GAMETES and ZYGOTE Sex cells: sperm and egg that are haploid. Contain 1 allele from each gene Contain 1 chromosome of each type Male gametes are smaller than female Fuse to create a zygote Zygote contains 2 chromosome of each type so are diploid Zygote have homologous pairs 2 alleles of each gene

Gregor Mendel Father of Genetics Crossed Pea Plants to show inheritance Conducted Good Science Research Lots of replicates and reliable data Law of segregation: During meiosis 2 alleles of each gene separate from each other to produce 4 haploid nuclei. Segregation allows new combinations in offspring.

Dominant, Recessive and Codominant Alleles Dominant masks recessive Dominant usually codes for a functional protein whereas recessive for a non- functional protein. Codominant have joint effects

phenotype Homozygous dominant genotype Homozygous recessive heterozygous

Genetic Diseases Most genetic disease are rare because they are caused by a recessive allele Must inherit a recessive allele from each parent to show the disease and this chance is very small. Heterozygous parents who do not show the disease are called carriers. Some diseases are result of sex- linkage, dominance or codominance.

Possible Allele Combinations Disease Alleles Possible Allele Combinations Cystic Fibrosis Recessive allele, must be inherited from both parents FF – normal Ff – normal, but carrier ff – cystic fibrosis Huntingtons Disease Dominant allele, no carriers HH- huntingtons Hh –huntingtons hh - normal

Possible Allele Combinations Disease Alleles Possible Allele Combinations Sickle Cell Anemia Codominant, gives 3 phenotypes HbAHbA – normal, not anemic HbAHbS – mild anemia, resistant malaria HbSHbS – severe anemia, susceptible malaria

Possible Allele Combinations Disease Alleles Possible Allele Combinations Color Blindness Sex-linked on the X chromosome, more common in males Female’s father must have it for female to show XBXB – normal female XBXb – normal female, but carrier XbXb – color blind female XBY – normal male XbY – color blind male Hemophilia XHXH - normal female XHXh – normal female, but carrier XhXh – hemophilia female XHY – normal male XhY – hemophilia male