gene a unit of heredity that controls the development of one trait made of dna
Post on 18-Dec-2015
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Allele• Member of a paired gene
– One allele comes from each parent• 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
Dwarfism = D
Normal height = d
DD = Dwarfism
Dd = Dwarfism
dd = Normal height
Examples of Alleles
Dwarf Band
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
Homologous Chromosomes
• Chromosomes of the same pair• Karyotypes are usually arranged with
homologous chromosomes paired together
MutagenAgent that causes mutations
•Cigarette smoke
•Pesticides
•X-rays
•Ulatraviolet light
•Nuclear radiation
Sex Chromosomes• Male have Xy
– Male gametes have either X or y
• Females have XX– Female gametes have X
X-Linked (vs Y- linked)Traits
• Why are there more X-linked that Y- linked disorders?
• Who suffers more frequently from sex-linked disorders? Why?
Trisomy 21: Down Syndrome
• Large tongue• Flat face• Slanted eyes• Single crease
across palm• Mental
retardation– Some are not
Trisomy 18: Edward Syndrome
• Heart defects• Displaced liver• Low-set ears• Abnormal hands• Severe
retardation• 98% abort• Lifespan < 1 year
Trisomy 13: Patau Syndrome
• Cleft lip and palate• Extra fingers & toes
– polydactylism
• Defects– Heart– Brain– Kidneys
• Most abort• Live span < 1
month
Klinefelter Syndrome• Breast
development• Small testes• Sterile• Low intelligence
– Not retarded
Klinefelter Website
Turner Syndrome
• Short• Not go
through puberty
• Produce little estrogen
• Sterile• Extra skin on
neck
Complete Dominance
Incomplete Dominance
CO-Dominance
Multiple Alleles
Sex-Linked Traits
Number of Alleles
2 2 2 3
Example of Alleles
Aa
AA’
AB
IA IB i XA Xa
Heterozygote Phenotype
Dominant parent Neither parent Both parents Dominant OR both parents
depends
Number of genotypes
3 3 3 6 5
Possible Genotypes
AA, Aa, aa AA, AA’, A’A’ AA, BB, AB IA IA, IB IA, IA I, IB IB, IBi, ii,
XA XA, XA Xa, XaXa, XAY, XaY,
Number of phenotypes
2 3 3 4 2
Possible phenotypes
A, B A, A’ , AA’ A, B, AB A, B, AB, O A, a
Classical Example
Pea plants 4 o clock flowers
Roan cows ABO Blood group
HemophiliaColor blindness
Example Blue eyes X purple eyes = blue eyes
Blue eyes X purple eyes = green eyes
Blue eyes X purple eyes = blue and purple eyes
various Males determines daughters and mother determines son
A man & woman are both carriers (heterozygous) for albinism. What is the chance their children will inherit albinism?
A man & woman are both carriers (heterozygous) for PKU disease. What is the chance their children will inherit 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?
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.
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
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