Different Genetic Outcomes and Human

GeneticsChapters 11.3 and 14.1

Mendel’s experiments further In his first experiment Mendel showed that the alleles for a trait

segregated independently Now he wondered if alleles for different traits were linked He conducted a dihybrid cross two traits

◦ Crossed a true-breeding yellow round seed plant (RRYY) with a true-breeding green wrinkled seed plant (rryy)

◦ F1 generation was 100% yellow and round◦ You can see this result with a 16 box punnett square◦ He then crossed the F1 offspring

9 yellow round 3 yellow wrinkled 3 green round 1 green wrinkled

◦ This led to Mendel’s principle of independent assortment Genes for traits segregate independently from each other during the

formation of gametes in meiosis This accounts for the wide variety of genetic variation in organisms

Exceptions to Mendel’s principles Incomplete dominance When one allele is

not completely dominant over another◦ Crossing a red flower and a white flower and the

offspring are pink Codominance two genes are dominant

and show◦ Cross a black chicken with a white chicken and

the offspring are black and white◦ Blood types in humans

A and B are dominant, O is recessive

Human Genetics Karyotype a picture of all the

chromosomes◦ Can be used to diagnose genetic disorders◦ Humans have 46 chromosomes or 23 pairs

The first 22 pairs are called autosomes, the last pair are the sex chromosomes

Females have two X chromosomes Males have an X and a Y

Pedigrees a tool used to show relationships within a family◦ Genetic counselors analyze pedigrees to

determine possible genotypes of family members

◦ Can be used to predict genetic diseases Genes and environment a phenotype is

only partially determined by genes, the environment plays a role as well◦ Ex: height is genetically determined but can be

affected by poor nutrition