Chapter 27:1 The Role of Chromosomes• Objectives:• 1. Compare the chromosomes number in body cells and sex cells• 2. Describe methods that doctors use to study chromosomes of a fetus• 3. Compare the chromosomes of males and females
Chromosome Number• Each human sperm or egg has 23 chromosomes• Each human body cell has 23 PAIRS of chromosomes. There are a total of 46 chromosomes in each human body cell• Different organism have different a number of chromosomes• The chromosomes in most living things are paired
Chromosome NumbersAnimal or Plant Number of Number of Chromosomes Chromosomes in Body Cells in Sex CellsPea 12 6Onion 14 7Cat 38 19Rabbit 44 22Human 46 23Chicken 78 39
A Way to tell Chromosome Number• Amniocentesis is a way for doctors to tell if a fetus has the correct chromosomes before it is born.• A needle is stuck into a womans abdomen and a little of the amniotic fluid is removed• The fluid is grown in the lab for about 10 days and they are able to count the number of chromosomes• They are able to study the chromosomes and determine if there are the correct number or if there is anything missing or anything extra on the chromosome.
Sex- A Genetic Trait 23 pairs of human chromosomes The sex chromosomes XX indicates a female The XY indicates a male The Y chromosome is only found in males Each sex cell would have only one type of sex chromosomes, either a XX for a female or an XY for a male.
This combination ofchromosomes would indicate a male
• Chromosomes numbered 1-22 are called autosomes. They are the same in a male or female.• The only chromosome that is different is the sex chromosome. It is either an XX or XY.• Since females have only one sex chromosome, they make only one type egg cell. It has the X chromosome only.• Males have the X and the Y chromosome so they can make two types of sperm cell. One containing the X chromosome and one containing the Y chromosome.
• The father determines the sex of the child.• If the child receives the X chromosomes from the father , it will be a male.• If the child receives the Y chromosomes from the father , it will be a female.