Study Guide – Chapter 8, 8.16 – 8.23
Mitosis results in two identical daughter cells – it consists of one duplication of DNA followed by one division = two daughter cells each with full copy of DNA. “Mother” cell splits into two and no longer exists, the daughter cells will start the process over again. New cell material is constantly getting rebuilt, recycled.
Meiosis results in four daughter cells each with ½ the original amount of DNA. It consists of one duplication of DNA (start with double normal amount) but is followed by two divisions resulting in 4 cells with ½ the amount.
Why do we need meiosis???? Produces sperm and egg – why??? In fertilization – the chromosomes from the sperm combine with the chromosomes of the egg. In the creation of sperm and egg (gametes) the number of chromosomes are cut in half – but not just randomly – one of each homologous pair is found in each gamete. So that when sperm and egg combine you get a pair of each chromosome restored.
8.16: Explain how figure 8.16 shows how meiosis contributes to genetic variation in offspring –
Why are the chromosomes in a pair shown in different colors?
The chromosomes of the pairs are homologous but not identical – the colors just show the difference in types of information on the pairs. For example, the ability to roll your tongue is the result of the expression of a dominant gene. On a pair of homologous chromosomes, one might have the gene to roll your tongue while the homologous chromosome may have the recessive version that does not allow tongue rolling.
In Figure 8.16, how many different combinations can you have?
4
In humans with 23 pairs of chromosomes, roughly how many different ways can our chromosomes be divided in meiosis? 223 = 8,388,608 ways
8.17: Read this section thoroughly. We’ve talked a lot about what homologous chromosomes are and this section uses an example to further clarify the concept. Write a clear explanation in your own words as to what homologous chromosomes are and how they are sorted in meiosis.
Homologous chromosomes are the same general information, but different versions of it.
Two divisions in meiosis –
8.18: What is crossing over?
In prophase I of meiosis – the chromosomes overlap and exchange pieces of each other at like sites to mix up the genes of the grandparents.
What kinds of chromosomes does it occur between?
Occurs between homologous
When does it occur?
In prophase I of meiosis.
What is genetic recombination?
Mixing up genes of our parents
How does crossing over contribute to genetic variation?
8.19: What is a Karyotype and what can it be used for?
Picture of chromosome – stain the chromosomes and then sort them according to matching characteristics into (for humans) 23 pairs. You can look for abnormalities in the number of chromosomes.
8.20: What is the cause of Down syndrome in terms of chromosome makeup?
Extra chromosome #21
What happens to the likelihood that a mother will have a child with Down syndrome as she reaches 40 years or older?
As women age, their eggs age and there is more likelihood of mistakes during final stages of meiosis.
8.21: What is nondisjunction and how does it lead to something like trisomy 21?
In anaphase of meiosis, the chromosomes did not split up from their partner so an egg ended up with multiple copies of chromosome 21.
8.22: What can cause an abnormal number of sex chromosomes?
What are some of the general side effects of an abnormal number of sex chromosomes?
8.23: There can also be some breakage and rearrangement that occurs in chromosomes – briefly describe the following:
Deletion
Duplication
Inversion
Translocation
Compare and contrast mitosis to meiosis by completing the table:
Review the key concepts on p. 149!!!