Interactive multiple-choice quiz: الدرس الأول في الأحياء Mendelian Genetics
This quiz covers the foundational experiments in Mendelian Genetics. It focuses on the characteristics of pea plants that made them ideal for Gregor Mendel's research. Understanding true-breeding traits is a key concept in genetic inheritance.
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اختبار شهادة تدريبي مؤقت للصف والمادة والفصل نفسه.
اختر إجابة واحدة لكل سؤال. عند الاختيار ستظهر النتيجة فورًا: الأخضر صحيح، والأحمر خطأ، وسيظهر تفسير الإجابة مباشرة إن كان متوفرًا. وبعد آخر سؤال ستظهر الدرجة النهائية تلقائيًا.
Why did Mendel choose pea plants for his experiments?
Explanation
Mendel chose pea plants because they have true-breeding varieties, which means they consistently produce offspring with the same traits over many generations, allowing for precise experimental control.
Question 2
Points: 10
Mendel observed 6,022 yellow seeds and 2,001 green seeds in the F2 generation. What is the approximate phenotypic ratio of yellow to green seeds?
Explanation
The counts 6,022 and 2,001 are approximately in a 3:1 ratio.
Question 3
Points: 10
The anthers are removed from one pea flower before pollen from another plant is applied. Which process is being performed?
Explanation
Removing the anthers prevents self-fertilization, and applying pollen from another plant produces cross-pollination.
Question 4
Points: 10
Which of the following is a phenotype?
Explanation
A phenotype is an observable characteristic, such as yellow seed color.
Question 5
Points: 10
Two heterozygous yellow-seed pea plants (Yy × Yy) are crossed. What is the expected genotypic ratio of the offspring?
Explanation
The genotypes occur as 1 YY : 2 Yy : 1 yy.
Question 6
Points: 10
Which statement is true for all heterozygous pea plants?
Explanation
A heterozygous individual carries two different alleles, either of which can enter a gamete.
Question 7
Points: 10
According to Mendel's law of independent assortment, which statement is correct?
Explanation
Allele pairs for genes on different chromosomes assort independently during gamete formation.
Question 8
Points: 10
All F1 offspring display the dominant trait even though they carry a recessive allele. Which type of inheritance does this represent?
Explanation
In complete dominance, one dominant allele is sufficient to determine the heterozygote's phenotype.
Question 9
Points: 10
A true-breeding purple-flowered pea plant (PP) is crossed with a true-breeding white-flowered plant (pp). What genotype will all F1 offspring have, and why will their flowers be purple?
Explanation
Each offspring receives P from one parent and p from the other, so all are Pp and show the dominant purple phenotype.
Question 10
Points: 10
Which term is another name for true-breeding?
Explanation
A true-breeding organism is homozygous for the trait being studied.
Question 11
Points: 10
A plant carrying one allele for tall stems and one for short stems is crossed with a pure-breeding short plant. The offspring are evenly divided between tall and short plants. Which genotypes represent the parents?
Explanation
The test cross Tt × tt produces 1/2 Tt tall plants and 1/2 tt short plants.
Question 12
Points: 10
The term phenotype refers to an organism's:
Explanation
Phenotype means the observable traits or physical appearance of an organism.
Question 13
Points: 10
In a dihybrid cross between two heterozygous pea plants (GgYy × GgYy), what phenotypic ratio is expected when the genes assort independently and show complete dominance?
Explanation
A standard heterozygous dihybrid cross with independent assortment gives a 9:3:3:1 phenotypic ratio.
Question 14
Points: 10
Which statement best describes Mendel's law of segregation?
Explanation
The law of segregation states that the two alleles of a gene separate when gametes form.
Question 15
Points: 10
True-breeding yellow-seed pea plants (YY) are crossed with true-breeding green-seed plants (yy). What is the genotype of every F1 offspring?
Explanation
Every offspring receives Y from the yellow parent and y from the green parent, producing Yy.
Question 16
Points: 10
In a monohybrid cross of heterozygous plants (Yy × Yy), what proportion of the offspring is expected to be homozygous dominant?
Explanation
The genotypic ratio is 1 YY : 2 Yy : 1 yy, so 1/4 is homozygous dominant.
