Inheritance A01 Flashcards
Allele
Different form of a gene- a variant for a particular gene at a given locus, that codes for an altered phenotype.
Dominant
Only one copy needed to show in phenotype.
Recessive
Two copies of a recessive allele needed to show in phenotype
Homozygous
Two of the same allele
Heterozygous
Two different alleles
Homologous chromosomes
A pair of chromosomes, one maternal/ one paternal carrying genes for the same characters at the same loci, capable of pairing up.
Co-dominant
Both genes will be expressed in the phenotype e.g. if one flower is white and the other is red offspring may be pink
State Mendel’s first and second laws
1st- The law of segregation: The characteristics of an organism are determined by factors which occur in pairs. Only one member of a pair of factors can be represented in a single gamete.
2nd- The law of independent assortment
‘Each member of an allelic pair may combine randomly with either of another pair.’
What does pure-breeding mean?
Parents are homozygous
In monohybrid inheritance what are the genotypes of the parent that Lead to a 3:1 ratio of dominant to recessive phenotypes?
A cross of two heterozygotes
In monohybrid inheritance what are the genotypes of the parents that lead to a 1:1 ratio of dominant to recessive phenotypes?
Homozygous recessive and a heterozygous
For a monohybrid cross, how many letters should there be in the genotype and the gametes?
2 letters in a genotype, 1 in a gamete
Describe how a 1:2:1 phenotype ratio arises
Cross between two heterozygous parents that shows complete/incomplete dominance.
Give the genotypes of the individuals that would when mated give a 9:3:3:1 ratio of phenotype
Heterozygous
What does the term linkage mean?
Genes on the same chromosome and do not segregate independently at meiosis
Which chromosome determines maleness?
Y
Give all the possible genotypes of a female without colour blindness
XN XN, XN Xn
Give the genotypes of a male with colour blindness and a male without colour blindness
XN Y, Xn Y
Explain why sex-linked characteristics are more frequently displayed in the phenotype in males than in females
Females have two copies of the X chromosome. Colour blindness is recessive and x-linked; therefore, females can also carry a normal copy. Boys only have one copy of the allele so if inherit the recessive form will definitely be colour blind.
Write a null hypothesis for a x2 test to assess whether the results of a cross where 24 individuals have the dominant phenotype and 16 have the recessive phenotype conform to the 3:1 ratio expected.
There is no significant difference between the observed and expected phenotypes, any difference is due to chance.
How would you work out the degrees of freedom you to use?
- Describe how many sets of data (number of different phenotypes) you have. =n
- Calculate how much the sets can vary.
This is called the degrees of freedom
What does the critical value mean?
You find the critical value for chi2 by using the probability table; you find the number of degrees of freedom and the 0.05 probability and this gives you the critical value for chi2.
What conclusions can you reach if the critical value is bigger than the calculate value of X2?
If your value of Chi2 is less than the critical value at p=0.05 you accept the null hypothesis- there is no significant difference between observed and expected values, and the difference between observed and expected values are due to chance alone, e.g., random fertilisation.
If your value of Chi2 is equal to or greater than the critical value at p=0.05, you reject the null hypothesis- there is a significant difference between observed and expected values, and the difference between observed and expected values are not due to chance, e.g., linkage.
