medical genetics
DESCRIPTION
Medical Genetics. Human Anatomy and Physiology II Oklahoma City Community College. Dennis Anderson. Produces daughter cells with 46 chromosomes Used in growth and repair. Mitosis. Mitosis. DNA is duplicated Doubled chromosomes form from duplicated DNA Each cms has 2 identical chromatids. - PowerPoint PPT PresentationTRANSCRIPT
Medical Genetics
Human Anatomy and Physiology II
Oklahoma City Community College
Dennis Anderson
Mitosis
• Produces daughter cells with 46 chromosomes• Used in growth and repair
Mitosis
• DNA is duplicated• Doubled
chromosomes form from duplicated DNA
• Each cms has 2 identical chromatids
Chromatid
Chromatid
Chromosomes line up in a single row.
Mitosis Metaphase
Chromosomes separate
Each chromatid becomes a single chromosome
Meiosis
• Reduce the chromosome number to half that of body cells
• Produce gametes– Egg– Sperm
Chromosomes line up in a double row.
Meiosis Metaphase
Chromosomes separate
Each each daughter cell gets doubled chromosomes
Doubled Chromosomes Separate in Second Meiotic Division
Mitosis Metaphase
Meiosis Metaphase
Cms 1 Cms 1
Cms 2 Cms 2
Double Filed Chromosomes
• Daughter cells receive ONE of each cms pair
• Daughter cells receive ONE allele for most traits
• New combinations of alleles possible
Gene
• A unit of heredity that controls the development of one trait
• Made of DNA
Allele
• Member of a paired gene– One allele comes from each parent
• Represented by a single letter
Dwarfism = D
Normal height = d
DD = Dwarfism
Dd = Dwarfism
dd = Normal height
Examples of Alleles
Dwarf Band
Dominant & Recessive Alleles
• Dominant alleles are expressed
• Recessive alleles are not expressed in the presence of a dominant allele– Recessive alleles are only expressed if both
recessive alleles are present
Homozygous
• Both alleles alike
• AA or aa
Heterozygous
• Alleles are different
• Aa
Genotype
• Genetic make up
• Represented by alleles
• DD & Dd are genotypes for dwarfism
Phenotype
• A trait
• Genotype determines the phenotype
• Dwarfism is a phenotype
Codominant
• Two different alleles are both dominant
• A = allele for type A blood
• B = allele for type B blood
• AB = results in type AB blood
Karyotype
• Picture of chromosomes from an individual
Homologous Chromosomes
• Chromosomes of the same pair
• Karyotypes are usually arranged with homologous chromosomes paired together
Mutation
• Change in a gene or chromosome
• Causes an abnormal trait
MutagenAgent that causes mutations
Cigarette smoke
Pesticides
X-rays
Ulatraviolet light
Nuclear radiation
Homologous chromosomes line up in a double file in metaphase I of meiosis
Homologous Pairs Separate
Four Gametes With Single Chromosomes
Fertilization
Nondisjunction
Trisomy
Sex Chromosomes
Sex Chromosomes
• Male have Xy– Male gametes have either X or y
• Females have XX– Female gametes have X
AutosomesChromosomes 1-22
X-Linked Traits
• Alleles are on the X chromosome
• Females have two alleles
• Males have one allele– Only one X chromosome
Normal Male
Normal Female
Trisomy 21Down Syndrome
Down Syndrome
• Large tongue• Flat face• Slanted eyes• Single crease across
palm• Mental retardation
– Some are not
Maternal Age & Down Syndrome
Trisomy 18Edward Syndrome
Edward Syndrome
• Heart defects• Displaced liver• Low-set ears• Abnormal hands• Severe retardation• 98% abort• Lifespan < 1 year
Trisomy 13Patau Syndrome
Patau Syndrome• Cleft lip and palate• Extra fingers & toes
– polydactylism
• Defects– Heart– Brain– Kidneys
• Most abort• Live span < 1 month
Klinefelter Syndrome
Klinefelter Syndrome
• Breast development• Small testes• Sterile• Low intelligence
– Not retarded
Klinefelter Website
Turner Syndrome
Turner Syndrome
• Short• Not go through
pruberty• Produce little estrogen• Sterile• Extra skin on neck
Fetal Testing
Sickle Cell Anemia
• RBCs sickle shaped
• Anemia
• Pain
• Stroke
• Leg ulcers
• Jaundice
• Gall stones
• Spleen, kidneys & lungs
Sickle Cell Anemia
• Recessive allele, s codes for hemoglobin S – Long rod-like molecules– Stretches RBC into sickle shape
• Homozygous recessive, ss have sickle cell anemia
• Heterozygous, Ss are carriers
Hemophilia
Blood clotting impaired
Recessive allele, h
carried on X cms
X-linked recessive trait
More common in males
Albinism
• Lack of pigment– Skin
– Hair
– Eyes
Amino Acids Melanin PigmentEnzyme
A a
AA = Normal pigmentation
Aa = Normal pigmentation
aa = Albino
PKU Disease
• Phenylalanine excess• Mental retardation if
untreated
Molly’s Story
Phenylalanine TyrosineEnzyme
P p
PP = Normal
Pp = Normal
pp = PKU
A man & woman are both carriers (heterozygous) for albinism. What is the chance their children will inherit albinism?
