monohybrid cross full explaination
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Explanation:
A monohybrid cross is a genetic mix between two individuals who have homozygous genotypes, or genotypes that have completely dominant or completely recessive alleles, which result in opposite phenotypes for a certain genetic traitmonohybrid cross is a cross between two organisms with different variations at one genetic chromosome of interest.[1][2] The character(s) being studied in a monohybrid cross are governed by two or multiple variations for a single locus. To carry out such a cross, each parent is chosen to be homozygous or true breeding for a given trait (locus). When a cross satisfies the conditions for a monohybrid cross, it is usually detected by a characteristic distribution of second-generation (F2) offspring that is sometimes called the monohybrid ratio.
Figure 1: Inheritance pattern of dominant (red) and recessive (white) phenotypes when each parent (1) is homozygous for either the dominant or recessive trait. All members of the F1 generation are heterozygous and share the same dominant phenotype (2), while the F2 generation exhibits a 6:2 ratio of dominant to recessive phenotypes (3).
Generally, the monohybrid cross is used to determine the dominance relationship between two alleles. The cross begins with the parental generation. One parent is homozygous for one allele, and the other parent is homozygous for the other allele. The offspring make up the first filial (F1) generation. Every member of the F1 generation is heterozygous and the phenotype of the F1 generation expresses the dominant trait.[3] Crossing two members of the F1 generation produces the second filial (F2) generation. Probability theory predicts that three quarters of the F2 generation will have the dominant allele's phenotype. And the remaining quarter of the F2s will have the recessive allele's phenotype. This predicted 3:1 phenotypic ratio assumes Mendelian inheritance.
1822–1884) was an Austrian monk who theorized basic rules of inheritance.[4] From 1858 to 1866, he bred garden peas (Pisum sativum) in his monastery garden and analyzed the offspring of these matings. The garden pea was chosen as an experimental organism because many varieties were available that bred true for qualitative traits and their pollination could be manipulated. The seven variable characteristics Mendel investigated in pea plants were. [5]
seed texture (round vs wrinkled)
seed color (yellow vs green)
flower color (white vs purple)
growth habit (tall vs dwarf)
pod shape (pinched or inflated)
pod color (green vs yellow)
flower position (axial or terminal)
.[6] Peas are normally self-pollinated because the stamens and carpels are enclosed within the petals. By removing the stamens from unripe flowers, Mendel could brush pollen from another variety on the carpels when they ripened.[7]
the peas produced in the second or hybrid generation were round.
All the peas of this F1 generation have an Rr genotype. All the haploid sperm and eggs produced by meiosis received one chromosome 7. All the zygotes received one R allele (from the round seed parent) and one r allele (from the wrinkled seed parent). Because the R allele is dominant to the r allele, the phenotype of all the seeds was round. The phenotypic ratio in this case of Monohybrid cross is 1:1:1:1.
P gametes
(round parent)
R R
P gametes
(wrinkled parent)
r Rr Rr
r Rr Rr
Second cross Edit
Mendel then allowed his hybrid peas to self-pollinate. The wrinkled trait—which did not appear in his hybrid generation—reappeared in 25% of the new crop of peas.
Random union of equal numbers of R and r gametes produced an F2 generation with 25% RR and 50% Rr—both with the round phenotype—and 25% rr with the wrinkled phenotype.
F1 gametes
R r
F1 gametes R RR Rr
r Rr rr
Third cross Edit
Mendel then allowed some of each phenotype in the F2 generation to self-pollinate. His results:
All the wrinkled seeds in the F2 generation produced only wrinkled seeds in the F3.
One-third (
Round Wrinkled
45 12
27 8
24 7
19 16
32 11
26 6
88 24
22 10
28 6
25 7
Total: 336 Total: 107 ml
explain his results, Mendel formulated a hypothesis that included the following: In the organism there is a pair of factors that controls the appearance of a given characteristic. (They are called genes.) The organism inherits these factors from its parents, one from each. A factor is transmitted from generation to generation as a discrete, unchanging unit. (The r factor in the F2 generation passed through the round-seeded F1 generation. In spite of this, the rr seeds in the F2 generation were no less wrinkled than those in the P generation.) When the gametes are formed, the factors separate and are distributed as units to each gamete. This statement is often called Mendel's rule of segregation. If an organism has two unlike factors (called alleles) for a characteristic, one may be expressed to the total exclusion of the other (dominant vs recessive).
Test of the hypothesis Edit
A good hypothesis meets several standards.
It
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