Patterns of inheritance Flashcards
chlorosis and factors which cause it
- plant cells not producing normal amount of chlorophyll - leaves look pale or yellow, reduces ability to make food by photosynthesis
caused by: - lack of light - turn off chlorophyll production to conserve resources
- mineral deficiencies - eg. iron - needed as cofactor by some enzymes that make chlorophyll
- virus infections - interfere with metabolism of cells - can no longer support synthesis of chlorophyll
genotype
- combination of alleles an organism inherits for a characteristic - genetic makeup
phenotype
- observable characteristic of an organism
- can be affected by genes (inheritance) or environment (modifications)
continuous variation and genetic causes
2 extremes, any value within a range
- variation caused by genes and environment
- controlled by multiple genes - polygenes
- eg. height/weight
discontinuous variation
individuals fall into distinct groups
- variation mostly caused by genetics
- controlled by one or two genes
- eg. blood group
monogenetic inheritance
- inheritance of a single gene
homozygous genetic cross - monogenetic inheritance (GG x gg)
- crossing GG (dominant green) with gg (recessive yellow)
- all offspring are heterozygous and green as all inherit a G - F1 generation
heterozygous genetic cross - monogenetic inheritance (Gg x Gg)
- crossing Gg with Gg - both green
- 1/4 will be yellow - gg
- 3/4 will be green - 1 GG, 2 Gg
codominance
- 2 different alleles coding for a gene and both are dominant
- both alleles are expressed in phenotype
- eg. allele codes for enzyme catalysing production of red pigment - red flower and allele codes for altered version of enzyme which doesn’t catalyse production of any pigment - white flower
- red flowers, white flowers and pink flowers can all be produced
multiple alleles in codominance eg blood group
- 1 characteristic coded for by a gene with more than 2 versions - multiple alleles
- organisms only carry 2 versions of the gene - one on each homologous chromosome, so only 2 alleles present in each individual, but multiple alleles exist in other organisms for this characteristic
blood group as example of multiple alleles in codominance
- IA (antigen A), IB (antigen B), IO (neither antigen)
- IA and IB are codominant, IO is recessive of both alleles
results in 4 blood groups: - A - IAIA or IAIO
- B - IBIB or IBIO
- AB - IAIB
- O - IOIO
how is sex determined? differences between X and Y chromosome
- 23rd pair of chromosomes - sex chromosomes
- females - XX
- males - XY
- X chromosome - large and contains many genes not involved in sexual development
- Y chromosome - small, contains almost no genetic info
sex linkage
- some characteristics are determined by genes carried on sex chromosomes (sex linked)
- Y is smaller so some genes on X chromosome, males only have 1 copy of
- any characteristic caused by recesssive section on X chromosome, is missing on Y so occurs more frequently in males
haemophilia - sex linked disorder
- blood clots extremely slowly due to absence of blood-clotting factor - injury causes prolonged bleeding
- affected haemophilia genotypes: X^h X^h (female) and X^h Y (male)
- males only inherit one copy of the gene involved in haemophilia
- a male who inherits the recessive copy of the allele will have haemophilia, if he inherits the dominant allele, he won’t
- a female can have haemophilia if she inherits 2 copies of the recessive allele
- majority of haemophilia sufferers are male
dihybrid inheritance
- inheritance of 2 different characteristics caused by 2 genes, which could be on different pairs of homologous chromosomes and have 2 or more alleles
- eg. round/wrinkled seeds and green/yellow seeds
expected ratio of 2 heterozygous individual for both traits - dihybrid inheritance
9:3:3:1
eg. round/wrinkled, green/yellow
9 - yellow round
3 - yellow wrinkled
3 - green round
1 - green wrinkled
why can the actual ratio of phenotypes differ from the expected?
- fertilisation of gametes is random
- genes being studied may be on the same chromosome (linked genes) so if no crossing over occurs here, the 2 characteristics will be inherited together
autosomal linkage
- genes that are linked are found on one of the other pairs of chromosomes
- linked genes are inherited as one unit
- linked genes cannot undergo crossing over in meiosis - expected ratio not produced in offspring
recombination frequency
- measures amount of crossing over in meiosis
- recombinant organism - different allele combinations to both parents
- recombination frequency = no. recombinant frequency/total no. offspring
recombinant offspring and what reduces the liklihood of it?
- different combinations of alleles than either parent
- genes close to each other on chromosome -less likely to be separated during crossing over so fewer recombinant offspring produced
chi-squared
(don’t learn formula)
- measures difference between observed and expected ratio
- X^2 = sum of (O-E)^2/E
O = observed frequencies
E = expected frequencies
- large chi-squared value - statistically significant difference between observed and expected results - probability that it’s due to chance is low
epistasis and diff types
- the interaction of 2 non-linked genes (different homologous chromosomes) which causes one gene to affect the expression of the other in the phenotype
- antagonistic - work against each other, the presence of one gene stops the expression of the other (can be recessive or dominant)
- complementary - the presence of one gene encourages the expression of the other
epistatic gene
the gene suppressing the expression of the hypostatic gene in antagonistic epistasis
hypostatic gene
the gene being suppressed by the epistatic gene in antagonistic epistasis
gene pool
the sum total of all the genes in a population at any given time
The Hardy Weinberg principle assumptions
- in a stable population with no disturbing factors, the allele frequencies will remain constant from one generation to the next and there will be no evolution
