A chemical molecule that carries hereditary information
Explication
DNA is the molecule that carries hereditary information inside cells. Chromosomes are made from condensed DNA, so they are not the same thing as DNA itself.
Segments of DNA that contain instructions for inherited traits
Explication
Genes are specific DNA segments that carry instructions for inherited traits. Chromosomes contain genes, but genes are the units that help determine characteristics.
23 pairs of chromosomes
Explication
Human cells have 23 pairs of chromosomes, which makes 46 chromosomes in total. The option with 23 chromosomes is incomplete.
39 pairs of chromosomes
Explication
Dogs are given as having 39 chromosome pairs. This shows that chromosome number differs between species.
XX
Explication
The source associates XX with a female and XY with a male. XX is the correct sex-chromosome pair for a woman in this material.
Pair 21 has three chromosomes instead of two
Explication
Trisomy 21 means there are three chromosomes in pair 21 instead of the usual two. It is a genetic condition linked to chromosome information.
The transmission of genetic characteristics from parents to children
Explication
Inheritance is the passing of genetic characteristics from parents to children. A mutation is different because it changes DNA rather than describing transmission.
Half from the mother and half from the father
Explication
The source states that a child receives half of their chromosomes from the mother and half from the father. This explains why children resemble their parents but are not identical.
Different versions of the same gene
Explication
Alleles are different versions of the same gene. They are the reason one trait can have multiple forms, such as different eye-color or blood-group versions.
A, B, and O
Explication
The source gives A, B, and O as blood-group alleles. These are examples of different versions of one gene.
With only one copy present in the genotype
Explication
A dominant allele is expressed with just one copy. In contrast, a recessive allele needs two copies to show its effect.
M is dominant over B, so M+B gives M
Explication
The source states that the brown allele M is dominant over the blue allele B, so M+B gives M. Blue appears only when two blue alleles are present.
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DNA — definition?
Genetic material carrying hereditary info.
Chromosomes — role?
Contain DNA and genes inside the nucleus.
Genes — function?
Determine inherited traits.
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