M6 S2 : Patterns of inheritance Flashcards
What is continuous variation?
When the individuals in a population vary within a range.
What is discontinuous variation?
Is when there are two or more distinct categories. Each individual falls into one of these categories.
What is phenotypic variation?
The variation of an organisms phenotype (characteristics it displays)
What is inheritance?
How you got the genes you have and how likely you are to pass them on to your children.
What is a gene?
A gene is a sequence of bases on a DNA molecule that codes for (contains the instructions for) a protein (polypeptide) which results in a characteristic.
What are alleles
Different versions of the same gene. Order of bases in an allele is slightly different as each allele codes for different versions of the same characteristic.
What is a locus?
the fixed position where the allele of each gene is found on each chromosome in a pair.
Explain why most animals and plants (including humans) have two alleles for each gene?
This is because we inherit one copy of each chromosome from a pair from our parents.
What does the genotype of an organism mean?
What alleles it has. It could be a list, but usually it’s just the alleles for one characteristic at a time ( like genotype BB for eye colour in one person and Bb for eye colour in another).
What does phenotype of an organism mean?
The characteristics the alleles produce ( like one person has brown eyes and another has blue eyes).
What does homozygous mean?
An organism that carries 2 copies of the same allele ( Like BB or bb ).
What does heterozygous mean?
An organism that carries 2 different alleles ( like Bb ).
What is a dominant allele?
An allele whose characteristic appears in the phenotype when there is at least 1 copy. Shown by a capital letter ( like brown eyes, B , is dominant so a person will have brown eyes for BB and Bb ).
What is a recessive allele?
Alleles whose characteristic only show in the phenotype when both copies present. Shown in lower case ( like for blue eyes , b , a person will have blue eyes if genotype is bb ) .
What are codominant alleles?
When both alleles are expressed in the phenotype because neither is recessive.
What is a carrier?
A carrier is a person carrying an allele which is not expressed in the phenotype, but it can be passed on to offspring.
What are genetic diagrams?
They show the possible genotypes of offspring, so they can be used to predict the genotypes and phenotypes of offspring that would be produced if 2 parents are crossed ( bred ).
How many alleles do body cells from individuals have?
2 alleles. Gametes ( sex cells ) contain 1 allele for each gene. When gametes from the 2 parents fuse together, the alleles they contain form genotype of offspring.
What is monogenetic inheritance?
The inheritance of a characteristic controlled by a single gene.
What does F1 generation mean?
The first set of offspring.
What do monogenetic crosses show?
They show the likelihood of different alleles of that gene ( so different versions of the characteristic ) being inherited by offspring of the parents.
What is a phenotypic ratio?
The ratio of different phenotypes in the offspring. In practise the ratio will be slightly different due to chance.
What is the phenotypic ratio for a monogenetic cross involving codominant alleles with 2 heterozygous parents?
1 : 2 : 1 phenotypic ratio for homozygous for one allele : heterozygous : homozygous for other allele.
How do you represent alleles that show codominance?
Show the main gene as a capital letter, then the alleles as subscript capitals.
What is the phenotypic ratio for a monogenetic cross with 2 heterozygous parents?
3 : 1 ratio of dominant : recessive characteristics.
What is dihybrid inheritance?
The inheritance of 2 characteristics which are controlled by different genes. Each of the 2 genes have different alleles.
What is the phenotypic ratio between 2 heterozygous parents in a dihybrid cross?
9 : 3 : 3 : 1. Dominant first : dominant both : dominant first, recessive second : recessive first dominant second : recessive both
What does a dihybrid cross show?
Shows the likelihood of offspring inheriting certain combinations of the 2 characteristics from particular parents.
What is the F1 generation of dihybrid cross between homozygous dominant parent and a homozygous recessive parent ( like RRYY * rryy )?
All the offspring are heterozygous.
What does heterogametic mean?
Have 2 different kinds of sex chromosomes ( like males with XY ).
For recessive epistatic alleles, what is the phenotypic ratio when you cross a homozygous recessive parent with a homozygous dominant parent in the F2 generation?
9 : 3 : 4, dominant both : dominant epistatic, recessive other : recessive epistatic in F2 generation.
For a dominant epistatic allele, what is the phenotypic ratio when crossing a homozygous recessive parent with a homozygous dominant parent in F2 generation?
12 : 3 : 1, dominant epistatic : recessive epistatic, dominant other : recessive both in F2 generation.
What is a Chi-squared test?
A statistical test that is used to see if the results of an experiment support a theory.
What is a theory?
A possible explanation for something.
What is a hypothesis?
A specific testable statement.
What is the null hypothesis always?
There is no significant difference between the observed and expected results.
How do you do a Chi-squared test?
Calculate the Chi-squared value and then compare it to the critical value. If the result of Chi-squared test shows the observed and expected results are not significantly different, then unable to reject null hypothesis.
How do you calculate the number of offspring expected (E) ?
E = total number of offspring divided by (ratio total * predicted ratio)
How do you calculate the degree of freedom?
Number of classes (phenotypes) - 1
When comparing the Chi-squared value to the critical value how do we know when to reject the null hypothesis?
- Chi-squared value is greater than or equal to the critical value then reject the null hypothesis.
- Chi-squared value is less than critical value then failure to reject the null hypothesis.
What is the critical value?
The value of Chi-squared that corresponds to a 5% level of probability that difference between observed and expected results is due to chance.
What does homogametic mean?
Have only one kind of sex chromosome.
What does it mean if a characteristic is sex-linked?
The alleles that code for the characteristic are found on a sex chromosome.
Why are males more likely than females to show recessive phenotypes?
Males have only one X chromosome they often have only one allele for sex linked genes. As they only have one copy of this allele from sex-linked gene, they express the characteristic of this allele, even if it is recessive.
What is an autosome?
A fancy name for any chromosome that isn’t a sex chromosome.
What are genes on the same autosome said to be?
Linked.
What is epistasis?
The allele of one gene masks (blocks) the expression of the alleles of other genes.
