Question

heredity and genes
all living things must reproduce, or make more living things like themselves. if a species did not reproduce, all living things of its kind would die out. the reproductive system of humans allows people to make more humans, or to have children.
when people have children, they pass on certain traits and characteristics. this is called heredity. heredity affects the way you look and the way you act. you may have noticed that when adults look at a new baby, they often talk about which parent the baby looks like. this is because the baby has inherited its looks from its parents. as a child grows, there may be times when the child looks more like the mother, and times when the child looks more like the father. there will be certain things the child does that will remind people of the mother or the father, or even of some other relative. all these things are inherited. other things, such as likes and dislikes and personal fitness, are not inherited. these are the result of the person’s lifestyle and environment.
when you study cells, you learn that the nucleus of a cell contains chromosomes. on the chromosomes are genes. genes determine how offspring will look and act. each child receives genes from both parents, but some genes are stronger than others are. these genes are called dominant. the weaker genes are called recessive.
here is an example. the gene for brown hair is a dominant gene. we say that brown hair is a dominant trait. blond hair is a recessive trait. if both parents have brown hair, their children will probably have brown hair. if one parent has brown hair and the other parent has blond hair, the children will still most likely have brown hair, but it is possible for a child to have blond hair. if both parents are blond, then the child will probably be blond.
the combinations can be seen in a chart like this. a brown - haired mother may carry a blond - haired gene, because the brown - haired gene will dominate. she may pass on genes like this: bb.
a blond - haired father cannot have a brown - haired gene. he must pass on genes like this: bb.
to see what combinations of genes the children can receive, we can make a chart.
in this family, it is possible that half of the children could have blond hair, or there is a 50% chance that a child could have blond hair.
suppose a brown - haired father has genes that are bb. a blond - haired mother has genes that are bb. work the chart below to find the combinations of genes the children can receive. then answer the questions.

1. what is the chance that a child will have brown hair? ____________
2. what is the chance that a child will have blond hair? ____________

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Explanation:

Step1: Set up the Punnett - square

The father has genes BB and the mother has genes bb. The father can only pass on B genes and the mother can only pass on b genes. The Punnett - square has two rows (from mother) and two columns (from father). The mother's genes are b and b, and the father's genes are B and B.

Step2: Fill in the Punnett - square

When we fill in the Punnett - square, we get Bb in all four boxes. Since the brown - hair gene (B) is dominant, all offspring will have brown hair.

Step3: Calculate probabilities

Since all four combinations in the Punnett - square are Bb (brown - haired), the probability of a child having brown hair is $\frac{4}{4}=100\%$, and the probability of a child having blond hair (bb) is $\frac{0}{4}=0\%$.

Answer:

1. 100%
2. 0%