Lesson 16: Mendelian Genetics Flashcards
What is a gene?
Segment of DNA that (often) codes for a protein
What is a trait?
Genetically determined characteristic or the expression of proteins
What are alleles?
Alternate forms of a gene
What is a phenotype?
Physical appearance of a trait (what it looks like)
What is a genotype?
Genetic make up of a trait (the letters)
What is a dominant allele?
Always expressed if present
What is a recessive allele?
Only expressed if NO dominant allele is present
What is a homozygous allele?
Two of the same alleles
What is a heterozygous allele?
Two different alleles
What is the P Generation?
Also known as the true breeding or parental generation. Always gonna be homozygous dominant or homozygous recessive for trait
What is Mendels first law of genetics?
Law of dominance
What does the law of dominance state?
An organism with a dominant allele will express the dominant trait and an organism with a recessive allele will ONLY have the trait expressed if the dominant allele is NOT present
What is Mendels second law of genetics?
Law of segregation
What is the law of segregation?
Each individual has two factors (alleles) for each trait. Alleles separate during the formation of gametes. Fertilization gives each new individual two alleles for each trait.
What is Mendels third law?
Law of independent assortment
What is the law of independent assortment?
Each pair of alleles segregated (assorts) independently of other traits in meiosis. The inheritance pattern of one trait will NOT affect the inheritance pattern of another. For a single human gamete, the possible ways for chromosomes to assort is an astounding 8,388,608 (2^23) possible combinations
What does crossing over provide?
Additional variation. Crossing over produces entirely new combinations of alleles on a chromosome
What is test cross?
Used to discover the unknown genotype of a known phenotype (the dominant phenotype). Cross a true-breeding recessive individual (yy) with a dominant phenotype (Yy or YY). Ratio reveals the unknown genotype. If ANY with the recessive trait appear, unknown MUST be heterozygous
What is a pedigree?
Inheritance can be traced using a pedigree
How can you tell the difference between a dominant inheritance and recessive inheritance on a pedigree?
Dominant inheritance:
All affected individuals will have a parent who also has the trait (ex: huntingtons disease)
Recessive inheritance:
An affected individual can arise from 2 unaffected parents (ex: cystic fibrosis (CF) and Phenylketonuria (PKU))
What are the 7 special cases in genetics that Mendel didn’t account for?
Multiple alleles, codominance, incomplete dominance, incomplete penetrance, pleiotropic effects, epistatic interactions, and polygenic inheritance
What is multiple alleles/codominance?
Some traits have more than two alleles. In these cases, sometimes more than one allele can act as a dominant allele. BOTH dominant alleles show up (ex: ABO blood type)
What is incomplete dominance?
Occurs when one allele is not completely dominant over another (ex: red flower + white flower= pink flower)
What is incomplete penetrsnce?
Alleles have a “true” dominant/recessive relationship, but dominant doesn’t always determine the phenotype (ex: polydactyly- autosomal dominant, but not all who inherit the gene have additional fingers)
