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Mendelian Genetics
Chapter 9
What you need to know!
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Terms associated with genetics
problems: P, F1, F2
Mendel’s laws of inheritance
Thank you Mendel
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Gregor Mendel was an
Austrian monk
In the 1860’s he made
incredible genetic
breakthroughs
He is considered the
father of modern
genetics
Mendel’s Work
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Mendel analyzed various
characteristics of peas
He studied the peas over
multiple generations
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P = parent generation
F1 = 1st generation of
offspring (children)
F2 = 2nd generation of
offspring (grandchildren)
Mendel’s Findings
1.
2.
There are alternative forms of genes
that account for variations in inherited
characteristics. (alleles)
For each characteristic, an organism
inherits two alleles, one from each
parent. These alleles may be the
same or different.
(homozygous/heterozygous)
Mendel’s Findings
3.
If the two alleles of an inherited pair
differ, then one determines the
organism’s appearance and is called
the dominant allele. (rule of
dominance)
Law of Segregation
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When we pass our genes to our
children, our alleles are segregated into
different gametes (egg/sperm)
A sperm or egg carries only 1 allele for
each inherited trait because allele pairs
segregate during meiosis
Law of Independent
Assortment
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Most genes are
independent (not
inherited together)
Genes are
determined randomly
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i.e. Dimples & Height,
Hair Line & Finger
Length
Gene Linking
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Certain genes are
connected (i.e. dark
hair with dark skin,
or Sex with
baldness)
Genes are more
likely to be linked if
they are close
together on the
same chromosome
Sex Linked Genes
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Sex linked genetic defects are
the most common type of defects
and are FAR more common in
males
Men do not have any backup
chromosomes for sex (only 1 X
and 1 Y)
So if there’s a problem on one,
men will develop that problem
(baldness, color blindness, etc.)
Sex Chromosomes
Example
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Baldness is sex linked:
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R normal hair (RR, Rr)
r baldness (rr)
Both R and r are found on the X chromosome
Female: XRXR = ?
XRXr = ?
XrXr = ?
Male:
XRY = ?
XrY = ?