Genetics part 2 Flashcards
Overall basic timeline of meiosis?
Pre-meiotic S-phase (DNA is doubled), so each now each chromosome has 2 sister chromatids attached at centromere
Recombination (crossing over)
Meiosis I homolog segregation (homologous pairs are seperated)
Meiosis II, sister chromatid separation (seperates the pairs)
What occurs in prophase I?
Chromosomes condense
Homologous pairs form
Forming a synaptonemal complex
Recombination occurs
What occurs in metaphase I?
Each pair of homologues (tetrad) line up at equator
Centromers don’t divide (unlike in mitosis)
Orientation of pairs is random with respect to one another (so can end up on either side of the equator)
What occurs in anaphase I?
Chromosomes, each with 2 chromatids move to separate poles
What occurs telophase I?
2 new daughter cells will each contain one of each chromosome, however the chromosomes still consist of 2 chromatids
So products are haploid, as there is only one of each chromosome
What occurs in Metaphase II, then anphase II, then telophase II?
Individual chromosomes line up at metaphase plate
Centromers split, chromatids separate to opposite poles
Each daughter cell contains one chromosome of each type, so 4 daughter haploid cells are produced from the 2 haploid cells
What is the genotype?
The combination of specific alleles that they carry
The alleles at the locus
What is phenotype?
Observable characteristics
What is an allele?
Alternate forms of a gene
What’s a homozygote?
Identical, eg YY, or yy
What’s a heterozygote?
Different, eg. Yy
What’s a gene?
Basic unit of biological information, specific segment of DNA that encodes a protein
What’s it called if we look at 2 genes instead of 1?
Dihybrid cross
How do you find the gametes in a dihybrid cross?
If parents are Aa, and Bb
Gametes will be, AB, Ab, aB, ab
Due to independent assortment during metaphase I, they line up on potentially different sides of the equator
What ratio does a dihybrid cross produce, when both parents are heterozygous (F1)?
9:3:3:1
In diploids wild type alleles are normally?
Dominant
In diploids mutant alleles are normally?
Recessive
What’s incomplete dominance?
When heterozygoes shown an intermediate phenotype, eg red x white = pink
Genotypic ratio = phenotypic ratio
What is Co-dominance?
Where heterozygoes show phenotype of both alleles
What are multiple alleles?
When there are more than 2 alleles for a gene
What is pleiotropy?
Where one gene contributes to more than one trait
What’s an example of the complications of dominance and pleiotropy?
Sickle-cell syndrome
Normal - no symptoms
Carrier - Some symptoms, not affected by malaria
Diseased - all symptoms, not affected by malaria
What can gene combinations cause?
Novel phenotypes, a new unique apperance the parents didn’t have
Alleles of one gene can mask effects of alleles at another gene (epistasis)
How to see of mutants are mutants in the same gene?
If breed them together and all offspring show mutant trait, then they are
If they aren’y won’t get the mutant trait = complementation, genes have helped each other as one set is recessive in each