Download Chapter 14 Human Genetics

Chapter 14 Human Genetics
14.1 Human Chromosomes
• Genome = the full set of genetic information that
an organism carries in its DNA
• Karyotype = the complete diploid set of
chromosomes grouped together
▫ Arranged in order of decreasing size
Fig. 12-3a, p. 187
Fig. 12-3b, p. 187
Human Karyotype
• Cells are photographed in mitosis when
chromosomes are condensed and easy
to see
• 46 chromosomes (23 pair)
▫ 2 sex chromosomes (determine male or
female)
 XX = Female
 XY = Male
 1200 genes are found on the X
chromosome
 140 genes are found on the Y chromosome
▫ 44 autosomes (the other 44
chromosomes)
Human genetic disorders
• Changes in a gene’s DNA sequence can change
proteins
• Changes in the proteins can directly affect a
phenotype
Chromosomal Disorders
• Caused by an error in meiosis
▫ Nondisjunction =
chromosomes don’t separate
correctly
▫ Results in gametes with too
few or too many chromosomes
Chromosomal Disorders
• Down’s syndrome
▫ 3 copies (trisomy) of chromosome pair 21 (47
total)
 Mental retardation and birth defects
• Turner’s syndrome
▫ One X chromosome (45 total) –
 sterile female whose sex organs don’t develop at
puberty
• Klinefelter’s syndrome
▫ XXY (47 total)
 Sterile male
• Trisomy 21
Down Syndrome
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
Klinefelter’s Syndrome
• 1/500-1/1000 males
• less testosterone than normal (less facial hair,
infertility)
• Tall
Disorders caused by individual genes recessive
▫ cystic fibrosis
 Most cases of CF are caused by deletion of 3 bases in
the gene (CFTR) that allows chloride ions to pass
through membranes
 Causes digestive problems and produce thick, heavy
mucus that clogs their lungs and breathing passages
 Carried by 1/25 people with European ancestry
Disorders caused by individual genes recessive
• 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.
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
 A form of dwarfism
▫ Polydactyly
 6 fingers or toes
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)
X-Chromosome inactivation
• In females, most genes in one of the X
chromosomes are switched off forming a region
in the nucleus known as a bar body
▫ In calico cats, a gene that controls the color of coat
spots is on the X chromosome
▫ In different parts of the body, different X
chromosomes are switched off – making it a
mixture of orange and black
Disorders caused by individual genes –
codominant and multiple alleles
• ABO Blood Types
▫ A (IA) and B (IB) are codominant
▫ O (i) is recessive
The Human Genome
• By using tools that cut, separate, and replicate
DNA base by base, scientists can read the
sequences in DNA from any cell.