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10 سوالات: ایم ڈی کیٹ حیاتیات، جوابات اور وضاحت کے ساتھ۔
In which phase of mitosis do the chromosomes line up at the equator of the cell?
درست جواب: Metaphase
In metaphase the chromosomes line up on the metaphase plate. In anaphase the sister chromatids separate.
Crossing over takes place during:
درست جواب: Prophase I of meiosis
Homologous chromosomes pair up in prophase I and exchange segments. This produces new combinations of alleles.
How many chromosomes are present in a normal human gamete?
درست جواب: 23
Human body cells have 46 chromosomes. Meiosis halves this, so each gamete has 23.
A cross between two heterozygous tall plants (Tt x Tt) gives tall and short offspring in the ratio:
درست جواب: 3 : 1
The offspring are TT, Tt, Tt and tt in the ratio 1:2:1. TT and Tt are tall, so tall to short is 3:1.
Which base pairs with adenine in DNA?
درست جواب: Thymine
In DNA, adenine pairs with thymine by two hydrogen bonds, and guanine pairs with cytosine by three. Uracil replaces thymine in RNA.
A test cross is used to find the genotype of an individual by crossing it with:
درست جواب: A homozygous recessive individual
Crossing with a homozygous recessive shows the unknown parent's alleles in the offspring. Any recessive offspring means the parent carries a recessive allele.
Down syndrome is caused by:
درست جواب: Trisomy of chromosome 21
Down syndrome results from three copies of chromosome 21, usually through non-disjunction in meiosis.
Which experiment demonstrated that DNA replication is semi-conservative?
درست جواب: Meselson and Stahl
Meselson and Stahl used heavy nitrogen to show that each new DNA molecule keeps one old strand and gets one new strand.
Haemophilia is inherited as:
درست جواب: An X-linked recessive trait
The gene is on the X chromosome. Males have one X, so one recessive allele is enough to show the disease, which is why it is more common in males.
The offspring of AaBb x AaBb (independent assortment, complete dominance) show a phenotypic ratio of:
درست جواب: 9 : 3 : 3 : 1
This is Mendel's dihybrid cross. The four phenotypes appear in the ratio 9:3:3:1.