Biology-Mr.Willets
Pedigree/Family Tree
In humans and certain other animals, we are interested in what genetic traits their ancestors had. A diagram showing our ancestral lines is called a pedigree or family tree.
In such a diagram, males are represented by squares and females by circles. A square and a circle joined by a horizontal line represents a marriage (or in animals, a mating). Squares and circles connected to this line represent offspring.
The squares and circles can be labeled with the names of the people if so desired. There are several methods that can be used to indicate what trait each person has. If you are doing phenotypes, you can fill in the shapes with different colors. If you are doing genotypes, clear can be pure recessive, colored in can be pure dominant and half colored in can be hybrid. With genotypes, it is often easier to just write the letters inside the shape. That is what you will do.
If a person's trait in the pedigree is not known, a question mark is usually written inside the shape.
Here is a sample pedigree showing 3 generations:
What are the relationships between:
1 and 5 ___________________________1 and 2____________________________
1 and 10 __________________________4 and 5 ____________________________
3 and 5 ___________________________5 and 8 ____________________________
8 and 10 __________________________1 and 3 ____________________________
The ability to taste the chemical PTC is controlled by a dominant gene. Non-tasters are pure recessive.
John and Emma Smith had three children: Bill, Sue and Tom. Ed
and Jill Jones had two children: Mary and Richard. Tom Smith married
Mary Jones and they have 3 children Bob, Tim and Tina
John is a taster, Emma is not. Bill is a non-taster, Sue and Tom are
both tasters.
Ed and Jill are both tasters. Mary is a taster, Richard is a
non-taster. Tim is a taster, Tina is a non-taster. Bob is too young
to test yet.
Make a family tree for these families. Inside each circle or square put TT, Tt, tt, T_ , or ? depending on what you can figure out about each person. Write the first name of the person under the circle or square. Do a rough draft first- neatness counts. And please- follow the directions!!!
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MENDELIAN INHERITANCE IN HUMANS- There are several human traits that follow the basic Mendelian rules of inheritance. The following may be of interest to you.
1. Mid-digital Hair
Hair on the fingers is controlled by a dominant gene. Sometimes, the
amount of hair is so slight that a magnifying glass is needed to see
it.
2. Bent Little Finger-
The fancy name for this is Type A 3 brachydactylia. The top of the
little finger bends towards the ring finger. This is controlled by a
dominant gene.
3. Tongue Rolling
The ability to roll one's tongue is controlled by a dominant gene.
Tongue rolling can be quite fancy.
4. Widow's Peak
Sometimes known as "Eddie Munster Hairline", a widow's peak is
controlled by a dominant gene.
5. Earlobe Attachment
The inheritance of an free or unattached earlobe is caused by a
dominant gene. The attached lobe is a homozygous recessive condition.
The size and shape of the earlobe are controlled by other genes.
6. Facial Dimples
Natural indentations at the corners of the mouth (dimples) are
controlled by a dominant allele. Dimples are inherited as an
irregular dominant which means there are exceptions to the basic
rules
7. PTC Tasting
There is a chemical - phenylthiocarbamide - which some people taste
(tasters) and others
don't (non-tasters). There are paper strips available that have this
chemical on it. If you are a taster, and suck on this paper, you will
experience a rather unpleasant bitter taste. If you are a non-taster,
it will taste like paper. The allele for being a taster is dominant.
About 70% of the white American population are tasters. Almost 91% of
black Americans are tasters.
8. Hitch-hiker's Thumb
The gene that produces thumb(s) whose top bends backwards at about
45° is the recessive allele.
9. Length of Big Toe
If the big toe (officially known as the hallux) is longer than the
second toe (the index toe?), then the person is homozygous for a
recessive gene. The dominant allele produces a hallux that is
shorter.
Sex Influenced Traits - The following traits are affected by the sex of the person.
10. Relative Finger Lengths
The relative lengths of the index finger compared to the ring finger
is controlled by a pair of genes where the dominance of one over the
other changes depending on the sex of the person.
The allele for shorter index finger is dominant in males but recessive in females. If a person has two genes for shorter index finger, the index finger will be shorter. If a person has two genes for longer index finger, the index finger will be longer. If a person is hybrid, the index finger will be shorter if the person is a male but will be longer if the person is a female.
11. Male Pattern Baldness
The gene that controls loss of hair is dominant in males but
recessive in females. It follows the same type of inheritance pattern
as described in #10 above.
Holandric Traits-
These are traits carried by genes found only on the Y chromosome and
therefore are traits that only males have. One such trait is
hypertrichosis or hairy ears.