Download Chapter 15: The Chromosomal Basis of Inheritance

Chapter 15: The Chromosomal Basis of Inheritance
Mendel was the first to propose the idea that ________ are located on __________________.
It is known that human somatic cells have _________ chromosomes and have approximately
____________ genes.
What can you conclude about the number of genes on each chromosome?
_____________________________________________________________________________
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Thomas Hunt Morgan
In the early 1900’s Thomas Hunt Morgan worked with __________________ (fruit flies) and
confirmed Mendel’s idea that genes are located at ____________ ____________ on
chromosomes.
Discoveries
1. Morgan discovered that the ____ and ____ chromosomes (sex
chromosomes) are responsible for determining the sex of an
organism
XX = ____________
XY = ____________
2. Morgan discovered that there are genes on the sex chromosomes
which led to his most well known discovery; ______ linkage
____________ _______ – genes located on the sex chromosomes
- ____________= located on the X chromosome
- ____________= located on the Y chromosome
_________ ______ – genes located on the same chromosome
- linked genes tend to be inherited ____________ because the chromosome is passed on
as a ______
- example: the genes for red hair and freckles are located on the same chromosome so
people that have red hair usually have freckles
Sometimes however, genes on the same chromosome can be inherited separately. This is due to
_________ ______
_________ ______ – when segments of genes on homologous chromosomes trade places
- crossing over does not create new genes of delete old ones
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- crossing over only changes the locations of genes creating genetic variation
Chromosome Mapping
_________ ______ – a diagram showing the location of genes on a chromosome
- if two genes are very close together it is _________ that the two genes (traits) will be
separated during crossing over
- if genes are far apart from one another it is _________ _________ that the two genes
will separate during crossing over
- the ___________ of crossing over between two linked genes is ____________ to
the distance between them
______ ______ – used to determine the probability that crossing over between genes will occur
- genes that split up due to crossing over 1% of the time are said to be ______ ______
______ part
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Genes A and B are linked at 18 map units between them. A heterozygous individual Ab/aB
could possibly produce four gametes. List the gametes and the frequencies with which each
gamete would be produced.
Sex Chromosomes
In humans sex is determined by the ______ chromosome in the male gamete (sperm)
- if the father donates an X the zygote will be _________
- if the father donates a Y the zygote will be _________
However, other organisms have different chromosomal systems for determining sex
1. Grasshoppers = ______system
2. Birds = _________ system
3. Bees = ____ sex chromosomes
- 32 chromosomes = ______
- 16 chromosomes = ______
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Sex-Linked Genes
Sex chromosomes (especially the ______) have genes for many characteristics and proteins
- sex-linked usually refers to ___________ characters
___ ______traits (sex-linked) – genes located on the X chromosome
- __________________ – inability to see certain colors
- _________________ – wasting away of muscles
- _________________ – failure of blood to clot
______-_________ ______ – when the presence of sex hormones influence the expression of
certain human traits
- males and females can have the same _____________ but have completely different
_____________
- example: ________________________
X-Inactivation
Even though females have two X chromosomes, ______ of the X chromosomes in each cell
becomes __________________
______ ________ – an inactive X chromosome that is normally found in the nucleus of somatic
cells of a female
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Errors in Chromosome Inheritance
__________________ – when chromosomes fail to separate during meiosis
- causes gametes to lack (22) or have an extra chromosome (24)
-
_____________ – a zygote lacking a chromosome (45)
- _____________ – a zygote with one extra chromosome (47)
1. _________________ – having an extra 21st chromosome
- short stature, heart defects, mental retardation
2. _________________ – males with an extra X chromosome
(XXY)
- male sex organs, female characteristics, usually sterile
3. _________________– females that have only one X chromosome (XO)
- sex organs don’t develop and secondary sex characteristics
fail to develop
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