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