WARMUP Copy each of these into your notebook
WARM-UP: Copy each of these into your notebook, and label each as “agree” or “disagree”. 1. Humans produce two types of cells: body cells and sex cells. 2. Environmental factors can cause variation among individuals. 3. Two parents always produce the best offspring. 4. Cloning produces identical individuals from one cell. 5. All organisms have two parents. 6. Asexual reproduction occurs only in microorganisms.
Launch Lab 1. Turn to page 385 of your textbook. 2. Complete the lab at the top of the page, answering the questions and making observations in your notebooks. 10 -15 minutes
What is Sexual Reproduction? ▪ A type of reproduction in which the genetic material from two different cells combine, producing an offspring. ▪ The cells that combine are called sex cells, and form in reproductive organs. ▪ The female sex cell, an egg, forms in an ovary. ▪ The male sex cell, a sperm, forms in a testis.
What is Sexual Reproduction? ▪ During a process called fertilization, an egg cell and a sperm cell join together. ▪ The new cell that forms from fertilization is called a zygote. ▪ The zygote then develops into a new organism.
What is Sexual Reproduction?
POP QUIZ 1. What is sexual reproduction? 2. How are a litter of kittens of different colors similar to your model offspring in the launch lab?
WARM-UP: Answer in NB
Diploid Cells ▪ Organisms that reproduce sexually have 2 types of cells… body cells and sex cells. ▪ Body cells are diploid, which means they have pairs of chromosomes. ▪ Pairs of chromosomes that have genes for the same traits arranged in the same order are called homologous chromosomes. ▪ One chromosome is inherited from each parent.
Diploid Cells ▪ Different organisms have different numbers of chromosomes… Humans have 46 chromosomes, or 23 homologous pairs. ▪ If a zygote has too few or too many chromosomes, it will not develop properly. ▪ For example, a genetic condition called Down syndrome occurs when a person has an extra copy of chromosome 21.
Diploid Cells
POP QUIZ 1. How many chromosomes does the human body contain? 2. What are homologous chromosomes? 3. Why are the chromosomes in a human diploid cell homologous, or similar, rather than identical?
Haploid Cells ▪ Sex cells are haploid, which means they only have one chromosome from each chromosome pair. ▪ In meiosis, one diploid cell divides and makes four haploid cells. ▪ Meiosis ONLY occurs during the formation of sex cells.
POP QUIZ 1. What is the purpose of meiosis? 2. How do diploid cells differ from haploid cells?
Meiosis ▪ Meiosis involves two divisions of the nucleus and cytoplasm, called meiosis I and meiosis II. ▪ This results in 4 haploid cells with half the number of chromosomes as the original cell. ▪ In meiosis I, the chromosomes duplicate and are divided into 2 daughter cells. ▪ In meiosis II, the cells divide again, creating 2 more daughter cells each (4 total)
Meiosis
POP QUIZ 1. What are the two phases of meiosis called? 2. If there are two divisions of the nucleus, why aren’t there four times as many chromosomes in sex cells? 3. What happens to the haploid cells that are produced by the process of meiosis?
Why is Meiosis Important? ▪ Meiosis forms sex cells with the correct haploid number of chromosomes. ▪ This maintains the correct diploid number of chromosomes in organisms when sex cells join. ▪ Meiosis also creates genetic variation by producing haploid cells.
POP QUIZ 1. What is the name for a fertilized egg? 2. Is a zygote haploid or diploid? 3. What do you think could be some advantages of increased genetic variation? DO #13 for homework. I WILL CHECK IT!
Advantages of Sexual Reproduction 1. Genetic Variation 2. Selective Breeding
Genetic Variation ▪ Sexual reproduction produces offspring that have a new combination of DNA. ▪ Offspring are NOT likely to inherit the same DNA from the same parents. ▪ This results in genetic variation among individuals. ▪ These differences could be an advantage if the environment changes.
Genetic Variation
Selective Breeding ▪ The goal of selective breeding is to produce organisms with desired characteristics ▪ Virtually all of the fruits and vegetables we eat are the result of selective breeding. ▪ After a while, varieties of fruits and vegetables bear little resemblance to the ancestor species.
Selective Breeding
POP QUIZ 1. Why is sexual reproduction beneficial? 2. Would it be possible for two siblings that are not identical twins to receive the same set of genes from their parents?
Disadvantages of Sexual Reproduction ▪ Sexual reproduction takes time and energyorganisms have to grow and develop until they are mature enough to produce sex cells. ▪ Searching for a mate can take a long time and requires energy. –It also may expose individuals to predators, diseases, or harsh environmental conditions
POP QUIZ 1. What are the disadvantages of sexual reproduction? 2. Can you think of any other disadvantages of sexual reproduction?
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