CAN YOU PLEASE HELP ME UNDERSTAND HOW YOU GET THE NONRECOMBINANT AND RECOMBINANT

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CAN YOU PLEASE HELP ME UNDERSTAND HOW YOU GET THE NONRECOMBINANT AND RECOMBINANT PROGENY? THANK YOU

180 CHAPTER 7 When crossing over takes place between the genes for (a) leaf type and height, two of the four gametes produced are recombinants. When there is no crossing over, all four resulting gametes are nonrecombinants. Because each crossover produces half recombinant gametes and half nonrecombinant gametes, the majority of gametes produced by the heterozygous parent will be nonrecom- binants (Figure 7.6a gametes produced by the homozygous recessive par ent, which contain only the recessive alleles, resulting in mostly nonrecombinant progeny and a few recombinant progeny (Figure 7.6b). In this testcross, we see that 55 of the progeny have normal leaves and are tall and that 5 have mottled leaves and are dwarf. These plants are t nonrecombinant progeny, containing the original com binations of traits that were present i the 123 progeny, 15 have new combinations of traits that recombinationGamete were not seen in the parents: 8 have normal leaves and are dwarf, and 7 have mottled leaves and are tall. These plants are the recombinant progeny Mottled leaves, dwarf eaves, tall ese gametes then unite with ob Meioses with and without crossing over together resultm d in less than 50% rn on average formation formation No crossing ssin over The results of a cross such as the one illustratedin Figure 7.6 reveal several things. A testcross for two independently assorting genes is expected to produce a 1 : 1: 1: 1 pheno- typic ratio in the progeny. The progeny of this cross clearly do not exhibit such a ratio, so we might suspect that the genes are not assorting independently. When linked genes undergo some crossing over, the result is mostly nonrecombinant progeny and a few recombinant progeny. This result is what we observe Figure 7.6, so we conclude that the two genes show evidence of linkage with some crossing over Nonrecombinant Nonrecombinant Recombinant gametes (100%) gametes(50%) garmetes (50%) Fertilization 18 among the progeny of the testcross illustrated in Normal Mottled NormalMottled Calculating Recombination Frequency leaves, tal leaves, dwar leaves, dwarf leaves The percentage of recombinant progeny produced in a cross is called the recombination frequency (or rate of recombina tion), which is calculated as follows: recombination frequency- number of recombinant progeny total number of progeny x 100% In the testcross shown in Figure 7.6, 15 progeny exhibit new combinations of traits, so the recombination frequency is 15 number x 100% x 100% = 12.2% Recombinant Nonrecombinant progeny 55 + 53 +8 +7 Thus, 12.2% of the progeny exhibit new combinations of traits resulting from crossing over. The recombination fre- quency can also be expressed as a decimal fraction (0.122). over r, nonrecombinant progeny predominate. 7.6 Crossing over between linked genes produces nonrecombinant and recombinant offspring. In this testcross genes are linked, and there is some crossing over THINK-PAIR-SHARE Question 2 aoriqnal Combinokons

Explanation / Answer

In the above figure, a cross between heterozygous plant and homozygous recessive plant produces multiple offsprings. During meiosis, if crossing over takes place then both recombinant and nonrecombinant gametes appear. If there is no crossing over then only nonrecombinant gamete appears.

In figure below, the cross over products are test crossed with its homozygous recessive parent.The cross over gametes are MD, mD, Md, md. If they are crossed with md then the offsprings would be

1. MD
. ----- . ( nonrecombinant, exhibits parental properties)

. md

. md
2. ----- (non recombinant)

. md

3. mD
----- ( recombinant)

. md

4.
Md
----- (recombinant

md

That is how to get the recombinant and nonrecombinant genone.

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