C20 - Patterns of inheritance and variation Flashcards
What is chlorosis?
Leaves appear yellow/pale due to insufficient chlorophyll production
What causes chlorosis
Change in phenotype usually due to environmental factors:
Lack of light- plants turn chlorophyll production to conserve energy
Mineral deficiency - lack of Fe/Mg (Fe needed as cofactor by enzymes making chlorophyll, mg used to make chlorophyll)
Virus infection - affect metabolism of cells (yellowing of infected tissues that can no longer make chlorophyll)
-normal genes coding for chlorophyll production
Why does animal body mass vary?
Determined by both genetic and environmental factors
-dramatic variation usually result of environmental factors
-genetic mutations can impact fat deposition
How is genetic variation created?
Formation of gametes
Sexual reproduction - random fusion of gametes
Inheritance if different alleles from each parent
What is an allele
Different versions of the same gene
What is a genotype?
Genetic makeup of organism
What is a phenotype?
Observable characteristics of an organism
What are modifications?
Any changes the environment makes to a phenotype
What is a dominant allele?
Version of gene which will always be expressed if present
What is a recessive allele?
Erosion of gene only expressed if two copies of allele present
What does homozygous mean?
Two identical alleles for a characteristic
What is heterozygous?
Two different alleles for a characteristic
What is continuous variation?
Characteristic that can take any value within a range
What is discontinuous variation?
A characteristic that can only appear is specific values (discrete)
-distinct groups
Differences between continuous and discontinuous variation
What is monogenic inheritance?
Characteristic inherited on a single gene
Monogenic heterozygous cross
Monogenic homozygous cross
What is codominance
When different alleles of a gene are equally dominant and both are expressed on the phenotype
Codominant cross
What is an example of a gene with multiple alleles?
Blood group
Immunoglobulin gene decides for production of different antigens present on surface of rbc
I^A - produce antigen A
I^B - produce antigen B
I^O - produce neither antigen
A and B are codominant whilst O is recessive
Sex chromosomes in males and females
Males - XY
Females - XX
X chromosome is large and contains many genes not involved in sexual development
Y chromosome is small and contains little genetic information
What is sex linked genes?
Genes carried on sex chromosomes
Why are recessive characteristics caused by allele on X chromosomes more common in men?
They don’t have Y ?
What is haemophilia
Sex-linked genetic disorder
Cause blood which clots slowly due to absences of protein blood clotting factor
Inheritance of haemophilia from haemophiliac male
Inheritance of haemophilia from healthy female
What is dihybrid inheritance
A characteristic inherited on two genes
Dihybrid cross
What is the expected phenotypic ratio of heterozygous x heterozygous dihybrid cross
9:3:3:1
What is autosomal linkage?
Genes present on the same non-sex chromosomes
What are linked genes?
Genes present in the same chromosome
How are linked genes inherited?
As one unit
No independent assortment unless alleles separated by chiasmata
What is recombinant
New combination of alleles/ DNA from 2 sources
How are recombinant offspring produced
Through crossing over, genes further away on chromosome
What is the recombination frequency?
(Number of recombinant offspring / total number of offspring) x 100
What does a recombination frequency of 50% indicate
No linkage, genes on separate chromosomes
What does a recombination frequency of less than 50% show?
Gene linkage, random process of independent assortment hindered
As degree of crossing over reduces (how close genes are on chromosome), recombination frequency decreases
What is a chi-squared test?
Used to determine the significance of the difference between observed and expected count data
What is epistasis?
Effect of one gene on the expression of another gene
What is hypostasis
Gene that is affected by another gene
What is recessive epistasis
Presence of 2 recessive alleles led to lack of affect on another gene
What is dominant epistasis
Presences of allele leads to lack of affect on another gene
Example of recessive epistasis
Gene at E locus is epistasis to hypostatic gene at B locus
