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Life Science Chapter 5 - Summary Notes
The main idea of this chapter is that sex cells contain half the genome of a parent.† They combine to form a complete genome for the child.† 23 pairs of chromosomes carry all the genes that code for all our physical characteristics.† A gene can have an unexpressed recessive allele that ďhidesĒ itself until a future generation.
∑ Heredity is the passing of traits from parents to offspring.
∑ Traits do not always pass straight to the next generation.† For example, if one parent is tall and another is short, the offspring canít be both tall and short at the same time.
∑ There are dominant traits and recessive traits.† Dominant traits are displayed in the next generation, but recessive traits are hidden by dominant traits.
∑ Recessive traits can show up in future generations.† Even if they arenít in the very next generation, they are still a part of that generationís genes.
∑ Each parent donates an allele to the offspring.† A gene has two alleles.
∑ The exact two alleles an offspring inherits from its parents are the offspringís genotype.
∑ An organismís outward display of its genes is called its phenotype.† For example, if a pea plantís genotype includes a tall allele and a short allele, its phenotype will be tall.† The plant will be tall.
∑ People have 23 pairs of chromosomes, or 46 total chromosomes, in each cell.† Sex cells are the only exception.† They have half as many chromosomes because a fatherís sex cell combines with the motherís to produce the 46 total chromosomes in the offspring.
∑ A fatherís sex cell is a sperm.† A motherís is an egg, or ova.
∑ Genes are located on chromosomes.† Thatís how traits are passed on!
∑ Sex chromosomes determine whether a child turns out male or female.† Two X alleles make a girl, and an X allele and Y allele make a boy.