Inheritance Flashcards
Definition of an allele
Alternate forms of a gene
Definition of a gene: unit of inheritance
Also sequence of nucleotides where its sequence of bases contains the information that controls the synthesis of a polypeptide
Definition of dominant
Allele trait that is fully expressed in phenotype under both homozygous and heterozygous type conditions
Definition of recessive
Allele trait that is only expressed in phenotype under homozygous genotype conditions
Definition of codominant
Allele that contributes equally to the phenotype (red and white, not pink in Camellia flowers, C^w C^r)
Definition of homozygous
Both alleles are identical for the trait
Definition of heterozygous
Two different alleles for one trait (one dominant one recessive, or two codominant)
Definition of phenotype
Physical/observable characteristics of an organism (descriptors)
Definition of genotype
Genetic makeup of an organism (letters)
List the components of a genetic diagram
Key Parent phenotype Parent genotype Gamates Random fertilisation Offspring genotype Offspring phenotype Phenotypic ratio
Why is the observed and expected ratio different
Small sample size and random fertilisation causes differences between the expected ratios
How to use a test cross and interpret its results
Crossing target organism with a homozygous recessive organism
Homozygous: always dominant offspring, dominant homozygous. Always recessive offspring, recessive homozygous.
Heterozygous: sometimes dominant sometimes not
What does autosomal mean
Chromosomes that do not determine one’s sex (not the 23rd pair)
List sex determination contents
Key (let x represent the X chromosome, let y represent the Y chromosome) Parent phenotype Parent genotype Gamates Random fertilisation Offspring genotype Offspring phenotype Phenotypic ratio
What are X-linked disorders
Found in the X sex chromosome. Since females have 2, disorder must be dominant/homozygous recessive to show. For males with 1, no carriers: yes or no.
Examples of X-linked disorders
Red-green colour blindness, Duchenne muscle dystrophy (progressive muscle weakening, loss of coordination, absence of key muscle protein dystrophin), haemophilia (blood clotting absent)
^^ all are recessive
Definition of mutation and their causes
Changes in gene sequence or chromosomal structure of a gene
Caused by chemicals or radiation
Increases genetic variation by increasing number of alleles per gene
Sickle cell anemia and Down syndrome
Mutation in the haemoglobin gene’s base sequence, cause mutant haemoglobin protein synthesis, lower o2 carrying capacity, forms sickle-shaped cells
Mutation during meiosis, zygote inherited 3 copies (trisomy) of chromosome 21 instead of 2 (mental retardation, heart and respiratory defects)
Definition of variation
Differences in physical traits in individuals of the same species. Genetic variation inheritable, environmental conditions affect but not hereditary
Continuous and discontinuous variation
Continuous: no distinct groups (height, weight), controlled by environment, histogram used
Discontinuous: distinct groups (hair and eye colour), controlled by a few genes, uninfluenced by environment
Definitions of: allele, dominant, recessive, codominant, homozygous, heterozygous, phenotype, genotype
Allele: alternate forms of a gene
Dominant: allele trait fully expressed under both homozygous and heterozygous type conditions
Recessive: allele trait only expressed under homozygous conditions
Codominant: allele that contributes equally to the phenotype
Homozygous: both alleles are identical for the trait
Heterozygous: two alleles for one trait
Phenotype: physical/observable characteristics of an organism (adjectives)
Genotype: genetic makeup of an organism (letters)
