Karyotyping BSC 2010L

Humans Haploid # of chromosomes: 23 Diploid #: 46 Remember: Have 23 pairs 1 of each pair came from mom 1 of each pair came from dad Note that we have 22 pairs of autosomal chromosomes and 1 pair of sex chromosomes

Dominant vs. Recessive Traits Each pair of chromosomes is referred to as HOMOLOGOUS CHROMOSOMES Have the same genes For each gene there can be 2 alleles (different forms) Look at picture below: B = brown eyes b = blue eyes Brown is dominant so this person’s phenotype would be brown eyes

Dominant vs. Recessive Traits Incomplete Dominance Form of inheritance where heterozygous alleles are both expressed, combined phenotype Example: a plant with white flowers and plant with red flowers has offspring with pink flowers Codominant Both alleles are expressed Example: Blood types in humans If a person has the A allele and the B allele, then both A and B are expressed on the surface of the red blood cell

Sex-linked Genes Genes located on the sex chromosomes (23rd pair in humans) Examples: Color-blindness Hemophilia Males only need 1 gene on X chromosome to have trait – look at boy on far right