chapter 7: genotypes and phenotypes Flashcards
define genotype
a genotype is the combination of alleles an organism possesses for a specific gene
difference between homozygous and heterozygous genotypes
- individuals with 2 of the same allele are homozygous (homozygous dominant or homozygous recessive)
- individuals with 2 different alleles are heterozygous → carriers
write genotypes with only two alleles
- same letter used for both alleles
- dominant trait - capital
- recessive trait - lowercase
- eg dimples: present (D), absent (d)
- possible genotypes: DD, Dd, dd
- possible phenotypes: dimples, dimples, no dimples
write genotypes with multiple alleles
- for genes w multiple alleles, different letters are assigned to each
- all of the alleles have the same letter used, but have different superscripts for the diff alleles
- eg. I$^A$, I^B
write genotypes for sex-linked genes
sex-linked traits are represented with a CAPITAL X and a superscript letter representing the allele
eg. X^R → normal vision, X^r→ colour blind
- ALLELE IS ON X CHROMOSOME
define phenotype
are the physical expression of the genes an organism possesses for a specific trait
expression of dominant and recessive phenotypes and use genotypes to show this
expression of phenotype:
- dominant allele is always expressed when present
genotypes:
- uses one letter for both alleles
- dominant allele is a capital letter
- the recessive allele is a lowercase letter
describe the expression of codominant phenotypes and use genotypes to show this
PHENOTYPIC EXPRESSION:
- codominance occurs when alleles are both FULLY expressed, eg both green and purple petals
GENOTYPE
- the same capital letter is used to represent the genes eg. H- for hair type
- the alleles are shown as a superscript letter eg. H$^S$ for straight hair and H$^C$ for curly hair
- eg. I$^A$I$^B$- BLOOD TYPE AB
describe the expression of incompletely dominant phenotypes and use genotypes to show this
- occurs when alleles ARE EXPRESSED TOGETHER, WHEN THEY BLEND, eg red+white → pink
- eg. H$^S$H$^C$ → WAVY HAIR
explain the influence of the environment on phenotypes, using specific examples
environmental factors can be internal or external and can act on an organism so its final phenotype is due to varying contributions of genotype and environment
- hydrangeas:
- acidic pH soil→ bright blue hydrangeas
- basic pH soil→ pink/red hydrangeas
- PKU (phenylketonuria)
- genotype pp + low PHE diet → normal phenotype
- genotype pp _ high PHE diet → PKU phenotype
- cats + temperature
- siameses kitten born all white, develop pigmentation caused by a gene that code for production of tyrosinase that is heat sensitive
- tyrisinase produces pigment when temperature is lower than core body temp of kitten
- pigmentation appears on coolest parts
describe epigenetic inheritance
- the expression of your genes change during your lifetime
- epigenetics changes causes changes to your genes WITHOUT changing the code
- epigenetics literally mean above genetics
- the study of how cells with identical genotypes can show different phenotypes.
- once established, epigenetic tags remain for the life of a cell and are transmitted to all daughter cells
- they are not usually passed on to the next generation as typically the DNA of a fertilised egg is cleared of the epigenetic tags
- in some cases, the epigenetic tags on the DNA are not erased but are conserved and passed to the next generation
identify factors that cause epigenetic change
- packaging of DNA
- DNA that is tightly packed will cause genes to be silenced
- if DNA is loosened, genes can become active
- DNA can be loosened because of stress
- labelling DNA
- adding an epigenetic tag that doesn’t alter the base sequence of genes
- these tags are chemicals (methyl groups) and can silence genes or make them active
- methyl groupsare one example of an epigenetic tag
- the addition of methyl groups is calledmethylation and active genes are found to have fewer methyl groups than inactive genes
- so tagging genes with methyl groups to their C–G bases can permanently switch those genes ‘off’
stress, disease, parental care can also cause epigenetic changes
examples of the importance of epigenetics
- used for cell differentiation
- during the embryonic stage, different genes are switched on or off in different cells
- epigenetic factors can start stem cells down different developmental paths
what is epigenetics
study of how your behaviors and environment can cause changes to the way your genes work
