Human Karyotypes

Karyotypes = pictures of homologous
chromosomes lined up during metaphase 1

23 pairs of chromosomes (1 set from the
mother & 1 set from the father)
-
-
22 pairs are autosomes
1 pair is sex chromosomes
XX = female ♀ & XY = male ♂
About Chromosomes
Chomosomes = structures of
tightly coiled chromatin
(DNA)
Homologous chromosomes =
chromosomes of same size &
shape carry the same genes
for the same traits
Chromosomal Theory of Inheritance
“Genes are located on chromosomes”
Genes
-
are hereditary units of DNA
control characteristics & abnormalities
exist in different forms called alleles
ALLELES
Dominant – shows
Recessive – shows
whenever present
- designated w/capital letters
T = tall
-
-
only if the organism
is homozygous
masked w/dominant
alleles
designated
w/lowercase letters
t = short
GENOTYPE = genetic makeup
HOMOZYGOUS (Pure)
-
organism has 2
identical alleles for a
trait
TT or
tt
HETEROZYGOUS (hybrid)
-
organism has 2
different alleles for a
trait
Tt
PHENOTYPE
Physical appearance an organism develops as
a result of its genotype
Phenotype
Pure tall plant
Genotype
Pure short plant
Hybrid tall plant
tt (homozygous recessive)
Tt (heterozygous)
TT (homozygous dominant)
Mendel’s Peas