What is meiosis?
In asexual reproduction there is only one parent and one set of chromosomes. The chromosomes are duplicated. The offspring are just like the parent.

Sexual reproduction is different. In sexual reproduction, there are two parents – two sets of chromosomes. A new organism is formed with one set of chromosomes from each parent. The offspring inherits traits from both parents.

Think of yourself, for example In some ways you are like your mother. In other ways you are like your father. You have inherited traits from both your parents.

How are chromosomes exchanged during sexual reproduction? The chromosomes of body cells are paired. The chromosomes of sex cells are not paired. Chromosomes of sex cells are single chromosomes. Therefore, a sperm or an egg cell has only half as many chromosomes as a body cell.

When fertilization takes place, the sperm chromosomes join the egg chromosomes. Together, they add up to the full number of chromosomes found in body cells

The fertilized egg, or zygote, now has chromosomes from both parents. It also has traits from both parents.

Reproductive cells are also called gametes [GAM-eets]. Gametes develop from special cells in the body. The process by which gametes form is called meiosis [my-OH-sis]. You can cee the process of meiosis on the next page.

ONLY HALF THE STORY! TRUE OR FALSE

image2.png image3.pngBody cells are produced by mitosis. But sperm and egg cells do not form In the space provided, write “true” if the sentence is true.

this way. Reproductive cells are formed with meiosis. Each gamete has Write “false” if the sentence is false.

only half the usual number of chromosomes. But when the sperm and egg

join, the zygote has the full number of chromosomes. ______ 1. The chromosomes of the body cells are paired.

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A human body cell has 46 chromosomes. ______ 2. The process by which gametes form is meiosis.

The chromosomes are paired. So there

are 23 pairs. ______ 3. A human body cell has 23 chromosomes.

______ 4. In sexual reproduction, an offspring inherit traits from only one parent.

______ 5. Fertilization links the chromosomes of gametes.

______ 6. Every organism has the same number of chromosomes.

Each human sperm cell has 23 single

chromosomes. ______ 7. Spindle fibers form twice during meiosis.

______ 8. A gamete has the same number of chromosomes as a body cell.

______ 9. A gamete has twice the number of cells as a body cell.

______ 10. A frog gamete has 13 chromosomes. Every frog body cell, then, has 26

Each human egg cell has 23 single chromosomes.

chromosomes.

FILL IN THE BLANK

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Complete each statement using a term or terms from the list below. Write your answers in the spaces provided. Some words may be used more than once.

one set parent just like

half traits paired

Fertilization links the gamete chromosomes. two one meiosis

1. In asexual reproduction there is only one __________________.

– 2. In asexual reproduction, __________ of chromosomes is passed on from parent to offspring

They zygote, then has a total of 46 chromo 3. In asexual reproduction, offspring are ______________ the parent.

somes. 23 are from the mother, 23 are from

the father. 4. In sexual reproduction, there are ___________ parents. Offspring inherit __________from

both parents.

The zygote starts to divide after fertilization.

It divides by mitosis. It divides over and over 5. Gamete cells are produced by cell division called _____________. again at it develops.

6. A sperm or egg cell has only _________ as many chromosomes as a body cell.

7. Chromosomes in a body cell are _________________.

MORE ABOUT MEOISIS

Scientists often study fruit flies because they have large numbers of chromosomes that are easy to count.

· Every body cell of a fruit fly has 8 chromosomes.

· Every fruit fly gamete (sperm of egg) has 4 chromosomes.

image6.png 1. Body cells reproduce by a process called ______________________________.

2. Gamete cells are formed by a process called ____________________________.

3. a) How many chromosomes does the egg cell of a fruit fly have? __________.

b) Sperm cells? ___________

4. What do chromosomes control? ______________________________________.

5. How many chromosomes does a fruit fly zygote have? ____________________.

6. How many chromosomes will each body cell have? _______________________.

7. The offspring will have traits of the mother and father. Why?________________

_________________________________________________________________

Why must a gamete have only one half the number of chromosomes found in body cells?

________________________________________________________________________

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