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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