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

Down Syndrome•Trisomy 21

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.