1. Chromosomes and Human Inheritance
Chapter 12

2. Disorders caused by individual genes - dominant
Individuals with the disorder only need 1 allele to have the disorder
Huntington’s Disease
Caused by a repeat of the sequence CAG
Mental retardation and uncontrollable movements that usually don’t appear until middle age
Achondroplasia (mom and son)
A form of dwarfism
Polydactyly
6 fingers or toes

3. Disorders caused by individual genes – some say recessive – really codominant
To have the disorder you need 2 copies of the gene
Sickle cell disease
Defect in hemoglobin (oxygen carrying molecule in red blood cells) causes red blood cells to “sickle”
Carried by 1/12 African Americans
Carriers are healthy but are highly resistant to malaria.

4. 12.1 Human Chromosomes
In humans, two sex chromosomes are the basis of sex – human males have XY sex chromosomes, females have XX
All other human chromosomes are autosomes – chromosomes that are the same in males and females

5. Sex Determination in Humans
Sex of a child is determined by the father
Eggs have an X chromosome; sperm have X or Y

6. Sex Determination in Humans
The SRY gene on the Y chromosome is the master gene for male sex determination
Triggers formation of testes, which produce the male sex hormone (testosterone)
Without testosterone, ovaries develop and produce female sex hormones (estrogens)
What makes a boy a boy and a girl a girl? It’s not that simple……….
SRY gene

7. Karyotyping Karyotype Construction of a karyotype
A micrograph of all metaphase chromosomes in a cell, arranged in pairs by size, shape, and length
Detects abnormal chromosome numbers and some structural abnormalities
Construction of a karyotype
Colchicine stops dividing cells at metaphase
Chromosomes are separated, stained, photographed, and digitally rearranged

8. Figure 12.3
Karyotyping, a diagnostic tool that reveals an image of a single cell’s diploid complement of chromosomes. This human karyotype shows 22 pairs of autosomes and a pair of X chromosomes.
Figure It Out: Was this cell taken from a male or female?
Answer: Female
Fig. 12-3a, p. 187

9. Figure 12.3
Karyotyping, a diagnostic tool that reveals an image of a single cell’s diploid complement of chromosomes. This human karyotype shows 22 pairs of autosomes and a pair of X chromosomes.
Figure It Out: Was this cell taken from a male or female?
Answer: Female
Fig. 12-3b, p. 187

10. Down Syndrome
Trisomy 21

11. Turner Syndrome 1/ 2,000 live female births
Short stature, loss of ovarian function, lack or incomplete development at puberty
Heart defect, infertility, webbed neck

12. Klinefelter’s Syndrome
1/500-1/1000 males
Small testes and less testosterone than normal (less facial hair, infertility, breast development)
Tall

13. Nondisjunction
Chromosomes don’t separate in
meiosis

14. Chromosomal Mutations
Deletion – involves the loss of part of a chromosome
Duplication – involves an extra copy of part or all of the chromosome
Inversion – reverses the direction of part of the chromosome
Translocation – when part of one chromosome breaks off and attaches to another

15. Changes in Chromosome Structure
Cri-du-chat – “Cat’s cry”
Deletion in Chromosome 5
Mental impairment, abnormally shaped larynx that causes infants to make distinct cat-like meow , low set ears

16. Disorders caused by individual genes – sex-linked
Genes in sex-linked disorders are found on the X or Y chromosome (most are on X)
Color blindness (X chromosome)
Humans have 3 genes for color vision – all on the X
Red-green colorblindness = 1/12 males & 1/200 females
Males have 1 X chromosomes – females have 2 (the allele for colorblindness can be masked in females)

17. Colorblindness

18. Hemophilia – Remember the Romanovs?
X-linked recessive
interferes with blood clotting – bruise easily, internal bleeding causes joint problems

19. Duchenne Muscular Dystrophy (DMD)
1/3500 people – x-linked recessive
Causes abnormal dystrophin (a protein that supports muscle fibers) that causes muscle cells to die
Progressive disorder – usually diagnosed between 3 and 7, wheelchair by 12 and early death from heart or respiratory failure.

20. Sex linked problems
1) A female is a carrier for hemophilia and the dad is normal
What percent of sons will have hemophilia?
What percent of daughters will have hemophilia?

21. 2) Show how a daughter can be a carrier for colorblindness from either her mom or dad.

22. Pedigree Analysis

23. How is this trait inherited?

24. How is this trait inherited. What is the genotype of individual III 1
How is this trait inherited? What is the genotype of individual III 1? I 2?

25. How is this trait inherited?

27. Well…..it’s not that simple……
Epigenetics – “above the genome”
Factors that control gene expression that do not change the DNA or RNA
Nova – Ghost in Your Genes!!!!