1. Human Genetics

2. Chromosomes Genes are found on chromosomes
Chromosomes are rod-shaped structures located in the nucleus of every cell in an organism.
Control all the traits of an organism.
Sex cells are produced during a process called meiosis “Me”.
Only half the information of an organism can be handed down to an offspring.
Parent = 46 chromosomes
Sex cell = 23 chromosomes
Chromosome
Nucleus
Chromatid
Centromere
Chromatid
Cell

3. Mitosis vs. Meiosis Sex Cells Body Cells “Me” “My toes” 4 4 8 8 4 4 42 2 2 2

4. Karyotype A picture of the 23 chromosome pairs a person has.
Can be used to identify the sex of an individual or see if an individual has any abnormalities.
Normal
Karyotype 23

5. Sex Chromosomes
The 23rd set of chromosomes are called the sex chromosomes.
Determine the sex of the offspring:
Male = XY
Female = XX 23

6. Determining Gender Mom = XX Dad = XY Genotype: 50% - XX 50% - XY
Phenotype:
50% = Female
50% = Male X X X XX XX XY XY Y

7. Sex-Linked Traits
All the genes on the X or Y chromosome are inherited together.
This means that certain traits are always inherited with certain sex chromosomes.
Examples:
X-linked traits
Color-blindness
Hemophilia
Y-linked traits
Hairy ears

8. X-Linked Traits
Color Blindness – Inability to distinguish different colors, usually reds and greens.
Recessive trait (Xb), Normal vision (XB)
Inherited on the X chromosome
More common in males. Why?
You only need one affected X chromosome to inherit the trait. (XY)
Females can inherit one affected X chromosome but not show the trait (XX)= carriers
Males Females
XBY - normal
XbY – color blind
XBXB – normal
XBXb – carrier but normal
XbXb – color blind

10. Color Blindness Xb Xb XB XBXb XBXb XbY XbY Y Mom = XbXb = Colorblind
Dad = XBY
= Normal
Genotypes:
50% - XBXb
50% - XbY XB
XBXb
XBXb
XbY
XbY Y
Questions:
What percentage of children are carriers, who?
What percentage of children are color blind, who?
Can males ever be carriers, why?
What percentage of the children are normal?
_50%_- females
50%_- males
NO – only receive 1 X
50%

11. X-Linked Traits Hemophilia – blood clotting disorder. Males Females
Recessive trait (Xh), Normal clotting (XH)
Inherited on the X chromosome
More common in males. Why?
You only need one affected X chromosome to inherit the trait.
Males Females
XHY - normal
XhY – hemophiliac
XHXH – normal
XHXh – carrier but normal
XhXh – hemophiliac

12. Hemophilia XH Xh XH XHXH XHXh Y XHY XhY
Mom = XHXh = carrier Dad = XHY = Normal XH
XHXH
XHXh
Genotype:
25% - XHXH
25% - XHXh
25% - XHY
25% - XhY
Questions:
What percentage of the children are carriers, who?
What percentage of the children are hemophiliacs, who?
What percentage of the children are normal? Y
XHY
XhY
_25% - females
25% - males
75%

13. Y-Linked Traits
Hairy Ears – a trait handed down on the Y chromosome that produces men with hairy ears.
Why not hairy eared women?
Women don’t inherit Y chromosomes!
Males Females
XYH - normal
XYh – hairy ears
XX – normal

14. Hairy Ears X X X XX XX Yh XYh XYh
Mom = XX = normal Dad = XYh = hairy eared X XX XX
Genotype:
50% - XX
50% - XYh
Questions:
What percentage of the children are carriers, who?
What percentage of the children are hairy eared, who?
Can females have hairy ears, why? Yh
XYh
XYh 0%
50% - males
No – no Y chromosome

15. Pedigree Charts
Another model for understanding inheritance is a pedigree chart.
Each level represents a new generation.
Lines connect offspring to parents
Males are squares and females are circles.
Blank squares or circles usually represent individuals who do not carry a recessive trait
Shaded in squares or circles represent individuals who carry recessive traits.
Circles that are partially shaded in represent carriers, females who carry a recessive trait but do not show the trait and would therefore be considered normal.

16. 1 2 3 4
Questions:
What is the Mom considered in the Parent generation?
How many offspring did the parents have?
How many of the offspring, in the second generation, are:
Normal, who?
Carriers, who?
Colorblind, who?
Carrier 4 3
1 – female
1 - male

17. Nondisjunction – “Not Coming Apart”
Nondisjunction – the failure of chromosome pairs to separate properly during cell division.
Result is a cell with an imbalance of chromosomes.

18. Kleinfelter’s Syndrome
47, XXY Syndrome – males have an extra X chromosome.
Most common sex chromosome disorder.
Characteristics:
Smaller testicles
Reduced fertility
Karyotype

19. Down Syndrome – “trisomy 21”
3 copies of chromosome 21
Characteristics:
Mental & developmental disabilities
Almond-shaped eyes
Deep crease on palms of hands
Short limbs

21. Mutations Mutation – A change in a gene or chromosome.
If in a body cell, it affects only the organism carrying it.
Example: Cancer
If in a sex cell (egg, sperm), mutation can be passed on to an offspring.
Found in 3 ways:
Positive
Negative
Neutral

22. Positive Mutation Positive – Benefits the organism
Example: Mutation causes disease resistance
Plants that can resist disease or drought
Humans that can resist HIV infection
Mutations that cause pleasing new feather colors in birds

23. Neutral Mutations Neutral – Does not benefit or harm the organism
Example: Extra toes and fingers
Example: White skin

24. Negative Mutations
Negative – Harms the organism or reduces its chances of having offspring
Example: Sickle-cell anemia
Often in people of African descent
Blocks blood vessels, causes pain,
strokes, death
Can also be a positive mutation
Africa – lots of malaria
One copy of the mutant gene
protects people from malaria