Lecture 12 Flashcards
Life cycle
adult → meiosis → sperm or egg → fertilization → mitosis → embryo → mitosis → fetus → mitosis → child to adult.
sexual reproduction is not only for increasing or maintaining population size, but essential for
for genetic diversity in eukaryotes (prokaryotes reproduce only asexually
relationship between DNA, genes, loci, alleles, and chromosomes.
Gene: a segment of DNA that influences the structure & function of an organism by encoding & directing the synthesis of mRNA, tRNA, rRNA & ultimately a polypeptide.
Gene locus: a specific place along the chromosome where a given gene is located. Genes are arranged in a fixed order along the chromosome
Allele: One of two or more variants of a gene pair that occur at the same locus (Ex P allele vs p allele, or A vs B vs O allele for blood type). A diploid individual inherits two alleles for each gene, one from each parent (so either ex AB or AO or AA, not ABO). Alleles can be dominant, recessive, co-dominant, or show incomplete dominance.
Homologous pair of chromosomes: each with genes for the same characters. One inherited from female parent, one inherited from male parent.
Monohybrid cross
mating between individuals who have different alleles at one genetic locus of interest (obviously, the 2 individuals will differ at many loci, but the monohybrid cross deals with only 1 locus). The character(s) being studied in a monohybrid cross are governed by two alleles for a single locus. To carry out such a cross, each parent is chosen to be homozygous (aka true breeding) for a given trait (locus) ex PP x pp
Dihybrid cross:
A dihybrid cross involves a study of inheritance patterns for organisms differing in two traits of interest. Mendel invented the dihybrid cross to determine if different traits of pea plants, such as flower color and seed shape, were inherited independently. An example of a dihybrid cross would be PPDD x ppdd, where P is purple, p is white flowers AND D is drooping, d is straight stems.
4 parts of Mendel’s model of inheritance.
There are alternate versions of genes (alleles)
For each character: an organism inherits 2 alleles, 1 from each parent
If the 2 alleles at a locus differ: the dominant allele determines the organism’s appearance
2 alleles separate (segregate) during meiosis & end up in different gametes ie each parent passes on 1 copy (not 2) of each allele.
Mendel’s Law of independent assortment
alleles of two (or more) different genes get sorted into gametes independently of one another. In other words, the allele a gamete receives for one gene does not influence the allele received for another gene.
difference between a dominant allele and a recessive allele
Dominant allele: an allele of a gene whose expression is observable in a heterozygote; the phenotype of the heterozygote (ex Tt) is indistinguishable from that of the dominant homozygote (TT). Dominance typically occurs when one of the two alleles is recessive, that is, non-functional at the molecular level.
Recessive allele: an allele whose expression is observable only in the homozygous form (tt), ie when the dominant allele is absent. This allele is usually non-functional; either no protein is produced or a modified
version of the protein, that is either only partially functional or completely non-functional, is produced.
Inbreeding
production of offspring from the mating or breeding of individuals or organisms that are closely related genetically.
inbreeding doesn’t CAUSE genetic defects, it only increases the chance of being homozygous for a gene that is associated with a disorder.
