2 Genetics Flashcards
Define genotype.
The genetic constitution of an organism- the alleles an organism has.
Define phenotype.
The expression of the genetic constitution and its interaction with the environment.
Define allele.
A different version of a gene. Can be many different alleles of a single gene, but most plants and animals, including humans, on,y carry 2 alleles of each gene, one from each parent. The order of bases in each allele is slightly different, they code for different versions of the same characteristic. They’re represented using letters.
Define dominant allele.
An allele whose characteristic appears in the phenotype even when there’s only one copy.
Define recessive allele.
An allele whose characteristic only appears in the phenotype if 2 copies are present.
Define codominant allele.
Alleles that are both expressed in the phenotype, neither one is recessive.
Define locus.
The fixed position of a gene on a chromosome. Alleles of a gene are found at the same locus on each chromosome in a pair.
Define homozygote.
An organism that carries 2 copies of the same allele.
Define heterozygote.
Organism that carries 2 different alleles.
Explain sex-linkage.
- genetic information for gender is carried on 2 sex chromosomes
- females have 2 X chromosomes and males have 1 X and 1 Y
- characteristic is said to be sex- linked when allele that codes for it is located on a sex chromosome.
- Y chromosome smaller + carries fewer genes so most genes on sex chromosomes are only carried on X chromosome.
- as males only have X chromosome, they often have 1 allele for sex-linked genes. So they express the characteristic of this allele even if it’s recessive. Makes men more likely to show recessive phenotypes for genes that are sex-linked
Explain autosomal linkage.
- autosome is any chromosome that isn’t a sex chromosome. Autosomal genes are genes located on the autosomal
- genes on same autosome said to be linked as they’ll satay together during independent segregation of chromosomes in meiosis 1, their alleles passed on to offspring together.
- won’t happen if crossing over splits them up first
- closer together 2 genes are on autosome, more closely they’re said to be linked because crossing over less likely to split them up
- if 2 genes autosomal linked won’t get phenotypic ratio you expect in offspring of a cross.
What phenotypic ration will you get from 2 autosomally linked genes
In dihybrid cross between 2 heterozygous parents the phenotypic ratio is more likely to be that expected for a monohybrid cross between 2 heterozygous parents (3:1) because 2 autosomally-linked alleles are inherited together. This means higher proportion of offspring will have their parents heterozygous genotype and phenotype.
What is meant by epistasis?
Epistasis arises when the allele of one gene affects or masks the expression of another in the phenotype.
What is the chi-squared test?
statistical test which can be used to establish whether difference between observed and expected results is small enough to occur purely due to chance. It can be used to test the null hypothesis. A null hypothesis is one in which the results of a scientific investigation will produce no statistical significance
What is criteria to be met in order to use chi-squared?
- sample size must be relatively large, over 20
- data must fall into discrete categories
- only raw counts and not percentages, rate, etc can be used
- used to compare experimental results with theoretical ones.
