Ch.9 Patterns of inheritance
Blending- Hereditary material- Both parents contribute genetic material.
Inheritable factors, genes are passed from generation to generation
Pea experimentsWorked with 7 traitsUsed purebreeding plants first then crossed them.
Know the vocabularyHomozygous- TT or tt - the same versionHeterozygous- Tt- two different versionsPhenotype - What you see ( look like)Genotype - The genes TT,Tt, or tt
Mendels Pea Crosses
Law of independent assortment.
homologous chromosomes move independently.Ex. Chromosome with A or a will go separate from chromosome with B or b.
Law of SegregationHomologous pairs segregate during gamete formation(meiosis) and pair again after fertilizationEx. If a pea is Pp then half the gametes will receive a P and half a p.
Incomplete dominanceIncomplete dominance leads to a blending of traits, red + white yields pink
CodominanceCodominance - A and B are both dominant to O but not to each other, giving the AB blood type
EpistasisOne gene has an effect on another. C leads to deposition of color while B or b leads to color BBcc would be white even though the genes code for black color.
Polygenic inheritanceCombinations of genes can yield cumulative effects. The more dominant alleles the more color.
Environmental EffectsSometimes the environment can change the way a gene is expressed, like these hydrangia, and the color based on pH of the soil.
PleiotropyOne gene can have an effect on other parts of the body. The sickle cell gene which causes problems with blood cells has far reaching affects on the body.
Sample problemsMendel crossed short and tall pea plants(purebred cross) TT x tt = P gen. t tT Tt Tt All offspring are heterozygousT Tt Tt All are tall (Tt)
Mendel crossed round, yellow pea plants to wrinkled, green pea plants (RRYY x rryy) The only possible gametes are RY from parent 1 and ry from parent 2 so ry ryRY RrYyRrYy All offspring are roundRY RrYy RrYy and yellow (RrYy)
Monohybrid Cross -two heterozygotes matedTt xTt T tT TT Tt 1TT:2Tt:1ttt Tt tt 3 tall: 1 short
Dihybrid crossHeterozygotes for 2 traits are crossed RrYy x RrYyYou can make the folowing gametes for each parent RY,Ry,rY,ry, this means a four by four box as in the next slide
Dihybrid crosses can also be done like this; R r Y yR RR Rr Y YY Yyr Rr rr y Yy yy
Now calculate the chances of RRYY (1/4 x 1/4)RRYy (1/4 x2/4) RrYY (2/4 x 1/4)RRyy (1/4 x 1/4) RrYy ( 2/4 x 2/4)Rryy (2/4 x 1/4) rrYY (1/4 x/1/4)rrYy (1/4 x 2/4) rryy (1/4 x 1/4)