are heterozygous. Mary has AO, John has BO, Joan has OO, James has AO, Pete has BO.
    
22. 50% chance of B, 50% chance of O.
    
23. No there was not. It would be impossible for Mr Doe and Mrs Doe to have a child with O blood type because Mrs Doe can only produce gametes with A or B which will always be dominant over O.
    
24. Yes, both parents could be heterozygous (BO) and would then be able to have children that are OO (25% chance).
    
25. Because females have 2 X chromosomes. If one of the X chromosomes has a mutation they have another correct allele on their other X chromosomes. Males only have one shot with certain traits because they only have 1 X chromosome. If there is a problem with that allele they will express the recessive phenotype.
    
26. See 25
    
27. If parents know their genotype, which was probably determined using a pedigree, they can calculate the probability of their child inheriting a specific trait. For some parents this could deter them from having children.
    
28. In science a large sample size is always important. It is impossible to say that something is statistically correct without repeating it many times, you always have to account for randomness and error.
    
29. G
    
30. Farmers could selectively breed for sheep that can only produce white offspring, which would be sheep with the genotype WW.
    
31. The best option would be to cross the two together, if there is only one phenotype visible than this is the dominant trait, if both phenotypes are present, let's say two hairy and two naked, than create an F2 generation to see what the phenotypic ratio would be.
    
32. Inbreeding is discouraged because it limits genetic diversity and recessive traits (which many diseases are) tend to surface more often.
    
33. If the trait never appears in males than most likely having it is so lethal that the males don't even make it to birth.
    

Females can be carriers if one X chromosome carries the allele for the recessive trait and the other carries the allele for the dominant trait. Since females have 2 X chromosomes the dominant trait will be expressed and the recessive will do unnoticed, but the female still has a 50/50 chance of passing the recessive trait on to the offspring. If the offspring is a male, they will only receive 1 X chromosome in total (because their father gave them their Y chromosome), and the recessive trait will be expressed.