Question

heredity
heredity is the passing on of characteristics from parent to child. it affects how people look, grow, and learn. heredity is the reason children often resemble their parents in some way. however, children from the same parents look somewhat different from one another because they have inherited different characteristics from their parents.
at conception, the fathers sperm joins the mothers egg. the egg and sperm each contain 23 chromosomes. the union of the egg and sperm produce a fertilized egg called a zygote, which has 46 chromosomes arranged in pairs. the fertilized egg divides into two cells, which divide into two cells, and so on. the chromosomes in these cells contain genes, which determine the characteristics that living things inherit from their parents. the deoxyribonucleic acid (dna) in the genes is what contains the heredity information.
individual pairs of chromosomes determine a persons eye color, hair color, sex, body type, and other characteristics. dominant traits like dark hair are inherited when the gene for that trait is present on both chromosomes in a pair or on only one chromosome in a pair. however, genes for recessive traits like blue eyes must come from both parents in order for the trait to be passed on.
a punnett square can be used to predict how genes are likely to combine when passed from parents to offspring. the genes for each trait are represented by two letters. two capital letters, such as bb, indicate dominant genes that will result in the dominant trait (brown eyes). two small letters, such as bb, indicate recessive genes that will result in the recessive trait (blue eyes). a capital letter and small letter, such as bb, indicate a dominant and a recessive gene. the dominant trait will occur (brown eyes), but the individual will also carry the recessive gene. if the genes of a parent with dominant genes (bb) are crossed with the genes of a parent with hybrid genes (bb) the square would look like the one to the right. (the letters from each row and each column are combined.) there is a 2 out of 4 (50%) chance the offspring will have the pure dominant genes (bb), and a 2 out of 4 chance the offspring will have the hybrid genes (bb).
fill in the punnett squares below and answer the questions beneath each square.
1.
b b
b
b
what color are the parents eyes?
what is the likelihood the offspring will have brown eyes?
2.
b b
b
b
what color are the parents eyes?
what is the likelihood the offspring will have blue eyes?
3.
b b
b
b
what color are the parents eyes?
what is the likelihood the offspring will have blue eyes?

Explanation:

Step1: Recall eye - color genetics

Brown is dominant (B), blue is recessive (b).

Step2: Analyze first Punnett square

Parents are BB and BB. All offspring are BB, so brown eyes.

Step3: Analyze second Punnett square

Parents are Bb and Bb. Offspring genotypes are BB:Bb:bb = 1:2:1. So 1 out of 4 for blue eyes.

Step4: Analyze third Punnett square

Parents are bb and bb. All offspring are bb, so blue eyes.

Answer:

1.

• Parents' eye color: Brown
• Likelihood of offspring having brown eyes: 100% (4 out of 4)

2.

• Parents' eye color: One brown - eyed (BB or Bb) and one with a recessive gene (Bb or bb)
• Likelihood of offspring having blue eyes: 25% (1 out of 4)

3.

• Parents' eye color: Blue
• Likelihood of offspring having blue eyes: 100% (4 out of 4)