Genetics Flashcards
Midterm 1
Model Organisms
- Genetic discoveries made in a model organism are often true of related species and may even apply to all forms of
life. - Small size, small genome, large numbers of offspring, and short generation time are the common features
- Geneticists working with the same model organism share
stocks and information.
Genetics
study of heredity (transmission of properties from generation
to generation)
Continuous trait (Quantitative)
a trait that can take on a potentially infinite number of states over a continuous range (e.g. height)
Discontinuous (qualitative)
a trait that has a limited number of states with clearly defined differences (e.g. smooth vs wrinkled peas)
Gene discovery
1) collect mutants affecting the trait of interest
2) cross (mate) mutant individuals to wild-type individuals to see if their offspring show
ratios of wild-type-to-mutant phenotypes that are characteristic of single-gene inheritance.
3) Identify the function of the gene at the molecular level
4) Identify how the gene interacts with other genes to produce the trait in question
Variant
individual who inherits a trait that expresses differently from some
standard form
allele
variant form of a specific gene
Wild type
normal/most common form of a property/trait of an organism
Mutant
individual having an altered form of a property/trait (differs from the
normal form of the property/trait)
Phenotype
form taken by a trait (or group of traits) in a specific individual; detectable outward appearance of a specific genotype
Genotype
the allelic composition of an individual, commonly of a certain gene or set of genes
Mendel’s Law of Equal Segregation
- During meiosis, members of a gene pair segregate equally into gametes (pollen/sperm or eggs)
- Single gamete contains only one member of the gene pair
- At fertilization gametes fuse randomly to create zygote
Zygote
diploid cell formed by union of two haploid gametes (egg and sperm)
Monohybrid
heterozygote for one gene
Monohybrid cross
cross of 2 heterozygotes
Test cross
- cross individual of unknown genotype with homozygous recessive tester strain (a/a)
- If A/? x a/a → 1:1 (½ A/a and ½ a/a); then individual is heterozygous (A/a)
- If A/? x a/a → all progeny has dominant phenotype; then individual is homozygous (A/A)
- If tester strain not available: selfing A/? → 3:1 ratio, then individual is heterozygous (A/a)
True breeding
always produce the same phenotype with each
generation when interbred/selfed
mitosis
somatic cell division
meiosis
sexual cell division
meiocyte
- specialized diploid cell set aside to produce gametes by meiosis
Diploid Meiocyte: 2n -> n + n + n + n
haploid number
- The number of chromosomes in the basic genomic set of a species
Diploid: 2n -> 2n + 2n
Haploid: n -> n + n
Early S phase
- One DNA double helix per chromosome
- chromosomes = 2n
- DNA = 2C (one each from mom and dad with an allele of a gene)
Late S Phase
- DNA Replication
- Two DNA double helices per chromosome
- chromosomes = 2n (2 sister chromatids)
- DNA = 4C (since DNA got replicated)
M Phase
- sister chromatids separate to give two chromosomes that are distributed into two daughter cells
- chromosomes = 2n (2 sister chromatids)
- DNA = 4C
- Chromosomes = 4n (sister chromatids split apart)
-DNA = 4C - Chromosomes = 2n (2 chromosomes in each daughter cell)
-DNA = 2C
Mitosis in a diploid heterozygote
Aa→Aa+Aa
Meiosis in a diploid heterozygote
Aa→A+A+a+a
Aa→1/2 A and 1/2 a
ratio=1 A : 1 a
Single Nucleotide Changes
- Synonymous: same AA
- Nonsynonymous:
missense: different AA
nonsense: stop codon
Single Nucleotide Polymorphisms (SNPs)
- The “swap” of a single nucleotide with another is referred to either as a mutation, if present in <1% of the general population, or as SNP, if present at a frequency >1%.
- Most single-nucleotide changes are found outside
coding regions (noncoding) and have no impact on the
biological function of a protein (silent), though they may affect gene expression or splicing. - Variants found within the coding region may code for
functional changes in amino acid structure (missense) or predict premature protein (nonsense).
haplosufficient gene
- one wild-type allele (+) has enough function to produce a wild-type phenotype
- Recessiveness: heterozygote with a recessive and wild-type allele expressing wild-type phenotype
haploinsufficient gene
- a single wild-type allele (+) is not enough to promote
wild-type function - Dominance: heterozygote with a dominant allele and wild type allele expressing mutant phenotype
Gametes
- A haploid reproductive cell that can fuse with another haploid cell to form a zygote.
- Egg cells (ova) and sperm of multicellular eukaryotes.
Zygote
Diploid cell formed by union of two haploid gametes (egg and sperm)
Haploid
- Having one set of chromosomes (1n)
Diploid
- Having two sets of chromosomes (2n)
Sexual dimorphism
individuals are either male or female
Human sex chromosomes
- 46 chromosomes: 22 homologous pairs of autosomes (A) plus 2 sex chromosomes:
- females: 44A + XX
- males: 44A + XY
- X and Y sex chromosomes contain different sets of genes
homogametic sex
gametes of one type (females since XX)
heterogametic sex
gametes of two types (males since XY)
X and Y Chromosome divided into 2 regions
