- Define inheritance as the transmission of genetic information from generation to generation.
I feel like this point is pretty self-explanatory!
- Define the terms:
- Chromosome as a thread of DNA, made up of a string of genes
- Gene as a length of DNA that is a unit of heredity and codes for a specific protein; a gene may be copied and passed on to the next generation
- Allele as any of two or more alternative forms of a gene.
Again, the definitions are all there 😊 All you have to do is learn them.
- Define the terms:
- Haploid nucleus as a nucleus containing a single set of unpaired chromosomes (e.g. sperm and egg)
- Diploid nucleus as a nucleus containing two sets of chromosomes (e.g. in body cells).
Yet another self-explanatory point.
- Describe the inheritance of sex in humans (XX and XY chromosomes).
Sex gametes in humans (i.e. the sperm and egg) are formed through meiosis – a type of cell division in which a diploid parent cell divides into haploid daughter cells. (Cell division is covered in the next section).
This means each sex gamete has only one set of chromosomes.
There are two types of sex chromosomes in humans – the X chromosome and the Y chromosome.
Also, females have two X chromosomes in each diploid cell, so they are XX and males have one X and one Y chromosome, so they are XY.
This means that when eggs (the female gamete) are formed, the only sex chromosome they can have is X, so all eggs have the X chromosome.
When sperm are formed, however, they have a 50/50 chance of getting either the X chromosome or the Y chromosome.
In other words, half of the produced sperm will have an X chromosome and the other half will have a Y chromosome.
So, it is equally likely that a sperm with an X chromosome and a sperm with a Y chromosome will fertilise the egg, so the chances of the zygote being male or female are equal.
Notes submitted by Sarah.
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