Genetics Flashcards
What is a monohybrid cross?
A cross between two purebreeding lines each with different alleles for the character being studied (e.g. a cross between AA and aa). 100% of the offspring is heterozygous
What genotypic ratios are produced when the offspring of a monohybrid cross are crossed with themselves?
3:1 (Aa x Aa = 3 Aa and 1 aa)
Define: wildtype
The phenotype of the typical form of a species as it occurs in nature (the normal, non-mutated form)
What is a dihybrid cross?
A cross between two purebreeding lines each with two unrelated characters. 100% of the offspring is heterozygous. (E.g. AABB x aabb = 100% AaBb)
What genotypic ratios are produced when the offspring of a dihybrid cross are crossed with themselves?
9:3:3:1 (AB, Ab, aB, aa)
What is a testcross?
A cross between a homozygous recessive individual and an unknown individual
What is a backcross?
A cross between the F1 progeny and either of thier purebreeding parents.
Define: Epistasis
The interaction of genes that leads to the suppression of one such gene by another.
What is co-dominance?
When the alleles of two phenotypes are equally recognisable in the individual
What is incomplete dominance?
When an organism is heterozygous but does not display the phenotype of the dominant allele, rather an intermediate of the dominant and recessive genotypes
Describe X chromosome inactivation
Females carry double the amount of gene rich X chromosomes and so one is inactivated and condenses into a Barr body
Examples of the effect of environment on phenotypes
Siamese cats (lower body temp at extremeties causes darker fur), hydrangeas ( alkaline soil = pink, acid soil = blue)
What is hemizygous?
A gamete with only one gene present; either the result of a gene deletion or the chromosome is heterogametic (XY)
What is an autosome?
A non-sexual chromosome (e.g. in humans, not X and Y)
Turner’s syndrome
Affects female, absence of an X chromosome (XO), sterile, webbed neck skin
Klinefelter’s syndrome
Affects males, extra X chromosome (XXY), sterile
Triple X
Affects females (XXX), fertile
Double Y
Affects males (XYY), claimed to be aggressive
What is the SRY
The Sex Determining Region is a locus on the Y chromosome which determines maleness if present. (I.e. XX = female). Complete absence on the Y chromosome causes sterility.
What is Mendel’s Law of Independant Assortment?
Allele pairs separate independently during the formation of gametes. This means that traits are transmitted to offspring independently of one another. (E.g. double hetero x double homo recessive = 1:1:1:1)
When is Mendel’s Law of Independent Assortment not upheld?
If two genes in question are found on the same chromosome, crossing over creates new combinations (via recombination).
The frequency of crossing over is affected by?
Distance betweent the loci (the closer they are, the less likely they are to cross over)
Map Distance
= (no. of recombinant progeny / total no. of progeny) x 100
What are the 5 conditions of HWE
1) Random mating 2) large population 3) no gene flow 4) no mutation 5) no natural selection
Anisogamy
Large gametes (more robust), small gametes (higher frequency) therefore 2 populations will form (e.g. the Moa and kiwi)
