inheritance 💸 Flashcards
define genes
genes are a unit of inheritance with a specific sequence of nucleotides, as part of a DNA molecule that codes for a polypeptide
define allele
allele is one of two or more different forms of a gene
define a dominant allele
allele that can always be expressed in the phenotype, when it occurs in the homozygous or heterozygous condition
define a recessive allele
allele that is only expressed in the phenotype when it occurs in the homozygous condition
define homozygous
organism having two identical alleles of a particuler gene
define heterozygous
organism having two different alleles of a particular gene
define codominance
when both alleles have an equal effect on the phenotype of the offspring (equally dominant)
define genotype
the genetic makeup of an organism
define phenotype
an observable trait or physical appearance of an organism
order of genetic diagram drawing
1) key: let B represent dominant allele for.. , let b represent recessive allele for…
2) parental phenotype: A x B
3) parental genotype: A x B
4) gametes: O O O O
5) punnet square
6) offspring genotype: BB Bb Bb bb
7) offspring phenotype: A B
8) offspring phenotypic ratio: 3:1
why do the observed ratios differ from the expected ratios?
ratios are inaccurate for small sample size
describe a test cross
an individual with unknown genotype is crossed with one who is homozygous recessive, used to test whether individual is homozygous or heterozygous in the gene
- if all offspring show dominant, individual is homozygous dominant
- if offspring is mixed dominant recessive, individual is heterozygous
why is a homozygous individual used in a test cross
all of their gametes must contain the recessive allele of the gene, which will have no effect on the phenotype of the offspring
define multiple alleles
a gene that exists in more than two alleles
define mutation
mutation is a spontaneous or sudden change in the DNA sequence of genes, or chromosome structure or number.
what mutagens can increase the rate of mutation
1) radiation (ultraviolet, x-ray, gamma ray)
2) chemical mutagens (tar)
define variations and its causes
variations are the difference in traits between individuals of the same species, caused by genetic or environmental factors
compare continuous and discontinuous variation
phenotype: range of phenotypes vs range of phenotypes
affected by environment?: greatly vs unaffected
controlled by: many genes vs one of a few genes
data: quantitative, continuous range vs qualitative, discrete groups
describe the process of natural selection
1) spontaneous mutation leads to variation within the species
2) there is competition for finite resources (food, water, space etc)
3) state the aadvantageous characteristic
4) …which is best adapted to the environment, allowing them to survive till maturity.
5) they will have a higher chance of reproducing and passing down these desirable traits to the offspring
describe the process of artificial selection / selective breeding
1) the individuals showing the desired quality are selected (state the characteristics)
2) the individuals are used as breeding stoock
3) only the offspring showing the desired quality to the greatest extent are selected and used for breeding
