Karyotypes BIO 3.2.2 Predict offspring ratios based on a variety of inheritance patterns (including dominance, co-dominance, incomplete dominance, multiple alleles, and sex-linked traits).

Autosomes and Sex Chromosomes Sex chromosomes contain genes that determine an organism’s sex (gender). The remaining chromosomes that are not directly involved in determining the sex of an individual are called autosomes. Organize them on a karyotype by the size of the chromosome and position of the centrosome.

Male and Female Karyotypes

Sex determination In mammals, an individual carrying two X chromosomes is female. An individual carrying an X and a Y chromosome is male. In humans, the SRY gene is on the Y chromosome but if it is missing a 46, XY individual will appear female A sex-influenced trait, such as pattern baldness, is expressed differently in men than in women even if it is on an autosome and both sexes have the same genotype.

Nondisjunction When nondisjunction occurs one cell gets too many chromosomes and another cell get too few. If it occurs during Meiosis I all four cells will have the wrong number of chromosomes (2 will have too many and 2 will have too few) If it occurs during Meiosis II two cell will have the incorrect number of chromosomes (one will have too many and one will have too few)

Chromosome Abnormalities Down syndrome – 3 copies of chromosome #21 (trisomy 21)

Chromosomes Abnormalities Turner syndrome – female with only 1X chromosome (XO) (monosomy X)

Chromosome Abnormalities Klinefelter syndrome – male with XXY

Chromosome Abnormalities Patau syndrome – 3 copies of # 13

Doctors can detect these conditions before birth: Amniocentesis – removes amniotic fluid from around baby … Chromosomes are photographed and organized onto a chart called a karyotype.