Human Genetics

Multiple Alleles

• There are more than two possible genes that can be inherited for a trait.

• Examples– Flower color– Blood type

Sex-linked Traits

• Trait for which the gene is located on one of the sex chromosomes.

XHXH ~ female, normal

XHXh ~ female, normal carrier

XhXh ~ female, hemophiliac

XHY ~ male, normal

XhY ~ male, hemophiliac

Pedigrees

• A family tree that shows how a particular trait is passed from parents to offspring.

• Be able to read and interpret

Pedigree of a Sex-linked Trait

• Colorblindness is sex-linked.

• Blue box is colorblind

• White box is normal vision with two normal genes.

• Half blue/half white is a carrier with normal vision, but one abnormal gene.

Karyotypes

• Process in which cells undergoing mitosis are crushed, and their chromosomes paired up. This can reveal abnormalities as seen below.

Female – 2 X chromosomes

Nondisjunction• The failure of

chromosomes to separate during anaphase I or II of meiosis.

• Can result in too many chromosomes (Down Syndrome) or not enough (Turner Syndrome)

Autosomal Dominant Diseases

• If the abnormal gene is present, the person has the disease– Huntington’s Disease

Huntington’s Disease

• Chromosome 4• HH or Hh• Nerve cells degenerate• Symptoms include: mood swings, irritability,

loss of memory, and uncontrolled movements• People of western European descent

Autosomal Recessive disease

• Must have 2 abnormal forms of the gene for the disease to be present– Cystic Fibrosis– Tay Sachs– PKU (Phenylketonuria)– Sickle Cell Anemia

Cystic Fibrosis

• Chromosome 7• cc• Causes think, sticky mucus to build up in the

lungs, digestive tract, and other areas of the body

• Mainly Caucasians

Tay Sachs

• Chromosome 15• tt• Causes a buildup of a chemical

on the nerve cells• Babies lose or fail to gain

motor and mental skills• Paralysis usually occurs• Death at an early age• Jews of eastern European

descent and French-Canadians

PKU

• Chromosome 12• pp • Born without the ability to break down

phenylalanine• Smaller than normal head, epilepsy, and

mental retardation may occur when undiagnosed

• Caucasians and east Asians

Sickle Cell Anemia

• Chromosome 11• ss• Red blood cells form an abnormal crescent

shape• Pain; spleen, lung, and heart damage, and

anemia• People of African

descent

Sex-linked Diseases

• Gene for the disease is carried on the sex-chromosome– Colorblindness– Hemophilia

Colorblindness

• Carried on the X chromosome

• XbXb or XbY• Cannot distinguish

between colors• Affects all races and ethnic

groups

Hemophilia

• Carried on the X chromosome

• XhXh or XhY• Blood does not clot

well because missing the gene that codes for a blood clotting protein

• Affects all races and ethnic groups

Chromosomal Aneuploidy Diseases

• A disease caused by an abnormal number of chromosomes– Down Syndrome– Turner’s syndrome– Kleinfelter’s syndrome– XYY Male

Down’s Syndrome

• Autosomal anueploidy• Trisomy (three

chromosomes at 21)• Mental retardation,

upward slant to the eyes, decreased muscle tone, and a variation of other symptoms

Turner’s Syndrome

• Sex chromosome anueploidy

• Monosomy• Alters development in

females; shorter than average, infertile, extra skin on the neck, skeletal abnormalities, heart defects, and kidney problems

Kleinfelter’s Syndrome

• Sex chromosome anueploidy

• Trisomy (XXY)• Armpit and facial hair,

enlarged breasts, tall stature, and abnormal body proportions

• Increased possibility of learning disorders

XYY Male

• Sex chromosome anueploidy

• Trisomy (XYY)• Increased risk of

learning disabilities, delayed speech and language skills