1. Chapter 27
Human Genetics

2. The Role of Chromosomes
Chromosome Numbers in Living Things
Each human sperm or egg has 23 chromosomes.
Each human body cell has 23 pairs of chromosomes.
Different organisms have different numbers of chromosomes.

3. Human Cells
23 Chromosomes
Sex Cells
Chromosomes not paired
46 Chromosomes
Body Cells
Chromosomes arranged in 23 pairs

4. Detecting Genetic Disease
Section 1 The Role of Chromosomes
Chapter 27
Detecting Genetic Disease
Genetic screening examines a person’s genetic makeup and potential risks of passing disorders to offspring.
Amniocentesis is a way of looking at the chromosomes of a fetus.

5. Section 1 The Role of Chromosomes
Chapter 27
Doctors can also take a small piece of the placenta to obtain a sample of chromosomes.
The chromosomes are counted and studied to see whether parts are missing.
Karyotypes are charts where chromosomes are organized in pairs.

6. Chapter 27 Sex – A Genetic Trait Sex Chromosomes and Autosomes
Section 1 The Role of Chromosomes
Chapter 27
Sex – A Genetic Trait
Sex Chromosomes and Autosomes
Sex chromosomes contain genes that determine an organism’s sex (gender).
The remaining chromosomes that are not directly involved in determining the sex of an individual are called autosomes.

7. Sex – A Genetic Trait, continued
Section 1 The Role of Chromosomes
Chapter 27
Sex – A Genetic Trait, continued
Sex Determination
In mammals, an individual carrying two X chromosomes is female.
An individual carrying an X and a Y chromosome is male.

8. Karyotypes: Male and Female
Section 1 The Role of Chromosomes
Chapter 27
Karyotypes: Male and Female

9. What are your chances of having male or female offspring?
Section 1 The Role of Chromosomes
Chapter 27
What are your chances of having male or female offspring? X X X XX XY XX X X
Body Cell
Eggs X XY Y Y
Sperm
Body Cell
1female:1male

10. Chapter 27 Male or Female? Who determines the sex of the offspring?
Section 1 The Role of Chromosomes
Chapter 27
Male or Female?
Who determines the sex of the offspring?
The Father, because he donates the Y chromosome.

11. Chapter 27 Survey on Human Traits Section 2 Human Traits
Attached earlobes is a
Recessive trait.
Detached earlobes is a
Dominant trait.

12. Chapter 27 Survey on Human traits Section 2 Human Traits
Being able to roll your
Tongue is a dominant
Trait.
Not being able to roll your
Tongue is a recessive trait.

13. Section 2 Human Traits
Chapter 27
Survey on Human traits

14. Section 2 Human Traits
Chapter 27
Survey on Human traits

15. Chapter 27 Incomplete Dominance Section 2 Human Traits
Some traits are neither totally dominant nor totally recessive.
Incomplete dominance is when neither gene is totally dominant
to the other.

16. Section 2 Human Traits
Chapter 27
Incomplete Dominance
Snapdragons

17. Chapter 27 Incomplete Dominance Section 2 Human Traits RR RR’ R’R’
Sickle Cell Anemia
R = Round blood cells
R’ = Sickle Cells R R’ RR
RR’
R’R’ R R’

18. Chapter 27 Blood Types in Humans Section 2 Human Traits
There are four blood types in humans – A, B, AB and O.
A and B are dominant to O.

19. Genes on the X Chromosome
Section 2 Human Traits
Chapter 27
Genes on the X Chromosome
Sex-Linked Genes and Traits
Genes found on the X chromosome are X-linked genes.
A sex-linked trait is a trait whose gene is located on a sex chromosome.
Because males have only one X chromosome, a male who carries a recessive gene on the X chromosome will exhibit the sex-linked trait.

20. Genes on the X Chromosome
Section 2 Human Traits
Chapter 27
Genes on the X Chromosome
Color blindness is a problem in which red or green look like shades of gray or other colors.
The gene is carried on the X chromosome and is a recessive trait. XC Xc
XC XC
XCXc
XCY
XcY XC Y