Bio Chapter 9 Part 1

heredity

• the transmission of traits from one generation to the next

genetics

• the scientific study of heredity

character

• heritable feature that varies among individuals (e.g. eye pigmentation)

trait

• variant for a character (e.g. less melanin – blue or green eyes)

Gregor Mendel

• identified the fundamental principles of genetics in the 1850s and 1860s at an abbey in Austria (now part of Czech Republic)

alleles

• version of genes

• For each character, an organism inherits 2 of these of a gene, one from each parent

homozygous

• two identical alleles for a gene

• E.g. AA or aa

heterozygous

• two different alleles for a gene

• E.g. Aa

dominant allele

• If the 2 alleles are different, then one determines the organism’s appearance

recessive allele

• has no noticeable effect on the organism’s appearance

law of segregation

• you have 2 alleles for each gene, but your gametes only have 1

• Meiosis I: homologous chromosomes separate, so the allele pairs separate (one allele on each)

• Meiosis II: each individual allele is packaged into gamete cells (sperm and egg)

• Fertilization creates new allele pairings, one inherited from sperm and one from egg

allele pairs

• are created when gametes combine at fertilization

homologous chromosomes

• have the same genes at the same locations (loci)

• the gene alleles (versions) may be the same or different

• Every diploid cell has matching pairs of these

Punnett squares

• help visualize the probability of offspring inheriting a combination of alleles (and phenotypic trait) based on the parents’ genotypes

genotype

• genetic information

phenotype

• observable physical trait

Homozygous Dominant

ex.~ BB

Heterozygous

ex.~ Bb

Homozygous recessive

• bb

Law of independent assortment

• the inheritance of one character has no effect on the inheritance of another character

• Exception

  • linked genes located close together on the same chromosome tend to be inherited together

Recessive Disorder

• both alleles must be recessive

• Remember that the dominant phenotype results from the presence of at least one dominant allele

• In order to have and express a recessive disorder, you must have two recessive alleles (homozygous recessive; aa)

• People who are heterozygous are carriers of the recessive allele for the disorder

• Carriers are not affected by the disorder! There is a chance they can pass a recessive allele to a child

carriers

• People who are heterozygous are this of the recessive allele for the disorder