Question 17
Points: 10
In Mendel's controlled crosses, what was true of the P-generation plants for the trait being studied?
Explanation
Mendel began his controlled crosses with true-breeding, homozygous parental plants.
Question 18
Points: 10
Which principle states that allele pairs separate during gamete formation so that each gamete carries only one allele for each gene?
Explanation
This separation of allele pairs is Mendel's law of segregation.
Question 19
Points: 10
In the dihybrid cross YyRr × YyRr, what proportion of offspring is expected to be homozygous at both gene loci?
Explanation
At each locus, the probability of being homozygous is 1/2. Thus, 1/2 × 1/2 = 1/4 are homozygous at both loci.
Question 20
Points: 10
A plant produces the gametes YR, Yr, yR, and yr in equal frequencies. What does this demonstrate?
Explanation
Equal production of all four allele combinations demonstrates independent assortment of the two genes.
Question 21
Points: 10
Why did Mendel remove the male organs from flowers during controlled cross-pollination?
Explanation
Removing the anthers prevents the flower from fertilizing itself.
Question 22
Points: 10
True-breeding plants are:
Explanation
True-breeding plants carry identical alleles for the studied trait and are therefore homozygous.
Question 23
Points: 10
Why were pea plants well suited to Mendel's experiments?
Explanation
All three characteristics helped Mendel obtain and interpret reliable inheritance data.
Question 24
Points: 10
If Mendel's F1 yellow-seed plants (Yy) are crossed with green-seed plants (yy), what phenotypic ratio is expected?
Explanation
The cross Yy × yy produces 1/2 Yy yellow and 1/2 yy green offspring.
Question 25
Points: 10
In a Punnett square for the trihybrid cross AaBbCc × AaBbCc, how many squares are required?
Explanation
Each parent makes 23 = 8 gamete types, so the Punnett square has 8 × 8 = 64 cells.
Question 26
Points: 10
A plant has the genotype YyRr. If the genes assort independently, how many different gamete types can it produce?
Explanation
The possible gametes are YR, Yr, yR, and yr, for a total of four.
Question 27
Points: 10
Which genotypic ratio describes the nine genotype classes produced by the dihybrid cross YyRr × YyRr?
Explanation
Combining the 1:2:1 genotype ratio at each gene locus produces 1:2:1:2:4:2:1:2:1 across the nine genotype classes.
Question 28
Points: 10
Which design choice allowed Mendel to begin his crosses with known, consistent alleles for each studied trait?
Explanation
True-breeding parents consistently pass the same allele and therefore establish known starting genotypes.
Question 29
Points: 10
Mendel crossed true-breeding white-flowered and purple-flowered pea plants to study one trait. What type of cross was this?
Explanation
A cross that follows the inheritance of one contrasting trait is a monohybrid cross.
Question 30
Points: 10
Black fur (B) is dominant over white fur (b) in hamsters. What phenotypic ratio results from crossing a black hamster (Bb) with a white hamster (bb)?
Explanation
The cross Bb × bb produces equal numbers of Bb black and bb white offspring.
Question 31
Points: 10
In garden plants, purple flowers (P) are dominant over white flowers (p), and tall plants (T) are dominant over short plants (t). What phenotypic ratio is expected from PpTt × pptt?
Explanation
The heterozygous parent produces PT, Pt, pT, and pt gametes equally, whereas pptt produces only pt, giving a 1:1:1:1 ratio.
Question 32
Points: 10
Which statement best summarizes Gregor Mendel's contribution to genetics?
Explanation
Mendel's pea-plant experiments led him to propose discrete inherited factors, now called genes.
Question 33
Points: 10
Mendel transferred pollen from a tall pea plant to the flower of a short pea plant. Why did he first remove the male parts from the short plant's flower?
Explanation
Removing the male parts prevents self-pollination and ensures that fertilization uses pollen from the selected tall plant.
Question 34
Points: 10
A pure-bred tall pea plant (TT) is crossed with a pure-bred short pea plant (tt). If tallness is dominant, what is the genotype of all offspring?
Explanation
Every offspring receives T from the tall parent and t from the short parent, so all are Tt.
