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Earth Science 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 11 -:- Life Science 1 - 2 - 3 - 3b - 4 - 4b - 5 - 6 - 7 - 8 - 9 - 10 - 11 - 12 -:- Physical Science 3
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Life Science Chapter 5
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 “hides” 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 can’t 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 aren’t
in the very next generation, they are still a part of that generation’s 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 offspring’s genotype.
·
An organism’s outward display
of its genes is called its phenotype.
For example, if a pea plant’s 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 father’s sex cell combines with the mother’s to produce
the 46 total chromosomes in the offspring.
·
A father’s sex cell is a
sperm. A mother’s is an egg, or ova.
·
Genes are located on
chromosomes. That’s 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.