human genetics it’s all in the…. inheritance parents and offspring often share observable...
Post on 15-Dec-2015
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Inheritance• Parents and offspring often
share observable traits.
• Grandparents and grandchildren may share traits not seen in parents.
• Why do traits disappear in one generation and reappear in another?
A pedigree is a chart that shows how a trait and the genes that control it are
inherited within a family.
Genetic predictions
What is the chance that Ellen’s child has a sickle cell anemia allele (a)?
Ellen Michael
?
Ellen and Michael’s parents must be carriers.
A a
A
a
AA Aa
Aa aa
Ellen is not affected andcannot carry aa genotype
Chance child inherits sickle cell allele = 1/2
Overall chance child carries sickle cell allele from Ellen = 2/3 x 1/2 = 1/3
Chance Ellen is a carrier = 2/3
Ellen’s brother Michael hassickle cell anemia, an autosomal recessive disease.
Autosomal recessive inheritance
• Heterozygous individuals carry the recessive allele but exhibit the dominant phenotype.
• Males and females are equally affected and may transmit the trait.
• May skip generations.
Sex chromosomes determine gender
•Human males are the have two different sex chromosomes, (XY).
•Human females only have one (XX).
What determines gender?
Number of X chromosomes, or presence of Y chromosome?
X0 Female with Turner syndrome
Male with Klinefelter syndromeXXY
X-linked traits
Males• One X chromosome
• Inherited from mother
• Two possible genotypes• XNY• XnY
• Have trait or do not have trait- they can’t be a carrier!
Females• Two X chromosomes
• Inherited from both parents
• Three possible genotypes• XNXN
• XNXn
• XnXn
• Heterozygous individuals are carriers of recessive traits- they can pass it down to their offspring- especially their male children!
X-linked recessive traits
• Always expressed in males if the male inherits the recessive gene from the mother.
• Affected males: Inherited from mother
• Females need to be homozygous recessive to show the trait
• Affected females : Fathers affected or mother had the trait or carried it!
X-linked dominant inheritance
Expressed in females with one copy.
Males are often more severely affected.
Typically associated with miscarriage or lethality in males.
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