Life Science Chapter 26:1 Genetics, How and Why Outline _________________________ is the study of how traits are passed form parent to offspring. ___________________________ usually show some _______________________ of each __________________________. For a long time, _________________________________ did not understand how this could happen. Later, they found that the _____________________ of the _____________________________ were passed from offspring by _________________. Chromosomes Before you learn how _______________________ are passed from ______________________ to offspring, let’s review something about cells. Look at a cell in Figure 26-1. The large round part I the center is the __________________________. It has two main jobs. One is _____________________________________________________________ _______________________________________. The other is ______________________ _____________________________________________________. Inside the nucleus are the long, threadlike parts called ___________________________. Chromosomes can be seen best when ______________________________________________. During cell reproduction, ________________________________________________________. Suppose we look closer at two kinds of cells. One kind is a ________________________. Remember that body cells are cells that make up most of the ____________________________ _________________________________ in your body. Look at Figure 26-1a. Notice that the

_________________________________ has two of each ___________________________ ____________________________________________. The chromosomes in body cells are ______________________________. Another type of cell is __________________________ (Review: What is the other name these type of cells? __________________________________ ) The sex cell can be ______________________ ____________________________________. Notice Figure 26-1b that there are only ___________________ of each _______________________________ ________________________________________________________ present in the sex cells. Sex cells, then, have _________________________ as many ____________________________ as ________________________________________. Genes on Chromosomes All chromosomes contain ____________________. A gene is a small _______________________________________________________ that determines a _____________________________________________ of an organism. Exampled of traits are _________________________________________ and shape of body part such as ______________. Chemical processes inside the body, _________________________________ are also traits. Organisms have ______________________________ of different _________________. Genetics is really a study of the ________________________________ _______________________________________. Note that the word ________________________ contains the word ______________________. Genes are _________________________ on ____________________________, one next to another, must like ____________________________________________. Each

chromosome had different kinds of ________________ that _____________________ different _____________________. Figure 26-2 shows drawing of _______________________________. The locations of ____________________________________________ are shown. Remember that chromosomes in ___________________________ are _____________. The ____________________ on chromosomes in ________________________ are ______________________ too. There is _________________________ of each ________________________ on _________________________________________ of a ______________________________________________. You can see this pairing in ___________________________________. Each trait we study will have _________________ gene pair, or ________________________ that represent it. The ________________________ representing the ___________________ are located on ________________________________ that make a pair. Passing of Traits to Offspring How are traits passed from _____________________________________________ ____________________________? To answer this question, let’s use the traits of ________________________________________ in humans as an example. A person can have ___________________________________________________________. Figure 26-3 shows ___________________________________________________. What ____________________ would you expect to find in the __________________________ of each of these people? Suppose the ______________________ shows the ___________________________ ______________________________. Suppose the _____________________ shows the

_____________________________________________________________________. Which _____________________ would appear in their ___________________________? Figure26-3 shows __________________________________________________ the parents can make. The mother has the _____________________________ for _________________________________________ She can make ____________________ that have this ____________________. The ___________________ has the gene _____________ ___________________________________________. He can make _________________ that have this _______________________. What genes for ________________________________ will their _______________________________? The child will have ______________________ __________________________. In ________________________________, one sperm will ________________________ one _______________. Which ________________ and _______________ will join? We don’t know. We can see that it would make no ____________________________ in this example. Any child ___________________________ will have a gene from ______________________ _________________________ and _______________________________________________. From which parent did the child receive the _______________ for attached earlobes? (Answer: _______________________) From which parent did the child receive a gene for free earlobes? (Answer: ______________________) Dominate and Recessive Genes What does a ________________ with one _______________ for attached earlobes and one for ______________________________________ look like? Figure 26-4 shows you. Children born with ___________________________ will have free ______________________.

Why? Some ________________ can keep others from _________________________ their traits. Genes that keep other genes from showing their traits are called ______________________________________________. The _________________ that do not show their traits when ___________________________________________ are present are called ________________________________________________. In this example, the ______________ for ____________________________________ is ______________________. The _______________________ for _____________________________________ is _________________________________________. An ______________________________ with two recessive gene for a _________________ is said to be ___________________________________. Using the word ________________________ means that both ______________________ are the _____________________. In our example, the _________________________ is ___________________________________________ for ____________________________________________. The child with a gene for ______________________________________ and a gen fro _________________________________________ has two different genes. The child is ___________________________________________. A heterozygous individual is one with a _____________________________ and a __________________________ gene for a trait. Even though the heterozygous individual has the _______________________________________, the recessive trait does ___________________________. The trait of the _________________________________ gene shows.

Table 26-1 gives some traits in ___________________________________________. These traits are passed to the offspring in the same way ________________________________________. They are __________________________ or __________________________________. TABLE 26-1 What is dominant in flies? _________________________ What is recessive in pea plants? _______________________ What is dominant in humans? _______________________________ What is recessive in corn plants? ____________________________ What is dominant in dogs? _____________________________ When Both Parents are Heterozygous When one parent had both genes for _________________________________ and the other parent had both gens for __________________________________________, all their children had a ___________________________________________________. The children had ________________________________________. Now let’s suppose both parents have a _________________________________________________________________. What could their children look like? If the mother’s body cells have _______________________________________, she can make _____________________________ of eggs. Each ________________ will have a___________________ for _________________________________________ or a gene for ________________________________, but NOT BOTH. If the father’s body cells have ________________________________________ , he can make _________________________

of sperm. Each ________________ will have a___________________ for _________________________________________ or a gene for ________________________________, but NOT BOTH. Figure 26-5 shows the possible combinations when egg and sperm join. There are ___________________________ possible combinations. Table 26-2 shows what a child with each combination would look like. There are _______________________ chances that in _____________________ that a child would have _____________________________________ and a _____________ chance in ________________ that a child would have _____________________________________. We call this a _______ to _______ ratio. Review Questions: 1. How are chromosomes in sex cells (gametes) different from those in body cells?

2. One person is pure dominant for a trait while another is heterozygous for that same trait. How are their genes different?