Unit 5 Heredity 8-11% Flashcards
Heredity
Passing of traits from parent to offspring.
Genes
DNA sequences that code for proteins + determine an organism’s traits → located on chromosomes (gene locus).
Homologous Chromosomes
Pair of chromosomes (one from each parent) that carry the same genes, but different alleles.
*NOT IDENTICAL
Mendel’s Experiment
- He studied seven traits, each with two distinct forms (tall vs. short, purple vs. white).
- He started true-breeding plants (homozygous dominant) → passed down the same trait when pollinated.
- Crossed two true-breeding plants with different traits → F1 generation (hybrids) were all purple.
- F1 generation self-pollinated → F2 generation traits were in a 3:1 ratio.
Mendel’s Understand of Alleles
Organism have two alleles for each gene (one from each parent) resulting in genetic variation.
Mendel’s Law of Dominance
When an organism has two alleles for a gene, the dominant allele is expressed & the recessive allele is hidden.
Mendel’s Law of Segregation
Only one allele is passed to offspring because the 2 alleles for a gene separate during meiosis.
Mendel’s Law of Independent Assortment
Alleles for different genes are passed down independently of one another because homologous chromosomes split during meiosis.
Genotype vs. Phenotype
Genotype: genetic makeup (AA, Aa, aa).
Phenotype: observable traits, determined by genotypes.
In Mendelian genetics, heterozygous dihybrid crosses result in a ______ ratio because of ______ and ______.
9:3:3:1, independent assortment, complete dominance.
Non-Mendelian: Incomplete Dominance
Neither allele is complete dominant → mix of parent phenotypes.
Ex. red & white flowers produce pink offspring.
Non-Mendelian: Codominance
Both alleles in a heterozygote are expressed → both traits displayed.
Ex. A & B blood type are codominant→ AB.
Non-Mendelian: Multiple Alleles
Genes have more than two alleles.
Ex. A, B, & O blood types.
Non-Mendelian: Polygenic Inheritance
Traits influenced by multiple genes → gradient of phenotypes.
Ex. hair/eye color & height
Non-Mendelian: Environmental Influence
Environment affects gene expression → variation in phenotypes (even if they have the same genotype).
Non-nuclear inheritance involves genes that are located on chromosomes ______ of the ______.
Outside, nucleus.
Mitochondrial & Chloroplast DNA
Randomly assorted into gametes → mitochondrial traits are determined by the mother.
Wild vs. Mutant Phenotypes
Wild: common form of a trait.
Mutant: variation caused by mutation; less.
Morgan’s Sex-linked Gene Experiment
- True-breed red-eyed female (wild) x white-eyed female (mutant) → F1 offspring had red eyes.
- Crossed red-eyed female x red-eyed male → all females had red eyes, but it was 50/50 for males.
- Gene for eye color is on the X chromosome.
Non Mendelian: Sex-linked Genes
Traits are determined by genes located on the sex chromosomes (mainly X).
How are sex-linked traits inherited in males vs. females?
Males: 1 X chromosome → if they inherit mutant allele it will show up.
Females: 2 X chromosomes → need two mutant alleles to show up.
What are four ways to tell if a trait is sex-linked?
- More common in males.
- Trait skips generations in females, but shows up in sons.
- No male-to-male transmission.
- Daughters can be carriers.
Morgan’s Gene-Linkage Experiment
- Crossed flies that differed in body color (gray vs. black) & wing type (normal vs. vestigial).
- He expected a 1:1:1:1 ratio by crossing BbBv (gray, normal) x bbvv (black, vestigial).
- More parental-types than recombinants.
Non-Mendelian: Linked Genes
Genes located close together on the same chromosome tend be inherited together (do not assort independently).
