Post on 15-Jan-2016
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Human Heredity
Chapter 14-1
Biology
Mr. Hines
Decades ago, biology was limited to the study of living things other than humans.
We knew more about pea plants and fruit flies than humans.
Why?
It is unethical to perform experiments on humans.
Today, we can do this without harming humans.
So today, we know a lot about humans.
This section will deal with mostly human heredity
What is a karyotype?
During mitosis, the chromosomes inside of the nucleus become visible.
Scientists can take a photograph of the chromosomes.
The photograph is then enlarged and used to identify the chromosomes in humans.
Humans have 23 pair of chromosomes – one set from mom and one from dad.
Therefore, humans have a total of 46 chromosomes.
Furthermore, the chromosomes can be identified and labeled – numbers 1-23.
The chromosomes are then grouped and placed in the proper order.
Typically, they are in order from largest to smallest.
Chromosomes 23 are called sex chromosomes – Usually labeled X and Y
What is a karyotype?
A Karyotype is chart of the chromosomes displayed in the proper order.
A karyotype is made from a photograph of the chromosomes within the nucleus.
Here is a real karyotype
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22 of the 23 human chromosomes are called “autosomes.”
Again, the 23rd chromosomes are called “sex chromosomes.
So humans have 22 pair of autosomes and 1 pair of sex chromosomes.
Total chromosomes = 46
So, what are sex chromosomes
Sex chromosomes are what determines our sex.
Males and Females have certain traits – determined by the genes located on the 23rd chromosomes.
List some traits of males and females *males list female traits, *females list male traits
Punnett square for sex determination
Female chromosome = X
Male chromosome = Y
Which is dominant?
You decide?
If dad is a male and mom is a female
Then how do offspring inherit sex?
Remember, this is called segregation of alleles.
X and Y chromosomes will segregate into separate sex cells.
Male XY x Female XX
Cross XY and XX
What is the probability of having a boy or a girl?
Why?
Be able to answer that question on a test.
Pedigrees
A pedigree is a chart that helps us better understand the genetics in a particular family.
A pedigree also shows the relationships within a family.
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Color blindness and sex linked genes
Color blindness is a trait that some people have where they can not see certain colors.
There are 2 alleles for color vision
C = normal vision
c = color blind
Normal vision is Dominant
It is written like this
XC = normal vision
Xc = color blind
Y = the Y chromosome never carries the gene.
So we say that color blindness is sex linked – meaning that it can only be carried by the female X chromosome.
Consider this cross
Mom XCXc *mom has normal vision because she carries
the dominant C gene*mom is a carrier of the gene
Dad XCY*dad has normal vision because he has only
the dominant C gene
Punnett square
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Color blindness
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Lets say mom and dad have 4 children with the following
outcomeWrite the genotype next to each person
Perform a cross for this mother and father
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Perform a cross for this mother and father
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Perform a cross with this mother and father
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Create crossing that results in a colorblind female
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