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 ChromosomesChomosomes = 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

whenever present

- designated w/capital letters

T = tall

Recessive – shows only if the organism is homozygous

- masked w/dominant alleles

- designated w/lowercase letterst = 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 Genotype

Pure tall plant TT (homozygous dominant)

Pure short plant tt (homozygous recessive)

Hybrid tall plant Tt (heterozygous)

Mendel’s Peas