Question 35
Points: 10
Green seed color (y) is recessive to yellow seed color (Y). If both parents are hybrids (Yy × Yy), what percentage of their offspring is expected to have green seeds?
Explanation
One of the four expected genotypes is yy, so 25% of the offspring are expected to have green seeds.
Question 36
Points: 10
A white mouse from a true-breeding white line produces only brown offspring when crossed with a true-breeding brown mouse. What is the most likely genotype type of the white-fur trait?
Explanation
If every F1 offspring is brown, brown is dominant and the true-breeding white parent must be homozygous recessive.
Question 37
Points: 10
What is an allele?
Explanation
An allele is one of the alternative forms of a gene.
Question 38
Points: 10
A curled-ear cat is crossed with a non-curled-ear cat, and all F1 kittens have non-curled ears. Interbreeding the F1 cats produces a ratio of 3 non-curled : 1 curled. What can be concluded about the curled-ear trait?
Explanation
The trait that disappears in F1 and reappears in one-quarter of F2 is recessive.
Question 39
Points: 10
Which term describes an organism that carries two different alleles for a gene?
Explanation
A hybrid is heterozygous and carries two different alleles for a gene.
Question 40
Points: 10
Which process can generate new allele combinations between linked genes?
Explanation
Crossing over exchanges DNA between homologous chromosomes and can create new allele combinations among linked genes.
Question 41
Points: 10
The figure illustrates independent assortment during gamete formation in a YyRr individual. Which option correctly identifies the allele combinations labeled (1) and (2)?
Explanation
The four gametes are YR, Yr, yR, and yr. In the figure, label (1) is YR and label (2) is yR.
Question 42
Points: 10
In which situation are F2 offspring expected to show a 9:3:3:1 phenotypic ratio?
Explanation
The classic 9:3:3:1 ratio arises from a heterozygous dihybrid cross when the genes assort independently.
Question 43
Points: 10
In snapdragons, flower color shows incomplete dominance. A white-flowered plant (CwCw) is crossed with a pink-flowered plant (CrCw). What phenotypic ratio is expected?
Explanation
The white parent produces only Cw gametes, while the pink parent produces Cr and Cw gametes equally, yielding 50% pink and 50% white offspring.
Question 44
Points: 10
In the dihybrid cross YyRr × YyRr, yellow (Y) and round (R) are dominant. What fraction of the F2 offspring is expected to have yellow, round seeds?
Explanation
The probability of the dominant phenotype at each locus is 3/4, so 3/4 × 3/4 = 9/16.
Question 45
Points: 10
A YyRr individual produces four equally likely gametes: YR, Yr, yR, and yr. Which principle explains this result?
Explanation
Independent assortment allows the alleles of the two genes to combine independently in gametes.
Question 46
Points: 10
The figure shows a dihybrid Punnett square. Which genotype corresponds to the box labeled (A)?
Explanation
The gametes that intersect at box A contribute Y and y at the first locus and R and r at the second, producing YyRr.
Question 47
Points: 10
The figure shows a dihybrid Punnett square. Which genotype corresponds to the box labeled (A)?
Explanation
Box A is at the intersection of yr and yr gametes, so its genotype is yyrr.
Question 48
Points: 10
In chickens, rose comb (R) is dominant over single comb (r). A homozygous rose-comb chicken (RR) is crossed with a homozygous single-comb chicken (rr), producing F1 chickens with genotype Rr. When the F1 chickens are interbred, what F2 phenotypic ratio is expected?
Explanation
The cross Rr × Rr produces a 3:1 phenotypic ratio, or 75% rose comb and 25% single comb.
Question 49
Points: 10
In mink, brown fur (B) is dominant over silver-blue fur (b). A homozygous brown mink (BB) is crossed with a silver-blue mink (bb). If they produce eight offspring, how many are expected to have silver-blue fur?
Explanation
All offspring are Bb and have brown fur, so none is expected to have silver-blue fur.
Question 50
Points: 10
A family has five boys and no girls. What is the probability that the sixth child will be a girl?
Explanation
Each birth is an independent event, so the probability that the next child is a girl remains 1/2.
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