Flashcards in Genetics Deck (41)
a sequence of DNA bases that codes for a protein (polypeptide), which results in a characteristic
a different version of a gene (order of bases in each allele is slightly different - they code for different versions of the same characteristic)
the genetic constitution of an organism - alleles an organism has
the expression of the gene constitution and its interaction with the environment - an organism's characteristics
an allele whose characteristic appears in the phenotype even when there's only one copy
an allele whose characteristic only appears in the phenotype if two copies are present
alleles that are both expressed in the phenotype - neither one is recessive
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)
an organism that carries two copies of the same allele
an organism that carries two different alleles
a person carrying an allele which is not expressed in the phenotype but that can be passed on to offspring
What is diploid?
organism has 2 sets of chromosomes (so 2 alleles for each gene)
What are gametes?
-how many alleles do they contain?
-one allele for each gene
What is monohybrid inheritance?
the inheritance of a characteristic controlled by a single gene
What do monohybrid crosses show?
the likelihood of the different alleles of that gene being inherited by offspring of certain parents
What is dihybrid inheritance?
two different genes inherited at the same time
What chromosomes do females have?
What chromosomes do males have?
What is a sex-linked characteristic?
when the allele that codes for the characteristic is located on a sex chromosome
What is the difference between the sex chromosomes?
the Y chromosome is smaller than the X chromosome and carries fewer genes
(so most genes on sex chromosomes are only carried on the X chromosome)
Why are males more likely than females to show recessive phenotypes for genes that are sex-linked?
as males only have one X chromosome, they often only have one allele for sex-linked genes. so because they only have one copy, they express the characteristic of this allele even if its recessive.
What causes genetic disorders?
2 examples of genetic disorders caused by faulty alleles on sex chromosomes?
-why are they called X-linked?
colour blindness and haemophilia
-faulty alleles are carried on the X chromosome
What does autosome mean?
describes any chromosome that isn't a sex chromosome
What are autosomal genes?
genes located on the autosomes
What is autosomal linkage?
genes are on the same autosome are linked
Why will autosomally-linked genes be passed on to the offspring together?
-why might this not happen?
because they're on the same autosome, they'll stay together during the independent segregation of chromosomes in meiosis I, and their alleles will be passed on to the offspring together
-only reason it won't happen is if crossing over splits them up first
Why are two genes that are closer together on the autosome more closely linked?
crossing over is less likely to split them up
Can you predict phenotypic ratios if two genes are autosomally-linked?
if two genes are autosomally-linked, you won't get the phenotypic ratio you expect in the offspring of a cross
e.g. for a dihybrid cross between two heterozygous parents, you'd expect a 9:3:3:1 ratio in the offspring. Instead, its more likely to be that expected from a monohybrid cross between two heterozygous parents (3:1) because the two autosomally-linked alleles are inherited together. This means a higher proportion of the offspring will have their parents' (heterozygous) genotype and phenotype.
(this allows you to use the predicted phenotypic ratio to identify autosomal linkage)
What is a back cross?
crossing the offspring with one of the parents
What is epistasis?
allele of one gene masks the expression of the alleles of other genes
What is the epistatic gene?
the epistatic gene masks the expression of the other gene
Can you predict the phenotypic ratios of crosses involving epistatic genes?
crosses involving epistatic genes don't result in the expected phenotypic ratios BUT you can predict the phenotypic ratios for dihybrid crosses involving some epistatic genes
What is the phenotypic ratio produced in a dihybrid cross involving a recessive epistatic allele?
9 : 3 : 4
What is the phenotypic ratio produced in a dihybrid cross involving a dominant epistatic allele?
12 : 3 : 1
What is a chi-squared test used for?
statistical test that's used to see if the results of an experiment support a theory
How is it carried out?
1. theory is used to predict a result - expected result
2. experiment is carried out and actual result is recorded - observed result
3. write a null hypothesis - no significant difference between observed and expected results
Chi-squared value larger than or equal to critical value?
there IS a significant difference between observed and expected results (something other than chance is causing difference) - reject null hypothesis
Chi-squared value smaller than critical value?
there is NO significant difference between observed and expected results - accept null hypothesis
What is the accepted level of probability?
0.05 (5%) level of probability