Write a pedigree in which there are parents and 4 children, 1 girl and 1 boy are color blind and the other girl and boy are not.
I HAVE A FEW QUESTIONS-
?- For a girl to be colorblind does her mother have to be colorblind too or just a carrier?her father?
?- If two people are heterozygous for sickle-cell anemia what are the chances that their children will have it ?(in ratio)
To create a pedigree with parents and four children, where one girl and one boy are color blind and the other girl and boy are not, you can use the following notation:
Parents:
- Father
- Mother
Children:
- Child 1 (Girl) - Color blind
- Child 2 (Boy) - Not color blind
- Child 3 (Girl) - Not color blind
- Child 4 (Boy) - Color blind
To answer your first question about the inheritance of color blindness in girls, it is important to understand the mode of inheritance for color blindness. Color blindness is primarily linked to the X chromosome. In simple terms, females have two X chromosomes (XX), and males have one X and one Y chromosome (XY).
Since color blindness is a recessive trait, a girl can be color blind if both of her X chromosomes contain the defective gene. If the girl's father is color blind (XY) and her mother is a carrier (XcX), there is a chance that the girl may inherit one defective X chromosome from her mother and the other from her father, resulting in her being color blind (XcXc).
To answer your second question about the chances of passing on sickle-cell anemia, we need to consider the inheritance pattern of the disease. Sickle-cell anemia is an autosomal recessive disorder, meaning it is not linked to gender or to the sex chromosomes.
If both parents are heterozygous carriers for the sickle-cell allele (AS), there are different possibilities for their children's genotypes and phenotypes. The genotype combinations include:
- AA: No sickle-cell allele, not affected
- AS: One sickle-cell allele, not affected (carrier)
- SS: Two sickle-cell alleles, affected by sickle-cell anemia
Using a Punnett square can help determine the ratios of genotypes and phenotypes. In this case, crossing two heterozygous individuals (AS x AS) would yield the following ratios:
- 25% chance of having AA genotype (not affected)
- 50% chance of being AS genotype (not affected but carrier)
- 25% chance of having SS genotype (affected by sickle-cell anemia)
This results in a 1:2:1 ratio for unaffected, carrier, and affected individuals, respectively.