AA = Normal pigmentation
Aa = Normal pigmentation (carrier)
aa = Abino
Man = Aa Woman = Aa
A
a a
A
A
a
a
A AA
Aa
Aa
aa
AA
Aa
Aa
aa
Genotypes1 AA, 2Aa, 1aa
Phenotypes
3 Normal
1 Albino
Probability
25% for albinism
A man & woman are both carriers (heterozygous) for PKU disease. What is the chance their children will inherit PKU disease?
p
p
P PP
Pp
Pp
pp
P
PP = Normal
Pp = Normal (carrier)
pp = PKU disease
PP
Pp
Pp
pp
Genotypes1 PP, 2Pp, 1pp
Phenotypes
3 Normal
1 PKU disease
Probability
25% for PKU disease
A man with sickle cell anemia marries a woman who is a carrier. What is the chance their children will inherit sickle cell anemia?
s
s
s Ss
Ss
ss
ss
S
SS = Normal
Ss = Normal (carrier)
ss = Sickle Cell
Ss
Ss
ss
ss
Genotypes2 Ss, 2ss
Phenotypes
2 Normal (carriers)
2 Sickle cell
Probability
50% for Sickle cell
A man with heterozygous dwarfism marries a woman who has normal height. What is the chance their children will inherit dwarfism? Dwarfism is dominant.
d
d
D Dd
dd
Dd
dd
d
DD = Dwarf
Dd = Dwarf
dd = Normal
Dd
dd
Dd
dd
Genotypes2 Dd, 2dd
Phenotypes
2 Normal
2 Dwarfs
Probability
50% for Dwarfism
X-linked Recessive Traits
• Alleles are on the X chromosome
• Inheritance pattern different in males and females
XH XH = Normal Female
XH Xh = Normal Female (Carrier)
Xh Xh = Hemophilic Female
XHy = Normal Male
Xhy = Hemophiliac Male
A man with hemophilia marries a normal woman who is not a carrier. What is the chance their children will inherit hemophilia? Hemophilia is X-linked recessive.
y
XH
Xh XH Xh
XH
XH XH = Normal Female
XH Xh = Normal Female (Carrier)
Xh Xh = Hemophilic Female
XHy = Normal Male
Xhy = Hemophiliac Male
XH Xh
XHy XHy
Genotypes
2 XH Xh, 2XHy
Phenotypes
2 Carrier Females
2 Normal Males
Probability
O% for Hemophilia
y
XH
Xh XH Xh
XH
XH Xh
XHy XHy
A normal man marries a normal woman who is a carrier for hemophilia. What is the chance their children will inherit hemophilia?
y
Xh
XH
XH
XH XH = Normal Female
XH Xh = Normal Female (Carrier)
Xh Xh = Hemophilic Female
XHy = Normal Male
Xhy = Hemophiliac Male
XH XH XH Xh
XHy Xhy
Genotypes
XH XH , XH Xh, XHy, XhyPhenotypes
2 Normal Females
1 Normal Males
1 Male Hemophiliac
Probability50% for Male Hemophilic
0% for Female Hemophilic
y
Xh
XH XH XH
XH
XH Xh
XHy Xhy
The End