Download Human Heredity - Catawba County Schools

Human
Heredity
Ch 14
Human Chromosomes
• Karyotype – picture of chromosomes
grouped together in pairs
• 23 pairs (46 total)
• Two are sex chromosomes (pair #23)
– Female genotype – XX
– Male genotype – XY
• Autosomes – remaining 44 chromosomes
– Pair #s 1-22
• Gender of zygote is determined by male
Human Traits
• Pedigree – chart that shows
relationship in family
• Used to infer genotypes of family
members
Recessive alleles
• An abnormal gene shows up when an
abnormal allele affects the phenotype
• Recessive – only shows up when
_________
Dominant allele
• Expressed even if recessive allele
present
Sex-linked genes
• Only Genes located on X and Y
chromosomes
• X chromosome contains more
genes being larger
• Y chromosome is small so can’t
carry other traits besides the one
determining the male sex
characteristics
• Males MUST always express all of
their X genes
• ** You can tell a trait is sex-linked
if more males than females have it
in the population!!**
Chromosomal disorders
• Errors in meiosis
• Nondisjunction - Homologous
chromosomes fail to separate
• Abnormal numbers of
chromosomes in gametes
Sex chromosome disorders
• Disorders in the sex
chromosomes
• May only have one X
– Sterile, sex organs do not develop at
puberty
• Or be a male with two X
• Presence of Y chromosome
produces male sexual development
no matter how many X
• Lack of Y, the embryo develops as
a female
• http://www.zerobio.com/drag_gr11
/sexlink.htm