U2T5 - Keywords Flashcards
Genes + Patterns of Inheritance
Gene
Short section of chromosome that codes for particular polypeptide/protein/characteristic.
Allele
Particular form of a gene.
Homozygous
Both alleles of gene are same. (TT - homozygous dominant, tt - homozygous recessive)
Heterozygous
Alleles of same gene are different. (Tt) Effect of recessive allele masked by dominant allele.
Genotype
Gene arrangement of alleles to determine particular feature.
Phenotype
Outward appearance (tall/short). Results from gene expression + interaction in environment.
Gene Locus
Position of gene on chromosome.
Haploid
Single set of unpaired chromosomes. e.g. gamete. (n)
Diploid
2 complete sets of chromosomes, one from each parent. (2n)
n
Number of chromosomes. Humans have 23 pairs so 46 chromosomes.
Homologous Chromosomes
2 similar chromosomes that each carry same genes in same locus on chromosome so each cell has 2 copies of each gene.
Mendel’s Law of Segregation
The characteristics of an organism are determined by internal factors which occur in pairs. Only 1 of a pair of such factors can be represented in a single gamete.
Monohybrid Inheritance
Inheritance of 1 characteristic (round/wrinkled)
Backcross/Test Cross
Used to determine unknown genotypes. e.g. can’t know if Tt or TT as same phenotype. Breed plant with homo recessive plant to find out which it is. If homo recessive with hetero, 1:1 ratio. If homo dom with homo recessive, all offspring hetero. Used to confirm pedigree status.
Dominant
An allele that will be more likely to be expressed, takes priority over recessive allele. Not more common though e.g. dwarfism is dom but rare.
Autosomal
Not carried on sex chromosomes. The other 22 pairs of chromosomes.
Autosomal Recessive
Not carried on sex chromosomes, only occurs when you have 2 copies of recessive allele.
Heterozygous Advantage
Disease causing alleles which in heterozygous state give selective advantage. e.g. sickle cell anaemia allows resistance to malaria + CF carriers have resistance to typhoid.
Codominance
When both alleles are expressed and neither dominates the other. e.g. when red + white flowers bred, pink flowers produced. Uppercase letter used for both alleles. Smaller letter beside it indicates allele type. e.g. RR + WW. Can have partial dominance.
Sickle Cell Anaemia
Caused by mutation altering haemoglobin structure. Faulty gene recessive + in homo rec, when o2 partial pressures low in tissues, haemo less soluble + forms crystals in cell, resulting in sickle shaped cells which can stick in narrow blood vessels causing blockage + o2 starvation. Results in early death (anaemia as lots of RBCs destroyed). Most common in Africans where malaria incidence high. If hetero, gen health good as only 40% haemo affected. Suffer mild anaemia normally but have malaria resistance.. More common in malarial places.
Lethal Allele Combinations
Abnormal ratios in offspring. e.g. sickle cell anaemia combo of 2 recessive alleles lethal. If breed 2 yellow mice, don’t get all yellow offspring. Expected ratio is 3:1 but in reality, doesn’t happen. In yellow pairs, female has dead embryos in uterus whilst if yellow + grey, few if any found. All yellow mice hetero + carry grey allele.
Dihybrid Inheritance
Inheritance of 2 characteristics. When genes on sep chromosomes, they’re unlinked.
Mendel’s Law of Independent Assortment
Each member of an allelic pair may combine randomly with either of another pair.
Multiple Alleles
Genes have more than 2 alleles that can occupy the gene locus on a pair of homologous chromosomes at any one time in any individual.