20 Flashcards
What is chlorosis?
When the leaves of a plant look pale or yellow
Why does chlorosis occur?
As the cells are not producing the normal amount of chlorophyll. This reduces the plants ability to make food by photosynthesis
What environmental factors may cause chlorosis?
Lack of light
Mineral deficiencies
Virus infections
What is genotype?
The combination of alleles and organism inherits for a characteristic
What is phenotype?
The observable characteristics of an organism
What are modifications?
The changes an environment makes to a persons phenotype. These are not inherited.
What is. A dominant allele?
The version of a gene which will always be expressed if present in an organism.
What is a recessive allele?
Only expressed if two copies of this allele are present in an organism.
Homozygous genotype?
They have two identical alleles for a characteristic. Can either be homozygous dominant or homozygous recessive.
Heterozygous genotype?
They have two different alleles for a characteristic
Definition of continuous variation?
A characteristic that can take any value within a range such as height or weight
Definition of discontinuous variation
A characteristic that can only appear in specific values such as blood groups
Causes of continuous variation?
Genetic and environmental
Causes of discontinuous variation?
Mostly genetic
What is monogenic inheritance?
Inheritance of a single gene
How do you perform a genetic cross?
1) state phenotype of both parents
2) state genotype of both parents
3) state the gametes of each parent, its common to circle letters
4) use Punnett square to show results of random fusion of gametes during fertilisation -> label gametes on edge of square
5) state proportion of each genotype produced among offspring -> either in % or x/y
6)state corresponding phenotype for each possible genotype.
What happens in homozygous genetic cross?
- all offspring are heterozygous -> will all have dominant allele
- proven by Mendel using pea pod plants
What happens in heterozygous cross?
Ratio is 3:1, dominant to recessive
What is codominance? And what is the result?
When two different alleles occur for a gene -> both of which are equally dominant
The result is that both alleles of. The gene are expressed in the phenotype of the organism present.
What is an example of codominance?
Snapdragon flowers. Two equally dominant alleles exist, each of which codes for the colour of the flower.
Why are upper and lower case letters not used to represent alleles in codominance?
As it would imply one allele is dominant and the other is recessive
Multiple alleles
- When some genes have more than two versions of alleles
- As an organism carries only two versions of the gene, only two alleles can be present in an individual.
Whats an example of something determined by a gene with multiple alleles?
Blood group -> I^A and I^O are codominant but I^O is recessive
How is sex determined?
Females - XX chromosomes on the 23rd pair/sex chromosomes
Males - XY chromosomes on the 23rd pair/sex chromosomes
- sex is determined by whether the sperm fertilising the egg the egg has X or Y chromosome
How does X chromosome differ to the Y?
The X chromosome is much larger and contains many genes not involved in sexual development.
The Y chromosome is smaller and contains almost no genetic information but carries a gene that allows embryo to develop as a male.
What is sex linkage in characteristics?
When some characteristics are determined by genes carried on the sex chromosomes.
Why do sex linked characteristics occur?
As the Y chromosome is much smaller than the X and there are a number of genes in the X chromosome that males have only one copy of. Therefore, any characteristic caused by a recessive allele on the section of the X chromosome, which is missing on the Y chromosome, occurs more frequently in males.
What are some examples of sex linked disorders?
Haemophilia and colour blindness
What is haemophilia?
When blood clots extremely slowly due to the absence of a protein blood clotting factor. It could be fatal.
Why is haemophilia sex linked?
If a male inherits the recessive haemophilia allele (on X) they cannot have corresponding dominant allele on Y and so develop haemophilia.
Can females suffer from haemophilia?
Yes they can but at a much rarer rate as they can carry the gene but wont suffer from haemophilia if they carry the dominant allele in one of the X chromosomes.
What is dihybrid inheritance?
Inheritance of two genes
What does dihybrid inheritance show?
The inheritance of two different characteristics, caused by 2 genes, which may be located on different pairs of homologous chromosomes.
Whats the monohybrid cross ratio?
3:1
Whats the dihybrid cross ratio?
9:3:3:1
Whats the codominance cross ratio?
1:2:1
Whats the dominant epistasis cross ratio?
12:3:1
Whats the recessive epistasis cross ratio?
9:3:4
Whats the complimentary epistasis cross ratio?
9:7
Why might the ratio of phenotypes better different than expected?
-The fertilisation of gametes is a random process so in a small sample a few chance events can lead to a skewed ratio
-The genes being studied are both on same chromosome (linked genes). If no crossing over occurs the alleles for two characteristics will always be inherited together.
Whats autosomal linkage?
Genes present on the same, non sex chromosome
What are linked genes?
Genes present on the same chromosome
What does recombinant mean?
New combination of alleles/DNA from two sources.
Whats recombinant frequency equation?
Number of recombinant offspring / total no of offspring
What does a recombinant freq of 50% indicate?
No linkage and genes are on separate chromosomes.
Wht does a recombinant freq less than 50% indicate?
Is a gene linkage and random process of independent assortment has been hindered.
What is chi squared test for?
Statistical test that measures the size of the difference between the results you acc get and those you expected to get
What is chi squared test formula?
X^2 = sigma((O-E)^2 /E)
X^2 = test stastic
Sigma = the sum of
O = observed frequencies
E = expected frequencies
If x^2 is less than critical value what does that mean?
There is no significant difference between expected and observed
What does it mean if x^2 is greater than critical value?
There is a significant difference between expected and observed values
What is degrees of freedom and how is it calculated?
The number of comparisons being made.
n - 1. n = no of categories or possible outcomes present in analysis
