Transcript
HUMAN GENETICSHUMAN GENETICS
HUMAN GENETICSHUMAN GENETICS
• 1. WHAT ARE SOME EXAMPLES IN HUMANS OF CHROMOSOMAL EFFECTS?
• 2. WHAT ARE SOME EXAMPLES IN HUMANS OF AUTOSOMAL DOMINANT AND RECESSIVE TRAITS?
HUMAN GENETICSHUMAN GENETICS
• 3. WHAT ARE SOME OTHER FORMS OF INHERITANCE IN HUMANS?
• 4. WHAT IS A PEDIGREE?
• 5. HOW CAN GENETIC DISORDERS BE DETECTED?
1. WHAT ARE SOME 1. WHAT ARE SOME EXAMPLES IN HUMANS OF EXAMPLES IN HUMANS OF CHROMOSOMAL EFFECTS?CHROMOSOMAL EFFECTS?
Chromosomal InheritanceChromosomal Inheritance
All but one pair of chromosomes in males and females are the same.– Autosomes - Nonsex chromosomes
The different pair, sex chromosomes, determines the sex of an individual.– X-linked (sex-linked) is the term used for genes
carried on the X chromosome.
X-Linked AllelesX-Linked Alleles
X-linked alleles have a different pattern of inheritance than alleles on autosomes because the Y chromosome is blank for these alleles.– Inheritance of a Y chromosome cannot offset
the inheritance of an X-linked recessive allele.
Human X-Linked DisordersHuman X-Linked Disorders
Color Blindness– In humans, color vision receptors in the retina
are three different classes of cone cells. Only one type of pigment is present in each class of
cone cell.– The allele for blue-sensitive is autosomal, but the red- and
green-sensitive proteins are on the X chromosome.
Human X-Linked DisordersHuman X-Linked Disorders
Muscular Dystrophy– Absence of protein dystrophin allows calcium
to leak into muscle cells.
Hemophilia– Hemophilia A due to lack of clotting factor IX
and hemophilia B due to lack of clotting factor VIII.
Changes in Chromosome Changes in Chromosome NumberNumber
Monosomy and Trisomy– Monosomy (2n - 1) occurs when an individual
has only one of a particular type of chromosome.
– Trisomy (2n + 1) occurs when an individual has three of a particular type of chromosome.
Changes in Sex Chromosome Changes in Sex Chromosome NumberNumber
An abnormal sex chromosome number is the result of inheriting too many or too few X or Y chromosomes.– Nondisjunction during oogenesis or
spermatogenesis.
TURNER SYNDROME X0
TURNER SYNDROME XO KLINEFELTER XXY
Sex Chromosome SyndromesSex Chromosome Syndromes
Poly-X Females– More than two X chromosomes and extra Barr
bodies in the nucleus. Range from tall and thin to tall and severely retarded
depending on number of X chromosomes.
Jacobs Syndrome– XXY due to nondisjunction during spermatogenesis.
Taller than average
Changes in Chromosome Changes in Chromosome StructureStructure
Deletion– End of a chromosome breaks off, or two
simultaneous breaks lead to loss of an internal segment.
Translocation– Movement of a chromosome segment from one
chromosome to another, non-homologous chromosome.
WILLIAMS SYNDROMEWILLIAMS SYNDROME
ALAGILLE SYNDROME
Changes in Chromosome Changes in Chromosome StructureStructure
Duplication– Presence of chromosomal segment more than
once in the same chromosome. Known to occur as a result of an inversion in which
segment is turned 180o.
2. WHAT ARE SOME 2. WHAT ARE SOME EXAMPLES IN HUMANS OF EXAMPLES IN HUMANS OF AUTOSOMAL DOMINANT AUTOSOMAL DOMINANT
AND RECESSIVE TRAITS?AND RECESSIVE TRAITS?
Human Genetic DisordersHuman Genetic DisordersAutosome - Any chromosome other than a sex chromosome.– When a genetic disorder is autosomal dominant, an
individual with AA or Aa has the disorder.– When a genetic disorder is autosomal recessive, only aa individuals have the disorder.
Carriers - Individuals unaffected by a disorder but can have an affected child.
Human Genetic DisordersHuman Genetic DisordersAutosome - Any chromosome other than a sex chromosome.– When a genetic disorder is autosomal dominant, an
individual with AA or Aa has the disorder.– When a genetic disorder is autosomal recessive, only aa individuals have the disorder.
Carriers - Individuals unaffected by a disorder but can have an affected child.
Autosomal Recessive Autosomal Recessive DisordersDisorders
Tay-Sachs Disease– Progressive deterioration of psychomotor functions.
Cystic Fibrosis– Mucus in bronchial tubes and pancreatic ducts is
particularly thick and viscous.
Phenylketonuria– Lack enzyme for normal metabolism of phenylalanine.
Autosomal Dominant Autosomal Dominant DisordersDisorders
Neurofibromatosis– Tan or dark spots develop on skin and darken.
Small, benign tumors may arise from fibrous nerve coverings.
Huntington Disease– Neurological disorder leading to progressive
degeneration of brain cells, in turn causing severe muscle spasms and personality disorders.
3. WHAT ARE SOME 3. WHAT ARE SOME OTHER FORMS OF OTHER FORMS OF
INHERITANCE IN HUMANS?INHERITANCE IN HUMANS?
Multiple Allelic TraitsMultiple Allelic Traits
When a trait is controlled by multiple alleles, the gene exists in several allelic forms.– ABO blood types
Phenotype Genotype
A IAIA,IAi
B IBIB,IBi
AB IAIB
O ii
LARGE NUMBER OF TRIPLET REPEATS OF CGG AT FRAGILE SITE ON X CHROMOSOME
4. WHAT IS A PEDIGREE?4. WHAT IS A PEDIGREE?
5. HOW CAN GENETIC 5. HOW CAN GENETIC DISORDERS BE DISORDERS BE
DETECTED?DETECTED?
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