Transcript Human Genome notes

Human Genome
Karyotype – a picture of a cell’s chromosomes
group in homologous pairs
•Humans have 46
chromosomes
•Two of these are
sex chromosomes
(XX in females
and XY in males)
•The other 44 are
autosomes
• Eggs carry X chromosomes (23,X)
• Sperm can carry either an X or a Y chromosome
(23,X or 23,Y)
• Zygote would result as either 46, XX or 46, XY
• This is why about 50% offspring are male and
50% are female
Pedigree Charts
• Used to study human inheritance
• Shows how a trait is transmitted through a
family, one generation to the next
• Helps make inferences (guess) about
genotypes or whether certain alleles are
dominant or recessive.
• In pedigrees, circles represent females and
squares represent males
• Symbols that are shaded indicates the
individual expresses the trait
• No shading means the trait is not exhibited
• Important to understand that most traits are
polygenic and also can be influenced by
environment
Human Blood Groups
• Rh factor – Rh positive is dominant which
means Rh negative is recessive
• ABO blood grouping are multiple alleles
• IA and IB are codominant while i is recessive
Genetic Disorders-Autosomal
• PKU (Phenylketonuria) – Caused by a recessive
allele: Causes severe mental retardation
unless diagnosed early
• Huntington’s Disease – Caused by a dominant
allele: Causes neurological/muscular problems
and death in 40’s
• Sickle-cell Disease – Caused by a codominant
allele
• Cystic Fibrosis
• ALS (Lou Gehrig’s Disease)
Genetic Disorders - Sex-Linked
• Inheritance patterns on sex chromosomes will
be found on X chromosome (Y is too small
with little genetic information)
• Disorders called Sex-Linked
Colorblindness, Hemophilia,
Duchenne Muscular Dystrophy
Chromosomal Disorders
Nondisjunction - Caused during meiosis when
homologous chromosomes fail to separate.
• Leads to abnormal numbers of chromosomes
in the gametes
• Results in various disorders: Down’s
Syndrome and various sex chromosome
disorders
Down’s Syndrome
• Trisomy (three copies) of chromosome 21
• Produces mild to severe mental retardation
Turner’s Syndrome
• Female disorder where the person has only
one X chromosome (45,X)
• Sterile, which means unable to reproduce
• Sex organs never develop
Klinefelter’s Syndrome
• Male disorder where the person has an extra
X chromosome (47,XXY)
• Typically individual is sterile